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A comparison of the efficacy of organic and mixedorganic polymers with polyaluminium chloride in chemically assisted primary sedimentation (CAPS) a
b
b
c
G. De Feo , M. Galasso , R. Landi , A. Donnarumma & S. De Gisi
d
a
Department of Industrial Engineering , University of Salerno , Fisciano (SA) , Italy
b
Bierre Chimica srl , Fisciano (SA) , Italy
c
Civil and Environmental Engineer , Angri (SA) , Italy
d
Italian National Agency for New Technology, Energy and Sustainable Economic Development (ENEA), Environmental Department , Water Resource Management Laboratory , Bologna , Italy Accepted author version posted online: 31 Oct 2012.Published online: 28 Nov 2012.
To cite this article: G. De Feo , M. Galasso , R. Landi , A. Donnarumma & S. De Gisi (2013) A comparison of the efficacy of organic and mixed-organic polymers with polyaluminium chloride in chemically assisted primary sedimentation (CAPS), Environmental Technology, 34:10, 1297-1305, DOI: 10.1080/09593330.2012.745622 To link to this article: http://dx.doi.org/10.1080/09593330.2012.745622
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Environmental Technology, 2013 Vol. 34, No. 10, 1297–1305, http://dx.doi.org/10.1080/09593330.2012.745622
A comparison of the efficacy of organic and mixed-organic polymers with polyaluminium chloride in chemically assisted primary sedimentation (CAPS) G. De Feoa∗ , M. Galassob , R. Landib , A. Donnarummac and S. De Gisid a Department
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of Industrial Engineering, University of Salerno, Fisciano (SA), Italy; b Bierre Chimica srl, Fisciano (SA), Italy; c Civil and Environmental Engineer, Angri (SA), Italy; d Italian National Agency for New Technology, Energy and Sustainable Economic Development (ENEA), Environmental Department, Water Resource Management Laboratory, Bologna, Italy (Received 2 July 2012; final version received 25 October 2012 ) CAPS is the acronym for chemically assisted primary sedimentation, which consists of adding chemicals to raw urban wastewater to increase the efficacy of coagulation, flocculation and sedimentation. The principal benefits of CAPS are: upgrading of urban wastewater treatment plants; increasing efficacy of primary sedimentation; and the major production of energy from the anaerobic digestion of primary sludge. Metal coagulants are usually used because they are both effective and cheap, but they can cause damage to the biological processes of anaerobic digestion. Generally, biodegradable compounds do not have these drawbacks, but they are comparatively more expensive. Both metal coagulants and biodegradable compounds have preferential and penalizing properties in terms of CAPS application. The problem can be solved by means of a multicriteria analysis. For this purpose, a series of tests was performed in order to compare the efficacy of several organic and mixed-organic polymers with that of polyaluminium chloride (PACl) under specific conditions. The multi-criteria analysis was carried out coupling the simple additive weighting method with the paired comparison technique as a tool to evaluate the criteria priorities. Five criteria with the following priorities were used: chemical oxygen demand (COD) removal > turbidity, SV60 > coagulant dose, and coagulant cost. The PACl was the best alternative in 70% of the cases. The CAPS process using PACl made it possible to obtain an average COD removal of 68% compared with 38% obtained, on average, with natural sedimentation and 61% obtained, on average, with the best PACl alternatives (cationic polyacrylamide, natural cationic polymer, dicyandiamide resin). Keywords: CAPS; multi-criteria analysis; organic polymers; polyaluminium chloride; urban wastewater
Introduction CAPS is the acronym for chemically assisted primary sedimentation, which consists of adding chemicals to raw urban wastewater to increase the efficacy of primary sedimentation. The addition of the coagulation/flocculation process achieves efficiencies between 60% and 90% for the total suspended solids (TSS), 40% and 80% for the five-day biochemical oxygen demand (BOD5 ), 30% and 70% for the chemical oxygen demand (COD), 65% and 95% for phosphorus, and 80% and 90% for bacteria. Conversely, the simple primary sedimentation process may be able to remove 50% and 70% of TSS, 25% and 40% of BOD5 , 5% and 10% of phosphorus, and 50% and 60% of pathogens [1–3]. CAPS is not an innovative process [2,4], but nowadays it offers a valuable alternative both for energetic optimization and upgrading of urban wastewater treatment plants (UWWTPs) [3,5]. Moreover, its implementation does not require any significant structural interventions [6,7]. The most favourable conditions for the application of CAPS in a UWWTP are the presence of both a primary sedimentation tank and a sludge anaerobic digestion basin. ∗ Corresponding
author. Email: [email protected]
© 2013 Taylor & Francis
In general, the use of CAPS may be valuable in a UWWTP where the activated sludge process is designed with a high load as well as in a UWWTP with strong seasonal variation of the inlet hydraulic and organic load, typical of coastal regions [3,6,7]. The advantages of applying the CAPS process include: production of primary sludge with a subsequent increase in the production of biological gas from the anaerobic digestion phase [4,8]; reduction of the food/microorganisms ratio (F/M) with the subsequent reduction of the energy costs for the activated sludge process [3]; improvement of both the chemical characteristics of the secondary (biological) sludge (with its possible reuse in agriculture) and final effluent quality (due to a smaller production of non-settling solids) [9,10]. The disadvantages of the CAPS process are related to the pH alteration with possible damage to the activity of the microorganisms in the biological stage, the chemicals costs, and a slight complication of the process scheme [1,3,11,12]. Moreover, greater COD reduction in the primary sedimentation may have negative effects on nitrogen removal, but
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this aspect is site-specific. In fact, it depends on the value of the compliance limit as well as the COD/TKN ratio in the wastewater (TKN = total Kjeldahl nitrogen) [2–4]. The use of metal coagulants (such as ferric chloride, aluminium sulfate, etc.), which are usually the most effective in terms of COD removal can cause damage to the biological processes of anaerobic digestion with less biodegradable sludge [13,14]. In particular, the presence of pollutants such as zinc, cadmium, etc., can inhibit the methanogenic phase. Moreover, using aluminium and ferric salts as coagulants can produce residual metals in the treated water [15,16]. On the contrary, generally, biodegradable compounds do not have these drawbacks, but they are comparatively more expensive [17–19]. Both metal coagulants and biodegradable compounds have preferential and penalizing properties in terms of CAPS application. Thus, due to its intrinsic nature, the problem can be solved by means of a multi-criteria analysis as reported in De Feo et al. [2] for urban wastewater and with metal coagulants, and Aragonés-Beltrán et al. [20] for industrial wastewater. The principal aim of De Feo et al. [2] was to define a procedure for selecting the best combination of coagulant and dose when using jar tests. This aim was pursued using a self-developed multi-criteria analysis technique, positively checked with the analytic hierarchy process [21,22]. The following five criteria were used: COD percentage removal, sludge volume after 2 h, coagulant dose, coagulant cost, and pH percentage variation. The priorities among criteria were directly assigned without using a specific technique. De Feo et al. [2] performed a unique comparison with 40 alternatives combining different metal coagulants and doses. The principal aim of this study was to compare the efficacy of organic and mixed-organic polymers with that of polyaluminium chloride (PACl), which is usually used because it is both effective and inexpensive [23]. For this purpose, a series of tests was performed in a wastewater treatment and chemicals supply company in the Province of Salerno, in the Campania region of Southern Italy. For the Table 1.
Materials and methods Raw wastewater was collected from the influent to three urban wastewater treatment plants, of which UWWTP1 and UWWTP3 primarily treat domestic wastewater, while UWWTP2 primarily treats industrial wastewater (especially dairy wastewater). UWWTP1 is based on a flow chart without primary settling and with an activated sludge secondary treatment providing the prolonged aeration [26], with 5000 equivalent inhabitants. Both UWWTP2 and UWWTP3 are conventional activated sludge treatments with 60,000 and 300,000 equivalent inhabitants, respectively. A series of jar tests was performed in order to simulate the CAPS process. The samples for the jar tests were prepared in the laboratory by directly using raw wastewater or by adding to the basic raw wastewater 10–20 mL of activated sludge in a litre, obtaining four types of wastewater as reported in Table 1. Overall, adding activated sludge increases the efficacy of primary sedimentation in a conventional UWWTP [26]. Moreover, activated sludge was added to raw wastewater coming from UWWTP3 due to its very low value of COD ( turbidity, SV60 > coagulant dose, coagulant cost. In particular, with this assumption, the obtained percentage priorities were the following: COD removal = 33.33%; SV60 = 23.33%; turbidity = 23.33%; coagulant dose = 10.00%; coagulant cost = 10.00%.
