This article was downloaded by: [Eindhoven Technical University] On: 17 November 2014, At: 23:28 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
A study of subsurface wastewater infiltration systems for distributed rural sewage treatment a
a
a
a
Wei Qin , Junfeng Dou , Aizhong Ding , En Xie & Lei Zheng
a
a
College of Water Sciences, Beijing Normal University, Beijing 100875, People's Republic of China Published online: 18 Mar 2014.
To cite this article: Wei Qin, Junfeng Dou, Aizhong Ding, En Xie & Lei Zheng (2014) A study of subsurface wastewater infiltration systems for distributed rural sewage treatment, Environmental Technology, 35:16, 2115-2121, DOI: 10.1080/09593330.2014.894579 To link to this article: http://dx.doi.org/10.1080/09593330.2014.894579
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2014 Vol. 35, No. 16, 2115–2121, http://dx.doi.org/10.1080/09593330.2014.894579
A study of subsurface wastewater infiltration systems for distributed rural sewage treatment Wei Qin, Junfeng Dou∗ , Aizhong Ding, En Xie and Lei Zheng College of Water Sciences, Beijing Normal University, Beijing 100875, People’s Republic of China
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
(Received 28 May 2013; accepted 11 February 2014 ) Three types of subsurface wastewater infiltration systems (SWIS) were developed to study the efficiency of organic pollutant removal from distributed rural sewage under various conditions. Of the three different layered substrate systems, the one with the greatest amount of decomposed cow dung (5%) and soil (DCDS) showed the highest removal efficiency with respect to total nitrogen (TN), where the others showed no significant difference. The TN removal efficiency was increased with an increasing filling height of DCDS. Compared with the TN removal efficiency of 25% in the system without DCDS, the removal efficiency of the systems in which DCDS filled half and one fourth of the height was increased by 72% and 31%, respectively. Based on seasonal variations in the discharge of the typical rural family, the SWIS were run at three different hydraulic loads of 6.5, 13 and 20 cm/d. These results illustrated that SWIS could perform well at any of the given hydraulic loads. The results of trials using different inlet configurations showed that the effluent concentration of the contaminants in the system operating a multiple-inlet mode was much lower compared with the system operated under single-inlet conditions. The effluent concentration of a pilot-scale plant achieved the level III criteria specified by the Surface Water Quality Standard at the initial stage. Keywords: SWIS; distributed sewage; filling structure; hydraulic load; feeding mode
1. Introduction With the improvement of the living standards of farmers, rural sewage emissions have also increased in recent years. The concentrations of pollutants in wastewater have also gradually increased, although the majority of rural populations do not have sewage collection pipelines and treatment facilities. Thus, sewage flows in rural regions not only have an increasingly serious effect on surface water but also present a growing risk of groundwater contamination.[1] Subsurface wastewater infiltration systems (SWIS) have several advantages relative to other treatment systems, such as a simple construction, low operation and maintenance costs, and stable removal efficiency. Therefore, the development of SWIS has a great potential in rural areas, and many studies have been performed on the use of SWIS. Yang et al. [2] developed a layered SWIS filled using pure soil and sand and demonstrated a high removal efficiency with respect to chemical oxygen demand (COD) and ammonia nitrogen (NH+ 4 -N), whereas the removal efficiency of total phosphorus (TP) and total nitrogen (TN) did not reach optimal levels. Zhang et al. [3] added grass carbon at a proportion of 10% in the matrixes, and the average removal was enhanced from 83% and 69% without grass carbon to 95% and 80% for NH+ 4 -N and TN, respectively; however, the use of grass carbon had no effect on the TP removal. Wang et al. [4] found that the addition of a carbon source
∗ Corresponding
author. Email: [email protected]
© 2014 Taylor & Francis
could significantly increase the TN removal, although the TN concentration remained at >10 mg/L. Due to temporal fluctuations in the quality and quantity of rural distributed sewage, it is important to select a proper filling material and suitable operation model. The main purpose of this study was to evaluate the effectiveness of SWIS treatment using different filling substrates including fly ash and decomposed cow dung, which are common in rural areas, mixed with soil for the treatment of distributed rural sewage. The results of this study were used to select the best model for various hydraulic loads and feeding modes to provide a scientific basis for the application of SWIS in rural areas for the reduction of water pollution. 2. Materials and methods 2.1. System description The frames of the treatment systems were cylindrical (50 cm in diameter and 100 cm in height) and consisted of three clearly differentiated zones: a distribution zone, a treatment zone and a collection zone (Figure 1). The distribution zone was 10 cm in height and filled with gravel (2–10 mm in diameter). The water inlet pipe, which was perforated with a plum blossom shape, was 10 mm in diameter and placed 3 cm below the surface; the treatment zone was 80 cm in height and filled with two types of matrixes. The first fill
2116
W. Qin et al. wastewater 2~10mm gravel
distributing zone
wastewater 2~10mm gravel
wastewater 2~10mm gravel
nylon mesh
nylon mesh
nylon mesh
FAS treatment zone
FAS
DCDS
collection zone
treated water system 1
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
Figure 1.
system 2
treated water
treated water system 3
Schematic diagram of the SWIS.
was composed of fly ash (5%) and soil (95%) and was called FAS; the other was composed of decomposed cow dung (5%) and soil (95%) and was called DCDS. System one was filled with two uniform layers comprising 10 cm of FAS over 30 cm of DCDS; system two was filled with two layers comprising 40 cm of FAS over 40 cm of DCDS; system three was filled only with 80 cm of FAS. The collection zone was filled with gravel (2–10 mm in diameter) and isolated from the ground by a waterproof layer. Nylon (100 mesh) was placed between the different zones to support the fill material. Three different systems were established, and each was repeated three times to ensure the accuracy. The experiment consisted of three stages conducted over a 1-year period. The first stage lasting 3 months had a hydraulic load of 6.5 cm/d; subsequently, the system was operated at 13 cm/d for 3 months and then 20 cm/d for 3 months. In additional, the SWIS were run under two different inlet arrangement conditions, which were called ‘single inlet’ and ‘multiple inlet’. The experiment began in November 2011 and ended in October 2012. The composition of the influent, derived from domestic sewage wells, varied at different stages during the operation, as the sewage composition was significantly affected by the living habits of the local populace.
2.2.
