An integrated approach for monitoring efficiency and investments of activated sludge-based wastewater treatment plants at large spatial scale.

Science of the Total Environment 523 (2015) 201–218

Contents lists available at ScienceDirect

Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

An integrated approach for monitoring efficiency and investments of activated sludge-based wastewater treatment plants at large spatial scale Sabino De Gisi a,⁎, Gianpaolo Sabia b, Patrizia Casella b, Roberto Farina b a b

Department of Civil, Environmental, Land, Building Engineering and Chemistry (DICATECh), Technical University of Bari, Via E. Orabona 4, 70125 Bari, Italy Italian National Agency for New Technologies, Energy and Sustainable Economic Development, ENEA, Water Resource Management Lab., via Martiri di Monte Sole 4, 40129 Bologna (BO), Italy

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• We develop a Performance Assessment System able to identify critical plants/ processes. • A scenario analysis allowed the identification of the most suitable technologies. • Investment costs were evaluated for each plant using an updated inventory of costs. • We prioritized critical plants with an environmental impact assessment-based approach. • Results showed how the implemented approach is potentially extensible at EU-level.

a r t i c l e

i n f o

Article history: Received 8 January 2015 Received in revised form 23 March 2015 Accepted 23 March 2015 Available online xxxx Editor: D. Barcelo Keywords: Decision support Environmental impact assessment Integrated approach Investment costs Municipal WWTPs Performance Assessment System Prioritization

⁎ Corresponding author. E-mail address: [email protected] (S. De Gisi).

http://dx.doi.org/10.1016/j.scitotenv.2015.03.106 0048-9697/© 2015 Elsevier B.V. All rights reserved.

a b s t r a c t WISE, the Water Information System for Europe, is the web-portal of the European Commission (EU) that disseminates the quality state of the receiving water bodies and the efficiency of the municipal wastewater treatment plants (WWTPs) in order to monitor advances in the application of both the Water Framework Directive (WFD) as well as the Urban Wastewater Treatment Directive (UWWTD). With the intention to develop WISE applications, the aim of the work was to define and apply an integrated approach capable of monitoring the efficiency and investments of activated sludge-based WWTPs located in a large spatial area, providing the following outcomes useful to the decision-makers: (i) the identification of critical facilities and their critical processes by means of a Performance Assessment System (PAS), (ii) the choice of the most suitable upgrading actions, through a scenario analysis. (iii) the assessment of the investment costs to upgrade the critical WWTPs and (iv) the prioritization of the critical facilities by means of a multi-criteria approach which includes the stakeholders involvement, along with the integration of some technical, environmental, economic and health aspects. The implementation of the proposed approach to a high number of municipal WWTPs highlighted how the PAS developed was able to identify critical processes with a particular effectiveness in identifying the critical nutrient removal ones. In addition, a simplified approach that considers the cost related to a basic-configuration and those for the WWTP integration, allowed to link the critical processes identified and the investment costs. Finally, the questionnaire for the acquisition of data such as that provided by the Italian Institute of Statistics, the PAS defined and the database on the costs, if properly adapted, may allow for the extension of the integrated approach on an EU-scale by providing useful information to water utilities as well as institutions. © 2015 Elsevier B.V. All rights reserved.

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S. De Gisi et al. / Science of the Total Environment 523 (2015) 201–218

1. Introduction The need to manage reliable and suitable tools to consult the right information and monitor the evolution of regulations, plans and programmes in the environmental fields is an important priority for government institutions around the world especially in such times of economic crisis. This is the case of the Water Framework Directive (WFD: 2000/60/EC) as well as the Urban Wastewater Treatment Directive (UWWTD: EU 271/91 Directive) in Europe. In addition, considering the Integrated Water Services (IWS), which includes aqueducts, sewers, drinking water and wastewater treatment plants (WWTPs), the wastewater subsystem is highly relevant both in terms of infringement measures both to its weight from an economic point of view (according to Federconsumatori (2013), that in Italy monitors the tariff to users, the weight of the wastewater subsystem in economic terms, accounts for a percentage around 40–45%, second only to the aqueduct subsystem which presents a percentage of 50–55%). To address the problem of monitoring in the context of water policy, the European Commission (EU) relies upon a web-portal called WISE (Water Information System for Europe) (http://water.europa.eu/). Launched on 22 March 2007, WISE acquires information from the Member States and disseminates the quality state of the receiving water bodies (rivers, sea, etc.) as well as the efficiency of the municipal WWTPs to the public. Currently, WISE represents the baseline instrument adopted by the EU for monitoring advances in the fields of water policies. An interesting aspect at the basis of our idea is that the data contained on WISE are acquired by means of a questionnaire in turn elaborated according to the EU-statistical office (EUROSTAT) guidelines with reference to the water sector. Moreover, the Italian experience of recent years (De Gisi et al., 2014a) shows how the data is moved from the water utilities to the government institutions such as the Ministry of Environment. Thus, the most important aspect is precisely the completion of the questionnaire by water utilities, for each WWTP. In this context, why not develop WISE applications capable of giving useful information to water utilities as well as government institutions? For example, the assessment of the investments in the IWS which currently represents another significant challenge for governments institutions (Mirza and Haider, 2003; Rahm et al., 2013; Davies and Wright, 2014). We believe that when combining the use of the Italian Institute of Statistics (ISTAT) questionnaire (in turn, elaborated on the basis of the EUROSTAT guidelines), with the integrated approach here presented, it is possible to provide useful information (i.e., the investment assessment) to support the actions of the decision-makers. Consequently, with reference to a large spatial area that contains a high number of municipal WWTPs based on activated sludge processes, the aim of our study was to define and apply an integrated approach capable of monitoring the efficiency of WWTPs starting from the data acquired by the ISTAT questionnaires. Specifically, the developed approach allows for: ▪ The identification of critical facilities and their critical processes; ▪ The choice of the most suitable upgrading actions by means of a scenario analysis; ▪ The assessment of the investment costs for the improvement of the critical facilities identified previously and, finally; ▪ The prioritization of the most critical WWTPs on the basis of technical, environmental, economic and health aspects. In this regard, current literature presents several studies on this specific issue. With reference to the first aspect, the measuring of WWTP efficiency, current approaches are generally based on the “plan-do-check-act” philosophy where performance assessment plays a key-role (Cabrera et al., 2011; De Gisi et al., 2014b). For this purpose, performance indicators (pIs) are commonly adopted and defined in

relation to the goals of the study (ISO, 14001, 2004; Perotto et al., 2008). Furthermore, pIs can be combined into indices capable of summarizing and organizing the information available at higher-levels (Langhans et al., 2014). In the wastewater field, the conventional approach involves the use (as pIs) of water quality parameters such as COD (Chemical Oxygen Demand), BOD5 (Biochemical Oxygen Demand), TSS (Total Suspended Solids), Ntot (Total Nitrogen), Ptot (Total Phosphorous) and pathogens on a temporal basis (Gallego et al., 2008; Rodriguez-Garcia et al., 2012; Silva et al., 2014b). Whereas, unconventional ones are those of Colmenarejo et al. (2006) that used a so-called efficiency indicator, defined as an average of TSS, Ntot, COD and BOD5 removal, in order to compare the overall performance of different WWTPs. Barjoveanu et al. (2010) defined and applied a risk-based approach (EIRA method) in order to assess the impact on the receiving water bodies of municipal WWTPs while, Perotto et al. (2008) defined several pIs as (i) the total population equivalent (PE, corresponding to a five-day biodegradable organic load of 60 g BOD5/d), (ii) the PE served by inappropriate WWTP, (iii) the mass of biosolids that are disposed of yearly and (iv) the number per year of malfunctions or nuisance originated by the sewers/WWTP. An exciting concept has emerged from the studies by Silva et al. (2014a,b). They show how by adopting a Performance Assessment System (PAS) rather than pIs, it is possible to evaluate (i) the overall performance of the WWTP (in terms of treated water quality, plant efficiency, etc.) and (ii) the daily performance in terms of treated water quality, operating conditions and removal efficiencies (Silva et al., 2014b). With reference to the second aspect, the investment assessment (and monitoring), a lot of data are available in literature (Alegre and Almeida, 2009; Libhaber and Jaramillo, 2012). Data refer to the construction costs as well as the operational & maintenance ones (O&M). Some authors, such as Hernandez-Sancho et al. (2011), suggested a model for evaluating the O&M costs of several technologies capable of treating municipal wastewater. Others, such as Sipala et al. (2003), developed a web-based tool for the calculation of costs of different wastewater treatment and reuse scenarios. Both the works highlight how the cost assessment is only possible after the choice of technologies to be adopted. Moreover, reliable data related to the different units of process/treatment (UOPs), are not always available. Regarding the third aspect, the prioritization of critical WWTPs, mono-dimensional approaches are commonly used as reported in Barjoveanu et al. (2010). To the best of our knowledge and considering the aim of our work, an integrated approach (linking the aspects mentioned above) that, starting from the data acquired by means of statistical questionnaires, allows to measure the efficiency of WWTPs and then assess the investment costs as well as ranking of the most critical plants, does not exist. In fact, to date, this objective is pursued at scale of a single WWTP of which is known, in addition to the influent load, the volumes, altimetry, temperatures and other key parameters related to the treatment processes implemented. Such data are rarely available on a large spatial scale. In order to reach our objectives, an innovative PAS for WWTPs was defined and will be presented in the work. Our PAS is able to identify critical WWTPs and at the same time verify the treatment capacity of a plant in removing pollutants in relation to the discharged limit values (LVs) imposed by law. To date, as described above, pIs are commonly adopted while the verification of the real WWTP potential is made only after a site-specific analysis. Finally, our approach has been developed to allow its application on a large scale, such as the EU-context, in the ways that will be presented in the article. In order to verify the applicability of our proposal, we considered the data set related to large municipal WWTPs with a population equivalent greater than 50,000, located in Northern Eastern Italy and involving 4 districts (the Italian regions). The plants under study where chosen since they were evaluated to be representative of the overall national


situation in terms of treatment scheme. In fact, they adopt an activated sludge-based treatment scheme typically used in Italy since the 1980s up to today. In addition, these facilities were selected for the sake of completeness of the acquired data on their state. Since the chosen WWTPs discharge the treated wastewater into sensitive areas, particular attention is paid to nitrogen and phosphorus monitoring which are in the present study significant in order to define the methodological steps implemented. 2. Materials and methods In this section, the materials and methods are reported. However, in order to make our approach transparent and replicable, Appendix B contains the full version of Section 2 Materials and methods.