Results and discussion All of the obtained results are reported in Tables 3 (coagulants combinations 1–5) and 4 (coagulants combinations 6–10). Moreover, the values obtained for COD and turbidity are reported in Figures 1 and 2, respectively, for the first eight coagulants combinations. Each figure shows the COD (turbidity) value of the untreated wastewater which is the reference base (the tick continuous line), the COD
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G. De Feo et al. Values obtained for the five comparison criteria for the coagulants combinations 1–5. Criteria
Comparisons
Alternatives
PCT weight Maximize (max.) or minimize (min.)
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(1) Coag− 6 (10, 20, 30, 40, 50, 60 mg/L) vs. PACl (50 mg/L)
(2) Coag− 1 (200, 300, 400, 500, 600 mg/L) vs. PACl (50 mg/L)
(3) Coag− 5 (30, 40, 50, 60 mg/L) + polyanionic vs. PACl (50 mg/L) (4) Coag− 4 (40, 50, 60, 70 mg/L) + polyanionic vs. PACl (50 mg/L) (5) Coag− 2 (100, 150, 200, 250) + polycationic vs. PACl (50 mg/L)
Coag− 6− 10 Coag− 6− 20 Coag− 6− 30 Coag− 6− 40 Coag− 6− 50 Coag− 6− 60∗,∗∗ PACl− 50 Coag− 1− 200 Coag− 1− 300 Coag− 1− 400 Coag− 1− 500 Coag− 1− 600∗,∗∗ PACl− 50 Coag− 5− 30∗,∗∗ Coag− 5− 40 Coag− 5− 50 Coag− 5− 60 PACl− 50 Coag− 4− 40∗∗ Coag− 4− 50 Coag− 4− 60 Coag− 4− 70 PACl− 50∗ Coag− 2− 100∗∗ Coag− 2− 150 Coag− 2− 200 Coag− 2− 250 PACl− 50∗
COD removal [%]
SV60 [mL/L]
Dose [mg/L]
Cost [¤/kg]
Turbidity [NTU]
33.33 max.
23.33 min.
10,00 min.
10,00 min.
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Npi
18.3 28.7 37.7 39.6 46.7 53.4 59.8 27.5 36.3 51.8 49.6 53.5 37.3 52.1 60.7 54.2 52.1 51.3 17.0 10.5 11.1 5.8 63.1 58.2 56.3 53.3 57.1 65.5
4.5 6 7 6 7.5 5 20 7 10 12 13 15 18 10 15 17 15 13 2 2 2 2 15 16 18 16 18 28
10 20 30 40 50 60 50 200 300 400 500 600 50 30 40 50 60 50 40 50 60 70 50 50 100 150 200 50
2.30 2.30 2.30 2.30 2.30 2.30 0.30 1.20 1.20 1.20 1.20 1.20 0.30 1.50 1.50 1.50 1.50 0.30 1.20 1.20 1.20 1.20 0.30 1.20 1.20 1.20 1.20 0.30
61.2 49.9 44.4 44.2 38.9 16.9 18.4 27.9 18.8 11.7 10.4 6.42 11.5 5.95 5.12 7.32 9.32 7.2 23.9 21.2 21.9 22.6 4.14 23.2 24.4 26.6 25.9 3.4
0.666 0.619 0.643 0.679 0.694 1.000 0.935 0.717 0.720 0.880 0.866 1.000 0.922 1.000 0.972 0.807 0.762 0.937 0.628 0.565 0.550 0.500 1.000 0.765 0.668 0.658 0.643 1.000
∗ = the best multi criteria alternative. ∗∗ = the best alternative to the PACl.
(turbidity) value of the wastewater treated with PACl, which is the comparison base (the tick dashed line), and finally the values of COD (turbidity) related to the several tested coagulant doses which represent the alternatives to compare with the PACl value. In particular, the empty rhombus (on the y-axis) indicates the value of COD (turbidity) obtained for natural sedimentation. The CAPS process achieved better COD and turbidity values (i.e. lower) than that of natural sedimentation confirming the efficacy of the process consistent with the findings of previous studies [1–4]. Moreover, the efficacy of the CAPS process almost always increased with the dose of coagulant both in terms of COD and turbidity. Notably, the results obtained for COD removal were very promising, including a more than 80% reduction for combinations 7, 8, 9 and 10 both for PACl and biodegradable coagulants. The main reason for this result was the presence of activated sludge in the sample. This result
further corroborates the practice of adding activated sludge in the primary sedimentation, further aided with CAPS. Values between 50% and 75% were obtained only with natural sedimentation, greater than the literature values (25–40%), as reported in the introduction. Values between 80% and 90% and 65 and 90% were obtained with PACl and with the best alternative to PACl, respectively. On the whole, as shown in Figures 1(d) and 2(d), polyamine (i.e. Coag_4) was the single coagulant not properly working (removal less than 20%) with WW1 . This was because of the absence of affinity of polyamine with the considered wastewater, probably due to a scarce adsorptionbridging ability. On the contrary, polyamine showed a good adsorption-bridging ability for removing the disperse dye from dyeing wastewater [28]. For WW1 , excluding combination 4, average COD percentage removal was 49.5% for PACl and 53% for the best PACl alternative. Finally, also considering WW1 , the natural cationic polymer showed a
Environmental Technology Table 4.
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Values obtained for the five comparison criteria for the coagulants combinations 6–10. Criteria
Comparisons
COD removal [%]
SV60 [mL/L]
Dose [mg/L]
Cost [¤/kg]
Turbidity [NTU]
33.33 max.
23.33 min.
10,00 min.
10,00 min.
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Coag− 1− 50 Coag− 1− 100
56.4 55.5
3.5 4
50 100
1.20 1.20
10.3 7.26
0.884 0.819
Coag− 1− 150 Coag− 1− 200∗∗ Coag− 1− 250 PACl− 50∗ Coag− 3− 20 Coag− 3− 40 Coag− 3− 60∗∗ Coag− 3− 80 PACl− 50∗ Coag− 1− 100 Coag− 1− 150 Coag− 1− 200∗∗ Coag− 1− 50∗ Coag− 5− 30 Coag− 5− 40
59.0 60.7 60.0 63.0 88.3 90.7 91.4 91.5 90.5 82.4 83.1 84.4 85.0 76.6 65.6
5.5 6 7 14 23 24 25 27 26 32 31 29 25 9 8
150 200 250 50 20 40 60 80 50 100 150 200 50 30 40
1.20 1.20 1.20 0.30 1.20 1.20 1.20 1.20 0.30 1.20 1.20 1.20 0.30 1.2 1.2
4.28 3.25 3.9 3.2 22.6 8.6 6.3 7 7.62 11.4 8.76 8.41 8.85 6.57 8.52
0.840 0.893 0.813 1.000 0.857 0.921 0.966 0.911 1.000 0.761 0.806 0.825 1.000 0.756 0.701
Coag− 2− 10∗∗ Coag− 2− 20 Coag− 2− 30 PACl− 100∗ Coag− 5− 30 Coag− 5− 40
63.9 65.8 55.3 81.1 78.8 80.3
7 7 6 22 9 9
10 20 30 100 30 40
1.2 1.2 1.2 0.30 1.20 1.20
4.24 6.22 7.75 0.88 3.54 4.55
0.859 0.781 0.737 1.000 0.795 0.772
Coag− 4− 10∗∗ Coag− 4− 20 Coag− 4− 30 PACl− 100∗
74.8 79.1 77.8 84.1
8 7 6 20
10 20 30 100
1.20 1.20 1.20 0.30
3.66 4.63 4.05 1.03
0.887 0.857 0.883 1.000
Alternatives
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PCT weight Maximize (max.) or minimize (min.) (6) Coag− 2 (50 mg/L) + Coag− 1 (50, 100, 150, 200, 250 mg/L) + polycationic vs. PACl (50 mg/L)
(7) Coag− 3 (20, 40, 60, 80 mg/L) + polyanionic vs. PACl (50 mg/L) (8) Coag− 2 (100 mg/L) + Coag− 1 (100, 150, 200 mg/L) vs. PACl (50 mg/L) (9) Coag− 2 (10 mg/L) + Coag− 5 (30, 40 mg/L), Coag− 2 (10 mg/L) + Coag− 4 (10, 20, 30 mg/L) vs. PACl (100 mg/L)
(10) Coag− 2 (25 mg/L) + Coag− 5 (30,40 mg/L), Coag− 2 (25 mg/L) + Coag− 4 (10, 20, 30 mg/L) vs. PACl (100 mg/L)
∗ = the best multi-criteria alternative. ∗∗ = the best alternative to the PACl.