2~10mm gravel nylon mesh
2~10mm gravel nylon mesh
2~10mmgravel nylon mesh
Sampling and methods
Water samples were taken from both the raw waster and the effluent of the collection zone once per week after 2 weeks. − All samples were analysed for COD, TP, NH+ 4 -N, NO3 -N and TN in accordance with the Standard Methods for the Examination of Water and Wastewater.[5] The potassium dichromate method was used for the COD analysis, and − colorimetric methods were used for the NH+ 4 -N, NO3 -N, TN and TP analyses. Ultraviolet spectrophotometer (UV2450) was purchased from Hangzhou Science Instruments Co., Ltd (Hangzhou, China). Other chemical agents used in this study were all guaranteed reagents and obtained from Shanghai Chemical Regent Company of China. The data
were analysed by one-way analysis of variance (ANOVA) and by statistical analysis. 3. Results and discussion 3.1. Pollution removal using different treatments The experiments in SWIS with different filling structures were conducted during November of 2011 and January of 2012, and the influent had the following characteristics: pH 5.6–7, COD 61–616 mg/L, TP 0.68–9.91 mg/L, − NH+ 4 -N 7.7–39.4 mg/L, TN 10.4–55.1 mg/L and NO3 N 0.95–4.95 mg/L. The removal effects are shown in Figure 2. The temporal variation of the COD concentrations of the influent and effluent is shown in Figure 2. It was observed that the COD concentrations of the effluent of the three systems were approximately identical, with the average removal efficiencies of 88.8%, 85.8% and 88.3% in systems 1, 2 and 3, respectively. The highest removal efficiency was 97%, and the average removal efficiency was low because the COD concentration of the influent was too low at certain times. Compared with the other treatment systems, the removal efficiency of system 2 was low due to the high quantity of decomposed cow dung in the system. The microorganisms used the decomposed cow dung as the carbon source, and thus reducing the usage of COD from wastewater. As shown in Figure 2(b) and 2(c), the three treatment systems showed a high removal efficiency of TP and NH+ 4N, and the average removal efficiency was >96%. The effluent concentrations showed no significant differences among the various systems, indicating that the addition of fly ash and decomposed cow dung did not affect the TP and NH+ 4 -N removal performance. The addition of decomposed cow dung significantly improved the removal efficiency of TN and is shown in Figure 2(d). Compared with the TN removal efficiency of 25% in those systems without DCDS, the removal efficiency of the systems in which DSCS was used to fill half of the height (system 2) and one fourth of the height
Environmental Technology (a)
2117
(b)
700
10 600 8 TP (mg/L)
COD (mg/L)
500 400 300
6
4 200 2
100 0
0
20
40
60
0
80
0
20
40
60
80
Operation time (d)
(c)
(d)
60
40 50
35 30
40
25 TN (mg/L)
NH4-N (mg/L)
20 15
30
20
10 10 5 0
0
20
40
60
0
80
0
20
40
system 1
Figure 2.
80
60
Operation time (d)
Operation time (d) system 2
system 3
influent
Pollutant removal performances for the different treatments.
(system 1) was increased by 72% and 31%, respectively. Nitrogen removal is mainly dependent on the oxidation– reduction processes of nitrifying and denitrifying bacteria. The influent nitrogen dispersed near the distribution pipe with sufficient oxygen was oxidized to nitrate. During the downward infiltration, the oxygen concentration decreased with increasing soil depth, leading to anoxic or anaerobic conditions, which would favour denitrification.[6] The carbon/nitrogen ratio of the influent varied greatly and was relatively low in the later stages of the experiment. Thus, the influent carbon did not supply a sufficient energy source for denitrification. System 3 without decomposed cow dung had sufficient carbon sources for denitrification at the beginning of the experiment, although an accumulation of nitrate was observed as the carbon/nitrogen ratio was gradually reduced. The nitrate removal efficiency results for the different treatments (Figure 3) indicate that the effluent NO− 3 -N concentrations from systems 1 and 3 were higher than that of system 2. The denitrifying microorganisms in system 3 without decomposed cow dung remained stable at the later stage, and the NO− 3 -N concentrations were reduced with increasing denitrification intensity. The decomposed cow dung in system 2 with highest amount of DCDS provided sufficient organic carbon sources for denitrification,[7] and thus almost all of the nitrate could be reduced to nitrogen
18 16 14
NO3-N (mg/L)
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
Operation time (d)
12 10 8 6 4 2 0
0
20 system 1
Figure 3.
40 60 Operation time (d) system 2
Temporal changes in
NO− 3 -N
system 3
80
influent
concentrations.
gas. The effluent TN concentration remains low from the beginning of the experiment and mainly consisted of NH+ 4 -N. On the other hand, system 1, having decomposed cow dung and little DCDS, lacked an organic carbon source and showed minimal transformation of NO− 3 -N to N2 O or N2 .[8] These results indicate that the quantity of
2118
W. Qin et al. 6.5 cm/d
13 cm/d
20 cm/d
100
(b) 8
a 350
13 cm/d
6.5 cm/d
20 cm/d b 100
7 80
200 40
100
60 4 40
3 2
20
20 1
50 0 50
100 150 200 Operation time (d)
0
0
250
50
100
150
200
250
Operation time (d)
(c) 80
100
(d) 80
70
100
70 80
60 40 40
30
TN (mg/L)
50
80
60
Removal rates (%)
60
NH4-N (mg/L)
5
20
50
60
40 40
30 20
20
20 10
10
0
0 50
100
150
200
250
0
0 50
Operation time (d)
100
150
200
250
Operation time (d) effluent
Figure 4.
Removal rates (%)
60
TP (mg/L)
250
150
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
80
6
Removal rates (%)
COD (mg/L)
300
Removal rates (%)
(a) 400
influent
removal rate
Pollutant removal performances at different hydraulic loads.
