Comparison between a moving bed membrane bioreactor and a conventional membrane bioreactor on organic carbon and nitrogen removal

A membrane bioreactor filled with carriers instead of activated sludge named a moving bed membrane bioreactor (MBMBR) was investigated for simultaneously removing organic carbon and nitrogen in wastewater. Its performance was compared with a conventional membrane bioreactor (CMBR) at various influent COD/TN ratios of 8.9–22.1. The operational parameters were optimized to increase the treatment efficiency. COD removal efficiency averaged at 95.6% and 96.2%, respectively, for MBMBR and CMBR during the 4 months experimental period. The MBMBR system demonstrated good performance on nitrogen removal at different COD/TN ratios. When COD/TN was 8.9 and the total nitrogen (TN) load was 7.58 mg/l h, the TN and ammonium nitrogen removal efficiencies of the MBMBR were maintained over 70.0% and 80.0%, respectively, and the removed total nitrogen (TN) load reached to 5.31 mg/l h. Multifunctional microbial reactions in the carrier, such as simultaneous nitrification and denitrification (SND), play important roles in nitrogen removal. In comparison, the CMBR did not perform so well. Its TN removal was not stable, and the removed total nitrogen (TN) load was only 1.02 mg/l h at COD/TN ratio 8.9. The specific oxygen utilization rate (SOUR) showed that the biofilm has a better microbial activity than an activated sludge. Nevertheless, the membrane fouling behavior was more severe in the MBMBR than in the CMBR due to a thick and dense cake layer formed on the membrane surface, which was speculated to be caused by the filamentous bacteria in the MBMBR.     

Seasonal and annual performance of a full-scale constructed wetland system for sewage treatment in China

A full-scale constructed wetlands system with a total area of 80 ha and treatment capability of 2.0 × 10⁴ m³ d⁻¹ was completed in October 1998 in Rongcheng, Shandong Province, China. To evaluate wastewater treatment effectiveness and seasonal performance of the system, water samples were collected and analyzed from January 1999 to December 2004. Comparison of mean inlet and outlet concentrations showed that the constructed wetland system could effectively reduce the output of SS (71.8 ± 8.4%), BOD₅ (70.4 ± 9.6%), COD (62.2 ± 10.1%), total coliform (99.7%) and fecal coliform (99.6%). However, the percent reduction of ammonia nitrogen was relatively low (40.6 ± 15.3%), and total phosphorus showed the least efficient reduction (29.6 ± 12.8%). BOD₅, COD, ammonia nitrogen, and total phosphorus removal efficiencies displayed seasonal variations. BOD₅ and COD removal was more efficient in spring and summer than in autumn and winter whereas ammonia nitrogen and total phosphorus removal was more efficient in summer and autumn than in spring and winter. Annual variation analysis shows that COD, BOD₅, and ammonia nitrogen reduction efficiencies increased from 1999 to 2004. In contrast, mean total phosphorus reduction efficiency did not change from 2001 to 2002 and began to decrease from 2003 onwards.     

Side-by-side comparison of horizontal subsurface flow and free water surface flow constructed wetlands and artificial neural network (ANN) modelling approach

A horizontal subsurface flow (HSSF) and a free water surface flow (FWSF) constructed wetlands (4 m² of each) were set up on the campus of Harran University, Sanliurfa, Turkey. The main objective of the research was to compare the performance of two systems to decide the better one for future planning of wastewater treatment system on the campus. Both of the wetland systems were planted with Phragmites australis and Canna indica. During the observation period (10 months), environmental conditions such as pH, temperature and total chemical oxygen demand (COD), soluble COD, total biochemical oxygen demand (BOD), soluble BOD, total suspended solids (TSS), total phosphate (TP), total nitrogen (TN) removal efficiencies of the systems were determined. According to the results, average yearly removal efficiencies for the HSSF and the FWSF, respectively, were as follows: total COD (75.7% and 69.9%), soluble COD (85.4% and 84.3%), total BOD (79.6% and 87.6%), soluble BOD (87.7% and 95.3%), TN (33.2% and 39.4%), and TP (31.5% and 6.5%). Soluble COD and BOD removal efficiencies of both systems increased gradually since the start-up. After nine months of operation, above 90% removal of organic matters were observed. The treatment performances of the HSSF were better than that of the FWSF with regard to the removal of suspended solids and total COD at especially high temperatures. In FWSF systems, COD concentrations extremely exceeded the discharge limit values due to high concentrations of algae in spring months.The performance of the two systems was modelled using an artificial neural network-back-propagation algorithm. The ANN model was competent at providing reasonable match between the measured and the predicted concentrations of total COD (R = 0.90 for HSSF and R = 0.96 for FWSF), soluble COD (R = 0.90 for HSSF and R = 0.74 for FWSF) and total BOD (R = 0.94 for HSSF and R = 0.84 for FWSF) in the effluents of constructed wetlands.     

