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Comparison of constructed wetland and stabilization pond for the treatment of digested effluent of swine wastewater a
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Gang-Jin Liu , Dan Zheng , Liang-Wei Deng , Quan Wen & Yi Liu
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Biogas Institute of Ministry of Agriculture, No.13, 4th Section, South Renmin Road, Chengdu, Sichuan 610041, People's Republic of China Published online: 27 May 2014.
Click for updates To cite this article: Gang-Jin Liu, Dan Zheng, Liang-Wei Deng, Quan Wen & Yi Liu (2014) Comparison of constructed wetland and stabilization pond for the treatment of digested effluent of swine wastewater, Environmental Technology, 35:21, 2660-2669, DOI: 10.1080/09593330.2014.917709 To link to this article: http://dx.doi.org/10.1080/09593330.2014.917709
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Environmental Technology, 2014 Vol. 35, No. 21, 2660–2669, http://dx.doi.org/10.1080/09593330.2014.917709
Comparison of constructed wetland and stabilization pond for the treatment of digested effluent of swine wastewater Gang-Jin Liu, Dan Zheng, Liang-Wei Deng∗ , Quan Wen and Yi Liu Biogas Institute of Ministry of Agriculture, No.13, 4th Section, South Renmin Road, Chengdu, Sichuan 610041, People’s Republic of China
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(Received 3 December 2013; final version received 18 April 2014 ) A laboratory-scale horizontal subsurface flow constructed wetland (HSFCW) and a stabilization pond (SP) were constructed to compare their performances on the treatment of digested effluent of swine wastewater. After 457 days of operation, the removal efficiencies of the HSFCW were as follows: chemical oxygen demand (COD), 17–54%; total phosphorus (TP), 32–45% and ammonia nitrogen NH+ 4 − N, 27–88%, while they were 25–55%, 31–56% and 56–98%, respectively, for the SP, with a hydraulic retention time of 54 days and hydraulic loading of 0.01 m3 m−2 d−1 . The average removed loads for the −2 d−1 , while they were 0.25–4.45, HSFCW were as follows: COD, 0.25–4.33; TP, 0.01–0.11 and NH+ 4 − N, 0.34–2.54 g m −2 −1 0.02–0.13 and 0.72–2.87 g m d , respectively, for the SP. The SP performed better than the HSFCW because the SP showed a 20% of higher removal efficiency for NH+ 4 − N than the HSFCW. Especially, the COD removal rate of SP was 10% higher than the HSFCW when the influent concentration was at the lowest and highest stages. Meanwhile, given the lower costs, the SP is more suitable for the treatment of digested effluent of swine wastewater than the HSFCW. Keywords: constructed wetlands; digested effluent; stabilization pond; swine wastewater; effluent quality
1. Introduction The improvement of living standards in China has resulted in an increased demand for pork, which has in turn led to an increase in medium- and large-scale pig farms in China. This has also led to the generation of a large quantity of swine wastewater, which contains a variety of pollutants and therefore has the potential to cause serious environmental pollutions. At present, most farms use the anaerobic digestion process to treat swine wastewater because it can recover methane.[1] However, the concentration of pollutants in effluent from anaerobic reactors is still high. This is especially true for ammonia nitrogen, which is not removed by anaerobic digestion, and sometimes increases. Excess ammonia nitrogen may lead to the pollution of surface and ground water. Thus, the digested effluent must be further processed to meet the discharge standards (discharge standard of pollutants for livestock and poultry breeding (China)). For pig farms located far from the city with large amounts of land, natural treatment systems are an attractive choice because they are operationally passive and cost-effective for nutrient removal.[2] As a type of natural treatment systems, constructed wetlands (CWs) are widely used for the treatment of livestock wastewater.[3–5] Another popular natural treatment is the stabilization pond (SP). Most investigations of swine wastewater treatment systems that have been conducted to ∗ Corresponding
author. Email: [email protected]
© 2014 Taylor & Francis
date have focused on the performance of nitrogen removal, which include ammonia volatilization,[6,7] improved nitrogen treatment [8–11] and removal of organics.[12] Both the CWs and SP show a good performance for the treatment of swine wastewater.[13,14] Costa and Medri [15] obtained very high treatment efficiency using SP systems. Specifically, their systems removed approximately 97% of organic matter (biochemical oxygen demand (BOD) and chemical oxygen demand (COD)), 87% of TS, 91% of VS, 90% of TN and 93% of total phosphorus (TP). Hammer et al. [16] used CWs to treat swine wastewater with good results as indicated by the following average removal rates: BOD5 , 90.4%; TSS, 91.4%; faecal coliforms, 99.4%; faecal streptococci, 98.4%; NH+ 4 − N, 93.6%; total Kjeldahl nitrogen (TKN), 91.4%; TP, 75.9%. Nevertheless, in the practical application of the two systems, technicians, proprietors and policy-makers are most interested in determining which system is best for the treatment of swine wastewater. However, the results of studies obtained under different conditions are not comparable. Mara [17] and Liénard et al. [18] compared the land area requirements, costs, performance and maintenance operations of CWs and SP systems for municipal wastewater in terms of durability and reliability. Mara [17] suggested that SP systems were preferable to CWs because the CWs required 60–480% more land than the SP to produce an urban wastewater treat-
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ment directive quality effluent and the cost was about 2–6 times more than the SP. Despite these findings, few studies have been conducted to compare the use of these systems for swine wastewater treatment. Horizontal subsurface flow constructed wetland (HSFCW) is most commonly used for swine wastewater treatment. This study was conducted to compare the performance of a HSFCW and SP for the removal of main pollutants, including COD, TP and NH+ 4 − N, from digested effluent of swine wastewater and to determine which was most suitable for the treatment of swine wastewater. To achieve this goal, a HSFCW and SP were constructed for swine wastewater treatment under natural conditions. 2. Materials and methods 2.1. Wastewater The anaerobically digested effluent used in the experiment was collected from a biogas plant used to treat swine wastewater at a local pig farm with 7000 pigs in the central province of Sichuan, China. The characteristics of the digested effluent of swine wastewater are shown in Table 1. 2.2. Experimental setup The experiment was conducted using two laboratory-scale plastic tanks with an open top, with a depth of 30 cm, length of 50 cm and width of 40 cm and a volume of 54 L. The designing parameter was according to ‘Manual for Constructed Wetlands Treatment of Municipal Wastewaters’.[19] The tank that was used as the HSFCW was packed with three layers of gravel (voidage of 26.9%). The top layer was 5 cm thick and contained gravel with a diameter of 10–30 mm, while the middle layer was 10 cm thick and contained gravel with a diameter of 30–60 mm and the lower layer was 15 cm thick and contained gravel with a diameter ranging from 60 to 100 mm (Figure 1(b)). The tank that was used for the SP was not filled with the packing material. Digested effluent was poured into a 2 L Table 1. Characteristics of the influent and effluents from HSFCW and SP.
Parameters
Influent (mg L−1 )
Effluent of HSFCW (mg L−1 )
Effluent of SP (mg L−1 )
pH DO TP COD NH+ 4 −N NO− 3 −N NO− 2 −N TINa
8.0 ± 0.3 1.0 ± 0.9 25.0 ± 8.2 818 ± 272 508 ± 139 8.2 ± 4.2 1.52 ± 3.55 517 ± 137
7.9 ± 0.3 1.9 ± 0.9 14.8 ± 6.3 420 ± 141 273 ± 143 12.6 ± 13.4 4.81 ± 39 307 ± 120
8.3 ± 0.6 2.4 ± 1.2 14.0 ± 5.6 414 ± 121 154 ± 105 39.1 ± 43.6 21.4 ± 43.4 222 ± 74.3
a TIN NH+ 4
– total inorganic nitrogen (the value is the sum of − − N, NO− 3 − N and NO2 − N).
Figure 1.
Side view of the SP (a) and HSFCW (b).
glass bottle with a 10 mm diameter hole in the bottom that was at a higher position than tank (Figure 1(a)). The digested effluent flowed from the hole in the glass bottle to the bottom of the tank through a polyvinyl chloride (PVC) tube with an internal diameter of 20 mm. The effluent of the HSFCW and SP was discharged from their tops opposite the influent port through a latex tube with an internal diameter of 10 mm.
2.3.
Experimental operation
This study was conducted under natural conditions and the main operating conditions were shown in Table 2. During the experiment, the inflow was 1 L d−1 and the effluent was collected in a 1 L jar. The nominal hydraulic retention time (HRT) was 54 days (the ratio of the usable SP water volume to average flow rate) while the actual HRT of HSFCW was 14.5 days (the ratio of the usable HSFCW water volume to the average flow rate) considering the voidage of gravel. The HSFCW system was planted with Acorus calamus. Wastewater samples were collected from a wide-mouthed bottle and transferred to the laboratory for analysis at the end of each weekend.
2.4.
Analytical methods
Influent and effluent samples were collected every week and analysed immediately. The pH value and concentra− − tions of NH+ 4 − N, NO2 − N, NO3 − N, COD, TP and dissolved oxygen (DO) were routinely measured according to the standard methods.[20] Specifically, the NH+ 4 −N
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Table 2.
The operating conditions of HSFCW and SP.