decomposed cow dung added in the system directly affected the TN removal efficiency. 3.2. Pollution removal under different hydraulic loads According to the differences in seasonal discharge for a typical rural family, the SWIS were run at various hydraulic loads. System 2 was chosen to have the optimal structural conditions according to the TN removal efficiency and was run at hydraulic loads of 13 and 20 cm/d, termed medium and high loads, respectively. The system was run for 3 months, and samples were taken from the influent and effluent four times per month. The results are shown in Figure 4. The COD removal efficiency under all conditions is shown in Figure 4(a). Although the COD removal efficiency varied greatly, the lowest removal efficiency was >60%, and the average removal efficiency exceeded 80%. At the same time, it was also observed that the effluent COD concentration remained stable without obvious fluctuations. These results indicate that the stable effluent of system 2 could achieve the emission standard. The hydraulic loads have a large influence on the adsorption and precipitation of TP on the fill substrate.[9] A lower hydraulic load would lead to a lower effluent TP because a greater amount of phosphorus in the influent would
react with the fill material. However, as the hydraulic load increased, the retention time of phosphorus in the system became short, and then the effluent TP concentration increased. Figure 4(b) shows that the TP removal efficiency was stable with an average level of 98.7% under the low and medium load conditions. The removal efficiency varied greatly, and the effluent TP concentration increased in the late stage due to the higher infiltration rate. With respect to the influent TP, wastewater that consistently contained large amounts of phosphorus had an adverse effect on the adsorption of TP. Therefore, the optimal hydraulic load was 13 cm/d. The TN removal efficiency was generally low in the SWIS. Thus, the effluent TN concentration was the key factor for evaluating these systems. The main mechanisms responsible for eliminating nitrogen from sewage are nitrification and denitrification.[10,11] As shown in Figure 4(c), the SWIS had a stable NH+ 4 -N removal efficiency with an average level exceeding 95% under the medium and high load conditions. Under the low load conditions, the removal efficiency was greater than 90% with relatively large fluctuation. Based on the above analysis, it could be concluded that regardless of the hydraulic loads, the effluent NH+ 4 -N concentration was low. For the elimination of NH+ -N, sub4 strate adsorption and microorganism nitrification were the predominant mechanisms.[12,13] The fly ash in the system
had a strong adsorption capacity, having a large number of small openings,[14] and air could remain in these pores to supply oxygen for nitrification. In addition, the alkalinity necessary for nitrification could be supplied by fly ash based on immersion experiments. A study conducted by Zeng and Lou [15] showed that the pH value of the aqueous solution of a fly ash mixture was consistently >8.0. The fill material could recover its NH+ 4 -N adsorption ability after the microorganism completed the nitrification process, which resulted in a high NH+ 4 -N removal efficiency.[16] The process of denitrification requires suitable reducing conditions and an appropriate carbon-to-nitrogen ratio. In this test, the DCDS particles at the bottom of the SWIS were slender with a high viscosity. The very small pore spaces of the DCDS submerged in water could easily lead to anaerobic conditions.[17] The addition of decomposed cow dung could lessen the shortage of carbon sources to a certain extent. As shown in Figure 4(d), the average removal efficiency of TN was >96% and relatively stable under the low and medium loads conditions. The average TN removal efficiency was 88% under the high load conditions, which illustrated that SWIS could perform well under high hydraulic load conditions. 3.3. Pollutant removal under different inflow modes The SWIS were run under two different inlet arrangements with an intermittent operation, which was called ‘single inlet’ and ‘multiple inlet’. The single-inlet mode included a flooding period of 6 h and a drying period of 18 h, and the multiple-inlet mode included a flooding period of 3 h and a drying period of 9 h. The influent had the following characteristics: COD 45–216 mg/L, TP 0.56–2.73 mg/L, NH+ 4 -N 6.34–29.27 mg/L and TN 9.24–32.15 mg/L. The results are shown in Figures 5 and 6. The results showed that the effluent concentrations of COD, TP, NH+ 4 -N and TN were higher under single-inlet condition compared with the multiple-inlet conditions
2119
(Figures 5 and 6). The system had sufficient time for the oxygen level recover under the multiple-inlet conditions, and the microorganisms could maintain a high activity, which allowed for a high removal efficiency of pollutants. Figure 5 shows that there was no difference between the two different conditions with an average COD concentration of 20 mg/L. The mechanisms for phosphorus removal in sewage mainly consist of physical sedimentation, chemical adsorption, precipitation and biological processes within the fill substrate.[18] Under the single-inlet conditions, adsorption was the main process for the elimination of phosphorus, as the duration was too short to precipitate and reduce the adsorption capability of the substrate. However, the multiple-inlet approach provided enough time for precipitation and allowed the fill to adsorb phosphorus constantly. The inflow modes were important for the removal of NH+ 4 -N. Figure 6 illustrates a clear distinction in the + effluent NH+ 4 -N concentrations. The effluent NH4 -N concentrations for single-inlet and multiple-inlet modes were approximately 0.4 and 0.2 mg/L, respectively. The primary mechanism for NH+ 4 -N removal is nitrification by nitrifying bacteria, which are aerobic microorganisms. The influent oxygen level for the single-inlet mode was not sufficient for nitrifying bacteria, and thus only a small amount of NH+ 4 -N was transformed to nitrite and nitrate. However, the oxygen in the air could enter the SWIS from the surface before the depletion of oxygen under the multiple-inlet conditions. Thus, the process of nitrification in the multipleinlet mode was improved relative to the single-inlet configuration. With respect to the removal efficiency of TN, the effluent TN concentration for the single-inlet design was slightly higher than that of multiple-inlet system, although both modes were affected by the composition of the influent. Generally, as the oxygen level decreased with increasing soil depth, the surroundings became anaerobic, which was favourable for the growth of denitrifying bacteria. At the
0.030
30 multiple
0.025
25
0.020
20
0.015
15
0.010
10
0.005
5
0.000
0 270
284
298
312
326
340
270
284
298
Operation time (d) TP
Figure 5.
COD
Changes in the effluent TP and COD concentrations for different inflow modes.
312
326
340
COD (mg/L)
single
TP (mg/L)
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
Environmental Technology
2120
W. Qin et al. 0.9 0.8
single
multiple
0.7
TN (mg/L)
0.6 0.5 0.4 0.3 0.2 0.1 270
284
298
312
326
340
270
284
298
312
326
340
Operation time (d) NH4-N
Figure 6.
other forms
NO3-N
Changes in the NH+ 4 -N and TN concentrations for different inflow modes. 30
0.06 0.05
15
TP (mg/L)
criteria criteria
20 10 5 0
4
6
8
0.04 0.03
criteria
0.02 0.01 0.00
10 12 14 16 18
2
4
2.0 criteria criteria specified in Groundwater Quality standard criteria specified in Groundwater Quality standard 2 4 6 8 10 12 14 16 18
TN (mg/L)
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0
2
NO3-N (mg/L)
COD (mg/L)
25
NH4-N (mg/L)
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
0
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
6
8
10 12 14 16 18
criteria specified in Groundwater Quality standard
1.5 1.0 0.5 0.0
2
4
6
8
10 12 14 16 18
criteria criteria
2
4
6
8
10 12 14 16 18
sample time (weeks)
Figure 7.