Impact of carbon to nitrogen ratio on nutrient removal in a liquid–solid circulating fluidized bed bioreactor (LSCFB)

The performance of a liquid–solid circulating fluidized bed bioreactor (LSCFB) with anoxic and aerobic beds and lava rock as a biofilm carrier media was used to investigate the impact of the COD/N ratio on the process performance, with particular focus on total nitrogen removal. Three different COD/N ratios of 10:1, 6:1 and 4:1 were tested at an empty bed contact time of 0.82 h. More than 90% of the influent organic matter was removed throughout the study with 58% removal in the anoxic column in Phase III. Total nitrogen removal efficiencies in Phases I–III were 91%, 82% and 71% and simultaneous nitrification–denitrification (SND) occurred in the aerobic downer. The LSCFB demonstrated tertiary effluent quality at COD/N ratio of 10:1 and 6:1 with soluble biochemical oxygen demand (SBOD) <10 mg l^?1 and total nitrogen (TN) <10 mg l^?1.     

Sulfate reduction and microbial community of autotrophic biocathode in response to acidity

Microbial electrolysis cells (MECs) with autotrophic biocathode are a promising technology for removal of pollutants in wastewater. The aim of this study was to investigate the effect of initial acidity of wastewater on performance of sulfate-reducing biocathodes. MECs with biocathodes were operated with initial pH values of catholyte ranged from 3.0 to 7.0. The optimum initial pH value was 6.0 with a maximum sulfate reductive rate and biomass of 57 mg L⁻¹ d⁻¹ and 2.1 ± 0.4 mg g⁻¹, respectively. With initial pH 7.0, the pH value of catholyte increased to 9.8 ± 0.2 after an operation cycle, which resulted in low performance of the biocathode. A considerable sulfate reductive rate of 31 ± 0.85 mg L⁻¹ d⁻¹ was achieved with initial pH 3.0. Desulfovibrio sp. grew dominantly with abundance of 46%–66% in the cathode biofilm with initial pH values from 3.0 to 6.0 and contributed to the sulfate reduction. Clostridium and Parapedobacter also had high abundance in pH 6.0 cathode, indicated that interspecies electron transfer between electrochemical active and sulfate-reducing bacteria could play an important role in sulfate removal. The results suggest that acidity of catholyte is an important factor to be considered to utilize autotrophic biocathode MECs for wastewater treatment.     

Performance evaluation of constructed wetlands in a tropical region

Five emergent plant species were compared for their effectiveness in treating contaminants in a wetland system constructed on a military base in El Salvador. The system consisted of the subsurface flow (SSF), open water (OW) and free surface flow (SF) wetlands with a combined flow capacity of up to 151.4 m³ d^?1. Reliability and consistent performance in extreme conditions, such as those occurring during the tropical dry or wet seasons were important evaluation criteria. The discontinuous flow patterns typical of tropical climates necessitated the use of water balance calculations using climatic data such as rainfall and evapotranspiration. System characterization was achieved by computation of daily input and output mass loading rates for each individual constituent. Results suggest that Phragmites and Brachiaria were the most effective plants in SSF wetland. Brachiaria provided the added benefit of serving as a source of fodder and proved proficient, with N and P uptakes of 1.5–3.14% and 0.17–0.25% per dry plants’ biomass, respectively. Typha yielded the highest dry season removal efficiency within the SF (BOD₅: 80.78 ± 9.35%, COD: 65.18 ± 19.6%, TN: 58.59 ± 19.3%, oil and grease: 78.34 ± 10.55%, total dissolved phosphorus: 66.5 ± 20.7%). Phragmites–Typha treatment subset performed better year-round than either Thalia–Thalia or Brachiaria–Cyperus. Evaluated plants were capable of surviving and proliferating in extreme tropical climates.     

Characteristics of simultaneous organic and nutrient removal in a pilot-scale vertical submerged membrane bioreactor (VSMBR) treating municipal wastewater at various temperatures

A pilot-scale vertical submerged membrane bioreactor (VSMBR) with anoxic and oxic zones in one reactor was operated in an attempt to reduce the problems concerning effective removal of organic matter and nutrients from municipal wastewater. Source water with total chemical oxygen demand (TCOD)/total nitrogen (TN) ratio of 5.5 was treated at various temperatures (13–25 °C) over an interval of about 1 year. As a result, total suspended solid (TSS) and TCOD were removed by 100% and higher than 98%, respectively. Moreover, the average removal efficiencies of TN and total phosphorus (TP) were found to be 74% and 78% at 8 h-hydraulic retention time (HRT) and 60-days sludge retention time (SRT). Under these conditions, the specific removal rates (SRR) of TN and TP were found to be 0.093 kg N m⁻³ day⁻¹ and 0.008 kg P m⁻³ day⁻¹, and the daily production of excess sludge (DPES), 0.058 kg TSS day⁻¹.     