better performance in terms of COD and turbidity removal rather than PACl. However, these results may possibly be attributed to the high coagulant dosage (200–600 mg/L). From this point onwards, the results are presented and discussed in terms of multi-criteria analysis. Tables 3 and 4 contain all the results obtained for the five comparison criteria considered (percentage COD removal, SV60 , coagulant dose, coagulant cost, turbidity). In other words, they contain the alternatives matrix. The criteria priorities and the indication of maximizing or minimizing criteria are reported in the first two lines of the tables, respectively. The last column of Tables 3 and 4 shows the normalized priority index (Npi) obtained by combining the SAW technique coupled with the PCT tool. In particular, a value of Npi equal to 1 means that the corresponding alternative is the best alternative: this alternative was marked with an asterisk identifying the so-called ‘best multi-criteria alternative’. A
double asterisk indicates the best alternative to the PACl (i.e. the comparison target). The PACl was not the best multicriteria alternative when the asterisk and double asterisk are near a same value: this occurred three times out of ten cases, so PACl was the best multi-criteria alternative in 70% of the cases. The first case where PACl (with a dose of 50 mg/L) was not the best absolute alternative occurred with the application of a cationic polyacrylamide (with a dose of 60 mg/L) as a coagulant. The cationic polyacrylamides are copolymers of acrylamide and a co-monomer cation (having a quaternary amino group). The cationic groups introduced in the polymer have a positive charge in an aqueous solution. The cationizing monomers are: dimethylaminoethyl; dimethylaminoethylmethacrilato; dimethylaminopropylacrylamide. Polyacrylamide is widely used in sewage sludge treatment to enhance dewatering [28,29].
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Figure 1. COD values for the first eight coagulant combinations: (a) Coag_6 (10, 20, 30, 40, 50, 60 mg/L) vs. PACl (50 mg/L), type of wastewater = WW1 ; (b) Coag_1 (200, 300, 400, 500, 600 mg/L) vs. PACl (50 mg/L), type of wastewater = WW1 ; (c) Coag_5 (30, 40, 50, 60 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW1 ; (d) Coag_4 (40, 50, 60, 70 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW1 ; (e) Coag_2 (100, 150, 200, 250) + polycationic vs. PACl (50 mg/L), type of wastewater = WW2 ; (f) Coag_2 (50 mg/L) + Coag_1 (50, 100, 150, 200, 250 mg/L) + polycationic vs. PACl (50 mg/L), type of wastewater = WW2 ; (g) Coag_3 (20, 40, 60, 80 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW3 ; and (h) Coag_2 (100 mg/L) + Coag_1 (100, 150, 200 mg/L) vs. PACl (50 mg/L), type of wastewater = WW3 .
Synthetic polymers, in general, can have negative consequences in terms of the inhibition of anaerobic digestion because of the presence of acrylamide monomer (due to the degradation of polyacrylamide), which is highly toxic [30,31]. However, the product used, being a polysaccharide,
has no contraindications. In addition, the solution used was only at 1% of polyacrylamide. Figure 3 proposes a comparison among the percentage COD removals obtained with PACl, best PACl alternative and natural sedimentation.
Environmental Technology (a)
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Figure 2. Turbidity values for the first eight coagulants combinations: (a) Coag_6 (10, 20, 30, 40, 50, 60 mg/L) vs. PACl (50 mg/L), type of wastewater = WW1 ; (b) Coag_1 (200, 300, 400, 500, 600 mg/L) vs. PACl (50 mg/L), type of wastewater = WW1 ; (c) Coag_5 (30, 40, 50, 60 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW1 ; (d) Coag_4 (40, 50, 60, 70 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW1 ; (e) Coag_2 (100, 150, 200, 250) + polycationic vs. PACl (50 mg/L), type of wastewater = WW2 ; (f) Coag_2 (50 mg/L) + Coag_1 (50, 100, 150, 200, 250 mg/L) + polycationic vs. PACl (50 mg/L), type of wastewater = WW2 ; (g) Coag_3 (20, 40, 60, 80 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW3 ; and (h) Coag_2 (100 mg/L) + Coag_1 (100, 150, 200 mg/L) vs. PACl (50 mg/L), type of wastewater = WW3 .
Moreover, it reports a line corresponding with the COD removal of 40%. One of the main aims of CAPS is to improve the removal of organic material. It is therefore unnecessary to evaluate the alternatives with efficiency comparable to that of simple primary settling. In fact, the
multi-criteria analysis was able to identify, as the best alternative, an alternative assuring a COD removal of more than 40%: this was a direct consequence of the fact that the COD removal percentage was considered as the criterion with the highest priority. Furthermore, Figure 3 shows that the
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Best PACl alternative
Natural sedimentation
A comparison among the percentage COD removals obtained with PACl, the best PACl alternative and natural sedimentation.
best multi-criteria alternative assured a percentage COD removal significantly greater than natural sedimentation, confirming the efficacy of the CAPS process. The second case where PACl (with a dose of 50 mg/L) was not the best absolute alternative occurred with the application of a natural cationic polymer (with a dose of 600 mg/L) as a coagulant. In this case, the PACl was not able to assure a minimum 40% COD removal, while the natural cationic polymer showed an efficacy more than 50%. Finally, natural sedimentation was observed to be quite ineffective in removing COD. The best performance was reached with an elevated dose of the natural polymer, which is comparatively more expensive than PACl. In fact, cost effectiveness is one of the main reasons why PACl application is currently favoured. The third case where PACl (with a dose of 50 mg/L) was not the best absolute alternative was in the application of a dicyandiamide resin (with a dose of 30 mg/L) as a coagulant. The COD removal was similar to that of PACl and greater than 50% with around 30% more than natural sedimentation. The dicyandiamide resins are a series of organic polymers with different molecular weights belonging to the group of amino resins. These features allow rapid complexation and flocculation with the formation of aggregates and flakes that settle easily. They have a significant decolouring capacity when compared to other coagulants (useful for the treatment of textile and tannery wastewater). These capacities were used by Galasso et al. [32] to remove syntans in the treatment of tannery wastewater, due to soluble materials not being removed with the conventional chemical–physical processes. Conclusions The main conclusions of the study focused on comparing the efficacy of organic and mixed-organic polymers with PACl
(under specific condition) in chemically assisted primary sedimentation: • the PACl was the best alternative in 70% of the cases when applying a multi-criteria analysis based on the SAW method coupled with PCT, with five criteria (COD removal > turbidity, SV60 > coagulant dose, coagulant cost); • the CAPS process using PACl as a coagulant (with a dose of 50 mg/L) made it possible to obtain an average COD removal of 68% compared with 38% obtained, on average, with natural sedimentation and 61% obtained, on average, with the best alternative using organic and mixed-organic polymers; • the best PACl alternatives were the application of a coagulant: a cationic polyacrylamide (with a dose of 60 mg/L), a natural cationic polymer (with a dose of 600 mg/L) and, finally, a dicyandiamide resin (with a dose of 30 mg/L); • only the polyamine did not work properly because of the absence of an affinity for polyamine with the considered wastewater, probably due to a scarce adsorption-bridging ability. Acknowledgements The authors wish to thank Dr Sacha A. Berardo and Ms Meisha Hunter for their English revisions to the text, as well as the comments of three anonymous referees.