Effluent concentration under optimal conditions.
stage of denitrification, a higher removal efficiency was obtained for the reduction of NO− 3 -N. When the influent TN concentration was high, NO− 3 -N passed into the effluent due to the rapid infiltration, although the highest TN concentration remained below 1.0 mg/L. An anaerobic environment was not developed to meet the requirement of the denitrifying bacterium in the multiple-inlet mode, and thus microorganisms could not reduce all of the NO− 3 -N, which was the main form of TN.[19]
3.4.
Effluent concentration under the optimal conditions Based on the experimental results, the SWIS with DCDS filling half of the height was selected to treat the distributed rural sewage. It was found that despite changes in the contaminant concentrations, the system could maintain a high removal efficiency (Figure 7). The effluent concentration met the criteria specified in the Surface Water Quality Standard (GB3838-2002) at the initial stage.
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
Environmental Technology The effluent COD concentrations met the level IV criteria at the start-up state and achieved the level III criteria specified in Surface Water Quality Standard at the fourth week. Subsequently, the concentration of COD remained below 20 mg/L and met the level II criteria at the final time point. The effluent TP concentration remained below 0.05 mg/L, which satisfies the level II criteria of the Surface Water Quality Standard. Among the monitoring data, 79% met the level I criteria with little fluctuation. The optimal SWIS had the ability to produce a high COD and TP removal efficiency over a short period of time. The effluent NH+ 4 -N concentrations met the level I and II criteria at the beginning of the trial. The rates were 16%, 37% and 47% for the III, IV and V criteria, respectively, as specified by Groundwater Quality Standard (GB/T148489). The effluent TN concentrations met the level III and IV criteria at the beginning of the trial. The effluent NO− 3N concentration met the level I criteria specified by the Groundwater Quality Standard, which is far less than the limit values (≤10 mg/L) specified by the Surface Water Source of Drinking Water Supplement Project Standard (GBGB3838-2002). 4. Conclusions The SWIS with DCDS filling half of the height was the best framework for distributed rural sewage treatment. The amendment of decomposed cow dung greatly improved the removal efficiency of TN. Using the optimum configuration, the hydraulic loads had little influence on the removal efficiency of COD and NH+ 4 -N. The removal efficiency of the multiple-inlet mode was superior to the single-inlet mode, demonstrating that the multiple-inlet mode was favourable for the operation of the SWIS. Under the optimized constructions, the system maintained a high removal efficiency regardless of fluctuations in the contaminant concentrations. In addition, the effluent concentration met the level III criteria specified by the Surface Water Quality Standard at the initial stage. The optimized SWIS present an obvious advantage for the treatment of distributed rural sewage, and SWIS had broad potential applications for the treatment of sewage in rural areas. Funding This work was supported by the National Natural Science Foundation of China [No. 41203060].
References [1] Arye G, Dror I, Berkowitz B. Fate and transport of carbamazepine in soil aquifer treatment (SAT) infiltration basin soils. Chemosphere. 2011;82:244–252.
2121
[2] Yang J, Yan Q, Wu YF, Zhang J. Effect comparison of municipal wastewater in different mediums infiltration system. J Tongji Univ. 2009;39:1502–1507. Chinese. [3] Zhang J, Huang X, Shi HC, Hu HY, Qian Y. Sewage treatment in SWIS with pulverin. China Water Wastewater. 2004;20:41–43. Chinese. [4] Wang X, Sun TH, Li HB, Li YH, Pan J. Nitrogen removal enhanced by shunt distributing wastewater in a subsurface wastewater infiltration system. Ecol Eng. 2010;36: 1433–1438. [5] American Public Health Association (APHA). Standard Methods for the Examination of Water and Wastewater. Washington, DC: American Public Health Association/American WaterWorks Association/Water Environment Federation; 1999. [6] Li YH, Li HB, Sun TH, Wang X. Study on nitrogen removal enhanced by shunt distributing wastewater in a constructed subsurface infiltration system under intermittent operation mode. J Hazard Mater. 2011;189:336–341. [7] Chen JZ, Lee Y, Oleszkiewicz JA. Applicability of industrial wastewater as carbon source for denitrification of a sludge dewatering liquor. Environ Technol. 2013;34:731–736. [8] Kuschk P, Wiesner A, Weisbrodt Kappelmeyer U, Kastner E, Stottmeister M. Annual cycle of nitrogen removal by a pilotscale subsurface horizontal flow in a constructed wetland under moderate climate. Water Res. 2003;37:4236–4242. [9] Pratt C, Shilton A, Pratt S, Haverkamp RG, Bolan NS. Phosphorus removal mechanisms in active slag filters treating waste stabilization pond effluent. Environ Sci Technol. 2007;41:3296–3301. [10] Michael AU, William CB, Marjorie EB, Song J. Nitrogen removal in recirculating sand filter systems with upflow anaerobic components. J Environ Eng. 2007;133:464–470. [11] Quan ZX, Jin YS, Yin CR, Lee JJ, Lee ST. Hydrolyzed molasses as an external carbon source in biological nitrogen removal. Bioresour Technol. 2005;96:1690–1695. [12] Cervantes F, Delarosa D, Gomez J. Nitrogen removal from wastewater at low C/N with ammonium and acetate as electron donors. Bioresour Technol. 2001;79:165–183. [13] Cuyk SV, Siegrist R, Logan A, Masson S, Fischer E, Figueroa L. Hydraulic and purification behaviors and their interactions during wastewater treatment in soil infiltration systems. Water Res. 2001;35:953–964. [14] Tiwari S, Singh SN, Garg SK. Stimulated phytoextraction of metals from fly ash by microbial interventions. Environ Technol. 2012;33:2405–2413. [15] Zeng FQ, Lou GQ. Study on the pH value change of fly ash in water and alkali solution. J China Foreign Highway. 2010;30:281–284. Chinese. [16] Zhang J, Huang X, Liu CX, Shi HC, Hu HY. Nitrogen removal enhanced by intermittent operation in a subsurface wastewater infiltration system. Ecol Eng. 2005;25:419–428. [17] Chou YJ, Ouyang CF, Kuo WL, Huang HL. Denitrifying characteristics of the multiple stages enhanced biological nutrient removal process with external carbon sources. J Environ Sci Health. 2003;38:339–352. [18] Aulenbach DB, Nie MS. Studies on the mechanism of phosphorus removal from treated wastewater by sand. JWPCF. 1988;60:2089–2094. [19] Güvena D, Karahanb Ö, Byükgüngörc H, Sözen S. Storage phenomena in relation to carbon sources for denitrification. Desal Wat Treat. 2009;8:171–176.