203

For the first type, the ISTAT questionnaires, also elaborated on the basis of the guidelines defined by EUROSTAT (http://epp.eurostat.ec. europa.eu/portal/page/portal/eurostat/home/), were used. After the data acquisition, a further validation step was required since ISTAT surveys do not always provide clear information about the plants and the applied treatment scheme. This validation was performed by means of an investigation including the use of aerial photos. For other data (such as flow rate, inlet and outlet concentrations related to the principal parameters required by the Italian Law, D.Lgs 152, 2006) the validation step consisted of a first control carried out by ISTAT (verification of coherency between data acquired and those from the ISTAT time series) and a second control with a site-specific analysis taking into account each single plant. The data relating to the area in which the WWTPs are located were acquired by means of different sources:

2.1. Background information The study was carried out using data acquired in 2008 by ISTAT (2008) by submitting questionnaires to WWTPs operators. The available data set refers to large municipal WWTPs operating in the NorthEast of Italy in 2008 (see Fig. 1), based on CAS (conventional activated sludge process) or NR (activated sludge-based nutrients removal processes) treatment scheme with a primary sedimentation phase. All the WWTPs discharge the treated effluents into sensitive areas according to the UWWTD (EU Directive 91/271). The total number of WWTPs taken into account is 44 for a treatment capacity of 6,377,741 PE as shown in Table 1. The sample size is 69.8% of the correspondent population, very high if compared with those reported in literature about the use of questionnaires as an instrument for data acquisition (Sujauddin et al., 2008; De Feo and De Gisi, 2010). A copy of the questionnaire used (originally, in Italian) is reported in Appendix A (See Appendix A, Supplementary data). 2.2. Framework of our proposal The framework of our proposal is shown in Fig. 2. The first part is aimed at identifying critical WWTPs and defining the correspondent upgrading actions. Part 2 is aimed at assessing the investment costs, while part 3 at defining the ranking of the most critical WWTPs previously identified with the involvement of potential stakeholders. Thus, all the necessary information is provided in a readable and usable way to policymakers. To achieve these goals, three methodologies have been defined (See Fig. 2) and described in the Sections 2.2.2, 2.2.3 and 2.2.4, respectively. Instead, Section 2.2.1 refers to the data input acquisition. 2.2.1. Data acquisition and validation In our study, two types of data were acquired: (1) data related to the WWTP performance and operating conditions (treatment schemes) and (2) data concerning the territorial, economic and social context in which the plants are located.

▪ National Geoportal of the Italian Ministry of the Environment (http://www.pcn.minambiente.it/GN/); ▪ WISE WFD Database of the European Commission (http://www.eea. europa.eu/data-and-maps/data/wise_wfd); ▪ Italian National Institute of Statistic (ISTAT), data related to the economic activities (http://www.istat.it/it/archivio/turismo). While the first data are acquired by means of the ISTAT survey on water (with a bi-annual frequency), the second are freely available. Once acquired, the data are used for the realization of a GIS (Geographic Information System) as shown in Fig. 1 of the Appendix B (See Appendix B, Supplementary data). 2.2.2. Methodology 1: identification of critical WWTPs Consisting of five steps it is named identification methodology (Fig. 3). It is based on a multi-disciplinary approach containing notions on nutrient removal processes (in a WWTP based on activated sludge) as well as benchmarking (pIs). With reference to a specific WWTP and its relative UOPs, the following processes were taken into account: ▪ Processes for the removal of organic matter (BOD5); ▪ Processes for nitrogen and phosphorus removal (Ntot, Ptot); ▪ Solid/liquid separation after the secondary or tertiary treatment (where present); ▪ Fining processes (i.e., sand filtration, biofiltration-BFs, microfiltration, etc.) generally adopted in the case of wastewater reuse; ▪ Disinfection. The first step aims at identifying the critical WWTPs and the connected critical processes through the implementation of 11 pIs (See Table 1, Appendix B, Supplementary data) defined on the basis of the following main aspects: (1) WWTP technological equipment, (2) WWTP compliance of the treated water with the Italian Law

Study area: North East

Central North West

N W

South and Islands

E

S WWTP location

(a)

0

25

50

75

100 km

(b)

(c)

(d)

Fig. 1. WWTPs under study: (a) chorography of Northern Eastern Italy; (b) Trentino Alto Adige and Friuli Venezia Giulia districts; (c) Veneto district; (d) Emilia-Romagna district.

204


Table 1 Characteristic data of the municipal WWTPs considered in the study. District

PETOT

% Ind

WWTPs N.

Emilia-Romagna Friuli Venezia Giulia Trentino Alto Adige Veneto Total

2,856,151 680,000 1,558,955 1,282,635 6,377,741

18.3 66.6 46.1 9.2 28.4

21 3 9 11 44

Size [PE = population equivalent] 50,000 ≤ PE b 100,000

100,000 ≤ PE b 500,000

PE N 500,000

5 1 3 9 18

16 1 6 2 25

0 1 0 0 1

requirements (D.Lgs 152/2006) for discharging water in the environment, and (3) WWTP treatment capability to treat additional loads for future actions. The pI application allows getting an overall WWTP performance evaluation considering all the UOPs. The critical facilities are those showing performance gaps with respect to the optimum value defined for each indicator. In addition, Step 1 provides more information analysing the reasons of process/treatment criticalities: a UOP resulted critical for the lack of technological equipment and/or for a noncompliance with the Italian Law, is classified as TE (technological equipment) and/or as LR (legal requirement compliance). Furthermore, a WWTP can be classified as overloaded if the ratio PETOT,EFF/PETOT,DESIGN is higher than 1 where PETOT,EFF is the total effective population equivalent and PETOT,DESIGN is the total design population equivalent. If a plant is overloaded, it probably requires the construction of new basins as better described in section 2.2.2.5 of the Appendix B (See Appendix B, Supplementary data). On the whole, a WWTP is considered critical when simply one or more criticalities are verified. On the basis of the achieved results, each WWTP is classified as NC = noncritical, NCO = noncritical and overloaded, C = critical, CO = critical and overloaded (see Fig. 3).

The second step represents a detailed study of the only processes for nitrogen (N) and phosphorus (P) removal. The goal is to confirm or deny the criticalities identified in Step 1 relative to the N and P parameters. For this purpose, a new procedure based on the algorithm of Fig. 4 has been defined. The algorithm consists of 10 questions (indicated with qi, with i = 1,…, 10) related to the following goals: (1) check if the inlet wastewater is biodegradable; (2) check if there are appropriate conditions in order to develop nitrogen removal processes; and (3) check if there are appropriate conditions in order to develop phosphorous removal processes. Considering the single WWTP, its inlet pollution load (in terms of BOD5, COD, TSS, Ntot and Ptot) as well as its treatment scheme, Fig. 4a shows the mechanism for verifying the biodegradability of the inlet wastewater. Instead, Fig. 4b and c shows the mechanism for testing the WWTP nitrogen and phosphorous removal capabilities, respectively, With reference to nitrogen, after a first level verification in which the BOD5/TKN ratio as well the possible technologies suitable to balance it are analysed, a second level verification checks if NOUT,survey (acquired by the ISTAT questionnaire) is in the range (NOUT,1, NOUT,2). These last values represent the nitrogen effluent concentration range of the

Water utilities

Input data from ISTAT questionnaires about WWTPs efficiency

Identification of critical processes for each WWTP

Identification of critical WWTPs

METHODOLOGY 1: • Wastewater expertise; • Nitrogen and phosphorous removal; • Performance indicators expertise.

Definition of upgrading actions for each WWTP

Scenario analysis for the choice of the most suitable treatment scheme

(a) METHODOLOGY 2: Results from the Methodology 1

Assessment of the investment costs

Costs database from Italian WWTPs construction companies

• Wastewater expertise; • Costs expertise.

METHODOLOGY 3: Input data relate to: • The area in which the WWTP is located (considering different sources); • Further investigationof some critical WWTPs.

Ranking of the critical WWTPs to policy makers or water utilities

Prioritization of the critical WWTPs

• Environmental impact assessment expertise;

• Wastewater expertise; • Multi-criteria analysis (MCA) expertise;

• Stakeholder involvement.

(b) Fig. 2. Generic layout containing the three methodologies developed, showing the goals related (a) to the identification phase and (b) those relating to the cost assessment and prioritization.

Fig. 3. Framework of the proposed PAS (Performance Assessment System). The criteria for the identification of critical WWTPs and their critical processes are summarized below: pI1–pI11 (See Table 1 of Appendix B, Supplementary data); q1–q10 (See Fig. 4).


205

WWTP under investigation evaluated on the basis of the mass balance equations shown in Fig. 5. The range (NOUT,1, NOUT,2) is a function of the inlet pollution load as well as the WWTP treatment scheme as presented in Fig. 5. Based on the values obtained, the verification (see question q5 in Fig. 4b) may be positive (Yes), negative (No) or further detail (FD). The condition FD occurs when NOUT,Survey b NOUT,1 (or, similarly, if ErN,survey N ErN,2) implying that the WWTP under study works better than our prevision. Consequently, it is necessary to justify why the performances of the WWTP are better than those we expected. In this, if there are no elements to carry out this second level of verification (to explain the occurrence of the FD condition), only the results related to Step 1 are taken into account. In a similar manner to nitrogen, Fig. 4c shows the mechanism for testing the phosphorous removal capabilities of a WWTP. According to Fig. 3, the nitrogen and phosphorous removal processes may be: NC (non-critical); NCO (non-critical and overloaded); C (critical); CO (critical and overloaded); or N.A. (methodology nonapplicable, apply only the Step 1). The third step combines the results of Steps 1 and 2 considering only the processes for N and P removal. The detailed procedure is shown in Fig. 3 (see Sub-step 3.1) and allowed to obtain the final judgement (represented by Z in Fig. 3). In this, the single process may be: NC (non-critical); NCO (non-critical and overloaded); C (critical); or CO (critical and overloaded) (see Sub-step 3.2, Fig. 3). The fourth step allows to obtain the final set of critical WWTPs and their processes combining the results obtained after the implementation of Steps 1 and 3. In this way, the results of the detailed study related to the N and P processes are incorporated with those of the general framework. As presented in Fig. 3 (see sub-steps 4.1 and 4.2), the single process and consequently the single WWTP can be: NC; NCO; C; or CO. The fifth and final step allows to obtain the general framework of the upgrading actions which need to be implemented on critical WWTPs. In this, WWTPs that require upgrading actions are those classified as C and CO. The upgrading actions may concern the following critical UOPs: (i) process for BOD 5 removal; (ii) processes for N and P removal; (iii) solid/liquid separation after the secondary or tertiary treatments (where present); (iv) fining treatment; and (v) disinfection. On the basis of the specific plant characteristics (i.e., overloaded/ not overloaded, UOP presence/absence) (see Table 2), two types of upgrading actions were considered. The first type (A1) optimizes the management of a process identified as critical. While the second type (A2) represents a structural action carried out by means of the construction of new treatment basins. Finally, there is the need to link the upgrading actions with the most suitable treatment technologies. Section 2.2.2.5.1 of Appendix B (See Appendix B, Supplementary data) shows the criteria defined to achieve this goal. 2.2.3. Methodology 2: assessment of the investment costs In our study, with reference to a single WWTP, we intend the investment costs as the sum of the costs for the realization of new UOPs and the costs of restructuring of the existing UOPs. Both items refer to the construction costs. In a simplified manner, the operation and maintenance costs that also include the ordinary maintenance (Benedetti et al., 2006; Sipala et al., 2003; Tsagarakis et al., 2003), have not been considered. However, Appendix C (see Appendix C, Supplementary data) contains the cost elements for the O&M estimation. In order to optimize an existing WWTP, methodology 2 considers two types of costs: (1) construction costs (Cad) aimed at the implementation of new UOPs (i.e., the realization of a new basin implementing a new process) as well as the restructuring of the existing UOPs; (2) processes optimization costs (Cop) aimed at improving the operation of critical UOPs (i.e., costs for the control of the N-removal processes). The construction costs as well as the processes optimization ones are associated to actions A2 and A1, respectively (see Table 2). Consequently, in our proposal, the investment costs for the single WWTP are evaluated