References [1] C.S. Poon and C.W. Chu, The use of ferric chloride and anionic polymer in the chemically assisted primary sedimentation process, Chemosphere 39 (1999), pp. 1573–1582. [2] G. De Feo, S. De Gisi, and M. Galasso, Definition of a practical multi-criteria procedure for selecting the best coagulant in a chemically assisted primary sedimentation process for
Environmental Technology
[3]
[4]
Downloaded by [University of Colorado at Boulder Libraries] at 11:19 28 December 2014
[5] [6] [7] [8]
[9] [10]
[11] [12] [13] [14]
[15] [16] [17]
the treatment of urban wastewater, Desalination 230 (2008), pp. 229–238. G. De Feo, S. De Gisi, and M. Galasso, Chemically assisted primary sedimentation: A green chemistry option, in Green Technologies for Wastewater Treatment, G. Lofrano, ed., Springer, Dordrecht, Heidelberg, New York, London, 2012, pp. 1–18. R. Ramadori, D. Marani, V. Renzi, R. Passino, and A.C. Di Pinto, Rethinking sewage treatment by enhancing primary settling with low-dosage lime, Water Sci. Technol. 52 (2005), pp. 185–192. W. Ghyoot and W. Verstraete, Anaerobic digestion of primary sludge from chemical pre-precipitation, Water Sci. Technol. 36 (1997), pp. 357–365. H. Odegaard, P. Balmer, and I. Hanaus, Chemical precipitation in highly loaded stabilization ponds in cold climates, Water Sci. Technol. 19 (1987), pp. 71–77. H. Odegaard, Appropriate technology for wastewater treatment in coastal tourist area, Water Sci. Technol. 21 (1989), pp. 1–17. D. Marani, V. Renzi, R. Ramadori, and C.M. Braguglia, Size fractionation of COD in urban wastewater from a combined sewer system, Water Sci. Technol. 50 (2004), pp. 79–86. A.C. Chao and T.M. Keinath, Influence of process loading intensity on sludge clarification and thickening characteristics, Water Res. 13 (1979), pp. 1213–1223. G. Mininni, C.M. Braguglia, R. Ramadori, and M.C. Tomei, An innovative sludge management system based on separation of primary and secondary sludge treatment, Water Sci. Technol. 50 (2004), pp. 145–153. H. Odegaard, Optimized particle separation in the primary step of wastewater treatment, Water Sci. Technol. 37 (1998), pp. 43–53. P.A. Vesilind, Wastewater Treatment Plant Design, Water Environment Federation (WEF), Alexandria, 2003. S.K. Dentel and J.M. Gossett, Effect of chemical coagulation on anaerobic digestibility of organic materials, Water Res. 16 (1982), pp. 707–718. K.V. Akshaya, R.D. Rajesh, and B. Puspendu, A review on chemical coagulation/flocculation technologies for removal of colour from textile wastewaters, J. Environ. Manage. 93 (2012), pp. 154–168. A. Ndabigengesere and K.S. Narasiah, Quality of water treated by coagulation using Moringa oleifera seeds, Water Res. 32 (1998), pp. 781–791. Z. Song, C.J. Williams, and R.G.J. Edyvean, Coagulation and anaerobic digestion of tannery wastewater, Process. Saf. Environ. 79 (2001), pp. 23–28. T. Chen, B. Gao, and Q. Yue, Effect of dosing method and pH on colour removal performance and floc aggregation of polyferric chloride–polyamine dual-coagulant in synthetic dyeing wastewater treatment, Colloids Surf., A 355 (2010), pp. 121–129.
1305
[18] Y. Chun-Yang, Emerging usage of plant-based coagulants for water and wastewater treatment, Process Biochem. 45 (2010), pp. 1437–1444. [19] B. Gao, B. Liu, T. Chen, and Q. Yue, Effect of aging period on the characteristics and coagulation behaviour of polyferric chloride and polyferric chloride–polyamine composite coagulant for synthetic dying wastewater treatment, J. Hazard. Mater. 187 (2011), pp. 413–420. [20] P. Aragonés-Beltrán, J.A. Mendoza-Roca, A. Bes-Piá, M. García-Melón, and E. Parra-Ruiz, Application of multicriteria decision analysis to jar-test results for chemicals selection in the physical–chemical treatment of textile wastewater, J. Hazard. Mater. 164 (2009), pp. 288–295. [21] T.L. Saaty, Decision Making for Leaders. The Analytic Hierarchy Process for Decision in a Complex World, RWS Publications, Pittsburgh, USA, 2001. [22] A. Balasubramaniam and N. Voulvoulis, The Appropriateness of Multicriteria Analysis in environmental decision-making problems, Environ. Technol. 26 (2005), pp. 951–962. [23] Y.X. Zhao, B.Y. Gao, Y. Wang, H.K. Shon, X.W. Bo, and Q.Y. Yue, Coagulation performance and floc characteristics with polyaluminium chloride using sodium alginate as coagulant aid: A preliminary assessment, Chem. Eng. J. 183 (2012), pp. 387–394. [24] H. Ching-Lai and Y. Kwangsun, Multiple Attribute Decision Making, Springer Verlag, Berlin-Heidelberg, New York, 1981. [25] W. Mondy and R. Noe, Human Resource Management, Prentice-Hall, Upper Saddle River, NJ, 2008. [26] G. Tchobanoglous, F.L. Burton, and H.D. Stensel, Wastewater Engineering: Treatment and Reuse, Metcalf & Eddy, Inc, McGraw-Hill, New York, 2003. [27] APHA, Standard Methods for the Examination of Water and Wastewater, 19th ed., APHA-AWWA-WPCF, Washington, DC, 1995. [28] Y. Wang, B. Gao, Q. Yue, X. Zhan, X. Si, and C. Li, Flocculation performance of epichlorohydrin-dimethylamine polyamine in treating dyeing wastewater, J. Environ. Manage. 91 (2009), pp. 423–431. [29] E. Campos, M. Almirall, J. Mtnez-Almela, J. Palatsi, and X. Flotats, Feasibility study of the anaerobic digestion of dewatered pig slurry by means of polyacrylamide, Bioresour. Technol. 99 (2008), pp. 387–395. [30] IPCS, Acrylamide. Environmental Health Criteria 49, World Health Organization, Geneva, Switzerland, 1985. [31] G. Zhu, H. Zheng, P. Zhang, Z. Jiao, and J. Yin, Near-infrared spectroscopy as a potential tool with radial basis function for measurement of residual acrylamide in organic polymer, Environ. Technol. (2012), doi 10.1080/09593330.2012.683817. [32] M. Galasso, S. De Gisi, R. Landi, and G. De Feo, Il trattamento chimico-fisico di tannini sintetici mediante l’utilizzo di coagulanti misti organici, Ing. Ambientale 38 (2009), pp. 444–452.
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
A comparison of the efficacy of organic and mixedorganic polymers with polyaluminium chloride in chemically assisted primary sedimentation (CAPS) a
b
b
c
G. De Feo , M. Galasso , R. Landi , A. Donnarumma & S. De Gisi
d
a
Department of Industrial Engineering , University of Salerno , Fisciano (SA) , Italy
b
Bierre Chimica srl , Fisciano (SA) , Italy
c
Civil and Environmental Engineer , Angri (SA) , Italy
d
Italian National Agency for New Technology, Energy and Sustainable Economic Development (ENEA), Environmental Department , Water Resource Management Laboratory , Bologna , Italy Accepted author version posted online: 31 Oct 2012.Published online: 28 Nov 2012.