Parameters
HSFCW/SP
Temperature (◦ C) Feed water (L) HRT (d) COD loading rate (g m−2 d−1 ) −2 d−1 ) NH+ 4 − N loading rate (g m − NO3 − N loading rate (g m−2 d−1 ) −2 d−1 ) NO− 2 − N loading rate (g m Hydraulic load (m3 m−2 d−1 )
2–33 1 14.5/54 4.09 ± 1.36 2.54 ± 0.69 0.04 ± 0.02 0.01 ± 0.02 0.01
and NO− 2 − N were analysed with a UV–VIS spectrophotometer (UV-2450, Shimadzu, Japan) using different colorimetric methods while the NO− 3 − N was analysed using an ultraviolet spectrophotometric method. The COD was measured using the potassium chromate method. The TP and DO were measured using a TP automatic analyzer (IL500P, Lacha-Hach, USA) and oxygen meter (Oxi-315i, WTW, Germany), respectively. The pH was measured using an acidimeter (PHS-3C, DAPU, China) and the temperature was determined using a mercurial thermometer.
3. Results and discussion 3.1. COD removal During the experimental periods, the influent COD was 304–1246 mg L−1 , and the effluent COD values were 206– 794 mg L−1 for the HSFCW and 212–798 mg L−1 for the SP (Figure 2(a)), indicating removal efficiencies of 16–72% and 13–72% (Figure 2(b)), respectively. During weeks 18– 27 the influent COD (304–421 mg L−1 ) was lower than the rest of the period. The COD of the HSFCW and SP effluent was 254–344 and 241–341 mg L−1 and the average removal efficiencies during this period were 17% and 25%, respectively. During weeks 33–41, the influent concentration (1011–1155 mg L−1 ) was higher and the effluent concentrations ranged from 443 to 690 mg L−1 for the HSFCW and 432–597 mg L−1 for the SP, indicating removal efficiencies of 39% and 45%, respectively. The seasonal average removal efficiencies of the HSFCW were 48%, 54%, 42% and 41% in spring, summer, autumn and winter, respectively, while these values were 48%, 55%, 44% and 42% for the SP (Table 3). Moreover, the loads of COD removed, which comprise an important index of the pollutant removal capability, were 2.14, 2.55, 1.30 and 1.47 g m−2 d−1 in the HSFCW, and 2.14, 2.58, 1.35 and 1.52 g m−2 d−1 in the SP during spring, summer, autumn and winter, respectively. Both systems showed higher removal efficiencies in summer than in winter even though the influent COD values were similar. Throughout the experimental period, the SP had a higher removed load of COD than the HSFCW (Table 4). Overall, the effluent concentration and removal efficiency demonstrated that the SP was better for COD removal than the HSFCW.
In this study, the HSFCW and SP had similar seasonal average removal efficiencies for COD, which was in accordance with the results of a study conducted by Poach et al. [21] who found a 37-51% reduction in COD in marsh–pond–marsh CWs. However, in the present study, the HSFCW and SP displayed lower treatment efficiencies during the period in which the influent COD concentration was lower than 421 mg L−1 (Figure 2) and the temperature was 16.5◦ C, which was twice as high as the critical temperature (9–10◦ C).[5] Relatively high temperatures and low concentrations will increase pollutant removal.[21] Accordingly, the HSFCW and SP should have had a high removal efficiency that was identical to that observed in other studies. In contrast, when the temperature was below 7◦ C and the COD concentration was greater than 1011 mg L−1 , the removal efficiency was 20% higher than when the temperature was 16.5◦ C and the COD concentration was lower than 421 mg L−1 . These findings were opposite to those of Travieso et al. [22] Overall, this phenomenon indicated that the temperature had less of an effect on the removal of COD than influent concentration. The reason might be the decreased organic, as carbon source, reduced microorganisms amount because the transformations of COD involve microbial processes. However, biochemical and physical conversions of organic compounds are both primarily responsible for COD removal. Lee et al. [23] demonstrated that COD removal was accomplished by good cooperation between physical and microbial mechanisms, with the former mechanism accounting for 52–74% of the removal and the latter accounting for 26–48%. These results implied that concentration might be responsible for physical processes playing a leading role in COD removal, as well as the increasing COD concentration being accompanied by a rising removal rate. Generally, the greatest reductions accompany the highest influent concentrations.[24] These findings are similar to those of Costa and Medri,[15] who investigated the use of a SP system for the treatment of swine wastes. The SP showed approximately 10% higher COD removal than the HSFCW under the conditions of low influent concentration, high temperature or high influent concentration and low temperature. This might be caused by the higher DO concentration and the long HRT. High DO was led by the large contact area and stirring by wind in the SP to increase the concentration of DO. The HSFCW and SP had the same nominal HRT (54 days), but the HSFCW was packed with gravel (voidage of 26.9%) and had a shorter actual HRT (14.5 days) than the SP (54 days). 3.2. TP removal During the experiment, the influent concentration of TP was 8.74–43.5 mg L−1 , the effluent concentrations were 5.48–31.8 mg L−1 for the HSFCW and 5.32–26.5 mg L−1 for the SP (Figure 3(a)), while the treatment efficiencies were −32–72% for the HSFCW and −52–73% for the
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Figure 2.
Fluctuations of COD concentration (a) and removal efficiency (b) as a function of time in the HSFCW and SP.
Table 3.
Seasonal COD concentration, removal efficiency and removed load of HSFCW and SP. Effluent (mg L−1 )
Season Temperature (◦ C) Influent (mg L−1 ) Spring Summer Autumn Winter
12 ± 5 25 ± 2 21 ± 4 8±3
895 ± 215 936 ± 185 618 ± 319 716 ± 280
Removal efficiency (%) Removed load (g m−2 d−1 )
HSFCW
SP
HSFCW
SP
HSFCW
SP
467 ± 190 427 ± 120 359 ± 88 421 ± 159
467 ± 149 420 ± 101 349 ± 116 413 ± 110
47 ± 17 54 ± 9 34 ± 18 39 ± 13
45 ± 18 55 ± 8 38 ± 12 38 ± 15
2.14 ± 1.05 2.55 ± 0.72 1.30 ± 1.17 1.47 ± 0.85
2.14 ± 1.14 2.58 ± 0.74 1.35 ± 1.03 1.52 ± 0.96
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Table 4. COD, TP and NH+ 4 − N removal efficiency and removed load of HSFCW and SP. Removal efficiency (%) Removed load (g m−2 d−1 ) Parameters HSFCW
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COD TP NH+ 4 −N
45 ± 16 42 ± 14 48 ± 19
SP
HSFCW
SP
46 ± 15 46 ± 12 71 ± 17
1.99 ± 1.04 0.05 ± 0.03 0.93 ± 0.67
2.02 ± 1.05 0.06 ± 0.02 1.52 ± 0.63
SP (Figure 3(b)). The average treatment efficiencies were 35% for the HSFCW and 31% for the SP when the influent TP concentration was less than 20 mg L−1 , while they reached 42% and 45% when the influent TP concentration was greater than 20 mg L−1 . However, the influence of temperature on TP reduction was not obvious (Figure 3(b)). The seasonal TP treatment efficiencies were 44%, 43%, 43%, 28% for the HSFCW and 56%, 47%, 43%, 39% for the SP during the four seasons, while the seasonal removed loads of TP were 0.06, 0.05, 0.05, 0.07 g m−2 d−1 for the HSFCW and 0.07, 0.05, 0.05, 0.07 g m−2 d−1 for the SP, respectively (Table 5). Throughout the experiment, the TP treatment efficiencies of the HSFCW and SP were 0.05 and 0.06 g m−2 d−1 , respectively (Table 4). The results indicated that the capability of the SP to reduce TP was a little better than that of the HSFCW. The treatment efficiency of the SP observed in the present study was higher than that obtained in a study conducted by Poach et al. [9,21] which might be due to improved treatment efficiency as a result of the longer HRT.[25] Although the HRT of the SP was much longer than that of the HSFCW, the treatment efficiency of the SP was only 2% higher than that of the HSFCW. The removal efficiency and influent TP concentration changed without obvious fluctuation (Figure 3). Additionally, these factors did not show any relationships with large changes in temperature. However, data analysis conducted revealed that a lower influent TP concentration was associated with lower treatment efficiency, and that efficiency increased as TP increased. Moreover, the treatment efficiency of TP at high concentrations was 10% higher than when the TP in the influent was below 20 mg/L. This feature has similarities to the removal of COD. In addition, the TP removal was dominated by physical mechanisms as indicated by only 1.7–2.3% of the TP being removed by microbial assimilation.[23] These findings indicated that TP removal was almost completely unaffected by temperature (Figure 4). There was also no significant difference in TP reduction during winter and summer. These findings are similar to those of a study of dairy milkhouse wastewater treatment conducted by Newman et al. [5]