206


Fig. 4. Algorithm of the Step 2 of the PAS: (a) Testing wastewater (WW) biodegradability; (b) testing the N-removal capabilities; (c) testing the P-removal capabilities.

as the sum of the two types of costs reported above (Cad + Cop). Based on numerous Italian River Basin Management Plans (De Feo et al., 2012), Cad is evaluated as follows:

Cad ¼ Cif–Cie

ð1:1Þ

Cie ¼ Cin α μ

ð1:2Þ

where: ▪ Cif = construction costs considering the final configuration (treatment scheme) of the WWTP under study; ▪ Cie = residual values considering the existing WWTP (treatment scheme); ▪ Cin = construction costs considering the existing WWTP (treatment scheme); ▪ α = adjustment coefficient depending by the ratio Cif/Cin; ▪ μ = adjustment coefficient relating to the conservation status of the existing facilities. If the ratio Cif/Cin b 5, the value of α is evaluated with the following equation: α ¼ 1:25–0:25 ðCif=CinÞ:

ð1:3Þ

Otherwise, where Cif/Cin ≥ 5, α = 0. Instead, the value of μ is evaluated according to the class of quality of the infrastructures (considering basins and electromechanical components) as reported in Table 3. The values of Cin and Cif related to Eqs. (1.1), (1.2) and (1.3) are evaluated according to the contents of Tables 4 and 5 considering, respectively, the existing treatment scheme and the final treatment one. In detail, Table 4 shows the construction costs (€/PE) for two basic configurations: (1) activated sludge and aerobic sludge stabilization (typical of small–medium WWTPs); (2) activated sludge and anaerobic sludge digestion (typical of large WWTPs as in our case). While, Table 5 shows the percentage increase to be applied to the construction costs of Table 4 for the implementation of an additional process (i.e., denitrification, chemical phosphorous removal, etc.). It is important to observe how, the costs of Tables 4 and 5 are the result of a survey carried out by major Italian companies operating in the sector over the last decade. With reference to the Cop costs, commercially, several systems for optimizing the biological processes control are available. In our study, we considered a modern system based on an on-line measurement of ammonia concentration and dissolved oxygen directly in the oxidation basins (Collivignarelli et al., 2009). Based on our experience, we assumed a cost of 50,000 euro for the basic components of the system plus a variable cost depending by the number of treatment lines (equal to 5000 €/line). More information on the adopted system is reported in the full Materials and methods section (See Appendix B, Supplementary data).


Influent

Biological processes

Inlet wastewater

SECONDARY SEDIMENTATION

AEROBIC

207


Inlet wastewater

Effluent

Oxidation process for BOD removal

Ntot,IN

Effluent

Ptot,IN


Effluent

Ptot,OUT

Ntot,OUT Input:

A

q

Air

BOD5,IN; BOD5,OUT [mg/l]

Nitrogen in sludge heterotrophic biomass

Ntot,IN [mg/l]

Return activated sludge

N = Ntot,IN - Ntot,OUT

N

[m3/d];

Secondary activated sludge

N = (4-6)% (BOD5,IN - BOD5,OUT)

(a)

PE [inhabitants];

Phosphorus in sludge heterotrophic biomass

BOD5,IN; BOD5,OUT [mg/l] Ptot,IN [mg/l];

P [kgP/d] = 1,5% Xbio [kgSS/d]

Xbio ≈ (25-30) gSS/PE/d

P = mass of phosphorus removed through the sludge ( Pbio )

(b)

(c)

CHEMICAL

Influent

Chemical


AEROBIC


Inlet wastewater

Effluent


Ntot,IN

Effluent

BOD5,IN; BOD5,OUT [mg/l]

Nitrogen in sludge heterotrophic biomass

Ntot,IN [mg/l]


Effluent


(d) SECONDARY SEDIMENTATION

Effluent

Nden

Phosphorus removed through the sludge ( Pchem)

P [mg/l] = (85-90)% Ptot,IN [mg/l]

Alum, ferric chloride

(f)

Denitrification Nitrification/Oxidation processes

Ntot,IN Input:


Ntot,IN [mg/l]

Phosphorus in sludge heterotrophic biomass

BOD5,IN; BOD5,OUT [mg/l] Ptot,IN [mg/l];

P [kgP/d] = 1,5% Xbio [kgSS/d]

Xbio ≈ (22-30) gSS/PE/d

P = mass of phosphorus removed through the sludge ( Pbio)

N ≈ (15-25%) Ntot,IN

(h)

(i)

Nden ≈ (55-60%) Ntot,IN ANAEROBIC ANOXIC

Inlet wastewater


AEROBIC

Nitrogen removed through nitrification/denitrification processes

Nden Effluent

Inlet wastewater

Denitrification Nitrification/Oxidation processes

Air Input:



BPR and DEN/NITR/OXD processes (A2OTM)

Effluent

Ptot,OUT

Ntot,IN [mg/l]

Input:

Ntot,OUT

q [m3/d];

PBPR

Pused

Ptot,IN [mg/l].

Ntot,OUT = Ntot,IN – ( Nden + N)

N

q [m3/d];


Ptot,IN

Effluent

Ntot,IN

D

Ptot,OUT

P = Ptot,IN - Ptot,OUT

P

q [m3/d]; PE [inhabitants];

Nitrogen removed through the sludge

(g) Influent

Effluent

Input:

Ntot,OUT

Ntot,OUT = Ntot,IN – ( Nden + N)

N

q [m3/d];


Ptot,IN

Effluent

Air Return activated sludge


Inlet wastewater

Nitrogen removed through nitrification/denitrification processes

Inlet wastewater

C


P

(e) Nden ≈ (60-70%) Ntot,IN

AEROBIC

Ptot,OUT


q [m3/d]; Ptot,IN [mg/l]; Chemicals:

N = (4-6)% (BOD5,IN - BOD5,OUT)


ANOXIC

Ptot,IN Input:

N = Ntot,IN - Ntot,OUT

N

q [m3/d];

Air

Inlet wastewater

Ntot,OUT

Input:

B

Influent


P

q [m3/d];

Input:

Nitrogen removed through the sludge

Pused = phosphorus used for heterotrophic biomass synthesis

PBPR = phosphorus removed by BPR mechanism

Ptot,OUT = Ptot,IN – ( Pused + PBPR) Pused + PBPR = (70-90%) Ptot,IN

N ≈ (15-25%) Ntot,IN

(l)

(m)

(n)

Fig. 5. Mass balances for the assessment of N and P outlet concentrations (and ERs) as a function of the WWTP treatment scheme and the inlet load: (a) A = oxidation process for BOD removal; (b) mass balance for N-removal; (c) mass balance for P-removal; (d) B = oxidation process for BOD removal and chemical P-removal; (e) mass balance for N-removal; (f) mass balance for P-removal; (g) C = denitrification/nitrification/oxidation processes; (h) mass balance for N-removal; (i) mass balance for P-removal; (l) D = BPR (biological P-removal) and denitrification/nitrification/oxidation processes (A2O™); (m) mass balance for N-removal; (n) mass balance for P-removal. The inlet wastewater (for the treatment schemes A, B, C and D) comes from primary sedimentation with removals efficiencies of 25% and 60% for BOD5 and TSS, respectively (Metcalf and Eddy, 2003).

Table 2 Type of upgrading actions for the BOD5, Ntot and Ptot removal processes (only for WWTPs identified as critical and critical & overloaded). Aspect

Combination 1

Is the process already implemented? Is the WWTP overloaded?a Type of upgrading actionb Design parameter only for A2 type)c a

2.2.4. Methodology 3: prioritization of critical WWTPs The aim of methodology 3 is to identify the most critical WWTPs establishing the priority order of interventions for decision makers. The conceptual model defined is visible in Fig. 6a. The model shows how the final ranking is the result of a multi-criteria approach able to consider the following aspects: (1) size of the WWTP; (2) potential impacts induced on the environment (comprising natural and social

2

Yes Yes No A1 —

3

4

No

No

Yes No Yes A2 A2 A2 PEEFF,TOT–PEDES,TOT PEEFF,TOT PEEFF,TOT

The system is overloaded if PEEFF,TOT N PEDES,TOT. b A1 = action aimed at optimizing the management of the process; A2 = structural action with the construction of new basins. c PEEFF,TOT = total effective population equivalent; PEDES,TOT = Total design population equivalent.

Table 3 Values of the coefficient μ depending on the quality state of the WWTPs infrastructures. WWTP quality statea

Coefficient μ (adim)

Poor Discrete Good

0.2 0.5 0.8

a Refers to the infrastructures storage conditions (concrete, steel, etc.) as well as the electromechanical components ones (mixer, pumps, aerators, etc.).