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
A study of subsurface wastewater infiltration systems for distributed rural sewage treatment a
a
a
a
Wei Qin , Junfeng Dou , Aizhong Ding , En Xie & Lei Zheng
a
a
College of Water Sciences, Beijing Normal University, Beijing 100875, People's Republic of China Published online: 18 Mar 2014.
To cite this article: Wei Qin, Junfeng Dou, Aizhong Ding, En Xie & Lei Zheng (2014) A study of subsurface wastewater infiltration systems for distributed rural sewage treatment, Environmental Technology, 35:16, 2115-2121, DOI: 10.1080/09593330.2014.894579 To link to this article: http://dx.doi.org/10.1080/09593330.2014.894579
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2014 Vol. 35, No. 16, 2115–2121, http://dx.doi.org/10.1080/09593330.2014.894579
A study of subsurface wastewater infiltration systems for distributed rural sewage treatment Wei Qin, Junfeng Dou∗ , Aizhong Ding, En Xie and Lei Zheng College of Water Sciences, Beijing Normal University, Beijing 100875, People’s Republic of China
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
(Received 28 May 2013; accepted 11 February 2014 ) Three types of subsurface wastewater infiltration systems (SWIS) were developed to study the efficiency of organic pollutant removal from distributed rural sewage under various conditions. Of the three different layered substrate systems, the one with the greatest amount of decomposed cow dung (5%) and soil (DCDS) showed the highest removal efficiency with respect to total nitrogen (TN), where the others showed no significant difference. The TN removal efficiency was increased with an increasing filling height of DCDS. Compared with the TN removal efficiency of 25% in the system without DCDS, the removal efficiency of the systems in which DCDS filled half and one fourth of the height was increased by 72% and 31%, respectively. Based on seasonal variations in the discharge of the typical rural family, the SWIS were run at three different hydraulic loads of 6.5, 13 and 20 cm/d. These results illustrated that SWIS could perform well at any of the given hydraulic loads. The results of trials using different inlet configurations showed that the effluent concentration of the contaminants in the system operating a multiple-inlet mode was much lower compared with the system operated under single-inlet conditions. The effluent concentration of a pilot-scale plant achieved the level III criteria specified by the Surface Water Quality Standard at the initial stage. Keywords: SWIS; distributed sewage; filling structure; hydraulic load; feeding mode
1. Introduction With the improvement of the living standards of farmers, rural sewage emissions have also increased in recent years. The concentrations of pollutants in wastewater have also gradually increased, although the majority of rural populations do not have sewage collection pipelines and treatment facilities. Thus, sewage flows in rural regions not only have an increasingly serious effect on surface water but also present a growing risk of groundwater contamination.[1] Subsurface wastewater infiltration systems (SWIS) have several advantages relative to other treatment systems, such as a simple construction, low operation and maintenance costs, and stable removal efficiency. Therefore, the development of SWIS has a great potential in rural areas, and many studies have been performed on the use of SWIS. Yang et al. [2] developed a layered SWIS filled using pure soil and sand and demonstrated a high removal efficiency with respect to chemical oxygen demand (COD) and ammonia nitrogen (NH+ 4 -N), whereas the removal efficiency of total phosphorus (TP) and total nitrogen (TN) did not reach optimal levels. Zhang et al. [3] added grass carbon at a proportion of 10% in the matrixes, and the average removal was enhanced from 83% and 69% without grass carbon to 95% and 80% for NH+ 4 -N and TN, respectively; however, the use of grass carbon had no effect on the TP removal. Wang et al. [4] found that the addition of a carbon source
∗ Corresponding
author. Email: [email protected]
© 2014 Taylor & Francis
could significantly increase the TN removal, although the TN concentration remained at >10 mg/L. Due to temporal fluctuations in the quality and quantity of rural distributed sewage, it is important to select a proper filling material and suitable operation model. The main purpose of this study was to evaluate the effectiveness of SWIS treatment using different filling substrates including fly ash and decomposed cow dung, which are common in rural areas, mixed with soil for the treatment of distributed rural sewage. The results of this study were used to select the best model for various hydraulic loads and feeding modes to provide a scientific basis for the application of SWIS in rural areas for the reduction of water pollution. 2. Materials and methods 2.1. System description The frames of the treatment systems were cylindrical (50 cm in diameter and 100 cm in height) and consisted of three clearly differentiated zones: a distribution zone, a treatment zone and a collection zone (Figure 1). The distribution zone was 10 cm in height and filled with gravel (2–10 mm in diameter). The water inlet pipe, which was perforated with a plum blossom shape, was 10 mm in diameter and placed 3 cm below the surface; the treatment zone was 80 cm in height and filled with two types of matrixes. The first fill
2116
W. Qin et al. wastewater 2~10mm gravel
distributing zone
wastewater 2~10mm gravel
wastewater 2~10mm gravel
nylon mesh
nylon mesh
nylon mesh
FAS treatment zone
FAS
DCDS
collection zone
treated water system 1
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
Figure 1.
system 2
treated water
treated water system 3
Schematic diagram of the SWIS.
was composed of fly ash (5%) and soil (95%) and was called FAS; the other was composed of decomposed cow dung (5%) and soil (95%) and was called DCDS. System one was filled with two uniform layers comprising 10 cm of FAS over 30 cm of DCDS; system two was filled with two layers comprising 40 cm of FAS over 40 cm of DCDS; system three was filled only with 80 cm of FAS. The collection zone was filled with gravel (2–10 mm in diameter) and isolated from the ground by a waterproof layer. Nylon (100 mesh) was placed between the different zones to support the fill material. Three different systems were established, and each was repeated three times to ensure the accuracy. The experiment consisted of three stages conducted over a 1-year period. The first stage lasting 3 months had a hydraulic load of 6.5 cm/d; subsequently, the system was operated at 13 cm/d for 3 months and then 20 cm/d for 3 months. In additional, the SWIS were run under two different inlet arrangement conditions, which were called ‘single inlet’ and ‘multiple inlet’. The experiment began in November 2011 and ended in October 2012. The composition of the influent, derived from domestic sewage wells, varied at different stages during the operation, as the sewage composition was significantly affected by the living habits of the local populace.
2.2.