To cite this article: G. De Feo , M. Galasso , R. Landi , A. Donnarumma & S. De Gisi (2013) A comparison of the efficacy of organic and mixed-organic polymers with polyaluminium chloride in chemically assisted primary sedimentation (CAPS), Environmental Technology, 34:10, 1297-1305, DOI: 10.1080/09593330.2012.745622 To link to this article: http://dx.doi.org/10.1080/09593330.2012.745622
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Environmental Technology, 2013 Vol. 34, No. 10, 1297–1305, http://dx.doi.org/10.1080/09593330.2012.745622
A comparison of the efficacy of organic and mixed-organic polymers with polyaluminium chloride in chemically assisted primary sedimentation (CAPS) G. De Feoa∗ , M. Galassob , R. Landib , A. Donnarummac and S. De Gisid a Department
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of Industrial Engineering, University of Salerno, Fisciano (SA), Italy; b Bierre Chimica srl, Fisciano (SA), Italy; c Civil and Environmental Engineer, Angri (SA), Italy; d Italian National Agency for New Technology, Energy and Sustainable Economic Development (ENEA), Environmental Department, Water Resource Management Laboratory, Bologna, Italy (Received 2 July 2012; final version received 25 October 2012 ) CAPS is the acronym for chemically assisted primary sedimentation, which consists of adding chemicals to raw urban wastewater to increase the efficacy of coagulation, flocculation and sedimentation. The principal benefits of CAPS are: upgrading of urban wastewater treatment plants; increasing efficacy of primary sedimentation; and the major production of energy from the anaerobic digestion of primary sludge. Metal coagulants are usually used because they are both effective and cheap, but they can cause damage to the biological processes of anaerobic digestion. Generally, biodegradable compounds do not have these drawbacks, but they are comparatively more expensive. Both metal coagulants and biodegradable compounds have preferential and penalizing properties in terms of CAPS application. The problem can be solved by means of a multicriteria analysis. For this purpose, a series of tests was performed in order to compare the efficacy of several organic and mixed-organic polymers with that of polyaluminium chloride (PACl) under specific conditions. The multi-criteria analysis was carried out coupling the simple additive weighting method with the paired comparison technique as a tool to evaluate the criteria priorities. Five criteria with the following priorities were used: chemical oxygen demand (COD) removal > turbidity, SV60 > coagulant dose, and coagulant cost. The PACl was the best alternative in 70% of the cases. The CAPS process using PACl made it possible to obtain an average COD removal of 68% compared with 38% obtained, on average, with natural sedimentation and 61% obtained, on average, with the best PACl alternatives (cationic polyacrylamide, natural cationic polymer, dicyandiamide resin). Keywords: CAPS; multi-criteria analysis; organic polymers; polyaluminium chloride; urban wastewater
Introduction CAPS is the acronym for chemically assisted primary sedimentation, which consists of adding chemicals to raw urban wastewater to increase the efficacy of primary sedimentation. The addition of the coagulation/flocculation process achieves efficiencies between 60% and 90% for the total suspended solids (TSS), 40% and 80% for the five-day biochemical oxygen demand (BOD5 ), 30% and 70% for the chemical oxygen demand (COD), 65% and 95% for phosphorus, and 80% and 90% for bacteria. Conversely, the simple primary sedimentation process may be able to remove 50% and 70% of TSS, 25% and 40% of BOD5 , 5% and 10% of phosphorus, and 50% and 60% of pathogens [1–3]. CAPS is not an innovative process [2,4], but nowadays it offers a valuable alternative both for energetic optimization and upgrading of urban wastewater treatment plants (UWWTPs) [3,5]. Moreover, its implementation does not require any significant structural interventions [6,7]. The most favourable conditions for the application of CAPS in a UWWTP are the presence of both a primary sedimentation tank and a sludge anaerobic digestion basin. ∗ Corresponding
author. Email: [email protected]
© 2013 Taylor & Francis
In general, the use of CAPS may be valuable in a UWWTP where the activated sludge process is designed with a high load as well as in a UWWTP with strong seasonal variation of the inlet hydraulic and organic load, typical of coastal regions [3,6,7]. The advantages of applying the CAPS process include: production of primary sludge with a subsequent increase in the production of biological gas from the anaerobic digestion phase [4,8]; reduction of the food/microorganisms ratio (F/M) with the subsequent reduction of the energy costs for the activated sludge process [3]; improvement of both the chemical characteristics of the secondary (biological) sludge (with its possible reuse in agriculture) and final effluent quality (due to a smaller production of non-settling solids) [9,10]. The disadvantages of the CAPS process are related to the pH alteration with possible damage to the activity of the microorganisms in the biological stage, the chemicals costs, and a slight complication of the process scheme [1,3,11,12]. Moreover, greater COD reduction in the primary sedimentation may have negative effects on nitrogen removal, but
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this aspect is site-specific. In fact, it depends on the value of the compliance limit as well as the COD/TKN ratio in the wastewater (TKN = total Kjeldahl nitrogen) [2–4]. The use of metal coagulants (such as ferric chloride, aluminium sulfate, etc.), which are usually the most effective in terms of COD removal can cause damage to the biological processes of anaerobic digestion with less biodegradable sludge [13,14]. In particular, the presence of pollutants such as zinc, cadmium, etc., can inhibit the methanogenic phase. Moreover, using aluminium and ferric salts as coagulants can produce residual metals in the treated water [15,16]. On the contrary, generally, biodegradable compounds do not have these drawbacks, but they are comparatively more expensive [17–19]. Both metal coagulants and biodegradable compounds have preferential and penalizing properties in terms of CAPS application. Thus, due to its intrinsic nature, the problem can be solved by means of a multi-criteria analysis as reported in De Feo et al. [2] for urban wastewater and with metal coagulants, and Aragonés-Beltrán et al. [20] for industrial wastewater. The principal aim of De Feo et al. [2] was to define a procedure for selecting the best combination of coagulant and dose when using jar tests. This aim was pursued using a self-developed multi-criteria analysis technique, positively checked with the analytic hierarchy process [21,22]. The following five criteria were used: COD percentage removal, sludge volume after 2 h, coagulant dose, coagulant cost, and pH percentage variation. The priorities among criteria were directly assigned without using a specific technique. De Feo et al. [2] performed a unique comparison with 40 alternatives combining different metal coagulants and doses. The principal aim of this study was to compare the efficacy of organic and mixed-organic polymers with that of polyaluminium chloride (PACl), which is usually used because it is both effective and inexpensive [23]. For this purpose, a series of tests was performed in a wastewater treatment and chemicals supply company in the Province of Salerno, in the Campania region of Southern Italy. For the Table 1.
Materials and methods Raw wastewater was collected from the influent to three urban wastewater treatment plants, of which UWWTP1 and UWWTP3 primarily treat domestic wastewater, while UWWTP2 primarily treats industrial wastewater (especially dairy wastewater). UWWTP1 is based on a flow chart without primary settling and with an activated sludge secondary treatment providing the prolonged aeration [26], with 5000 equivalent inhabitants. Both UWWTP2 and UWWTP3 are conventional activated sludge treatments with 60,000 and 300,000 equivalent inhabitants, respectively. A series of jar tests was performed in order to simulate the CAPS process. The samples for the jar tests were prepared in the laboratory by directly using raw wastewater or by adding to the basic raw wastewater 10–20 mL of activated sludge in a litre, obtaining four types of wastewater as reported in Table 1. Overall, adding activated sludge increases the efficacy of primary sedimentation in a conventional UWWTP [26]. Moreover, activated sludge was added to raw wastewater coming from UWWTP3 due to its very low value of COD ( turbidity, SV60 > coagulant dose, coagulant cost. In particular, with this assumption, the obtained percentage priorities were the following: COD removal = 33.33%; SV60 = 23.33%; turbidity = 23.33%; coagulant dose = 10.00%; coagulant cost = 10.00%.