208


Table 4 Construction costs (€/PE) of large WWTPs for different basic configurationsa (modified by De Feo et al., 2012). Type of configuration

Treatment capacity [PE] 20,000

30,000

40,000

50,000

100,000

200,000

300,000

400,000

≥500,000

Activated sludge + aerobic sludge stabilization Activated sludge + anaerobic sludge digestion

185.0 –

175.0 –

165.0 –

120.0 125.0

– 105.0

– 95.0

– 85.0

– 75.0

– 65.0

a

Construction costs include the compulsory purchase and the costs for the hydraulic connections (pipes, channels, etc.). While, construction charges and fees (VAT) are not included.

environment); and (3) state of quality of the environment (intended as natural) as well as the socio/economic profile of the territorial context in which WWTP is located (in our study, the District, the Italian Province). In order to reach the goal (the ranking), the procedure of Fig. 6b was defined. Synthetically, it includes the following points:

critical processes are focused on the removal of the organic matter (BOD5), the solid/liquid WWTP separation capability (TSS) and the fining treatments (Table 2 of Appendix D, Supplementary data). Thus, agreeing with current literature on the most problematic processes of large WWTPs discharging into sensitive areas (Libralato et al., 2012) as well as the studies carried out by the Italian environmental agencies in the territories under study. These WWTPs, many of which were realized several decades ago, were designed (considering the secondary biological treatment) with the only aim to remove the organic matter and, then, adapted to the new legal requirements (EU Directive 91/271; D.Lgs 152, 2006), generating, in this sense, several problems. Furthermore, the absence of the most suitable treatments for disinfection such as peracetic acid or UV (probably due to the lack of awareness by operators and institutions inherent to the disinfection by-products (DBPs) formation and their aquatic ecosystems toxicity (Chhetri et al., 2014)), has generated other critical points. Table 2 of Appendix D (see Appendix D, Supplementary data) shows how the most critical processes are due to the lack of technological equipment (TE). However, excluding the disinfection (all of type TE), most of the critical processes (i.e., N and P removal processes) are those resulted to be non-compliant with the law (EU Directive 91/271; D.Lgs 152/2006). A closer analysis of the N and P removal processes, objective of Step 2, focuses on the capability of a WWTP to reach the target values imposed by the law. Table 6 shows the estimated ranges for NOUT (and Er NOUT) and POUT (and Er POUT) obtained applying the mass balances as defined and shown in Fig. 5. These results highlight how the WWTPs equipped with a treatment scheme type C and D are, in the most cases, able to reach the limits of the law. In particular, the Ers average values for the N-removal processes are 36.8%, 105.3%, 86.4% and 86.5% for the A, B, C and D treatment schemes, respectively. Similarly, considering the P-removal processes, the Ers average values for the treatment schemes A, B, C and D are, respectively, 70.0%, 88.7%, 60.7% and 82.0%. The estimated Ers are in line with the Italian Law as presented in Table 6. Furthermore, Table 6 shows how some WWTPs, equipped with A or B treatment schemes (as S3, S5, S6, S10, S24 and S31), were able to remove nitrogen with high percentages, almost equal to those obtainable with C or D treatment schemes. The PAS herein defined, thanks to the second level of verification, is aimed also at the investigation of the

▪ Definition of the goal (1); ▪ Definition of the evaluation criteria (2); ▪ Elaboration of the matrix “critical WWTPs/evaluation criteria” (called the alternative matrix) (3); ▪ Normalization of the alternative matrix (4); ▪ Definition of the weight vectors for the evaluation criteria (5); ▪ Definition of the index (called the PIx) for ordering the WWTPs with a subsequent sensitivity analysis (6); ▪ Identification of the ranking related to the most critical WWTPs (7). The detailed description of the seven points is reported in the full Materials and methods section (See Appendix B, Supplementary data). 3. Results and discussion 3.1. Methodology 1. Identification of critical WWTPs and their critical UOPs 3.1.1. Components of the PAS The five steps described in the Section 2.2.2 allow to obtain the PAS under study whose main components are reported as follows: (i) The WWTP matrix (Table 1 of Appendix D, Supplementary data) with the identification of the critical UOPs for each WWTP by means of the use of the only pIs (Table 2 of Appendix D, Supplementary data); (ii) the values of the Ers for N and P-removal processes for each WWTP (Table 6); (iii) insights concerning the N and P removal processes based on the algorithm of Fig. 4 (Table 7); (iv) the combination of Step 1 (only pIs) and step 2 for N and P removal processes (Table 3 of Appendix D, Supplementary data); (v) the determination of the final set of the critical UOPs for each WWTP (Table 8); and (vi) framework of the upgrading actions for each WWTP (Table 9). An initial diagnosis on the issues affecting the WWTPs under study and provided by the pIs of Table 1 of Appendix D (see Table 1, Supplementary data), has shown how the most common problems refer to the processes for nutrients removal and disinfection. In contrast, no

Table 5 Percentage increase to be applied to the construction costs for the realization of a new UOP (indicated as integration) (modified by De Feo et al., 2012). WWTP integration

Chemical phosphorus removal (simultaneous precipitation) Chemical phosphorous removal (post precipitation) Biological phosphorous removal Sand filtration Chemical–physical treatment UV disinfection Nitrification Denitrification MBR, BAF or MBBR processes Thermal drying of the sludge Energy recovery from biogas Sludge incineration Coverage of the single treatment unit (per unit)

Treatment capacity [PE] 20,000

30,000

40,000

50,000

100,000

200,000

300,000

400,000

≥500,000

3.0 16.0 12.0 16.0 7.0 9.0 11.0 7.0 75.0 – – – 4.0

3.0 16.0 10.0 13.0 7.0 9.0 11.0 7.0 75.0 – – – 5.0

3.0 16.0 8.0 10.0 7.0 9.0 10.0 7.0 75.0 – – – 6.0

2.5 15.0 8.0 10.0 6.0 8.0 10.0 6.0 75.0 – – – 7.0

1.5 13.0 6.0 8.0 5.0 6.5 10.0 6.0 75.0 15.0 10.0 45.0 8.0

1.5 11.0 4.5 7.5 4.0 6.0 10.0 6.0 75.0 14.0 7.0 30.0 9.0

1.5 9.0 3.0 7.0 3.0 5.5 10.0 6.0 75.0 13.0 4.0 15.0 10.0

1.5 7.0 1.5 6.5 2.0 5.0 10.0 6.0 75.0 12.0 1.5 10.0 11.0

1.5 5.0 1.5 6.0 1.5 4.5 10.0 6.0 75.0 11.0 1.5 5.0 12.0


209

Fig. 6. Prioritization phase: (a) Conceptual model highlighting the impacts on the environment (natural and social) induced by the WWTPs; (b) general layout highlighting the stakeholder involvement.

reasons for such high performances. In fact, Table 7 provided answers to the 10 questions reported in the Section 2.2.2. In order to better explain how to use the components of our PAS, the next section will address some case studies considering WWTPs with treatments schemes of types A and B, characterized by high performance in terms of N-removal (Er NOUT). Finally, Table 3 of Appendix D (see Appendix D, Supplementary data) shows the results of the combination of Steps 1 and 2 concerning the N and P removal processes as well as the final judgements (results of Step 3). While, Tables 8 and 9 show the final set of the critical UOPs for each WWTP (results of Step 4) and the framework related to the upgrading actions for the critical facilities identified with our proposal (results of Step 5), respectively. The results of Table 9, used in combination with the potential technological scenarios defined in Table 2 of Appendix B (see Appendix B, Supplementary data), allowed to choose the most suitable treatment scheme for each WWTP. Thus, a WWTP, critical for phosphorus removal, with a treatment scheme of type A and subjected to a structural action (the realization of a new basin), on the base of the results of the identification phase, may be interested in the realization of the following actions: (1) a sand filtration with a chemical addition (i.e., ferric chloride); and (2) a BPR (biological phosphorous removal) process. Based on economic considerations as well as on the variability of the influent load (Puig et al., 2010), the second solution was adopted, although it involves the realization of further tanks for the denitrification/nitrification processes (although the nitrogen is not a critical process). It is important to notice that, the choice of the new treatment scheme

for each WWTP allowed for the assessment of costs as reported in Section 3.2. 3.1.2. On the use of our PAS: case studies The objective is to show how applying only the pIs is not enough to establish whether a process is critical or not. Is the case of the S6 WWTP, critical for the N-removal process, as presented in Table 10 (columns 1–2, Table 10). After the more detailed investigation (summarized in columns 3–5 of Table 10), S6 was found to be not critical, revealing its potential ability to remove nitrogen. In fact, S6 implements the simultaneous nitrification–denitrification which promotes the nitrogen compound removal in a single reactor (Collivignarelli and Bertanza, 1999; Liu et al., 2010). In fact, under low dissolved oxygen (DO) concentration conditions, denitrification can take place in the floc interior where anoxic conditions can occur, while the nitrification process is promoted at the floc exterior (considering the activated-sludge floc). In activated-sludge tanks operated at low DO concentrations, both aerobic and anoxic zones exist (depending on mixing conditions and distance from the aeration point), so that nitrification and denitrification can occur in the same tank (Metcalf and Eddy, 2003). Table 10 highlights further examples of WWTPs that showed a better performance than we expected. Therefore, in order to confirm this result, it was necessary to extend the information related to the single WWTP by using literature data (when existing), aerial photographs (to observe the actual basin configuration) and finally, directly contacting the plant manager. Is the case of S5, S10 and S24 WWTPs with reference to the N removal-process.

210


Table 6 Comparison of N and P Er and outlet concentration values considering data acquired by ISTAT questionnaire and those estimated (Step 2). N.