3.3. Nitrogen removal During the experiment, the influent NH+ 4 − N concentration was 226–711 mg L−1 , while the effluent
concentrations were 51.5–533 mg L−1 for the HSFCW and 13.4–387 mg L−1 for the SP (Figure 4(a)), indicating removal efficiencies of 11–88% and 36–96%, respectively (Figure 4(b)). The average influent concentration −1 of NH+ from 1 to 26 weeks, after 4 − N was 419 mg L which it increased to 579 mg L−1 . Moreover, the average removal efficiencies of the HSFCW and SP were 60% and 80%, respectively, from 1 to 26 weeks, after which they decreased to 39% and 65%. The average removal efficiencies were 63% for the HSFCW and 81% for the SP when the temperature was high from 1 to 26 weeks as indicated by influent concentrations of 413–672 mg L−1 and effluent concentrations of 191–422 mg L−1 in the HSFCW and 24–266 mg L−1 in the SP. Afterwards, the average removal efficiencies decreased to 27% and 56% as the temperature was reduced from weeks 27 to 44, during which the influent concentration was 597–711 mg L−1 and the effluent concentrations were 162–533 mg L−1 for the HSFCW and 125–387 mg L−1 for the SP. The average seasonal NH+ 4 −N removal efficiencies during the four seasons were 27%, 48%, 68%, 20% for the HSFCW and 47%, 72%, 89%, 47% for the SP (Table 6), while the seasonal average removed −2 −1 loads of NH+ d 4 − N were 0.70, 1.33, 1.07, 0.61 g m for the HSFCW and 1.27, 1.99, 1.37, 1.45 g m−2 d−1 for the SP. The SP (1.52 g m−2 d−1 ) exhibited an average −2 −1 NH+ d higher than that of 4 − N removal of 0.59 g m the HSFCW (0.93 g m−2 d−1 ) (Table 4). Additionally, the average total inorganic nitrogen (TIN) removal efficiencies of the HSFCW and SP were 40% and 55%, respectively. In general, the effluent concentration, removal efficiency and removed load showed that the SP was better than the HSFCW at NH+ 4 − N removal. The average NH+ 4 − N removal by the HSFCW and SP were 1.18 and 1.77 g m−2 d−1 , respectively (Table 3). The results showed that the SP had better performance than the HSFCW during the experiment. Nitrogen in digested effluent is primarily in the form of NH+ 4 − N, and the principal mechanisms for NH+ − N elimination are vegetation 4 uptake, sedimentation, volatilization and nitrification.[26] Moreover, the removal of NH+ 4 − N is significantly influenced by pH, DO and temperature.[13,25,27] The vegetation uptake of N was 1.2–1.8%, which can be neglected in CW systems.[13] Nitrogen sedimentation is caused by struvite (MgNH4 PO4 ·6H2 O) precipitation. Struvite has a low solubility product (pK) that ranges from 13.08 to 13.29,[28] and struvite precipitation occurs when the combined con3− centrations of Mg2+ , NH+ 4 and PO4 exceed the struvite solubility limit.[29] Besides, even if a specialized plant is used for struvite sedimentation and magnesium hydroxide is added to improve performance on NH+ 4 − N removal, the NH+ − N removal rate is only about 6%.[30] 4 Nitrite and nitrate are the results of nitrification. The effluent concentrations of nitrite and nitrate in the SP were higher than in the HSFCW (Table 1). However, the TIN removal efficiency of SP (55%) was also higher than that of HSFCW (40%) because NH+ 4 − N was the
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Figure 3.
Fluctuations of TP concentration (a) and removal efficiency (b) as a function of time in the HSFCW and SP.
Table 5.
Seasonal TP concentration, removal efficiency and removed load of HSFCW and SP. Effluent (mg L−1 )
Season Temperature (◦ C) Influent (mg L−1 ) Spring Summer Autumn Winter
12.3 ± 5.1 25.7 ± 2.8 21.1 ± 4.5 8.3 ± 3.2
25.2 ± 4.65 19.5 ± 6.81 25.9 ± 7.59 33.1 ± 7.63
Removal efficiency (%) Removed load (g m−2 d−1 )
HSFCW
SP
HSFCW
SP
HSFCW
SP
11.9 ± 4.67 12.3 ± 3.59 13.9 ± 4.01 23.6 ± 5.30
10.4 ± 3.86 11.9 ± 3.83 15.5 ± 7.32 19.1 ± 4.38
44 ± 18 43 ± 13 43 ± 15 28 ± 11
56 ± 34 47 ± 12 43 ± 13 39 ± 11
0.06 ± 0.03 0.05 ± 0.02 0.05 ± 0.03 0.07 ± 0.03
0.07 ± 0.02 0.05 ± 0.02 0.05 ± 0.01 0.07 ± 0.03
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Figure 4.
Fluctuations of NH+ 4 − N concentration (a) and removal efficiency (b) as a function of time in the HSFCW and SP.
Table 6.
Seasonal NH+ 4 − N concentration, removal efficiency and removed load of HSFCW and SP. Effluent (mg L−1 )
Season Temperature (◦ C) Influent (mg L−1 ) Spring Summer Autumn Winter
12.3 ± 5.1 25.7 ± 2.8 21.1 ± 4.5 8.3 ± 3.2
546 ± 142 556 ± 92.1 308 ± 56.8 614 ± 34.7
HSFCW
SP
406 ± 139 292 ± 91.5 290 ± 66.8 157 ± 69.3 93.5 ± 33.3 33.6 ± 20.0 493 ± 25.2 324 ± 60.4
Removal efficiency (%) Removed load (g m−2 d−1 ) HSFCW
SP
HSFCW
SP
27 ± 12 48 ± 8 68 ± 13 20 ± 7
47 ± 8 72 ± 11 89 ± 6 47 ± 9
0.70 ± 0.32 1.33 ± 0.31 1.07 ± 0.38 0.61 ± 0.25
1.27 ± 0.38 1.99 ± 0.44 1.37 ± 0.25 1.45 ± 0.26
Environmental Technology Table 7.
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Fluctuations of seasonal concentrations of TIN and DO in HSFCW and SP. Effluent TINa (mg L−1 )
Season
HSFCW
SP
HSFCW
SP
Spring Summer Autumn Winter
533 ± 140 563 ± 89.3 316 ± 57.4 589 ± 77.2
413 ± 135 308 ± 63.0 198 ± 47.0 308 ± 152
297 ± 90.5 226 ± 57.4 186 ± 58.1 176 ± 36.1
2.89 ± 1.40 2.46 ± 0.86 1.42 ± 0.65 0.94 ± 0.28
4.01 ± 2.04 3.61 ± 2.53 2.44 ± 0.65 2.35 ± 0.38
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a TIN
− − – total inorganic nitrogen (the value is the sum of NH+ 4 − N, NO3 − N and NO2 − N).
dominant part of TIN. Therefore, this illustrated that nitrification was stronger in the SP than HSFCW. In the meantime, nitrification was limited in the HSFCW, which could not demonstrate that stronger denitrification has occurred in the HSFCW. The nitrification/denitrification rates were 1.17 g N m−2 d−1 /1.05 g N m−2 d−1 in HSFCW and 1.77 g N m−2 d−1 /1.52 g N m−2 d−1 in SP. Nitrification is affected by a number of factors including temperature, pH, DO and HRT. The average DO concentration in the SP was significantly higher than that in the HSFCW owing to the large contact area and stirring by wind (Table 7). Increased temperature led obviously to stronger nitrification, resulting in increased NH+ 4 − N removal efficiency (Figure 4(b)). A low loading rate and long HRT would increase the treatment efficiency.[25] The actual HRT of the SP (54 days) was significantly longer than that of the HSFCW (14.5 days). The longer HRT of the SP was one of the most important factors resulting in stronger nitrification. In short, these advantages of the SP improved its ability to convert NH+ 4 − N. Poach et al. [7] estimated that 7–16% of nitrogen in wetlands is removed through NH3 volatilization. Accordingly, this nitrogen removal pathway should not be ignored even though it is not the primary mechanism. NH3 volatilization from swine wastewater lagoons has been shown to be correlated to wind speed, water temperature, wastewater ammonia concentration and wastewater pH.[7,31] Therefore, the following equation [32] can be used to calculate NH3 volatilization: 10pH CFA , = 6344/(273+T ) + 10pH ) CTAN (e
(1)
CFA , free ammonia concentration (mg L−1 ); CTAN , total −1 ◦ NH+ 4 − N concentration (mg L ); T , temperature ( C). Table 8.