2~10mm gravel nylon mesh
2~10mm gravel nylon mesh
2~10mmgravel nylon mesh
Sampling and methods
Water samples were taken from both the raw waster and the effluent of the collection zone once per week after 2 weeks. − All samples were analysed for COD, TP, NH+ 4 -N, NO3 -N and TN in accordance with the Standard Methods for the Examination of Water and Wastewater.[5] The potassium dichromate method was used for the COD analysis, and − colorimetric methods were used for the NH+ 4 -N, NO3 -N, TN and TP analyses. Ultraviolet spectrophotometer (UV2450) was purchased from Hangzhou Science Instruments Co., Ltd (Hangzhou, China). Other chemical agents used in this study were all guaranteed reagents and obtained from Shanghai Chemical Regent Company of China. The data
were analysed by one-way analysis of variance (ANOVA) and by statistical analysis. 3. Results and discussion 3.1. Pollution removal using different treatments The experiments in SWIS with different filling structures were conducted during November of 2011 and January of 2012, and the influent had the following characteristics: pH 5.6–7, COD 61–616 mg/L, TP 0.68–9.91 mg/L, − NH+ 4 -N 7.7–39.4 mg/L, TN 10.4–55.1 mg/L and NO3 N 0.95–4.95 mg/L. The removal effects are shown in Figure 2. The temporal variation of the COD concentrations of the influent and effluent is shown in Figure 2. It was observed that the COD concentrations of the effluent of the three systems were approximately identical, with the average removal efficiencies of 88.8%, 85.8% and 88.3% in systems 1, 2 and 3, respectively. The highest removal efficiency was 97%, and the average removal efficiency was low because the COD concentration of the influent was too low at certain times. Compared with the other treatment systems, the removal efficiency of system 2 was low due to the high quantity of decomposed cow dung in the system. The microorganisms used the decomposed cow dung as the carbon source, and thus reducing the usage of COD from wastewater. As shown in Figure 2(b) and 2(c), the three treatment systems showed a high removal efficiency of TP and NH+ 4N, and the average removal efficiency was >96%. The effluent concentrations showed no significant differences among the various systems, indicating that the addition of fly ash and decomposed cow dung did not affect the TP and NH+ 4 -N removal performance. The addition of decomposed cow dung significantly improved the removal efficiency of TN and is shown in Figure 2(d). Compared with the TN removal efficiency of 25% in those systems without DCDS, the removal efficiency of the systems in which DSCS was used to fill half of the height (system 2) and one fourth of the height
Environmental Technology (a)
2117
(b)
700
10 600 8 TP (mg/L)
COD (mg/L)
500 400 300
6
4 200 2
100 0
0
20
40
60
0
80
0
20
40
60
80
Operation time (d)
(c)
(d)
60
40 50
35 30
40
25 TN (mg/L)
NH4-N (mg/L)
20 15
30
20
10 10 5 0
0
20
40
60
0
80
0
20
40
system 1
Figure 2.
80
60
Operation time (d)
Operation time (d) system 2
system 3
influent
Pollutant removal performances for the different treatments.
(system 1) was increased by 72% and 31%, respectively. Nitrogen removal is mainly dependent on the oxidation– reduction processes of nitrifying and denitrifying bacteria. The influent nitrogen dispersed near the distribution pipe with sufficient oxygen was oxidized to nitrate. During the downward infiltration, the oxygen concentration decreased with increasing soil depth, leading to anoxic or anaerobic conditions, which would favour denitrification.[6] The carbon/nitrogen ratio of the influent varied greatly and was relatively low in the later stages of the experiment. Thus, the influent carbon did not supply a sufficient energy source for denitrification. System 3 without decomposed cow dung had sufficient carbon sources for denitrification at the beginning of the experiment, although an accumulation of nitrate was observed as the carbon/nitrogen ratio was gradually reduced. The nitrate removal efficiency results for the different treatments (Figure 3) indicate that the effluent NO− 3 -N concentrations from systems 1 and 3 were higher than that of system 2. The denitrifying microorganisms in system 3 without decomposed cow dung remained stable at the later stage, and the NO− 3 -N concentrations were reduced with increasing denitrification intensity. The decomposed cow dung in system 2 with highest amount of DCDS provided sufficient organic carbon sources for denitrification,[7] and thus almost all of the nitrate could be reduced to nitrogen
18 16 14
NO3-N (mg/L)
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
Operation time (d)
12 10 8 6 4 2 0
0
20 system 1
Figure 3.
40 60 Operation time (d) system 2
Temporal changes in
NO− 3 -N
system 3
80
influent
concentrations.
gas. The effluent TN concentration remains low from the beginning of the experiment and mainly consisted of NH+ 4 -N. On the other hand, system 1, having decomposed cow dung and little DCDS, lacked an organic carbon source and showed minimal transformation of NO− 3 -N to N2 O or N2 .[8] These results indicate that the quantity of
2118
W. Qin et al. 6.5 cm/d
13 cm/d
20 cm/d
100
(b) 8
a 350
13 cm/d
6.5 cm/d
20 cm/d b 100
7 80
200 40
100
60 4 40
3 2
20
20 1
50 0 50
100 150 200 Operation time (d)
0
0
250
50
100
150
200
250
Operation time (d)
(c) 80
100
(d) 80
70
100
70 80
60 40 40
30
TN (mg/L)
50
80
60
Removal rates (%)
60
NH4-N (mg/L)
5
20
50
60
40 40
30 20
20
20 10
10
0
0 50
100
150
200
250
0
0 50
Operation time (d)
100
150
200
250
Operation time (d) effluent
Figure 4.
Removal rates (%)
60
TP (mg/L)
250
150
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
80
6
Removal rates (%)
COD (mg/L)
300
Removal rates (%)
(a) 400
influent
removal rate
Pollutant removal performances at different hydraulic loads.