S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S21 S22 S23 S24 S25 S26 S27 S28 S29 S30 S31 S32 S33 S34 S35 S36 S37 S38 S39 S40 S41 S42 S43 S44

Flow-charta

D C A D B B D C D A C D D D D C C D D D D D D B D D D D D D A D D D D D D D B D D D D D

Data estimatedb

Data by ISTAT questionnaire NOUT, survey [mg/l]

Er NOUT,survey [%]c

POUT, survey [mg/l]

Er POUT,survey [%]d

NOUT, 1 [mg/l]

NOUT, 2 [mg/l]

Er NOUT,1 [%]c

Er NOUT,2 [%]c

POUT, 1 [mg/l]

POUT, 2 [mg/l]

Er POUT,1 [%]d

Er POUT,2 [%]d

Er NOUT Averagec

Er POUT Averaged

16.3 18.6 10.9 12.6 20.7 9.7 5.5 6.3 6.4 13.7 16.9 7.8 12.1 13.9 4.6 12.3 13.9 10.0 6.5 14.0 9.9 16.4 17.5 15.8 10.4 9.6 9.7 9.6 9.3 7.7 5.7 14.2 5.1 10.4 8.1 13.9 4.1 11.7 6.5 16.1 15.1 5.3 12.0 16.4

69.3 53.5 72.8 79.6 63.3 70.1 78.6 82.2 82.7 45.0 60.0 84.7 73.5 81.7 93.1 62.3 46.3 61.5 91.9 61.0 86.0 67.9 69.4 73.8 82.9 79.9 82.5 84.6 84.5 75.1 62.0 58.7 79.8 67.7 84.5 41.6 91.0 59.9 40.8 77.1 75.6 82.5 69.1 62.7

0.73 1.20 1.20 1.08 1.79 1.03 0.46 3.01 1.05 1.01 1.47 0.68 0.26 0.44 2.68 2.11 1.54 1.10 0.24 0.45 0.51 0.55 0.62 1.53 1.10 1.00 0.60 0.70 0.40 1.10 0.70 0.90 0.80 0.90 1.50 0.67 1.60 1.02 1.10 0.60 0.58 0.85 0.38 0.70

89.1 14.3 70.0 89.2 79.1 88.8 88.3 33.5 81.2 75.4 66.8 85.0 94.9 96.7 69.9 59.1 51.7 73.2 97.4 89.6 97.6 91.9 93.7 82.5 86.4 89.6 92.6 93.3 91.7 78.8 72.0 79.5 81.0 72.7 83.1 81.3 73.0 73.6 15.9 96.9 93.8 81.1 99.4 85.6

2.4 1.8 13.1 2.8 ~0 ~0 1.2 1.6 1.7 3.6 1.9 2.3 2.1 3.4 3.0 1.5 1.2 1.2 3.6 1.6 3.2 2.3 2.6 ~0 2.7 2.1 2.5 2.8 2.7 1.4 ~0 1.5 1.1 1.4 2.4 1.1 2.1 1.3 0.0 3.2 2.8 1.4 1.7 2.0

12.0 9.0 22.0 13.9 ~0 ~0 5.8 8.0 8.3 13.5 9.5 11.0 10.3 17.1 15.0 7.3 5.8 5.9 18.1 8.1 15.9 11.5 12.8 ~0 13.7 10.7 12.5 14.1 13.5 7.0 ~0 7.7 5.7 7.2 11.8 5.4 10.3 6.6 4.3 15.8 13.9 6.8 8.7 9.9

95.5 95.5 26.9 95.5 121.0 140.3 95.3 95.5 95.4 30.0 95.5 95.5 95.4 95.5 95.5 95.4 95.4 95.4 95.5 95.5 95.5 95.5 95.4 147.9 95.6 95.6 95.5 95.5 95.5 95.5 75.6 95.6 95.6 95.7 95.4 95.4 95.4 95.5 99.1 95.5 95.5 95.4 95.6 95.4

77.4 77.5 17.9 77.4 81.0 93.5 77.4 77.4 77.6 20.0 77.5 78.5 77.4 77.5 77.4 77.6 77.6 77.3 77.5 77.4 77.5 77.5 77.6 98.6 77.5 77.6 77.4 77.4 77.5 77.3 50.4 77.6 77.4 77.6 77.4 77.3 77.4 77.4 60.8 77.5 77.5 77.5 77.6 77.5

0.60 0.12 2.10 0.90 0.77 0.83 0.35 1.25 0.50 0.69 1.76 0.41 0.46 1.19 0.80 2.17 1.25 0.37 0.82 0.39 1.91 0.61 0.89 0.79 0.73 0.86 0.73 0.94 0.43 0.47 0.10 0.40 0.38 0.30 0.80 0.32 0.53 0.35 0.12 1.76 0.84 0.41 5.38 0.44

1.81 0.43 2.50 2.70 1.16 1.25 1.06 2.00 1.51 1.49 2.36 1.23 1.38 3.57 2.41 2.83 1.68 1.11 2.47 1.17 5.74 1.83 2.68 1.18 2.19 2.59 2.19 2.81 1.30 1.40 0.20 1.19 1.13 0.90 2.40 0.97 1.60 1.04 0.18 5.28 2.51 1.22 16.1 1.32

91.1 91.4 47.5 91.0 91.0 91.0 91.1 72.4 91.1 83.2 60.2 91.0 91.0 91.0 91.0 57.9 60.8 91.0 91.0 91.0 91.0 91.0 91.0 91.0 91.0 91.0 91.0 91.0 91.0 90.9 96.0 90.9 91.0 90.9 91.0 91.1 91.0 90.9 90.8 91.0 91.0 90.9 91.0 91.0

73.1 69.3 37.5 73.0 86.4 86.5 73.0 55.8 73.0 63.7 46.7 72.9 72.9 73.0 72.9 45.1 47.4 72.9 73.0 72.9 73.0 73.0 73.0 86.5 73.0 73.0 73.0 73.0 72.9 73.0 92.0 73.0 73.1 72.7 73.0 73.0 73.0 73.1 86.2 73.0 73.0 72.9 73.1 72.9

86.5 86.5 22.4 86.5 101.3 116.9 86.4 86.5 86.5 25.0 86.5 87.0 86.4 86.5 86.5 86.5 86.5 86.3 86.5 86.5 86.5 86.5 86.5 123.3 86.5 86.6 86.5 86.5 86.5 86.4 63.0 86.6 86.5 86.6 86.4 86.4 86.4 86.5 80.0 86.5 86.5 86.4 86.6 86.5

82.1 80.4 42.5 82.0 88.7 88.7 82.0 64.1 82.0 73.4 53.4 81.9 82.0 82.0 82.0 51.5 54.1 82.0 82.0 82.0 82.0 82.0 82.0 88.7 82.0 82.0 82.0 82.0 82.0 82.0 94.0 81.9 82.0 81.8 82.0 82.0 82.0 82.0 88.5 82.0 82.0 81.9 82.0 81.9

a Activated sludge-based biological processes: A = oxidation; B = oxidation and chemical P-removal; C = denitrification/nitrification/oxidation processes; D = biological P-removal and C processes. b Values are estimated using the mass balances reported in Fig. 5 of the manuscript. c The Italian Law (D.Lgs 152/2006), for N-removal processes, refers to values of 70–80% for WWTPs with PE ≥ 10,000 PE. d While, for P-removal processes, the Italian Law refers to values of 80% for WWTPs greater than 10,000 PE.

Examples listed above highlight how the detailed studies developed according to our proposal allow to better define if a process is critical or not (considering the N and P removal processes) although some questions remain unanswered (i.e., why does a plant not work properly). In fact, they require site-specific investigations and direct inspection, at a scale of WWTP.

3.1.3. Comparison between the PAS and the only pIs The results shown previously may be ends in themselves. Thus, Fig. 7 shows the comparison between the results of our PAS and those related to the application of only the pIs, presented in De Gisi et al. (2014b). In particular, the number of critical WWTPs was 33 (75.0%) and 34 (77.3%) for a total of 44, considering, respectively, the PAS (see Fig. 7a) and the only pIs (see Fig. 7b). These results show how the adoption of only the pIs may overestimate the number of critical WWTPs.

In line with the above, Fig. 7c and d shows how the number of critical processes related to the PAS and only the pIs, was 49 and 56, respectively. In this case, only the pIs may overestimate the number of critical processes. Furthermore, Fig. 7c and d highlights how our PAS is more selective with reference to the N-removal processes compared to the only pIsbased approach. In fact, considering the total number of critical processes, the percentage of N-removal processes were 42.9% (see Fig. 7c) and 41.1% (see Fig. 7d) for the PAS and only the pIs, respectively. Although the difference is only 2%, considering the minimal uncertainties related to the input data (previously validated), the obtained results appear to be interesting. In fact, taking into account that the WWTPs under study have high scores in terms of technological equipment as well as performance (De Gisi et al., 2014b), it is expected that this percentage may be even higher if we consider less performance plants such as those that discharge into non-sensitive areas. It is important to highlight that, in this last case, a different set of WWTPs is considered


211

Table 7 Insights concerning the N and P removal processes (Step 2). WWTP N.

S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S21 S22 S23 S24 S25 S26 S27 S28 S29 S30 S31 S32 S33 S34 S35 S36 S37 S38 S39 S40 S41 S42 S43 S44

Testing Flow-charta


Results How are the processes?l

Aspect 1:C:N:P ratios

Aspect 2: nitrogen removal

Aspect 3: phosphorus removal

q1b

q2c

q3d

q4e

q5f

q6g

q7h

q8i

q9j

q10k

Nitrogen

Phosphorous

Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes No Yes

– – – – – – – – – – – 1 – – – – – – – – – – – – – – – – – – – – – – – – – 1 – – – – No –

Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes No Yes No Yes Yes Yes Yes – No

– – Lack of info – – – – – – – – 1 – – – – – – – – – – – – – – – – – – – – – Lack of info – 1 – 1 – – – – – Lack of info

No No – Yes Fd Fd Yes Yes Yes Fd No Yes No Yes Yes No No No Yes No Yes No No Fd Yes Yes Yes Yes Yes No Fd No Yes – Yes No Yes No No No No Yes – –

– – – – 5 3 – – – 3 – – – – – – – – – – – – – 3 – – – – – – 3 – – – – – – – – – – – – –

Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes Yes No Yes No Yes No Yes Yes – No

– – – – – – – – – Lack of info – 1 – – – – – – – – – – – – – – – – – – – – 2 – – 1 – 1 – 3 – – – Lack of info

Yes No FD Yes No Yes Yes No Yes – FD Yes FD FD No FD Yes Yes FD Yes FD FD FD No Yes Yes FD FD FD Yes FD Yes Yes Yes Yes Yes Yes Yes No FD FD Yes – –

– – N.J.m – – – – – – – 4 – 2 2 – 4 – – 2 – 2 4 4 – – – 4 4 4 – N.J.m – – – – – – – – 2 4 – – –

C C N.A. NCO NCO NC NC NC NC NC C NC C NC NC C C C NC CO NC C C NC NC NC NC NC NC CO NC C NC N.A. NC C NC C C C C NC N.A. N.A.