DO (mg L−1 )
Influent TINa (mg L−1 )
The influent CFA concentration was 2.41–92.5 mg L−1 and the effluent CFA concentration of the HSFCW and SP were 1.37–67.8 and 1.51–74.2 mg L−1 , respectively. The results calculated using Equation (1) is shown in Table 8. However, considering the pH (>7) and the NH+ 4 − N concentration of influent and effluent, it is estimated that 1–30% of the NH+ 4 − N load could be removed in the HSFCW and 1–22% in the SP via ammonia volatilization. Poach et al. [6] demonstrated that ammonia volatilization accounted for 23–36% of the N load when the total N load was greater than 1.5 g m−2 d−1 . The methods used to reduce ammonia volatilization generally focus on nitrification because weakening nitrification will increase ammonia volatilization.[11] Conversely, strengthening nitrification will decrease ammonia volatilization.[9] Whether it is partial nitrification,[6] continuous marsh systems or dilute liquid swine manure,[10] the purpose is to lower NH+ 4 − N concentration. In general, nitrogen loss can be expressed by TIN. In the present study, the effluent TIN concentration in the SP (222 mg L−1 ) was lower than that in the HSFCW (307 mg L−1 ) for effluent with lower concentrations of NH+ 4 − N (Table 7). Furthermore, the SP is less expensive than CWs and other treatment processes.[17] The operational cost of SP (0.1–0.2 Yuan m−3 ) is lower than HSFCW (0.1–0.4 Yuan m−3 ). In 2000, the cost of CW was 0.22–0.66 Yuan m−3 in America.[19] However, the construction cost of SP is 200–500 Yuan m−3 , which is very much less than the range 700–1000 Yuan m−3 for a HSFCW. In addition, blockage is one of the most serious problems associated with CWs, and it has the potential to break down the entire project. In addition, fluctuations in concentration
Seasonal concentration of free ammonia, pH and temperature in HSFCW and SP. −1 NH+ 4 − N (mg L )
Free ammonia (mg L−1 )
pH
Season
Temperature (◦ C)
HSFCW
SP
HSFCW
SP
HSFCW
SP
Spring Summer Autumn Winter
12 ± 5 25 ± 2 21 ± 4 8±3
406.5 ± 43.6 289.7 ± 29.4 93.5 ± 17.1 286.5 ± 25.9
291.5 ± 30.7 157 ± 19.0 33.6 ± 9.35 131.9 ± 21.8
8.1 ± 0.2 7.9 ± 0.3 7.6 ± 0.2 7.9 ± 0.2
8.4 ± 0.3 8.4 ± 0.1 7.8 ± 0.2 8.3 ± 0.3
8.8 ± 1.5 18.3 ± 3.6 2.6 ± 0.8 1.8 ± 0.5
15.4 ± 4.1 18.6 ± 5.9 2.8 ± 0.7 1.3 ± 0.4
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would affect the growth of plants. However, these factors are not an issue in SP systems.
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4.
Conclusions
The SP performed better than the HSFCW for NH+ 4 −N removal and the removal rate can reach as high as 96% in SP. There were no obvious differences for COD and TP removal between SP and HSFCW from the whole experiment. However, the SP showed a 10% higher removal efficiency for COD than the HSFCW when the influent concentration was at the lowest and highest stages. TP removal efficiency of the SP and HSFCW increased with the increase of influent TP concentration. Low temperature and high influent concentration led to low NH+ 4 − N removal efficiency. The SP has 20% higher of removal efficiency than the HSFCW. Overall, the results of this study indicate that the SP is suitable for the treatment of digested effluent of swine wastewater. The better performance of the SP than the HSFCW obtained in this study was novel and its conclusion possesses guiding effects on practical engineering. Funding The authors acknowledge the financial support from China Agriculture Research System [CARS-36].
References [1] Deng LW, Zheng P, Chen ZA. Anaerobic digestion and posttreatment of swine wastewater using IC–SBR process with bypass of raw wastewater. Process Biochem. 2006;41:965– 969. [2] Hill V, Pasternak J, Rice J, Marra M, Humenik F, Sobsey M, Szogi A, Hunt P. Economics of nitrogen and enteric microbe reductions in alternative swine waste treatment techniques. Proceedings NCSU Animal Waste Management Symposium; 1999 Jan; Raleigh, NC, USA. p. 27–28. [3] Hunt P, Szögi A, Humenik F, Rice J, Matheny T, Stone K. Constructed wetlands for treatment of swine wastewater from an anaerobic lagoon. Trans ASAE. 2002;45:639–647. [4] Knight RL, Payne VW, Borer RE, Clarke RA, Pries JH. Constructed wetlands for livestock wastewater management. Ecol Eng. 2000;15:41–55. [5] Newman JM, Clausen JC, Neafsey JA. Seasonal performance of a wetland constructed to process dairy milkhouse wastewater in Connecticut. Ecol Eng. 1999;14:181–198. [6] Poach M, Hunt P, Reddy G, Stone K, Matheny T, Johnson M, Sadler E. Ammonia volatilization from marsh–pond–marsh constructed wetlands treating swine wastewater. J Environ Qual. 2004;33:844–851. [7] Poach M, Hunt P, Sadler E, Matheny T, Johnson M, Stone K, Humenik F, Rice J. Ammonia volatilization from constructed wetlands that treat swine wastewater. Trans ASAE. 2002;45:619–927. [8] Hunt P, Matheny T, Ro K, Vanotti M, Ducey T. Denitrification in anaerobic lagoons used to treat swine wastewater. J Environ Qual. 2010;39:1821–1828. [9] Poach M, Hunt P, Reddy G, Stone K, Johnson M, Grubbs A. Effect of intermittent drainage on swine wastewater treatment by marsh–pond–marsh constructed wetlands. Ecol Eng. 2007;30:43–50.
[10] Poach M, Hunt P, Vanotti M, Stone K, Matheny T, Johnson M, Sadler E. Improved nitrogen treatment by constructed wetlands receiving partially nitrified liquid swine manure. Ecol Eng. 2003;20:183–197. [11] Westerman P. Application of mixed and aerated pond for nitrification and denitrification of flushed swine manure. Appl Eng Agric. 2002;18:351–360. [12] Vymazal J, Kröpfelová L, Švehla J, Chrastný V, Štíchová J. Trace elements in Phragmites australis growing in constructed wetlands for treatment of municipal wastewater. Ecol Eng. 2009;35:303–309. [13] Forbes DA, Reddy G, Hunt PG, Poach M, Ro KS, Cyrus JS. Comparison of aerated marsh-pond-marsh and continuous marsh constructed wetlands for treating swine wastewater. J Environ Sci Health, Part A. 2010;45:803–809. [14] Ro KS, Hunt PG, Johnson MH, Matheny TA, Forbes D, Reddy GB. Oxygen transfer in marsh–pond–marsh constructed wetlands treating swine wastewater. J Environ Sci Health, Part A. 2010;45:377–382. [15] Costa RHRd, Medri W. Modelling and optimisation of stabilisation ponds system for the treatment of swine wastes: organic matter evaluation. Braz Arch Biol Technol. 2002;45:385–392. [16] Hammer D, Pullin B, McCaskey T, Eason J, Payne V. Treating livestock wastewaters with constructed wetlands. Constructed wetlands for water quality improvement. 1993; 343–347. [17] Mara D. Constructed wetlands and waste stabilization ponds for small rural communities in the United Kingdom: a comparison of land area requirements, performance and costs. Environ Technol. 2006;27:753–757. [18] Liénard A, Boutin C, Molle P, Racault Y, Brissaud F, Picot B. Constructed wetlands and waste stabilization ponds for municipal wastewater treatment in France: comparison of performance and maintenance operations in terms of durability and reliability, in 9ème conférence sur les marais artificiels et 6ème conférence sur le lagunage naturel; 2004; Avignon, France. [19] U.S. Environmental Protection Agency. Manual for constructed wetlands treatment of municipal wastewaters. EPA/625/R-99/010, Cincinnati; 2000. [20] APHA, AWWA, WEF. Standard methods for the examination of water and wastewater. 20th ed. Washington, DC: American Public Health Association/American Water Works Association/Water Environment Federation; 1998. [21] Poach M, Hunt P, Reddy G, Stone K, Johnson M, Grubbs A. Swine wastewater treatment by marsh–pond–marsh constructed wetlands under varying nitrogen loads. Ecol Eng. 2004;23:165–175. [22] Travieso L, Sánchez E, Borja R, Benítez F, Raposo F, Rincón B, Jiménez A. Evaluation of a laboratory-scale stabilization pond for tertiary treatment of distillery waste previously treated by a combined anaerobic filter–aerobic trickling system. Ecol Eng. 2006;27:100–108. [23] Lee CY, Lee CC, Lee FY, Tseng SK, Liao CJ. Performance of subsurface flow constructed wetland taking pretreated swine effluent under heavy loads. Bioresour Technol. 2004;92:173–179. [24] Neralla S, Weaver RW, Lesikar BJ, Persyn RA. Improvement of domestic wastewater quality by subsurface flow constructed wetlands. Bioresour Technol. 2000;75:19–25. [25] Reddy G, Hunt PG, Phillips R, Stone K, Grubbs A. Treatment of swine wastewater in marsh–pond–marsh constructed wetlands. Water Sci Technol. 2001;44:545–550. [26] Reed SC, Crites RW, Middlebrooks EJ. Natural systems for waste management and treatment. New York: McGraw-Hill; 1995.
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Downloaded by [Selcuk Universitesi] at 10:22 22 December 2014
[27] Hunt PG, Matheny TA, Szögi AA. Denitrification in constructed wetlands used for treatment of swine wastewater. J Environ Qual. 2003;32:727–735. [28] Hanhoun M, Montastruc L, Azzaro-Pantel C, Biscans B, Frèche M, Pibouleau L. Temperature impact assessment on struvite solubility product: a thermodynamic modeling approach. Chem Eng J. 2011;167:50–58. [29] Ohlinger K, Young T, Schroeder E. Predicting struvite formation in digestion. Water Res. 1998;32:3607–3614.
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[30] Münch EV, Barr K. Controlled struvite crystallisation for removing phosphorus from anaerobic digester sidestreams. Water Res. 2001;35:151–159. [31] Harper LA, Sharpe RR, Parkin TB, De Visscher A, Van Cleemput O, Byers FM. Nitrogen cycling through swine production systems. J Environ Qual. 2004;33:1189–1201. [32] Anthonisen A, Loehr R, Prakasam T, Srinath E. Inhibition of nitrification by ammonia and nitrous acid. J Water Pollut Control Fed. 1976;48:835–852.