Removal of total nitrogen by Cyperus alternifolius from wastewaters in simulated vertical-flow constructed wetlands

The vertical-flow constructed wetland (VFCW) is a promising engineering technique for removal of excess nutrients and certain pollutants from wastewaters. This study investigated the uptake and removal of total nitrogen (TN) by Cyperus alternifolius from domestic wastewaters in simulated VFCWs. A total of eight simulated VFCW treatments, including two different substrates, two different wet-to-dry ratios, and with and without C. alternifolius species (2 × 2 × 2 = 8), were employed for an operation period of 2 years in this study. Results show that more TN was removed from the influent with the presence of C. alternifolius compared to without this plant species. A linear correlation existed between the aboveground biomass and its TN content. An increase in total biomass by 100 g resulted in an increase in TN accumulation in the aboveground biomass by 2.4 g. Large amounts of TN were removed by the aboveground biomass compared to those by substrate adsorption. Results suggest that C. alternifolius played a discernable role in removal of TN from wastewaters in the simulated VFCWs.     

NOB suppression and adaptation strategies in the partial nitrification–Anammox process for a poultry manure anaerobic digester

Poultry manure contains high levels of ammonia, which result in a suboptimal bioconversion to methane in anaerobic digesters (AD). A simultaneous process of nitrification, Anammox and denitrification (SNAD) in a continuous granular bubble column reactor to treat the anaerobically digested poultry manure was implemented. Thus, two strategies to achieve high efficiencies were proposed in this study: (1) ammonia overload to suppress nitrite oxidizing bacteria (NOB) and (2) gradual adaptation of the partial nitrification–Anammox (PN–A) biomass to organic matter. During the NOB-suppression stage, microbial and physical biomass characterizations were performed and the NOB abundance decreased from 31.3% to 3.3%. During the adaptation stage, with a nitrogen loading rate of 0.34 g L⁻¹ d⁻¹, a hydraulic retention time of 1.24 d and an influent COD/N ratio of 2.63 ± 0.02, a maximum ammonia and total nitrogen removal of 100% and 91.68% were achieved, respectively. The relative abundances of the aerobic and the anaerobic ammonia-oxidizing bacteria were greater than 35% and 40% respectively, during the study. These strategies provided useful design tools for the efficient removal of nitrogen species in the presence of organic matter.     

Performance evaluation of a newly developed flow diverted bed system for stream restoration

The flow diverted bed (FDB) system was developed to improve the stream water quality. This system (Run 2) had two wetlands where the flow from the upper layer (aerobic) in the first wetland could be redirected to the lower layer (anaerobic) in the second wetland by the flow diverter, and vice versa. In addition, the yellow-soil media placed at the bottom layer allowed a larger influx in the lower layer and had a sorption capacity of phosphate ions. The removal efficiencies of COD and TN at Run 2 [hydraulic loading rate (HLR) = 177 cm/d] was 1.7–3.6 times higher than that at Run 1 (HLR = 192 cm/d) without the diverter. The values of void fraction, dimensionless variance, dispersion number, Peclet number and velocity for this system were found to be 0.6637, 0.2847, 0.1717, 5.8241, and 53.2 m/d, respectively. The reducing trend of each pollutant was exponentially decreased along the overall length of this system. Also, the transport was dominated by convection (plug flow) rather than dispersion (complete mix). The volumetric removal rate constants for COD, SS, TKN, TN, and TP were found to be 4.854, 7.988, 1.388, 1.625, and 1.767 d⁻¹ via the first-order rate model. Consequently, the flow diverter and yellow-soil media in this system played an important role in enhancing the treatability of pollutants and operating at a higher HLR.     

Growth and nutrient removal properties of a freshwater microalga Scenedesmus sp. LX1 under different kinds of nitrogen sources

Microalgae have received much attention for the inorganic nutrient removal in tertiary treatment of domestic wastewater. Effect of different kinds of nitrogen sources on the growth and nitrogen/phosphorus removal properties of a newly isolated freshwater microalga, Scenedesmus sp. LX1, from a low-nutrient environment condition was studied and reported in this paper. The order of specific growth rate of the microalga with different nitrogen sources was NH₄-N > urea-N > NO₃-N. With nitrate or urea as nitrogen source, the microalga could grow well and remove both nitrogen and phosphorus efficiently (90% nitrogen and nearly 100% phosphorus were removed). However, with ammonium as the nitrogen source, the maximum algal density was relatively low, and the nitrogen and phosphorus removal efficiencies were as low as 31.1% and 76.4%, respectively. This was caused by the inhibitory effect of algal culture's acid pH due to H⁺ releasing from NH₄⁺ during algal cultivation process.     