NC C N.A. NCO CO NC NC C NC N.A. NC NC NC NC C NC NC NC NC NCO NC NC NC C NC NC NC NC NC NCO N.A. NC NC NC NC NC NC NC C NC NC NC N.A. N.A.

a Activated sludge-based biological processes: A = oxidation; B = oxidation and chemical phosphorus removal; C = denitrification/nitrification/oxidation processes; D = biological phosphorus removal and C processes. b q1 = Is the inlet WW biodegradable? Replies: yes; no. c q2 = In the plant, are there technologies increasing WW biodegradability? Replies: yes (1 = equalization; 2 = primary chemical–physical treatment; 3 = combination of equalization and chemical–physical treatment); no; lack of information. d q3 = Is the BOD5/TKN ratio balanced? Replies: yes; no. e q4 = If no (see question q3), considering the plant, are there technologies to balance BOD5/TKN ratio? Replies: yes (1 = equalization; 2 = addition of exogenous carbon); no; lack of information. f q5 = Is NOUT,survey in the range [NOUT,1; NOUT,2]? Replies: yes (NOUT,survey ɛ [NOUT,1; NOUT,2]); no (NOUT,survey N NOUT,2); FD (NOUT,survey b NOUT,1). g q6 = In the case of FD (see question q5), considering the plant, are these conditions (presence of an equalization phase; presence of sand filtration, submerged biofilter for nitrogen removal; presence of a simultaneous denitrification; high capacity to remove BOD) satisfied? Replies: yes (1 = the plant has an equalization phase; 2 = the plant is equipped with a sand filtration or submerged biofilter, other technologies for nitrogen removal; 3 = the plant has a simultaneous denitrification; 4 = the values estimated with the use of our models differs little from NOUT,1; 5 (only for the WWTPs with A and B treatment scheme) = the plant has an high capacity to remove the BOD5 and consequently, the Nitrogen, See Fig. 5b, e); no (In this case, the methodology defined in the step 2 does not apply: N.J. (no judgement is possible)). h q7 = Is the BOD5/P ratio balanced? Replies: yes; no. i q8 = If no (see question q7), considering the plant, are there technologies to balance BOD5/P ratio? Replies: yes (1 = equalization; 2 = addition of chemicals for phosphorous removal; 3 = other technologies); no; lack of information. j q9 = Is POUT,survey in the range [POUT,1; POUT,2]? Replies: yes (POUT,survey ɛ [POUT,1; POUT,2]); no (POUT,survey N POUT,2); FD (POUT,survey b POUT,1). k q10 = In the case of FD (see question q9), considering the plant, are these conditions (presence of an equalization phase; presence of sand filtration, sand filtration in combination with chemical addition, submerged biofilter for phosphorous removal; presence of a chemical phosphorous removal) satisfied? Replies: yes (1 = the plant has an equalization phase; 2 = the plant is equipped with a sand filtration or sand filtration in combination with chemical addition or submerged biofilter, other technologies for phosphorous removal; 3 = the plant has a chemical phosphorous removal; 4 = the values estimated with the use of our models differs little from POUT,1); no (In this case, the methodology defined in the step 2 does not apply: N.J. (no judgement is possible)). l Typology of process: C = critical; CO = critical and overloaded; NC = non-critical; NCO = non-critical and overloaded; N.A. = Methodology non-applicable. Apply only the Step 1. m In this case, no judgement can be expressed. The process is N.A.

212


Table 8 Final set of critical UOPs for each WWTP (Step 4). N.

PETOT [inhabitants]

Wastewater is reused?

The plant is overloaded?

S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S21 S22 S23 S24 S25 S26 S27 S28 S29 S30 S31 S32 S33 S34 S35 S36 S37 S38 S39 S40 S41 S42 S43 S44 TOT

57,363 66,259 88,612 97,910 80,856 63,204 95,813 60,702 50,000 80,000 50,000 53,052 70,320 56,246 57,500 52,000 83,000 100,000 95,315 222,898 158,966 131,559 103,294 129,282 318,513 358,448 136,000 124,742 250,000 348,749 500,000 120,000 120,000 160,675 138,180 130,479 330,000 233,945 177,707 108,000 159,972 100,000 208,180 250,000 7,590,207

No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No 0

No No No Yes Yes No No No No No No No No No No No No No No Yes No No No No No No No No No Yes No No No No No No No No No No No No No No 4

a b c d

Processes/treatmenta BOD5

TSS

Nitrogen

Phosphorus

Finingb

Disinfection

Plant's typec

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 0

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 0

* * * – – – – – – – * – * – – * * * – * – * * – – – – – – * – * – * – * – * * * * – * * 21

– * * – * – – * – * – – – – * – – – – – – – – * – – – – – – * – – – – – – – * – – – – – 9

– – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 0

* – – * * * – – – – – * – – – * * – – * * * * * – – – – – – – * * – – * – – * * * * – – 19

C C C CO CO C NC C NC C C C C NC C C C C NC CO C C C C NC NC NC NC NC CO C C C C NC C NC C C C C C C C 33d

(*) = critical process/treatment; (–) = noncritical process/treatment; Fining treatments are sand filtration, microfiltration, etc. Plant's type: C = critical; CO = critical and overloaded; NC = non-critical; NCO = non-critical and overloaded. Refers to the total critical processes (C + CO).

(however, representative of the Italian situation in terms of treatment schemes). Briefly, these results show how the adoption of the PAS highlights a smaller number of critical processes and, at the same time, allows to identify a larger number of critical N-removal processes with respect to those obtained applying only the pIs. Therefore, our PAS is more selective with respect to the N-removal processes. Finally, Fig. 8 shows how the percentage of critical N-removal processes were 62.2%, 73.9% and 70.0% with reference to Step 1, the Step 2 and Step 3, respectively. Instead, the percentage of the critical Premoval processes were 37.8%, 26.1% and 30.0%. These results highlight how Step 2 allows identifying a larger number of critical N-removal processes with respect to only Step 1. Moreover, the PAS, based on a combination of Steps 1 and 2, is able to rebalance the final results. 3.2. Methodology 2: assessment of the investment costs Table 11 shows the results of methodology 2 related to the assessment of the investment costs for the critical WWTPs. For each WWTP,

the costs for the upgrading actions (the addition of new UOPs) and those for the processes optimization were evaluated. In particular, an average total cost of 3.7, 5.9 and 12.8 millions of euro with reference to plants with a size of [50,000; 100,000], ]100,000; 200,000] and N200,000 PE, respectively, was observed (see Table 11). As described shortly, the validation of these results was complex since the data were not publicly available. The viewed documents focused above all on the legislative acts of the local authorities (in Italian, Autorità d'Ambito) which control the water utilities as well as the financial statements of some water utilities. These documents refer to the state of the WWTPs under study, before 2008, year of the acquisition of the data about the plants by means of the ISTAT questionnaires. Fig. 9a shows how the investment costs are strongly affected by the μ coefficient (the adjustment coefficient relating to the conservation status of the existing facilities). In average terms, an increase of about 50% and 70% with respect to the cost related to a WWTP with μ = 0.8 (the best quality), for μ = 0.5 and μ = 0.2, respectively, may be observed. This makes the assessment of the μ coefficient a very important aspect. Fig. 9c, d and e shows three examples of WWTPs with different


213

Table 9 Framework of the upgrading actions for the critical WWTPs (Step 5). N.

S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S21 S22 S23 S24 S25 S26 S27 S28 S29 S30 S31 S32 S33 S34 S35 S36 S37 S38 S39 S40 S41 S42 S43 S44 TOT

PETOT [inhabitants]

57,363 66,259 88,612 97,910 80,856 63,204 95,813 60,702 50,000 80,000 50,000 53,052 70,320 56,246 57,500 52,000 83,000 100,000 95,315 222,898 158,966 131,559 103,294 129,282 318,513 358,448 136,000 124,742 250,000 348,749 500,000 120,000 120,000 160,675 138,180 130,479 330,000 233,945 177,707 108,000 159,972 100,000 208,180 250,000 7,590,207

Flow-charta


Overloaded?

No No No Yes Yes No No No No No No No No No No No No No No Yes No No No No No No No No No Yes No No No No No No No No No No No No No No

Type of plantb

C C C CO CO C NC C NC C C C C NC C C C C NC CO C C C C NC NC NC NC NC CO C C C C NC C NC C C C C C C C

Disinfectione

Upgrading actions BOD5 removal

Nitrogen removal

Phosphorous removal

A1c

A2d

A1c

A2d

A1c

A2d



Yes Yes No No No No No No No No Yes No Yes No No Yes Yes Yes No No No Yes Yes No No No No No No No No Yes No Yes No Yes No Yes No Yes Yes No Yes Yes 17

No No Yes No No No No No No No No No No No No No No No No Yes No No No No No No No No No Yes No No No No No No No No Yes No No No No No 4

No No No No No No No No No No No No No No Yes No No No No No No No No No No No No No No No No No No No No No No No No No No No No No 1

No Yes Yes No Yes No No Yes No Yes No No No No No No No No No No No No No Yes No No No No No No Yes No No No No No No No Yes No No No No No 8

Yes No No Yes Yes Yes No No No No No Yes No No No Yes Yes No No Yes Yes Yes Yes Yes No No No No No No No Yes Yes No No Yes No No Yes Yes Yes Yes No No 19

a Typology of secondary biological processes: A = Oxidation; B = Oxidation and phosphorus chemical removal; C = denitrification/nitrification/oxidation processes; D = biological phosphorus removal and C processes; b Type of plant (C = critical; CO = critical and overloaded; NC = non-critical; NCO = non-critical and overloaded); c A1 = actions aimed at optimizing the managementof the single process/treatment. d A2 = structural action with the construction of new basins. e The improvement of disinfection phase is based on treatment with less impact (in terms of DBPs production) on the receiving water body such as peracetic acid, UV. In addition, tertiary treatment (sand filtration, microfiltration, etc.) were not considered as they should be implemented only in the case of wastewater reuse.

quality states characterized by the following μ coefficient: μ = 0.8, μ = 0.5 and μ = 0.2, respectively. In addition, Fig. 9a shows the sensitivity analysis of the results on the base of the μ coefficient. Generally, the decision-makers need to know the investment costs to upgrade a critical WWTP as well as the convenience of the interventions. Thus, Fig. 9b highlights both the costs to upgrade the critical WWTPs and those for a new realization (in terms of €/PE). In the cases of the S16, S20, S31 and S34 WWTPs (see Fig. 9b) the realization ex-novo of plants resulted to be more convenient than upgrading. These outcomes are useful in driving the decision-makers to identify all the WWTPs characterized by a non-economic convenience in intervening. The results of Fig. 9b were in line with the construction costs reported in literature above all considering the Mediterranean countries. Sipala et al. (2003) showed a unit cost of about 95 €/PE and 77 €/PE for Italian WWTPs with a size of 100,000 and 200,000 PE, respectively.