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Comparison of constructed wetland and stabilization pond for the treatment of digested effluent of swine wastewater a
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Gang-Jin Liu , Dan Zheng , Liang-Wei Deng , Quan Wen & Yi Liu
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Biogas Institute of Ministry of Agriculture, No.13, 4th Section, South Renmin Road, Chengdu, Sichuan 610041, People's Republic of China Published online: 27 May 2014.
Click for updates To cite this article: Gang-Jin Liu, Dan Zheng, Liang-Wei Deng, Quan Wen & Yi Liu (2014) Comparison of constructed wetland and stabilization pond for the treatment of digested effluent of swine wastewater, Environmental Technology, 35:21, 2660-2669, DOI: 10.1080/09593330.2014.917709 To link to this article: http://dx.doi.org/10.1080/09593330.2014.917709
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Environmental Technology, 2014 Vol. 35, No. 21, 2660–2669, http://dx.doi.org/10.1080/09593330.2014.917709
Comparison of constructed wetland and stabilization pond for the treatment of digested effluent of swine wastewater Gang-Jin Liu, Dan Zheng, Liang-Wei Deng∗ , Quan Wen and Yi Liu Biogas Institute of Ministry of Agriculture, No.13, 4th Section, South Renmin Road, Chengdu, Sichuan 610041, People’s Republic of China
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(Received 3 December 2013; final version received 18 April 2014 ) A laboratory-scale horizontal subsurface flow constructed wetland (HSFCW) and a stabilization pond (SP) were constructed to compare their performances on the treatment of digested effluent of swine wastewater. After 457 days of operation, the removal efficiencies of the HSFCW were as follows: chemical oxygen demand (COD), 17–54%; total phosphorus (TP), 32–45% and ammonia nitrogen NH+ 4 − N, 27–88%, while they were 25–55%, 31–56% and 56–98%, respectively, for the SP, with a hydraulic retention time of 54 days and hydraulic loading of 0.01 m3 m−2 d−1 . The average removed loads for the −2 d−1 , while they were 0.25–4.45, HSFCW were as follows: COD, 0.25–4.33; TP, 0.01–0.11 and NH+ 4 − N, 0.34–2.54 g m −2 −1 0.02–0.13 and 0.72–2.87 g m d , respectively, for the SP. The SP performed better than the HSFCW because the SP showed a 20% of higher removal efficiency for NH+ 4 − N than the HSFCW. Especially, the COD removal rate of SP was 10% higher than the HSFCW when the influent concentration was at the lowest and highest stages. Meanwhile, given the lower costs, the SP is more suitable for the treatment of digested effluent of swine wastewater than the HSFCW. Keywords: constructed wetlands; digested effluent; stabilization pond; swine wastewater; effluent quality
1. Introduction The improvement of living standards in China has resulted in an increased demand for pork, which has in turn led to an increase in medium- and large-scale pig farms in China. This has also led to the generation of a large quantity of swine wastewater, which contains a variety of pollutants and therefore has the potential to cause serious environmental pollutions. At present, most farms use the anaerobic digestion process to treat swine wastewater because it can recover methane.[1] However, the concentration of pollutants in effluent from anaerobic reactors is still high. This is especially true for ammonia nitrogen, which is not removed by anaerobic digestion, and sometimes increases. Excess ammonia nitrogen may lead to the pollution of surface and ground water. Thus, the digested effluent must be further processed to meet the discharge standards (discharge standard of pollutants for livestock and poultry breeding (China)). For pig farms located far from the city with large amounts of land, natural treatment systems are an attractive choice because they are operationally passive and cost-effective for nutrient removal.[2] As a type of natural treatment systems, constructed wetlands (CWs) are widely used for the treatment of livestock wastewater.[3–5] Another popular natural treatment is the stabilization pond (SP). Most investigations of swine wastewater treatment systems that have been conducted to ∗ Corresponding
author. Email: [email protected]
© 2014 Taylor & Francis
date have focused on the performance of nitrogen removal, which include ammonia volatilization,[6,7] improved nitrogen treatment [8–11] and removal of organics.[12] Both the CWs and SP show a good performance for the treatment of swine wastewater.[13,14] Costa and Medri [15] obtained very high treatment efficiency using SP systems. Specifically, their systems removed approximately 97% of organic matter (biochemical oxygen demand (BOD) and chemical oxygen demand (COD)), 87% of TS, 91% of VS, 90% of TN and 93% of total phosphorus (TP). Hammer et al. [16] used CWs to treat swine wastewater with good results as indicated by the following average removal rates: BOD5 , 90.4%; TSS, 91.4%; faecal coliforms, 99.4%; faecal streptococci, 98.4%; NH+ 4 − N, 93.6%; total Kjeldahl nitrogen (TKN), 91.4%; TP, 75.9%. Nevertheless, in the practical application of the two systems, technicians, proprietors and policy-makers are most interested in determining which system is best for the treatment of swine wastewater. However, the results of studies obtained under different conditions are not comparable. Mara [17] and Liénard et al. [18] compared the land area requirements, costs, performance and maintenance operations of CWs and SP systems for municipal wastewater in terms of durability and reliability. Mara [17] suggested that SP systems were preferable to CWs because the CWs required 60–480% more land than the SP to produce an urban wastewater treat-
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ment directive quality effluent and the cost was about 2–6 times more than the SP. Despite these findings, few studies have been conducted to compare the use of these systems for swine wastewater treatment. Horizontal subsurface flow constructed wetland (HSFCW) is most commonly used for swine wastewater treatment. This study was conducted to compare the performance of a HSFCW and SP for the removal of main pollutants, including COD, TP and NH+ 4 − N, from digested effluent of swine wastewater and to determine which was most suitable for the treatment of swine wastewater. To achieve this goal, a HSFCW and SP were constructed for swine wastewater treatment under natural conditions. 2. Materials and methods 2.1. Wastewater The anaerobically digested effluent used in the experiment was collected from a biogas plant used to treat swine wastewater at a local pig farm with 7000 pigs in the central province of Sichuan, China. The characteristics of the digested effluent of swine wastewater are shown in Table 1. 2.2. Experimental setup The experiment was conducted using two laboratory-scale plastic tanks with an open top, with a depth of 30 cm, length of 50 cm and width of 40 cm and a volume of 54 L. The designing parameter was according to ‘Manual for Constructed Wetlands Treatment of Municipal Wastewaters’.[19] The tank that was used as the HSFCW was packed with three layers of gravel (voidage of 26.9%). The top layer was 5 cm thick and contained gravel with a diameter of 10–30 mm, while the middle layer was 10 cm thick and contained gravel with a diameter of 30–60 mm and the lower layer was 15 cm thick and contained gravel with a diameter ranging from 60 to 100 mm (Figure 1(b)). The tank that was used for the SP was not filled with the packing material. Digested effluent was poured into a 2 L Table 1. Characteristics of the influent and effluents from HSFCW and SP.
Parameters
Influent (mg L−1 )
Effluent of HSFCW (mg L−1 )
Effluent of SP (mg L−1 )
pH DO TP COD NH+ 4 −N NO− 3 −N NO− 2 −N TINa
8.0 ± 0.3 1.0 ± 0.9 25.0 ± 8.2 818 ± 272 508 ± 139 8.2 ± 4.2 1.52 ± 3.55 517 ± 137
7.9 ± 0.3 1.9 ± 0.9 14.8 ± 6.3 420 ± 141 273 ± 143 12.6 ± 13.4 4.81 ± 39 307 ± 120
8.3 ± 0.6 2.4 ± 1.2 14.0 ± 5.6 414 ± 121 154 ± 105 39.1 ± 43.6 21.4 ± 43.4 222 ± 74.3
a TIN NH+ 4
– total inorganic nitrogen (the value is the sum of − − N, NO− 3 − N and NO2 − N).
Figure 1.
Side view of the SP (a) and HSFCW (b).
glass bottle with a 10 mm diameter hole in the bottom that was at a higher position than tank (Figure 1(a)). The digested effluent flowed from the hole in the glass bottle to the bottom of the tank through a polyvinyl chloride (PVC) tube with an internal diameter of 20 mm. The effluent of the HSFCW and SP was discharged from their tops opposite the influent port through a latex tube with an internal diameter of 10 mm.
2.3.
Experimental operation
This study was conducted under natural conditions and the main operating conditions were shown in Table 2. During the experiment, the inflow was 1 L d−1 and the effluent was collected in a 1 L jar. The nominal hydraulic retention time (HRT) was 54 days (the ratio of the usable SP water volume to average flow rate) while the actual HRT of HSFCW was 14.5 days (the ratio of the usable HSFCW water volume to the average flow rate) considering the voidage of gravel. The HSFCW system was planted with Acorus calamus. Wastewater samples were collected from a wide-mouthed bottle and transferred to the laboratory for analysis at the end of each weekend.
2.4.
Analytical methods
Influent and effluent samples were collected every week and analysed immediately. The pH value and concentra− − tions of NH+ 4 − N, NO2 − N, NO3 − N, COD, TP and dissolved oxygen (DO) were routinely measured according to the standard methods.[20] Specifically, the NH+ 4 −N
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Table 2.
The operating conditions of HSFCW and SP.