Results and discussion All of the obtained results are reported in Tables 3 (coagulants combinations 1–5) and 4 (coagulants combinations 6–10). Moreover, the values obtained for COD and turbidity are reported in Figures 1 and 2, respectively, for the first eight coagulants combinations. Each figure shows the COD (turbidity) value of the untreated wastewater which is the reference base (the tick continuous line), the COD
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G. De Feo et al. Values obtained for the five comparison criteria for the coagulants combinations 1–5. Criteria
Comparisons
Alternatives
PCT weight Maximize (max.) or minimize (min.)
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(1) Coag− 6 (10, 20, 30, 40, 50, 60 mg/L) vs. PACl (50 mg/L)
(2) Coag− 1 (200, 300, 400, 500, 600 mg/L) vs. PACl (50 mg/L)
(3) Coag− 5 (30, 40, 50, 60 mg/L) + polyanionic vs. PACl (50 mg/L) (4) Coag− 4 (40, 50, 60, 70 mg/L) + polyanionic vs. PACl (50 mg/L) (5) Coag− 2 (100, 150, 200, 250) + polycationic vs. PACl (50 mg/L)
Coag− 6− 10 Coag− 6− 20 Coag− 6− 30 Coag− 6− 40 Coag− 6− 50 Coag− 6− 60∗,∗∗ PACl− 50 Coag− 1− 200 Coag− 1− 300 Coag− 1− 400 Coag− 1− 500 Coag− 1− 600∗,∗∗ PACl− 50 Coag− 5− 30∗,∗∗ Coag− 5− 40 Coag− 5− 50 Coag− 5− 60 PACl− 50 Coag− 4− 40∗∗ Coag− 4− 50 Coag− 4− 60 Coag− 4− 70 PACl− 50∗ Coag− 2− 100∗∗ Coag− 2− 150 Coag− 2− 200 Coag− 2− 250 PACl− 50∗
COD removal [%]
SV60 [mL/L]
Dose [mg/L]
Cost [¤/kg]
Turbidity [NTU]
33.33 max.
23.33 min.
10,00 min.
10,00 min.
23.33 min.
Npi
18.3 28.7 37.7 39.6 46.7 53.4 59.8 27.5 36.3 51.8 49.6 53.5 37.3 52.1 60.7 54.2 52.1 51.3 17.0 10.5 11.1 5.8 63.1 58.2 56.3 53.3 57.1 65.5
4.5 6 7 6 7.5 5 20 7 10 12 13 15 18 10 15 17 15 13 2 2 2 2 15 16 18 16 18 28
10 20 30 40 50 60 50 200 300 400 500 600 50 30 40 50 60 50 40 50 60 70 50 50 100 150 200 50
2.30 2.30 2.30 2.30 2.30 2.30 0.30 1.20 1.20 1.20 1.20 1.20 0.30 1.50 1.50 1.50 1.50 0.30 1.20 1.20 1.20 1.20 0.30 1.20 1.20 1.20 1.20 0.30
61.2 49.9 44.4 44.2 38.9 16.9 18.4 27.9 18.8 11.7 10.4 6.42 11.5 5.95 5.12 7.32 9.32 7.2 23.9 21.2 21.9 22.6 4.14 23.2 24.4 26.6 25.9 3.4
0.666 0.619 0.643 0.679 0.694 1.000 0.935 0.717 0.720 0.880 0.866 1.000 0.922 1.000 0.972 0.807 0.762 0.937 0.628 0.565 0.550 0.500 1.000 0.765 0.668 0.658 0.643 1.000
∗ = the best multi criteria alternative. ∗∗ = the best alternative to the PACl.
(turbidity) value of the wastewater treated with PACl, which is the comparison base (the tick dashed line), and finally the values of COD (turbidity) related to the several tested coagulant doses which represent the alternatives to compare with the PACl value. In particular, the empty rhombus (on the y-axis) indicates the value of COD (turbidity) obtained for natural sedimentation. The CAPS process achieved better COD and turbidity values (i.e. lower) than that of natural sedimentation confirming the efficacy of the process consistent with the findings of previous studies [1–4]. Moreover, the efficacy of the CAPS process almost always increased with the dose of coagulant both in terms of COD and turbidity. Notably, the results obtained for COD removal were very promising, including a more than 80% reduction for combinations 7, 8, 9 and 10 both for PACl and biodegradable coagulants. The main reason for this result was the presence of activated sludge in the sample. This result
further corroborates the practice of adding activated sludge in the primary sedimentation, further aided with CAPS. Values between 50% and 75% were obtained only with natural sedimentation, greater than the literature values (25–40%), as reported in the introduction. Values between 80% and 90% and 65 and 90% were obtained with PACl and with the best alternative to PACl, respectively. On the whole, as shown in Figures 1(d) and 2(d), polyamine (i.e. Coag_4) was the single coagulant not properly working (removal less than 20%) with WW1 . This was because of the absence of affinity of polyamine with the considered wastewater, probably due to a scarce adsorptionbridging ability. On the contrary, polyamine showed a good adsorption-bridging ability for removing the disperse dye from dyeing wastewater [28]. For WW1 , excluding combination 4, average COD percentage removal was 49.5% for PACl and 53% for the best PACl alternative. Finally, also considering WW1 , the natural cationic polymer showed a
Environmental Technology Table 4.
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Values obtained for the five comparison criteria for the coagulants combinations 6–10. Criteria
Comparisons
COD removal [%]
SV60 [mL/L]
Dose [mg/L]
Cost [¤/kg]
Turbidity [NTU]
33.33 max.
23.33 min.
10,00 min.
10,00 min.
23.33 min.
Npi
Coag− 1− 50 Coag− 1− 100
56.4 55.5
3.5 4
50 100
1.20 1.20
10.3 7.26
0.884 0.819
Coag− 1− 150 Coag− 1− 200∗∗ Coag− 1− 250 PACl− 50∗ Coag− 3− 20 Coag− 3− 40 Coag− 3− 60∗∗ Coag− 3− 80 PACl− 50∗ Coag− 1− 100 Coag− 1− 150 Coag− 1− 200∗∗ Coag− 1− 50∗ Coag− 5− 30 Coag− 5− 40
59.0 60.7 60.0 63.0 88.3 90.7 91.4 91.5 90.5 82.4 83.1 84.4 85.0 76.6 65.6
5.5 6 7 14 23 24 25 27 26 32 31 29 25 9 8
150 200 250 50 20 40 60 80 50 100 150 200 50 30 40
1.20 1.20 1.20 0.30 1.20 1.20 1.20 1.20 0.30 1.20 1.20 1.20 0.30 1.2 1.2
4.28 3.25 3.9 3.2 22.6 8.6 6.3 7 7.62 11.4 8.76 8.41 8.85 6.57 8.52
0.840 0.893 0.813 1.000 0.857 0.921 0.966 0.911 1.000 0.761 0.806 0.825 1.000 0.756 0.701
Coag− 2− 10∗∗ Coag− 2− 20 Coag− 2− 30 PACl− 100∗ Coag− 5− 30 Coag− 5− 40
63.9 65.8 55.3 81.1 78.8 80.3
7 7 6 22 9 9
10 20 30 100 30 40
1.2 1.2 1.2 0.30 1.20 1.20
4.24 6.22 7.75 0.88 3.54 4.55
0.859 0.781 0.737 1.000 0.795 0.772
Coag− 4− 10∗∗ Coag− 4− 20 Coag− 4− 30 PACl− 100∗
74.8 79.1 77.8 84.1
8 7 6 20
10 20 30 100
1.20 1.20 1.20 0.30
3.66 4.63 4.05 1.03
0.887 0.857 0.883 1.000
Alternatives
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PCT weight Maximize (max.) or minimize (min.) (6) Coag− 2 (50 mg/L) + Coag− 1 (50, 100, 150, 200, 250 mg/L) + polycationic vs. PACl (50 mg/L)
(7) Coag− 3 (20, 40, 60, 80 mg/L) + polyanionic vs. PACl (50 mg/L) (8) Coag− 2 (100 mg/L) + Coag− 1 (100, 150, 200 mg/L) vs. PACl (50 mg/L) (9) Coag− 2 (10 mg/L) + Coag− 5 (30, 40 mg/L), Coag− 2 (10 mg/L) + Coag− 4 (10, 20, 30 mg/L) vs. PACl (100 mg/L)
(10) Coag− 2 (25 mg/L) + Coag− 5 (30,40 mg/L), Coag− 2 (25 mg/L) + Coag− 4 (10, 20, 30 mg/L) vs. PACl (100 mg/L)
∗ = the best multi-criteria alternative. ∗∗ = the best alternative to the PACl.