They refer to WWTPs with primary sedimentation, activated sludge biological treatment and anaerobic digestion of the sludge, as in our case. Whereas, Tsagarakis et al. (2003), with reference to Greece, revealed construction costs of about 5, 9 and 11 million of USD considering WWTP (always equipped as the facilities under study) with a size of 50,000, 100,000 and 200,000 PE, respectively. Finally, the unit costs of our proposal were slightly higher than those reported in Sipala et al. (2003) due to the increased costs in the water sector from 2000 to 2010, as evaluated by the Italian Regulatory Authority for Electricity Gas and Water (http://www.autorita.energia.it/). 3.3. Methodology 3: prioritization of the critical WWTPs Fig. 10a shows the results of the prioritization phase after the application of our methodology. The obtained ranking for all four

214


Table 10 Case studies showing how our PAS allows overcoming the limitations due to the adoption of the only pIsa. WWTP Current Reference framework flow-chartb 1

Logical path due to the PAS application 3

4

5

Table 7 shows how S5 has a high ability to remove the organic matter (BOD) and, consequently, nitrogen. In fact, for the treatment scheme type B, Er N is equal to 4–6% of the removed BOD5 (See Fig. 5e). Table 7 shows how S6 uses a simultaneous denitrification for the removal of nitrogen. Consequently, S6 is able to reach the limits of the law.

Although it is overloaded, on the base of our evaluation, S5 is potentially able to remove nitrogen. Not-critical.

The estimated Er [Er NOUT,1; Er NOUT,2] were compared with the information from literature (Autonomous Province of Trento, 2000).

On the base of our evaluation, S6 is potentially able to remove nitrogen. Not-critical.

The estimated Er [Er NOUT,1; Er NOUT,2] were compared with the information coming from the WWTP manager.

Table 7 shows how S10 uses a simultaneous denitrification for the removal of nitrogen. Consequently, S10 is able to reach the limits of the law.


The estimated Er [Er NOUT,1; Er NOUT,2] were compared with the information coming from the WWTP manager.

Table 7 shows how S24 uses a simultaneous denitrification for the removal of nitrogen. In addition, S24 has a high ability to remove the organic matter (BOD) and, consequently, nitrogen.


The estimated Er [Er NOUT,1; Er NOUT,2] were compared with the information from literature (Autonomous Province of Trento, 2000).

S5

B

According to Table 6 of Appendix B, S5 has a technological gap as well as isn't in line with the legal requirement (TE + LR). In addition, S5 is overloaded.

Table 6 shows how NOUT,survey is equal to 20.7 mg/l (N15 mg/l), with an Er of 63.3%, either way it is not in compliance with the Italian Law (D.Lgs 152/2006).

According to Table 6, on the base of its treatment scheme and the inlet pollution load, S5 may achieve Ers in the range [81%; 121%]. Why?

S6

B

According to Table 6 of Appendix B, S6 presents a technological gap (TE). However, S6 isn't overloaded.

Table 6 shows how NOUT,survey is equal to 9.7 mg/l (b15 mg/l), with an Er of 70.1%. S6n is in compliance with the Italian Law (D.Lgs 152/2006).

S10

A

According to Table 6 of Appendix B, S10 presents a technological gap (TE). However, S10 isn't overloaded.

S24

B

According to Table 6 of Appendix B, S24 has a technological gap as well as isn't in line with the legal requirement (TE + LR). However, S24 isn't overloaded.

Table 6 shows how NOUT,survey is equal to 13.7 mg/l (b15 mg/l), with an Er of 45.0%. S10 is in compliance with the Italian Law (D.Lgs 152/2006) in terms of concentration and not in terms of removal efficiency. Table 6 shows how NOUT,survey is equal to 15.8 mg/l (N10 mg/l) with an Er of 73.8%. S24 is in compliance with the Italian Law in terms of Er (Er NOUT,Survey is N70%) and not in terms of concentration.

According to Table 6, on the base of its treatment scheme and the inlet pollution load, S6 may achieve Ers in the range [93.5%; 140.3%]. Why? According to Table 6, on the base of its treatment scheme and the inlet pollution load, S10 may achieve Ers in the range [20.0%; 30.0%]. Why?

a b

References

2

According to Table 6, on the base of its treatment scheme and the inlet pollution load, S24 may achieve Ers in the range [98.6%; 147.9%]. Why?

In these examples, we considered only the processes for the N removal. Types of treatment: A = oxidation; B = oxidation and P-chemical removal; C = denitrification/nitrification/oxidation processes; D = biological P-removal and C treatment.

decision-maker profiles was similar and highlighted the most critical as being the WWTPs S30, S31 and S20. Despite the different weight applied to take into account the way of thinking and sensibility of the chosen profiles, the results were almost homogeneous and concordant. In comparison, Fig. 10b shows the ranking obtained applying only the EIRA method, as described in Barjoveanu et al. (2010). This method, based on the environmental risk as index (see Table 4 of Appendix B, Supplementary data), pointed out S24, S5 and S32 as the first three critical WWTPs. The EIRA method, on the basis of its logical approach, was led to highlight the WWTPs characterized by a bigger impact on water bodies (due to the presence of criticalities related to the N and P

removal). The conditions and relative problems inherent to these WWTPs have been widely documented in technical literature as shown in Nardelli et al. (2008). The methodology here proposed, besides applying the EIRA approach by using the index of environmental risk, takes into account other relevant parameters by also considering the technical, environmental, economic and social aspects. Thus, it generates a sort of “effect of mediation” minimizing the environmental risk index for the benefit of the other criteria. The WWTPs identified (S30, S31 and S20) have been those impacting on the receiving water bodies and, at the same time, on the anthropic environment. In the cases of the WWTPs S30 and S32, many cases of complaints by the population as well as by the media were reported, respectively due to the damage

Fig. 7. Results of the methodology 1: (a) Types of WWTPs (C = critical; CO = critical and overloaded; NC = non-critical; NCO = non-critical and overloaded) according to our proposal and (b) only pIs; types of critical processes for C & CO WWTPs according to our proposal and (d) only pIs.


215

Fig. 8. Comparison of the results of Steps 1 (application of the pIs), 2 (application of the mass balances for the N and P removal processes) and 3 considering only the processes for nutrient removal: (a) Step 1; (b) Step 2; (c) Step 3.

caused by the discharging of the treated wastewater in the lagoon of Venice (Zonta et al., 2007) and disorders related to bad odours perceived by people living near the plant (Hayes et al., 2014). Thus, the defined prioritization methodology has allowed integrating several inputs, further characterizing the plant contexts and main issues. Overall, the outcomes well fit with the ones achieved by applying the welldocumented EIRA approach, as highlighted by the shape similarity between Fig. 10a and b, but the detailed results have shown different WWTPs as the most critical situations in which to prioritize interventions and allocate economic resources. Therefore, the proposed

methodology permitted, synergistically with EIRA approach, a further in-depth analysis by complementing other aspects of ascertained priority for the decision-makers work, synergistically providing complementary information to decision-makers. 4. Some considerations on the application of our approach Since it is based on data collected every two years, the proposed approach allows for the monitoring of the WWTP efficiency over time. It allows to identify the critical issues that persist over the years providing,

Table 11 Assessment of the investment costs for upgrading the critical WWTPs identified with the methodology 1. N.

PETOT [inhabitants]

WWTP flow-charta

Investment costs Upgrading actionsb e

S1 S2 S3 S4 S5 S6 S8 S10 S11 S12 S13 S15 S16 S17 S18 S20 S21 S22 S23 S24 S30 S31 S32 S33 S34 S36 S38 S39 S40 S41 S42 S43 S44 TOT

57,363 66,259 88,612 97,910 80,856 63,204 60,702 80,000 50,000 53,052 70,320 57,500 52,000 83,000 100,000 222,898 158,966 131,559 103,294 129,282 348,749 500,000 120,000 120,000 160,675 130,479 233,945 177,707 108,000 159,972 100,000 208,180 250,000 4,424,484

D C A D B B C A C D D D C C D D D D D B D A D D D D D B D D D D D –

f

g

h

Cin [€]

Cif [€]

Cin/Cif

α

μ

Cie [€]

Cad [€]

8,701,152.0 9,697,504.6 10,372,085.3 12,690,794.3 9,320,555.3 7,775,866.7 9,063,065.2 9,681,840.0 7,750,000.0 8,174,733.6 11,486,484.9 9,903,426.3 7,531,744.0 10,804,104.0 13,492,500.0 12,330,757.4 20,334,501.5 16,322,753.2 13,225,108.7 13,433,987.1 31,747,500.0 33,962,500.0 15,082,120.0 15,082,120.0 20,233,435.9 17,252,300.4 26,964,277.9 17,577,502.1 14,651,674.2 19,219,492.1 12,850,000.0 24,770,536.3 28,237,500.0 –

8,701,152.0 10,274,558.2 12,552,046.0 12,690,794.3 11,827,188.6 8,311,228.1 9,617,927.7 9,853,600.0 7,750,000.0 8,654,059.9 11,486,484.9 9,903,426.3 8,004,541.0 11,414,589.9 13,492,500.0 26,046,484.4 21,272,068.4 17,132,514.0 13,886,097.9 16,879,638.4 34,791,845.4 39,162,500.0 15,833,160.0 15,833,160.0 20,233,435.9 18,056,697.4 26,964,277.9 21,934,121.1 15,338,656.8 20,161,450.1 13,492,500.0 24,770,536.3 28,237,500.0 –

1.00 1.06 1.21 1.00 1.27 1.07 1.06 1.02 1.00 1.06 1.00 1.00 1.06 1.06 1.00 2.11 1.05 1.05 1.05 1.26 1.10 1.15 1.05 1.05 1.00 1.05 1.00 1.25 1.05 1.05 1.05 1.00 1.00 –

1.00 0.99 0.95 1.00 0.93 0.98 0.98 1.00 1.00 0.99 1.00 1.00 0.98 0.99 1.00 0.72 0.99 0.99 0.99 0.94 0.98 0.96 0.99 0.99 1.00 0.99 1.00 0.94 0.99 0.99 0.99 1.00 1.00 –

0.80 0.50 0.80 0.80 0.80 0.50 0.80 0.80 0.80 0.80 0.80 0.50 0.20 0.50 0.80 0.50 0.80 0.80 0.50 0.80 0.80 0.80 0.80 0.80 0.20 0.80 0.80 0.80 0.80 0.80 0.80 0.80 0.50 –

6,960,921.6 4,776,620.6 7,861,676.1 10,152,635.5 6,955,117.5 3,821,013.2 7,139,479.6 7,711,120.0 6,200,000.0 6,443,921.7 9,189,187.9 4,951,713.1 1,482,709.0 5,325,741.3 10,794,000.0 4,450,912.8 16,080,087.8 12,896,250.4 6,529,930.7 10,058,059.5 24,789,130.9 26,130,000.0 11,915,488.0 11,915,488.0 4,046,687.2 13,640,960.9 21,571,422.3 13,190,677.9 11,583,942.9 15,187,202.0 10,151,500.0 19,816,429.1 14,118,750.0 –