Parameters
HSFCW/SP
Temperature (◦ C) Feed water (L) HRT (d) COD loading rate (g m−2 d−1 ) −2 d−1 ) NH+ 4 − N loading rate (g m − NO3 − N loading rate (g m−2 d−1 ) −2 d−1 ) NO− 2 − N loading rate (g m Hydraulic load (m3 m−2 d−1 )
2–33 1 14.5/54 4.09 ± 1.36 2.54 ± 0.69 0.04 ± 0.02 0.01 ± 0.02 0.01
and NO− 2 − N were analysed with a UV–VIS spectrophotometer (UV-2450, Shimadzu, Japan) using different colorimetric methods while the NO− 3 − N was analysed using an ultraviolet spectrophotometric method. The COD was measured using the potassium chromate method. The TP and DO were measured using a TP automatic analyzer (IL500P, Lacha-Hach, USA) and oxygen meter (Oxi-315i, WTW, Germany), respectively. The pH was measured using an acidimeter (PHS-3C, DAPU, China) and the temperature was determined using a mercurial thermometer.
3. Results and discussion 3.1. COD removal During the experimental periods, the influent COD was 304–1246 mg L−1 , and the effluent COD values were 206– 794 mg L−1 for the HSFCW and 212–798 mg L−1 for the SP (Figure 2(a)), indicating removal efficiencies of 16–72% and 13–72% (Figure 2(b)), respectively. During weeks 18– 27 the influent COD (304–421 mg L−1 ) was lower than the rest of the period. The COD of the HSFCW and SP effluent was 254–344 and 241–341 mg L−1 and the average removal efficiencies during this period were 17% and 25%, respectively. During weeks 33–41, the influent concentration (1011–1155 mg L−1 ) was higher and the effluent concentrations ranged from 443 to 690 mg L−1 for the HSFCW and 432–597 mg L−1 for the SP, indicating removal efficiencies of 39% and 45%, respectively. The seasonal average removal efficiencies of the HSFCW were 48%, 54%, 42% and 41% in spring, summer, autumn and winter, respectively, while these values were 48%, 55%, 44% and 42% for the SP (Table 3). Moreover, the loads of COD removed, which comprise an important index of the pollutant removal capability, were 2.14, 2.55, 1.30 and 1.47 g m−2 d−1 in the HSFCW, and 2.14, 2.58, 1.35 and 1.52 g m−2 d−1 in the SP during spring, summer, autumn and winter, respectively. Both systems showed higher removal efficiencies in summer than in winter even though the influent COD values were similar. Throughout the experimental period, the SP had a higher removed load of COD than the HSFCW (Table 4). Overall, the effluent concentration and removal efficiency demonstrated that the SP was better for COD removal than the HSFCW.
In this study, the HSFCW and SP had similar seasonal average removal efficiencies for COD, which was in accordance with the results of a study conducted by Poach et al. [21] who found a 37-51% reduction in COD in marsh–pond–marsh CWs. However, in the present study, the HSFCW and SP displayed lower treatment efficiencies during the period in which the influent COD concentration was lower than 421 mg L−1 (Figure 2) and the temperature was 16.5◦ C, which was twice as high as the critical temperature (9–10◦ C).[5] Relatively high temperatures and low concentrations will increase pollutant removal.[21] Accordingly, the HSFCW and SP should have had a high removal efficiency that was identical to that observed in other studies. In contrast, when the temperature was below 7◦ C and the COD concentration was greater than 1011 mg L−1 , the removal efficiency was 20% higher than when the temperature was 16.5◦ C and the COD concentration was lower than 421 mg L−1 . These findings were opposite to those of Travieso et al. [22] Overall, this phenomenon indicated that the temperature had less of an effect on the removal of COD than influent concentration. The reason might be the decreased organic, as carbon source, reduced microorganisms amount because the transformations of COD involve microbial processes. However, biochemical and physical conversions of organic compounds are both primarily responsible for COD removal. Lee et al. [23] demonstrated that COD removal was accomplished by good cooperation between physical and microbial mechanisms, with the former mechanism accounting for 52–74% of the removal and the latter accounting for 26–48%. These results implied that concentration might be responsible for physical processes playing a leading role in COD removal, as well as the increasing COD concentration being accompanied by a rising removal rate. Generally, the greatest reductions accompany the highest influent concentrations.[24] These findings are similar to those of Costa and Medri,[15] who investigated the use of a SP system for the treatment of swine wastes. The SP showed approximately 10% higher COD removal than the HSFCW under the conditions of low influent concentration, high temperature or high influent concentration and low temperature. This might be caused by the higher DO concentration and the long HRT. High DO was led by the large contact area and stirring by wind in the SP to increase the concentration of DO. The HSFCW and SP had the same nominal HRT (54 days), but the HSFCW was packed with gravel (voidage of 26.9%) and had a shorter actual HRT (14.5 days) than the SP (54 days). 3.2. TP removal During the experiment, the influent concentration of TP was 8.74–43.5 mg L−1 , the effluent concentrations were 5.48–31.8 mg L−1 for the HSFCW and 5.32–26.5 mg L−1 for the SP (Figure 3(a)), while the treatment efficiencies were −32–72% for the HSFCW and −52–73% for the
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Figure 2.
Fluctuations of COD concentration (a) and removal efficiency (b) as a function of time in the HSFCW and SP.
Table 3.
Seasonal COD concentration, removal efficiency and removed load of HSFCW and SP. Effluent (mg L−1 )
Season Temperature (◦ C) Influent (mg L−1 ) Spring Summer Autumn Winter
12 ± 5 25 ± 2 21 ± 4 8±3
895 ± 215 936 ± 185 618 ± 319 716 ± 280
Removal efficiency (%) Removed load (g m−2 d−1 )
HSFCW
SP
HSFCW
SP
HSFCW
SP
467 ± 190 427 ± 120 359 ± 88 421 ± 159
467 ± 149 420 ± 101 349 ± 116 413 ± 110
47 ± 17 54 ± 9 34 ± 18 39 ± 13
45 ± 18 55 ± 8 38 ± 12 38 ± 15
2.14 ± 1.05 2.55 ± 0.72 1.30 ± 1.17 1.47 ± 0.85
2.14 ± 1.14 2.58 ± 0.74 1.35 ± 1.03 1.52 ± 0.96
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Table 4. COD, TP and NH+ 4 − N removal efficiency and removed load of HSFCW and SP. Removal efficiency (%) Removed load (g m−2 d−1 ) Parameters HSFCW
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COD TP NH+ 4 −N
45 ± 16 42 ± 14 48 ± 19
SP
HSFCW
SP
46 ± 15 46 ± 12 71 ± 17
1.99 ± 1.04 0.05 ± 0.03 0.93 ± 0.67
2.02 ± 1.05 0.06 ± 0.02 1.52 ± 0.63
SP (Figure 3(b)). The average treatment efficiencies were 35% for the HSFCW and 31% for the SP when the influent TP concentration was less than 20 mg L−1 , while they reached 42% and 45% when the influent TP concentration was greater than 20 mg L−1 . However, the influence of temperature on TP reduction was not obvious (Figure 3(b)). The seasonal TP treatment efficiencies were 44%, 43%, 43%, 28% for the HSFCW and 56%, 47%, 43%, 39% for the SP during the four seasons, while the seasonal removed loads of TP were 0.06, 0.05, 0.05, 0.07 g m−2 d−1 for the HSFCW and 0.07, 0.05, 0.05, 0.07 g m−2 d−1 for the SP, respectively (Table 5). Throughout the experiment, the TP treatment efficiencies of the HSFCW and SP were 0.05 and 0.06 g m−2 d−1 , respectively (Table 4). The results indicated that the capability of the SP to reduce TP was a little better than that of the HSFCW. The treatment efficiency of the SP observed in the present study was higher than that obtained in a study conducted by Poach et al. [9,21] which might be due to improved treatment efficiency as a result of the longer HRT.[25] Although the HRT of the SP was much longer than that of the HSFCW, the treatment efficiency of the SP was only 2% higher than that of the HSFCW. The removal efficiency and influent TP concentration changed without obvious fluctuation (Figure 3). Additionally, these factors did not show any relationships with large changes in temperature. However, data analysis conducted revealed that a lower influent TP concentration was associated with lower treatment efficiency, and that efficiency increased as TP increased. Moreover, the treatment efficiency of TP at high concentrations was 10% higher than when the TP in the influent was below 20 mg/L. This feature has similarities to the removal of COD. In addition, the TP removal was dominated by physical mechanisms as indicated by only 1.7–2.3% of the TP being removed by microbial assimilation.[23] These findings indicated that TP removal was almost completely unaffected by temperature (Figure 4). There was also no significant difference in TP reduction during winter and summer. These findings are similar to those of a study of dairy milkhouse wastewater treatment conducted by Newman et al. [5]