decomposed cow dung added in the system directly affected the TN removal efficiency. 3.2. Pollution removal under different hydraulic loads According to the differences in seasonal discharge for a typical rural family, the SWIS were run at various hydraulic loads. System 2 was chosen to have the optimal structural conditions according to the TN removal efficiency and was run at hydraulic loads of 13 and 20 cm/d, termed medium and high loads, respectively. The system was run for 3 months, and samples were taken from the influent and effluent four times per month. The results are shown in Figure 4. The COD removal efficiency under all conditions is shown in Figure 4(a). Although the COD removal efficiency varied greatly, the lowest removal efficiency was >60%, and the average removal efficiency exceeded 80%. At the same time, it was also observed that the effluent COD concentration remained stable without obvious fluctuations. These results indicate that the stable effluent of system 2 could achieve the emission standard. The hydraulic loads have a large influence on the adsorption and precipitation of TP on the fill substrate.[9] A lower hydraulic load would lead to a lower effluent TP because a greater amount of phosphorus in the influent would
react with the fill material. However, as the hydraulic load increased, the retention time of phosphorus in the system became short, and then the effluent TP concentration increased. Figure 4(b) shows that the TP removal efficiency was stable with an average level of 98.7% under the low and medium load conditions. The removal efficiency varied greatly, and the effluent TP concentration increased in the late stage due to the higher infiltration rate. With respect to the influent TP, wastewater that consistently contained large amounts of phosphorus had an adverse effect on the adsorption of TP. Therefore, the optimal hydraulic load was 13 cm/d. The TN removal efficiency was generally low in the SWIS. Thus, the effluent TN concentration was the key factor for evaluating these systems. The main mechanisms responsible for eliminating nitrogen from sewage are nitrification and denitrification.[10,11] As shown in Figure 4(c), the SWIS had a stable NH+ 4 -N removal efficiency with an average level exceeding 95% under the medium and high load conditions. Under the low load conditions, the removal efficiency was greater than 90% with relatively large fluctuation. Based on the above analysis, it could be concluded that regardless of the hydraulic loads, the effluent NH+ 4 -N concentration was low. For the elimination of NH+ -N, sub4 strate adsorption and microorganism nitrification were the predominant mechanisms.[12,13] The fly ash in the system
had a strong adsorption capacity, having a large number of small openings,[14] and air could remain in these pores to supply oxygen for nitrification. In addition, the alkalinity necessary for nitrification could be supplied by fly ash based on immersion experiments. A study conducted by Zeng and Lou [15] showed that the pH value of the aqueous solution of a fly ash mixture was consistently >8.0. The fill material could recover its NH+ 4 -N adsorption ability after the microorganism completed the nitrification process, which resulted in a high NH+ 4 -N removal efficiency.[16] The process of denitrification requires suitable reducing conditions and an appropriate carbon-to-nitrogen ratio. In this test, the DCDS particles at the bottom of the SWIS were slender with a high viscosity. The very small pore spaces of the DCDS submerged in water could easily lead to anaerobic conditions.[17] The addition of decomposed cow dung could lessen the shortage of carbon sources to a certain extent. As shown in Figure 4(d), the average removal efficiency of TN was >96% and relatively stable under the low and medium loads conditions. The average TN removal efficiency was 88% under the high load conditions, which illustrated that SWIS could perform well under high hydraulic load conditions. 3.3. Pollutant removal under different inflow modes The SWIS were run under two different inlet arrangements with an intermittent operation, which was called ‘single inlet’ and ‘multiple inlet’. The single-inlet mode included a flooding period of 6 h and a drying period of 18 h, and the multiple-inlet mode included a flooding period of 3 h and a drying period of 9 h. The influent had the following characteristics: COD 45–216 mg/L, TP 0.56–2.73 mg/L, NH+ 4 -N 6.34–29.27 mg/L and TN 9.24–32.15 mg/L. The results are shown in Figures 5 and 6. The results showed that the effluent concentrations of COD, TP, NH+ 4 -N and TN were higher under single-inlet condition compared with the multiple-inlet conditions
2119
(Figures 5 and 6). The system had sufficient time for the oxygen level recover under the multiple-inlet conditions, and the microorganisms could maintain a high activity, which allowed for a high removal efficiency of pollutants. Figure 5 shows that there was no difference between the two different conditions with an average COD concentration of 20 mg/L. The mechanisms for phosphorus removal in sewage mainly consist of physical sedimentation, chemical adsorption, precipitation and biological processes within the fill substrate.[18] Under the single-inlet conditions, adsorption was the main process for the elimination of phosphorus, as the duration was too short to precipitate and reduce the adsorption capability of the substrate. However, the multiple-inlet approach provided enough time for precipitation and allowed the fill to adsorb phosphorus constantly. The inflow modes were important for the removal of NH+ 4 -N. Figure 6 illustrates a clear distinction in the + effluent NH+ 4 -N concentrations. The effluent NH4 -N concentrations for single-inlet and multiple-inlet modes were approximately 0.4 and 0.2 mg/L, respectively. The primary mechanism for NH+ 4 -N removal is nitrification by nitrifying bacteria, which are aerobic microorganisms. The influent oxygen level for the single-inlet mode was not sufficient for nitrifying bacteria, and thus only a small amount of NH+ 4 -N was transformed to nitrite and nitrate. However, the oxygen in the air could enter the SWIS from the surface before the depletion of oxygen under the multiple-inlet conditions. Thus, the process of nitrification in the multipleinlet mode was improved relative to the single-inlet configuration. With respect to the removal efficiency of TN, the effluent TN concentration for the single-inlet design was slightly higher than that of multiple-inlet system, although both modes were affected by the composition of the influent. Generally, as the oxygen level decreased with increasing soil depth, the surroundings became anaerobic, which was favourable for the growth of denitrifying bacteria. At the
0.030
30 multiple
0.025
25
0.020
20
0.015
15
0.010
10
0.005
5
0.000
0 270
284
298
312
326
340
270
284
298
Operation time (d) TP
Figure 5.
COD
Changes in the effluent TP and COD concentrations for different inflow modes.
312
326
340
COD (mg/L)
single
TP (mg/L)
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
Environmental Technology
2120
W. Qin et al. 0.9 0.8
single
multiple
0.7
TN (mg/L)
0.6 0.5 0.4 0.3 0.2 0.1 270
284
298
312
326
340
270
284
298
312
326
340
Operation time (d) NH4-N
Figure 6.
other forms
NO3-N
Changes in the NH+ 4 -N and TN concentrations for different inflow modes. 30
0.06 0.05
15
TP (mg/L)
criteria criteria
20 10 5 0
4
6
8
0.04 0.03
criteria
0.02 0.01 0.00
10 12 14 16 18
2
4
2.0 criteria criteria specified in Groundwater Quality standard criteria specified in Groundwater Quality standard 2 4 6 8 10 12 14 16 18
TN (mg/L)
0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0
2
NO3-N (mg/L)
COD (mg/L)
25
NH4-N (mg/L)
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
0
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
6
8
10 12 14 16 18
criteria specified in Groundwater Quality standard
1.5 1.0 0.5 0.0
2
4
6
8
10 12 14 16 18
criteria criteria
2
4
6
8
10 12 14 16 18
sample time (weeks)
Figure 7.