1,740,230.4 5,497,937.5 4,690,369.8 2,538,158.9 4,872,071.1 4,490,214.9 2,478,448.0 2,142,480.0 1,550,000.0 2,210,138.2 2,297,297.0 4,951,713.1 6,521,832.0 6,088,848.7 2,698,500.0 21,595,571.6 5,191,980.6 4,236,263.6 7,356,167.2 6,821,578.9 10,002,714.5 13,032,500.0 3,917,672.0 3,917,672.0 16,186,748.7 4,415,736.5 5,392,855.6 8,743,443.2 3,754,713.9 4,974,248.1 3,341,000.0 4,954,107.3 14,118,750.0 196,721,963.3

Processes optimization Copc[€]

Totald Cad + Cop [M€]

60,000.0 60,000.0 – – – – – – 60,000.0

1.800 5.558 4.690 2.538 4.872 4.490 2.478 2.142 1.610 2.210 2.362 5.017 6.587 6.159 2.759 21.596 5.192 4.316 7.426 6.822 10.003 13.033 3.998 3.918 16.282 4.486 5.468 8.743 3.820 5.039 3.411 5.024 14.199 198.0

65,000.0 65,000.0 65,000.0 70,000.0 60,000.0 – – 80,000.0 70,000.0 – – – 80,000.0 – 95,000.0 70,000.0 75,000.0 – 65,000.0 65,000.0 70,000.0 70,000.0 80,000.0 1,325,000.0

a Activated sludge-based biological processes: A = oxidation; B = oxidation and chemical P-removal; C = denitrification/nitrification/oxidation processes; D = biological P-removal and C treatment. b Investment costs aimed at the implementation of new processes/treatments for upgrading critical facilities (Actions A2, see Table 2). c Investment costs aimed at improving the operation of the critical UOPs (Actions A1, see Table 2). d Total investments in millions of Euro, sum of the costs of the upgrading actions and the costs for the processes optimization (Cad + Cop). e Cin = WWTP construction cost considering its current configuration (treatment scheme). f Cif = WWTP construction cost considering its final configuration (design configuration). g Cie = remaining value of the existing WWTP. h Cad = investment costs for the upgrading of critical WWTPs only considering structural actions (Actions A2). More details are reported in the Section 2.2.3 of the Appendix B.

216


34 32

Investments costs [Million ]

30 28 26

μ = 0.2 μ = 0.5 μ = 0.8

Costs for different values of μ

Range Estimated value

24

22 20 18 16 14

12 10 8

(c)

6 4 2 0

Critical WWTPs

(a) 160 150 140

Upgrading costs (estimated value) Costs for a new realization

S16

Investments costs [ /PE]

130 120 S34

110

(d)

100 90 80 S20

70 60 50 40 30

20 S31

10 0

Critical WWTPs

(b)

(e)

Fig. 9. Investment costs (sum of the costs for the realization of new UOPs and the costs of restructuring of the existing UOPs) relate to the upgrading of the critical WWTPs: (a) absolute values; (b) comparison with the costs for a new realization; (c) aerial photo of a WWTP with μ = 0.8 (high quality); (d) μ = 0.5 (moderate quality); (e) μ = 0.2 (poor quality).

S43

S44

S42

S1 1,0

S2

S40

S5

S39

S10

0,2

S11

0,0

S12

S34

S13

S33

S15

S32

S16 S17

S31 S30 S24 Pindex Balanced

S23 S22

Politician Pindex

S21 S20

S18

Pindex Environmentalist

(a)

S2

S3 S4

S40

S8

0,4

S36

S1 1,00 0,80

S41 S6

0,6

S38

S44

S42

S4

0,8

S41

S43

S3

S39

S6 S8

0,40

S38

S11

0,20

S36

S10

0,00

S34

S12

S33

S13

S32

S15

S31

S16 S30

S17

S24 Idealist Pindex

S5

0,60

S23 S22

S21 S20

Environmental Impact

S18

Environmental Risk

(b)

Fig. 10. Results of the application of Section 2.2.4 Methodology 3: Prioritization of critical WWTPs: Ranking based on (a) the application of our proposal considering four profiles of decision makers (balanced, environmentalist, idealist and politician) and (b) on the EIRA method (Barjoveanu et al., 2010).


in this sense, warning signs. Government institutions, as well as water utilities, may then investigate why the malfunctions (the critical UOP) are permanent. This is the case, for example, of the S24 WWTP, critical for the removal of phosphorus and which requires, however, structural actions covering all the biological treatments. The absence of available areas for the realization of new basins did not allow for the adoption of conventional solutions (i.e., the A2O™ configuration) for the benefit of innovative solutions which, however, do not always achieve acceptable performances. Consequently, the institution (the Autonomous Province of Trento) envisages the realization of a new WWTP, located in a new site, able to treat wastewaters currently conducted to S5 and S24 WWTPs (http://www.appa.provincia.tn.it/). This first consideration shows how the monitoring of the WWTP efficiency carried out with our approach may be useful for a preliminary assessment of the WWTP status quality (at large spatial scale) guiding, subsequently, site-specific investigations (at scale of WWTP). The second consideration concerns the monitoring of investments over time. Our approach is able to highlight how the resources are allocated for each WWTP. Even in this case, warning signs should be defined. For example, a WWTP receiving continuous resources during the years and that, at the same time, has a low performance. The third consideration refers to the possibility to extend our approach on an international scale such as the European one. Due to the fact that the data input related to the WWTP performance are acquired by means of the ISTAT questionnaire (in turn, elaborated on the basis of the EUROSTAT guidelines), our proposal could allow for this extension. However, how could we take into account the local conditions of the different countries? Steps 1 and 2 of Section 2.2.2 Methodology 1: identification of critical WWTPs, opportunely modified and related to the specific country environmental law requirements and the applied technological solutions in WWTP, can permit such an adaptation. In fact, while Step 1 takes into account the legislation of each country (by means of pIs, see Table 1 of Appendix B, Supplementary data), step 2, aimed at investigating the processes of nutrient removal, takes into account the treatment schemes which in turn may be representative of a specific territorial context. For example, Norway has adopted treatment schemes mainly based on chemical–physical processes as well as non-conventional biological treatments (Ødegaard et al., 1994). While, France mainly uses treatment schemes based on biofiltration processes. In addition, other specific conditions concerning the WWTP (i.e., temperature, altimetry) are taken into account indirectly through the estimation of the typical values of the Ers. The fourth and final consideration refers to the assessment of the efficiency of the treatment schemes showed in Fig. 5 in terms of nutrient removals. The use of statistical models such as the order-m conditional efficiency one developed by De Witte and Kortelainen (2013), could be an interesting and innovative perspective. 5. Conclusions An integrated and multidisciplinary approach based on three methodologies able to monitor the efficiency as well as the investment costs of municipal WWTPs, as a reflection of effective, ineffective and non-existent planning policies, was defined and applied. The implementation of the integrated approach to a high number of Italian municipal WWTPs, located in a large spatial area, with a treatment capacity greater than 50,000 PE and discharging the treated wastewater into sensitive areas according to the Council Directive 91/ 271/EEC, allowed to achieve the following results: ▪ The identification of critical WWTPs and their critical processes (UOPs) by means of the PAS defined in the study. The PAS, that includes a pI system (for the overall assessment of the WWTP efficiency) and a system based on Er-methodologies (able to verify if the plant, considering the inlet pollution load and the treatment

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scheme, could remove the total nitrogen and total phosphorous until reaching the limits set out by the law), was able to identify critical processes with a particular effectiveness in identifying the critical nutrient removal processes; ▪ The assessment of the investment costs (intended as the sum of the construction costs for the realization of a new UOP and the costs of restructuring existing UOPs) to upgrade the critical WWTPs by means of a simplified approach that considers the cost related to a basic-configuration and those for the WWTP addition. In particular, an updated database, results in decades of experience of Italian multinationals engaged in the realization of WWTPs all over the world, was presented; ▪ The prioritization of the critical WWTPs by means of a multi-criteria approach which has proved to be more appropriate in interpreting the real needs of the territory compared with a risk-based approach (EIRA), generally adopted in problems of this nature. The obtained results have shown how our approach may work synergistically with the EIRA method providing complementary information to decision-makers; ▪ The possibility to extend the integrated approach on an EU-level integrating the WISE system currently in operation. This is due to the fact that data input related to the WWTPs performance, are acquired by means of official questionnaires as those provide by the Italian National Institute of Statistics (ISTAT) in their turn prepared according to the EUROSTAT guideline. However, additional treatment schemes based on attached growth and combined biological treatment processes should be developed. Finally, the developed approach is also suitable for WWTPs up to 2000 PE (no less than) and discharging the treated wastewater into non-sensitive areas as long as activated sludge-based WWTPs are considered. Acknowledgments The authors would like to specially thank ISTAT (in particular Stefano Tersigni), the Italian Institute of Statistics, for allowing the use of data used in this work. The authors would like to thank Roberto Morabito and Pierpaolo Mulargia of ENEA for their excellent support within the project, Sacha A. Berardo for his English revision and four anonymous reviewers for their precious suggestions. Furthermore, we acknowledge the financial support from the Italian Ministry of Economic Development (Department of Development and Cohesion Policies). Appendix A. Supplementary data Supplementary data associated with this article can be found in the online version, at http://dx.doi.org/10.1016/j.scitotenv.2015.03.106. These data include Google map of the most important areas described in this article. References Alegre, H., Almeida, M.D.C., 2009. Strategic Asset Management of Water Supply and Wastewater Infrastructures. 1th ed. IWA Publishing, London. Autonomous Province of Trento, 2000. Wastewater treatment plants in the autonomous province of Trento. Characteristics, Operating Data and Yields 1st ed. Tipografia Esperia, Trento (in Italian). Barjoveanu, G., Cojocariu, C., Robu, B., Teodosiu, C., 2010. Integrated assessment of wastewater treatment plants for sustainable river basement management. Environ. Eng. Manag. J. 9 (9), 1251–1258. Benedetti, L., Bixio, D., Vanrolleghem, P.A., 2006. Benchmarking of WWTP design by assessing costs, effluent quality and process variability. Water Sci. Technol. 54 (10), 95–102. Cabrera, E., Dane, P., Theuretzbacher-Fritz, H., 2011. Benchmarking Water Services: Guiding Water Utilities to Excellence. 1st ed. IWA Publishing, London. Chhetri, R.K., Thornberg, D., Berner, J., Gramstad, R., Öjstedt, U., Sharma, A.K., Andersen, H.R., 2014. Chemical disinfection of combined sewer overflow waters using performic acid or peracetic acids. Sci. Total Environ. 490, 1065–1072.

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