3.3. Nitrogen removal During the experiment, the influent NH+ 4 − N concentration was 226–711 mg L−1 , while the effluent
concentrations were 51.5–533 mg L−1 for the HSFCW and 13.4–387 mg L−1 for the SP (Figure 4(a)), indicating removal efficiencies of 11–88% and 36–96%, respectively (Figure 4(b)). The average influent concentration −1 of NH+ from 1 to 26 weeks, after 4 − N was 419 mg L which it increased to 579 mg L−1 . Moreover, the average removal efficiencies of the HSFCW and SP were 60% and 80%, respectively, from 1 to 26 weeks, after which they decreased to 39% and 65%. The average removal efficiencies were 63% for the HSFCW and 81% for the SP when the temperature was high from 1 to 26 weeks as indicated by influent concentrations of 413–672 mg L−1 and effluent concentrations of 191–422 mg L−1 in the HSFCW and 24–266 mg L−1 in the SP. Afterwards, the average removal efficiencies decreased to 27% and 56% as the temperature was reduced from weeks 27 to 44, during which the influent concentration was 597–711 mg L−1 and the effluent concentrations were 162–533 mg L−1 for the HSFCW and 125–387 mg L−1 for the SP. The average seasonal NH+ 4 −N removal efficiencies during the four seasons were 27%, 48%, 68%, 20% for the HSFCW and 47%, 72%, 89%, 47% for the SP (Table 6), while the seasonal average removed −2 −1 loads of NH+ d 4 − N were 0.70, 1.33, 1.07, 0.61 g m for the HSFCW and 1.27, 1.99, 1.37, 1.45 g m−2 d−1 for the SP. The SP (1.52 g m−2 d−1 ) exhibited an average −2 −1 NH+ d higher than that of 4 − N removal of 0.59 g m the HSFCW (0.93 g m−2 d−1 ) (Table 4). Additionally, the average total inorganic nitrogen (TIN) removal efficiencies of the HSFCW and SP were 40% and 55%, respectively. In general, the effluent concentration, removal efficiency and removed load showed that the SP was better than the HSFCW at NH+ 4 − N removal. The average NH+ 4 − N removal by the HSFCW and SP were 1.18 and 1.77 g m−2 d−1 , respectively (Table 3). The results showed that the SP had better performance than the HSFCW during the experiment. Nitrogen in digested effluent is primarily in the form of NH+ 4 − N, and the principal mechanisms for NH+ − N elimination are vegetation 4 uptake, sedimentation, volatilization and nitrification.[26] Moreover, the removal of NH+ 4 − N is significantly influenced by pH, DO and temperature.[13,25,27] The vegetation uptake of N was 1.2–1.8%, which can be neglected in CW systems.[13] Nitrogen sedimentation is caused by struvite (MgNH4 PO4 ·6H2 O) precipitation. Struvite has a low solubility product (pK) that ranges from 13.08 to 13.29,[28] and struvite precipitation occurs when the combined con3− centrations of Mg2+ , NH+ 4 and PO4 exceed the struvite solubility limit.[29] Besides, even if a specialized plant is used for struvite sedimentation and magnesium hydroxide is added to improve performance on NH+ 4 − N removal, the NH+ − N removal rate is only about 6%.[30] 4 Nitrite and nitrate are the results of nitrification. The effluent concentrations of nitrite and nitrate in the SP were higher than in the HSFCW (Table 1). However, the TIN removal efficiency of SP (55%) was also higher than that of HSFCW (40%) because NH+ 4 − N was the
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Environmental Technology
Figure 3.
Fluctuations of TP concentration (a) and removal efficiency (b) as a function of time in the HSFCW and SP.
Table 5.
Seasonal TP concentration, removal efficiency and removed load of HSFCW and SP. Effluent (mg L−1 )
Season Temperature (◦ C) Influent (mg L−1 ) Spring Summer Autumn Winter
12.3 ± 5.1 25.7 ± 2.8 21.1 ± 4.5 8.3 ± 3.2
25.2 ± 4.65 19.5 ± 6.81 25.9 ± 7.59 33.1 ± 7.63
Removal efficiency (%) Removed load (g m−2 d−1 )
HSFCW
SP
HSFCW
SP
HSFCW
SP
11.9 ± 4.67 12.3 ± 3.59 13.9 ± 4.01 23.6 ± 5.30
10.4 ± 3.86 11.9 ± 3.83 15.5 ± 7.32 19.1 ± 4.38
44 ± 18 43 ± 13 43 ± 15 28 ± 11
56 ± 34 47 ± 12 43 ± 13 39 ± 11
0.06 ± 0.03 0.05 ± 0.02 0.05 ± 0.03 0.07 ± 0.03
0.07 ± 0.02 0.05 ± 0.02 0.05 ± 0.01 0.07 ± 0.03
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Figure 4.
Fluctuations of NH+ 4 − N concentration (a) and removal efficiency (b) as a function of time in the HSFCW and SP.
Table 6.
Seasonal NH+ 4 − N concentration, removal efficiency and removed load of HSFCW and SP. Effluent (mg L−1 )
Season Temperature (◦ C) Influent (mg L−1 ) Spring Summer Autumn Winter
12.3 ± 5.1 25.7 ± 2.8 21.1 ± 4.5 8.3 ± 3.2
546 ± 142 556 ± 92.1 308 ± 56.8 614 ± 34.7
HSFCW
SP
406 ± 139 292 ± 91.5 290 ± 66.8 157 ± 69.3 93.5 ± 33.3 33.6 ± 20.0 493 ± 25.2 324 ± 60.4
Removal efficiency (%) Removed load (g m−2 d−1 ) HSFCW
SP
HSFCW
SP
27 ± 12 48 ± 8 68 ± 13 20 ± 7
47 ± 8 72 ± 11 89 ± 6 47 ± 9
0.70 ± 0.32 1.33 ± 0.31 1.07 ± 0.38 0.61 ± 0.25
1.27 ± 0.38 1.99 ± 0.44 1.37 ± 0.25 1.45 ± 0.26
Environmental Technology Table 7.
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Fluctuations of seasonal concentrations of TIN and DO in HSFCW and SP. Effluent TINa (mg L−1 )
Season
HSFCW
SP
HSFCW
SP
Spring Summer Autumn Winter
533 ± 140 563 ± 89.3 316 ± 57.4 589 ± 77.2
413 ± 135 308 ± 63.0 198 ± 47.0 308 ± 152
297 ± 90.5 226 ± 57.4 186 ± 58.1 176 ± 36.1
2.89 ± 1.40 2.46 ± 0.86 1.42 ± 0.65 0.94 ± 0.28
4.01 ± 2.04 3.61 ± 2.53 2.44 ± 0.65 2.35 ± 0.38
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a TIN
− − – total inorganic nitrogen (the value is the sum of NH+ 4 − N, NO3 − N and NO2 − N).
dominant part of TIN. Therefore, this illustrated that nitrification was stronger in the SP than HSFCW. In the meantime, nitrification was limited in the HSFCW, which could not demonstrate that stronger denitrification has occurred in the HSFCW. The nitrification/denitrification rates were 1.17 g N m−2 d−1 /1.05 g N m−2 d−1 in HSFCW and 1.77 g N m−2 d−1 /1.52 g N m−2 d−1 in SP. Nitrification is affected by a number of factors including temperature, pH, DO and HRT. The average DO concentration in the SP was significantly higher than that in the HSFCW owing to the large contact area and stirring by wind (Table 7). Increased temperature led obviously to stronger nitrification, resulting in increased NH+ 4 − N removal efficiency (Figure 4(b)). A low loading rate and long HRT would increase the treatment efficiency.[25] The actual HRT of the SP (54 days) was significantly longer than that of the HSFCW (14.5 days). The longer HRT of the SP was one of the most important factors resulting in stronger nitrification. In short, these advantages of the SP improved its ability to convert NH+ 4 − N. Poach et al. [7] estimated that 7–16% of nitrogen in wetlands is removed through NH3 volatilization. Accordingly, this nitrogen removal pathway should not be ignored even though it is not the primary mechanism. NH3 volatilization from swine wastewater lagoons has been shown to be correlated to wind speed, water temperature, wastewater ammonia concentration and wastewater pH.[7,31] Therefore, the following equation [32] can be used to calculate NH3 volatilization: 10pH CFA , = 6344/(273+T ) + 10pH ) CTAN (e
(1)
CFA , free ammonia concentration (mg L−1 ); CTAN , total −1 ◦ NH+ 4 − N concentration (mg L ); T , temperature ( C). Table 8.