Effluent concentration under optimal conditions.
stage of denitrification, a higher removal efficiency was obtained for the reduction of NO− 3 -N. When the influent TN concentration was high, NO− 3 -N passed into the effluent due to the rapid infiltration, although the highest TN concentration remained below 1.0 mg/L. An anaerobic environment was not developed to meet the requirement of the denitrifying bacterium in the multiple-inlet mode, and thus microorganisms could not reduce all of the NO− 3 -N, which was the main form of TN.[19]
3.4.
Effluent concentration under the optimal conditions Based on the experimental results, the SWIS with DCDS filling half of the height was selected to treat the distributed rural sewage. It was found that despite changes in the contaminant concentrations, the system could maintain a high removal efficiency (Figure 7). The effluent concentration met the criteria specified in the Surface Water Quality Standard (GB3838-2002) at the initial stage.
Downloaded by [Eindhoven Technical University] at 23:28 17 November 2014
Environmental Technology The effluent COD concentrations met the level IV criteria at the start-up state and achieved the level III criteria specified in Surface Water Quality Standard at the fourth week. Subsequently, the concentration of COD remained below 20 mg/L and met the level II criteria at the final time point. The effluent TP concentration remained below 0.05 mg/L, which satisfies the level II criteria of the Surface Water Quality Standard. Among the monitoring data, 79% met the level I criteria with little fluctuation. The optimal SWIS had the ability to produce a high COD and TP removal efficiency over a short period of time. The effluent NH+ 4 -N concentrations met the level I and II criteria at the beginning of the trial. The rates were 16%, 37% and 47% for the III, IV and V criteria, respectively, as specified by Groundwater Quality Standard (GB/T148489). The effluent TN concentrations met the level III and IV criteria at the beginning of the trial. The effluent NO− 3N concentration met the level I criteria specified by the Groundwater Quality Standard, which is far less than the limit values (≤10 mg/L) specified by the Surface Water Source of Drinking Water Supplement Project Standard (GBGB3838-2002). 4. Conclusions The SWIS with DCDS filling half of the height was the best framework for distributed rural sewage treatment. The amendment of decomposed cow dung greatly improved the removal efficiency of TN. Using the optimum configuration, the hydraulic loads had little influence on the removal efficiency of COD and NH+ 4 -N. The removal efficiency of the multiple-inlet mode was superior to the single-inlet mode, demonstrating that the multiple-inlet mode was favourable for the operation of the SWIS. Under the optimized constructions, the system maintained a high removal efficiency regardless of fluctuations in the contaminant concentrations. In addition, the effluent concentration met the level III criteria specified by the Surface Water Quality Standard at the initial stage. The optimized SWIS present an obvious advantage for the treatment of distributed rural sewage, and SWIS had broad potential applications for the treatment of sewage in rural areas. Funding This work was supported by the National Natural Science Foundation of China [No. 41203060].
References [1] Arye G, Dror I, Berkowitz B. Fate and transport of carbamazepine in soil aquifer treatment (SAT) infiltration basin soils. Chemosphere. 2011;82:244–252.
2121
[2] Yang J, Yan Q, Wu YF, Zhang J. Effect comparison of municipal wastewater in different mediums infiltration system. J Tongji Univ. 2009;39:1502–1507. Chinese. [3] Zhang J, Huang X, Shi HC, Hu HY, Qian Y. Sewage treatment in SWIS with pulverin. China Water Wastewater. 2004;20:41–43. Chinese. [4] Wang X, Sun TH, Li HB, Li YH, Pan J. Nitrogen removal enhanced by shunt distributing wastewater in a subsurface wastewater infiltration system. Ecol Eng. 2010;36: 1433–1438. [5] American Public Health Association (APHA). Standard Methods for the Examination of Water and Wastewater. Washington, DC: American Public Health Association/American WaterWorks Association/Water Environment Federation; 1999. [6] Li YH, Li HB, Sun TH, Wang X. Study on nitrogen removal enhanced by shunt distributing wastewater in a constructed subsurface infiltration system under intermittent operation mode. J Hazard Mater. 2011;189:336–341. [7] Chen JZ, Lee Y, Oleszkiewicz JA. Applicability of industrial wastewater as carbon source for denitrification of a sludge dewatering liquor. Environ Technol. 2013;34:731–736. [8] Kuschk P, Wiesner A, Weisbrodt Kappelmeyer U, Kastner E, Stottmeister M. Annual cycle of nitrogen removal by a pilotscale subsurface horizontal flow in a constructed wetland under moderate climate. Water Res. 2003;37:4236–4242. [9] Pratt C, Shilton A, Pratt S, Haverkamp RG, Bolan NS. Phosphorus removal mechanisms in active slag filters treating waste stabilization pond effluent. Environ Sci Technol. 2007;41:3296–3301. [10] Michael AU, William CB, Marjorie EB, Song J. Nitrogen removal in recirculating sand filter systems with upflow anaerobic components. J Environ Eng. 2007;133:464–470. [11] Quan ZX, Jin YS, Yin CR, Lee JJ, Lee ST. Hydrolyzed molasses as an external carbon source in biological nitrogen removal. Bioresour Technol. 2005;96:1690–1695. [12] Cervantes F, Delarosa D, Gomez J. Nitrogen removal from wastewater at low C/N with ammonium and acetate as electron donors. Bioresour Technol. 2001;79:165–183. [13] Cuyk SV, Siegrist R, Logan A, Masson S, Fischer E, Figueroa L. Hydraulic and purification behaviors and their interactions during wastewater treatment in soil infiltration systems. Water Res. 2001;35:953–964. [14] Tiwari S, Singh SN, Garg SK. Stimulated phytoextraction of metals from fly ash by microbial interventions. Environ Technol. 2012;33:2405–2413. [15] Zeng FQ, Lou GQ. Study on the pH value change of fly ash in water and alkali solution. J China Foreign Highway. 2010;30:281–284. Chinese. [16] Zhang J, Huang X, Liu CX, Shi HC, Hu HY. Nitrogen removal enhanced by intermittent operation in a subsurface wastewater infiltration system. Ecol Eng. 2005;25:419–428. [17] Chou YJ, Ouyang CF, Kuo WL, Huang HL. Denitrifying characteristics of the multiple stages enhanced biological nutrient removal process with external carbon sources. J Environ Sci Health. 2003;38:339–352. [18] Aulenbach DB, Nie MS. Studies on the mechanism of phosphorus removal from treated wastewater by sand. JWPCF. 1988;60:2089–2094. [19] Güvena D, Karahanb Ö, Byükgüngörc H, Sözen S. Storage phenomena in relation to carbon sources for denitrification. Desal Wat Treat. 2009;8:171–176.