better performance in terms of COD and turbidity removal rather than PACl. However, these results may possibly be attributed to the high coagulant dosage (200–600 mg/L). From this point onwards, the results are presented and discussed in terms of multi-criteria analysis. Tables 3 and 4 contain all the results obtained for the five comparison criteria considered (percentage COD removal, SV60 , coagulant dose, coagulant cost, turbidity). In other words, they contain the alternatives matrix. The criteria priorities and the indication of maximizing or minimizing criteria are reported in the first two lines of the tables, respectively. The last column of Tables 3 and 4 shows the normalized priority index (Npi) obtained by combining the SAW technique coupled with the PCT tool. In particular, a value of Npi equal to 1 means that the corresponding alternative is the best alternative: this alternative was marked with an asterisk identifying the so-called ‘best multi-criteria alternative’. A
double asterisk indicates the best alternative to the PACl (i.e. the comparison target). The PACl was not the best multicriteria alternative when the asterisk and double asterisk are near a same value: this occurred three times out of ten cases, so PACl was the best multi-criteria alternative in 70% of the cases. The first case where PACl (with a dose of 50 mg/L) was not the best absolute alternative occurred with the application of a cationic polyacrylamide (with a dose of 60 mg/L) as a coagulant. The cationic polyacrylamides are copolymers of acrylamide and a co-monomer cation (having a quaternary amino group). The cationic groups introduced in the polymer have a positive charge in an aqueous solution. The cationizing monomers are: dimethylaminoethyl; dimethylaminoethylmethacrilato; dimethylaminopropylacrylamide. Polyacrylamide is widely used in sewage sludge treatment to enhance dewatering [28,29].
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400
350
300
300
250 200 150
50 0 10
20 30 40 Coag_6 dose (mg/L)
60
0
Untreated
(d)
400
200 300 400 Coag_1 dose (mg/L)
350
300
300
250 200 150
Coag_1
500
600
Untreated
400
350
250 200 150
100
100
50
50 0 0
10
20 30 40 Coag_5 dose (mg/L)
PACl (50 mg/L)
Coag_5
50
60
0
Untreated
10
20
30 40 50 Coag_4 dose (mg/L)
PACl (50 mg/L)
(f)
400
350
300
300
250 200 150
Coag_4
60
70
Untreated
400
350 COD (mg/L)
COD (mg/L)
100
PACl (50 mg/L)
COD (mg/L)
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(h)
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1200
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1000 COD (mg/L)
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50 0
(e)
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100 150 Coag_1 dose (mg/L)
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Coag_1
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Figure 1. COD values for the first eight coagulant combinations: (a) Coag_6 (10, 20, 30, 40, 50, 60 mg/L) vs. PACl (50 mg/L), type of wastewater = WW1 ; (b) Coag_1 (200, 300, 400, 500, 600 mg/L) vs. PACl (50 mg/L), type of wastewater = WW1 ; (c) Coag_5 (30, 40, 50, 60 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW1 ; (d) Coag_4 (40, 50, 60, 70 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW1 ; (e) Coag_2 (100, 150, 200, 250) + polycationic vs. PACl (50 mg/L), type of wastewater = WW2 ; (f) Coag_2 (50 mg/L) + Coag_1 (50, 100, 150, 200, 250 mg/L) + polycationic vs. PACl (50 mg/L), type of wastewater = WW2 ; (g) Coag_3 (20, 40, 60, 80 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW3 ; and (h) Coag_2 (100 mg/L) + Coag_1 (100, 150, 200 mg/L) vs. PACl (50 mg/L), type of wastewater = WW3 .
Synthetic polymers, in general, can have negative consequences in terms of the inhibition of anaerobic digestion because of the presence of acrylamide monomer (due to the degradation of polyacrylamide), which is highly toxic [30,31]. However, the product used, being a polysaccharide,
has no contraindications. In addition, the solution used was only at 1% of polyacrylamide. Figure 3 proposes a comparison among the percentage COD removals obtained with PACl, best PACl alternative and natural sedimentation.
Environmental Technology (a)
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(b)
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(g)
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Coag_2
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100 150 Coag_1 dose (mg/L)
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(h)
120
Coag_1
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250
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120
100 Turbidity (NTU)
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Coag_6
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Coag_3
70
80
Untreated
0
50
100 150 Coag_1 dose (mg/L)
PACl (50 mg/L)
Coag_1
200
Untreated
Figure 2. Turbidity values for the first eight coagulants combinations: (a) Coag_6 (10, 20, 30, 40, 50, 60 mg/L) vs. PACl (50 mg/L), type of wastewater = WW1 ; (b) Coag_1 (200, 300, 400, 500, 600 mg/L) vs. PACl (50 mg/L), type of wastewater = WW1 ; (c) Coag_5 (30, 40, 50, 60 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW1 ; (d) Coag_4 (40, 50, 60, 70 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW1 ; (e) Coag_2 (100, 150, 200, 250) + polycationic vs. PACl (50 mg/L), type of wastewater = WW2 ; (f) Coag_2 (50 mg/L) + Coag_1 (50, 100, 150, 200, 250 mg/L) + polycationic vs. PACl (50 mg/L), type of wastewater = WW2 ; (g) Coag_3 (20, 40, 60, 80 mg/L) + polyanionic vs. PACl (50 mg/L), type of wastewater = WW3 ; and (h) Coag_2 (100 mg/L) + Coag_1 (100, 150, 200 mg/L) vs. PACl (50 mg/L), type of wastewater = WW3 .
Moreover, it reports a line corresponding with the COD removal of 40%. One of the main aims of CAPS is to improve the removal of organic material. It is therefore unnecessary to evaluate the alternatives with efficiency comparable to that of simple primary settling. In fact, the
multi-criteria analysis was able to identify, as the best alternative, an alternative assuring a COD removal of more than 40%: this was a direct consequence of the fact that the COD removal percentage was considered as the criterion with the highest priority. Furthermore, Figure 3 shows that the
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WW 2
WW 1
Percentage COD removal (%)
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WW 4
WW 3
*
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*
70
*
*
80 * Best multicriteria alternative
*
*
*
60
*
*
*
1
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50 40 30 20 10 0
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5
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Figure 3.
Best PACl alternative
Natural sedimentation
A comparison among the percentage COD removals obtained with PACl, the best PACl alternative and natural sedimentation.
best multi-criteria alternative assured a percentage COD removal significantly greater than natural sedimentation, confirming the efficacy of the CAPS process. The second case where PACl (with a dose of 50 mg/L) was not the best absolute alternative occurred with the application of a natural cationic polymer (with a dose of 600 mg/L) as a coagulant. In this case, the PACl was not able to assure a minimum 40% COD removal, while the natural cationic polymer showed an efficacy more than 50%. Finally, natural sedimentation was observed to be quite ineffective in removing COD. The best performance was reached with an elevated dose of the natural polymer, which is comparatively more expensive than PACl. In fact, cost effectiveness is one of the main reasons why PACl application is currently favoured. The third case where PACl (with a dose of 50 mg/L) was not the best absolute alternative was in the application of a dicyandiamide resin (with a dose of 30 mg/L) as a coagulant. The COD removal was similar to that of PACl and greater than 50% with around 30% more than natural sedimentation. The dicyandiamide resins are a series of organic polymers with different molecular weights belonging to the group of amino resins. These features allow rapid complexation and flocculation with the formation of aggregates and flakes that settle easily. They have a significant decolouring capacity when compared to other coagulants (useful for the treatment of textile and tannery wastewater). These capacities were used by Galasso et al. [32] to remove syntans in the treatment of tannery wastewater, due to soluble materials not being removed with the conventional chemical–physical processes. Conclusions The main conclusions of the study focused on comparing the efficacy of organic and mixed-organic polymers with PACl
(under specific condition) in chemically assisted primary sedimentation: • the PACl was the best alternative in 70% of the cases when applying a multi-criteria analysis based on the SAW method coupled with PCT, with five criteria (COD removal > turbidity, SV60 > coagulant dose, coagulant cost); • the CAPS process using PACl as a coagulant (with a dose of 50 mg/L) made it possible to obtain an average COD removal of 68% compared with 38% obtained, on average, with natural sedimentation and 61% obtained, on average, with the best alternative using organic and mixed-organic polymers; • the best PACl alternatives were the application of a coagulant: a cationic polyacrylamide (with a dose of 60 mg/L), a natural cationic polymer (with a dose of 600 mg/L) and, finally, a dicyandiamide resin (with a dose of 30 mg/L); • only the polyamine did not work properly because of the absence of an affinity for polyamine with the considered wastewater, probably due to a scarce adsorption-bridging ability. Acknowledgements The authors wish to thank Dr Sacha A. Berardo and Ms Meisha Hunter for their English revisions to the text, as well as the comments of three anonymous referees.