DO (mg L−1 )
Influent TINa (mg L−1 )
The influent CFA concentration was 2.41–92.5 mg L−1 and the effluent CFA concentration of the HSFCW and SP were 1.37–67.8 and 1.51–74.2 mg L−1 , respectively. The results calculated using Equation (1) is shown in Table 8. However, considering the pH (>7) and the NH+ 4 − N concentration of influent and effluent, it is estimated that 1–30% of the NH+ 4 − N load could be removed in the HSFCW and 1–22% in the SP via ammonia volatilization. Poach et al. [6] demonstrated that ammonia volatilization accounted for 23–36% of the N load when the total N load was greater than 1.5 g m−2 d−1 . The methods used to reduce ammonia volatilization generally focus on nitrification because weakening nitrification will increase ammonia volatilization.[11] Conversely, strengthening nitrification will decrease ammonia volatilization.[9] Whether it is partial nitrification,[6] continuous marsh systems or dilute liquid swine manure,[10] the purpose is to lower NH+ 4 − N concentration. In general, nitrogen loss can be expressed by TIN. In the present study, the effluent TIN concentration in the SP (222 mg L−1 ) was lower than that in the HSFCW (307 mg L−1 ) for effluent with lower concentrations of NH+ 4 − N (Table 7). Furthermore, the SP is less expensive than CWs and other treatment processes.[17] The operational cost of SP (0.1–0.2 Yuan m−3 ) is lower than HSFCW (0.1–0.4 Yuan m−3 ). In 2000, the cost of CW was 0.22–0.66 Yuan m−3 in America.[19] However, the construction cost of SP is 200–500 Yuan m−3 , which is very much less than the range 700–1000 Yuan m−3 for a HSFCW. In addition, blockage is one of the most serious problems associated with CWs, and it has the potential to break down the entire project. In addition, fluctuations in concentration
Seasonal concentration of free ammonia, pH and temperature in HSFCW and SP. −1 NH+ 4 − N (mg L )
Free ammonia (mg L−1 )
pH
Season
Temperature (◦ C)
HSFCW
SP
HSFCW
SP
HSFCW
SP
Spring Summer Autumn Winter
12 ± 5 25 ± 2 21 ± 4 8±3
406.5 ± 43.6 289.7 ± 29.4 93.5 ± 17.1 286.5 ± 25.9
291.5 ± 30.7 157 ± 19.0 33.6 ± 9.35 131.9 ± 21.8
8.1 ± 0.2 7.9 ± 0.3 7.6 ± 0.2 7.9 ± 0.2
8.4 ± 0.3 8.4 ± 0.1 7.8 ± 0.2 8.3 ± 0.3
8.8 ± 1.5 18.3 ± 3.6 2.6 ± 0.8 1.8 ± 0.5
15.4 ± 4.1 18.6 ± 5.9 2.8 ± 0.7 1.3 ± 0.4
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would affect the growth of plants. However, these factors are not an issue in SP systems.
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4.
Conclusions
The SP performed better than the HSFCW for NH+ 4 −N removal and the removal rate can reach as high as 96% in SP. There were no obvious differences for COD and TP removal between SP and HSFCW from the whole experiment. However, the SP showed a 10% higher removal efficiency for COD than the HSFCW when the influent concentration was at the lowest and highest stages. TP removal efficiency of the SP and HSFCW increased with the increase of influent TP concentration. Low temperature and high influent concentration led to low NH+ 4 − N removal efficiency. The SP has 20% higher of removal efficiency than the HSFCW. Overall, the results of this study indicate that the SP is suitable for the treatment of digested effluent of swine wastewater. The better performance of the SP than the HSFCW obtained in this study was novel and its conclusion possesses guiding effects on practical engineering. Funding The authors acknowledge the financial support from China Agriculture Research System [CARS-36].
References [1] Deng LW, Zheng P, Chen ZA. Anaerobic digestion and posttreatment of swine wastewater using IC–SBR process with bypass of raw wastewater. Process Biochem. 2006;41:965– 969. [2] Hill V, Pasternak J, Rice J, Marra M, Humenik F, Sobsey M, Szogi A, Hunt P. Economics of nitrogen and enteric microbe reductions in alternative swine waste treatment techniques. Proceedings NCSU Animal Waste Management Symposium; 1999 Jan; Raleigh, NC, USA. p. 27–28. [3] Hunt P, Szögi A, Humenik F, Rice J, Matheny T, Stone K. Constructed wetlands for treatment of swine wastewater from an anaerobic lagoon. Trans ASAE. 2002;45:639–647. [4] Knight RL, Payne VW, Borer RE, Clarke RA, Pries JH. Constructed wetlands for livestock wastewater management. Ecol Eng. 2000;15:41–55. [5] Newman JM, Clausen JC, Neafsey JA. Seasonal performance of a wetland constructed to process dairy milkhouse wastewater in Connecticut. Ecol Eng. 1999;14:181–198. [6] Poach M, Hunt P, Reddy G, Stone K, Matheny T, Johnson M, Sadler E. Ammonia volatilization from marsh–pond–marsh constructed wetlands treating swine wastewater. J Environ Qual. 2004;33:844–851. [7] Poach M, Hunt P, Sadler E, Matheny T, Johnson M, Stone K, Humenik F, Rice J. Ammonia volatilization from constructed wetlands that treat swine wastewater. Trans ASAE. 2002;45:619–927. [8] Hunt P, Matheny T, Ro K, Vanotti M, Ducey T. Denitrification in anaerobic lagoons used to treat swine wastewater. J Environ Qual. 2010;39:1821–1828. [9] Poach M, Hunt P, Reddy G, Stone K, Johnson M, Grubbs A. Effect of intermittent drainage on swine wastewater treatment by marsh–pond–marsh constructed wetlands. Ecol Eng. 2007;30:43–50.
[10] Poach M, Hunt P, Vanotti M, Stone K, Matheny T, Johnson M, Sadler E. Improved nitrogen treatment by constructed wetlands receiving partially nitrified liquid swine manure. Ecol Eng. 2003;20:183–197. [11] Westerman P. Application of mixed and aerated pond for nitrification and denitrification of flushed swine manure. Appl Eng Agric. 2002;18:351–360. [12] Vymazal J, Kröpfelová L, Švehla J, Chrastný V, Štíchová J. Trace elements in Phragmites australis growing in constructed wetlands for treatment of municipal wastewater. Ecol Eng. 2009;35:303–309. [13] Forbes DA, Reddy G, Hunt PG, Poach M, Ro KS, Cyrus JS. Comparison of aerated marsh-pond-marsh and continuous marsh constructed wetlands for treating swine wastewater. J Environ Sci Health, Part A. 2010;45:803–809. [14] Ro KS, Hunt PG, Johnson MH, Matheny TA, Forbes D, Reddy GB. Oxygen transfer in marsh–pond–marsh constructed wetlands treating swine wastewater. J Environ Sci Health, Part A. 2010;45:377–382. [15] Costa RHRd, Medri W. Modelling and optimisation of stabilisation ponds system for the treatment of swine wastes: organic matter evaluation. Braz Arch Biol Technol. 2002;45:385–392. [16] Hammer D, Pullin B, McCaskey T, Eason J, Payne V. Treating livestock wastewaters with constructed wetlands. Constructed wetlands for water quality improvement. 1993; 343–347. [17] Mara D. Constructed wetlands and waste stabilization ponds for small rural communities in the United Kingdom: a comparison of land area requirements, performance and costs. Environ Technol. 2006;27:753–757. [18] Liénard A, Boutin C, Molle P, Racault Y, Brissaud F, Picot B. Constructed wetlands and waste stabilization ponds for municipal wastewater treatment in France: comparison of performance and maintenance operations in terms of durability and reliability, in 9ème conférence sur les marais artificiels et 6ème conférence sur le lagunage naturel; 2004; Avignon, France. [19] U.S. Environmental Protection Agency. Manual for constructed wetlands treatment of municipal wastewaters. EPA/625/R-99/010, Cincinnati; 2000. [20] APHA, AWWA, WEF. Standard methods for the examination of water and wastewater. 20th ed. Washington, DC: American Public Health Association/American Water Works Association/Water Environment Federation; 1998. [21] Poach M, Hunt P, Reddy G, Stone K, Johnson M, Grubbs A. Swine wastewater treatment by marsh–pond–marsh constructed wetlands under varying nitrogen loads. Ecol Eng. 2004;23:165–175. [22] Travieso L, Sánchez E, Borja R, Benítez F, Raposo F, Rincón B, Jiménez A. Evaluation of a laboratory-scale stabilization pond for tertiary treatment of distillery waste previously treated by a combined anaerobic filter–aerobic trickling system. Ecol Eng. 2006;27:100–108. [23] Lee CY, Lee CC, Lee FY, Tseng SK, Liao CJ. Performance of subsurface flow constructed wetland taking pretreated swine effluent under heavy loads. Bioresour Technol. 2004;92:173–179. [24] Neralla S, Weaver RW, Lesikar BJ, Persyn RA. Improvement of domestic wastewater quality by subsurface flow constructed wetlands. Bioresour Technol. 2000;75:19–25. [25] Reddy G, Hunt PG, Phillips R, Stone K, Grubbs A. Treatment of swine wastewater in marsh–pond–marsh constructed wetlands. Water Sci Technol. 2001;44:545–550. [26] Reed SC, Crites RW, Middlebrooks EJ. Natural systems for waste management and treatment. New York: McGraw-Hill; 1995.
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Downloaded by [Selcuk Universitesi] at 10:22 22 December 2014
[27] Hunt PG, Matheny TA, Szögi AA. Denitrification in constructed wetlands used for treatment of swine wastewater. J Environ Qual. 2003;32:727–735. [28] Hanhoun M, Montastruc L, Azzaro-Pantel C, Biscans B, Frèche M, Pibouleau L. Temperature impact assessment on struvite solubility product: a thermodynamic modeling approach. Chem Eng J. 2011;167:50–58. [29] Ohlinger K, Young T, Schroeder E. Predicting struvite formation in digestion. Water Res. 1998;32:3607–3614.
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[30] Münch EV, Barr K. Controlled struvite crystallisation for removing phosphorus from anaerobic digester sidestreams. Water Res. 2001;35:151–159. [31] Harper LA, Sharpe RR, Parkin TB, De Visscher A, Van Cleemput O, Byers FM. Nitrogen cycling through swine production systems. J Environ Qual. 2004;33:1189–1201. [32] Anthonisen A, Loehr R, Prakasam T, Srinath E. Inhibition of nitrification by ammonia and nitrous acid. J Water Pollut Control Fed. 1976;48:835–852.