References [1] C.S. Poon and C.W. Chu, The use of ferric chloride and anionic polymer in the chemically assisted primary sedimentation process, Chemosphere 39 (1999), pp. 1573–1582. [2] G. De Feo, S. De Gisi, and M. Galasso, Definition of a practical multi-criteria procedure for selecting the best coagulant in a chemically assisted primary sedimentation process for
Environmental Technology
[3]
[4]
Downloaded by [University of Colorado at Boulder Libraries] at 11:19 28 December 2014
[5] [6] [7] [8]
[9] [10]
[11] [12] [13] [14]
[15] [16] [17]
the treatment of urban wastewater, Desalination 230 (2008), pp. 229–238. G. De Feo, S. De Gisi, and M. Galasso, Chemically assisted primary sedimentation: A green chemistry option, in Green Technologies for Wastewater Treatment, G. Lofrano, ed., Springer, Dordrecht, Heidelberg, New York, London, 2012, pp. 1–18. R. Ramadori, D. Marani, V. Renzi, R. Passino, and A.C. Di Pinto, Rethinking sewage treatment by enhancing primary settling with low-dosage lime, Water Sci. Technol. 52 (2005), pp. 185–192. W. Ghyoot and W. Verstraete, Anaerobic digestion of primary sludge from chemical pre-precipitation, Water Sci. Technol. 36 (1997), pp. 357–365. H. Odegaard, P. Balmer, and I. Hanaus, Chemical precipitation in highly loaded stabilization ponds in cold climates, Water Sci. Technol. 19 (1987), pp. 71–77. H. Odegaard, Appropriate technology for wastewater treatment in coastal tourist area, Water Sci. Technol. 21 (1989), pp. 1–17. D. Marani, V. Renzi, R. Ramadori, and C.M. Braguglia, Size fractionation of COD in urban wastewater from a combined sewer system, Water Sci. Technol. 50 (2004), pp. 79–86. A.C. Chao and T.M. Keinath, Influence of process loading intensity on sludge clarification and thickening characteristics, Water Res. 13 (1979), pp. 1213–1223. G. Mininni, C.M. Braguglia, R. Ramadori, and M.C. Tomei, An innovative sludge management system based on separation of primary and secondary sludge treatment, Water Sci. Technol. 50 (2004), pp. 145–153. H. Odegaard, Optimized particle separation in the primary step of wastewater treatment, Water Sci. Technol. 37 (1998), pp. 43–53. P.A. Vesilind, Wastewater Treatment Plant Design, Water Environment Federation (WEF), Alexandria, 2003. S.K. Dentel and J.M. Gossett, Effect of chemical coagulation on anaerobic digestibility of organic materials, Water Res. 16 (1982), pp. 707–718. K.V. Akshaya, R.D. Rajesh, and B. Puspendu, A review on chemical coagulation/flocculation technologies for removal of colour from textile wastewaters, J. Environ. Manage. 93 (2012), pp. 154–168. A. Ndabigengesere and K.S. Narasiah, Quality of water treated by coagulation using Moringa oleifera seeds, Water Res. 32 (1998), pp. 781–791. Z. Song, C.J. Williams, and R.G.J. Edyvean, Coagulation and anaerobic digestion of tannery wastewater, Process. Saf. Environ. 79 (2001), pp. 23–28. T. Chen, B. Gao, and Q. Yue, Effect of dosing method and pH on colour removal performance and floc aggregation of polyferric chloride–polyamine dual-coagulant in synthetic dyeing wastewater treatment, Colloids Surf., A 355 (2010), pp. 121–129.
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[18] Y. Chun-Yang, Emerging usage of plant-based coagulants for water and wastewater treatment, Process Biochem. 45 (2010), pp. 1437–1444. [19] B. Gao, B. Liu, T. Chen, and Q. Yue, Effect of aging period on the characteristics and coagulation behaviour of polyferric chloride and polyferric chloride–polyamine composite coagulant for synthetic dying wastewater treatment, J. Hazard. Mater. 187 (2011), pp. 413–420. [20] P. Aragonés-Beltrán, J.A. Mendoza-Roca, A. Bes-Piá, M. García-Melón, and E. Parra-Ruiz, Application of multicriteria decision analysis to jar-test results for chemicals selection in the physical–chemical treatment of textile wastewater, J. Hazard. Mater. 164 (2009), pp. 288–295. [21] T.L. Saaty, Decision Making for Leaders. The Analytic Hierarchy Process for Decision in a Complex World, RWS Publications, Pittsburgh, USA, 2001. [22] A. Balasubramaniam and N. Voulvoulis, The Appropriateness of Multicriteria Analysis in environmental decision-making problems, Environ. Technol. 26 (2005), pp. 951–962. [23] Y.X. Zhao, B.Y. Gao, Y. Wang, H.K. Shon, X.W. Bo, and Q.Y. Yue, Coagulation performance and floc characteristics with polyaluminium chloride using sodium alginate as coagulant aid: A preliminary assessment, Chem. Eng. J. 183 (2012), pp. 387–394. [24] H. Ching-Lai and Y. Kwangsun, Multiple Attribute Decision Making, Springer Verlag, Berlin-Heidelberg, New York, 1981. [25] W. Mondy and R. Noe, Human Resource Management, Prentice-Hall, Upper Saddle River, NJ, 2008. [26] G. Tchobanoglous, F.L. Burton, and H.D. Stensel, Wastewater Engineering: Treatment and Reuse, Metcalf & Eddy, Inc, McGraw-Hill, New York, 2003. [27] APHA, Standard Methods for the Examination of Water and Wastewater, 19th ed., APHA-AWWA-WPCF, Washington, DC, 1995. [28] Y. Wang, B. Gao, Q. Yue, X. Zhan, X. Si, and C. Li, Flocculation performance of epichlorohydrin-dimethylamine polyamine in treating dyeing wastewater, J. Environ. Manage. 91 (2009), pp. 423–431. [29] E. Campos, M. Almirall, J. Mtnez-Almela, J. Palatsi, and X. Flotats, Feasibility study of the anaerobic digestion of dewatered pig slurry by means of polyacrylamide, Bioresour. Technol. 99 (2008), pp. 387–395. [30] IPCS, Acrylamide. Environmental Health Criteria 49, World Health Organization, Geneva, Switzerland, 1985. [31] G. Zhu, H. Zheng, P. Zhang, Z. Jiao, and J. Yin, Near-infrared spectroscopy as a potential tool with radial basis function for measurement of residual acrylamide in organic polymer, Environ. Technol. (2012), doi 10.1080/09593330.2012.683817. [32] M. Galasso, S. De Gisi, R. Landi, and G. De Feo, Il trattamento chimico-fisico di tannini sintetici mediante l’utilizzo di coagulanti misti organici, Ing. Ambientale 38 (2009), pp. 444–452.