A comparative study of surface and subsurface flow constructed wetlands for treatment of combined sewer overflows: A greenhouse experiment

The use of surface flow (SFCWs) and subsurface flow constructed wetlands (SFCWs) for the treatment of combined sewer overflows was assessed at pilot scale. Synthetic wastewater was applied in three batches with decreasing concentrations to mimic concentration profiles that are obtained in the field during overflow events. Three simulated combined sewer overflows were applied on each wetland. Composite water samples (60 in total) were taken for a period of 8 days to study the removal of total nitrogen (Ntot), NH₄–N, NO₃–N, total COD (CODtot) and total phosphorus. Redox potential, which was monitored at various locations along the wetlands, was more negative in the SSFCWs. In general, removal occurred faster in the SSFCWs and the final concentrations were lower. The removal of Ntot was only 36.6 ± 3.3% in the SFCWs due to nitrification-limiting conditions. The conditions in the SSFCWs, in contrast, seemed to promote Ntot removal (removal efficiency 96.7 ± 1.9%). The removal of P was hampered in both wetland types by reducing conditions. P that was initially removed was released again from the substrates later on. First-order removal rate constants were derived for the removal of both CODtot (SSFCWs: 1.1 ± 0.3 m d^?1; SFCWs: 0.17 ± 0.06 m d^?1) and Ntot (SSFCWs: 0.4 ± 0.1 m d^?1; SFCWs: 1.7 ± 0.5 m d^?1).     

Application of anaerobic–aerobic sequential treatment system to real textile wastewater for color and COD removal

A sequential anaerobic packed column reactor and an activated sludge unit was operated continuously for treatment of a textile industry wastewater, in Izmir, Turkey. Metal sponges were used as support material in anaerobic unit and pre-activated textile dyestuff biodegrading PDW facultative anaerobic bacterial culture was immobilized on the support particles. Effects of hydraulic retention times in anaerobic unit (θ_H anaerobic = 12–72 h) and initial COD concentration (COD₀ = 3000 ± 200 mg/L and 800 ± 100 mg/L) at θ_H anaerobic = 24 h on color and COD removal performance of the system were investigated. The results indicated that over 85% decolorization and about 90% COD removal efficiency can be obtained up to θ_H anaerobic = 48 h but higher retention times causes decreasing in decolorization efficiency. Operating the system with real wastewater without adding any nutrients at θ_H anaerobic = 24 h resulted in over 60% improvement in color removal in studied wastewater compared to existing treatment plant.     

Effects of nitrobenzene concentration and hydraulic retention time on the treatment of nitrobenzene in sequential anaerobic baffled reactor (ABR)/continuously stirred tank reactor (CSTR) system

The effects of increasing nitrobenzene (NB) concentrations and hydraulic retention times (HRT) on the treatment of NB were investigated in a sequential anaerobic baffled reactor (ABR)/aerobic completely stirred tank reactor (CSTR) system. In the first step of the study, the maximum COD removal efficiencies were found as 88% and 92% at NB concentrations varying between 30 mg L^?1 and 210 mg L^?1 in ABR. The minimum COD removal efficiency was 79% at a NB concentration of 700 mg L^?1. The removal efficiency of NB was nearly 100% for all NB concentrations in the ABR reactor. The methane gas production and the methane gas percentage remained stable (1500 mL day^?1 and 48–50%, respectively) as the NB concentration was increased from 30 to 210 mg L^?1. In the second step of the study it was found that as the HRT decreased from 10.38 days to 2.5 days the COD removal efficiencies decreased slightly from 94% to 92% in the ABR. For maximum COD and NB removal efficiencies the optimum HRT was found as 2.5 days in the ABR. The total COD removal efficiency was 95% in sequential anaerobic (ABR)/aerobic (CSTR) reactor system at a minimum HRT of 1 day. When the HRT was decreased from 10.38 days to 1 day, the methane percentage decreased from 42% to 29% in an ABR reactor treating 100 mg L^?1 NB. Nitrobenzene was reduced to aniline under anaerobic conditions while aniline was mineralized to catechol with meta cleavage under aerobic conditions.     

Nutrient concentrations in tidal creeks as indicators of the water quality role of mangrove wetlands in Southwest Florida

Coastal mangroves have the potential to improve the water quality of urban and rural runoff before it is discharged into adjacent coastal bays and oceans; but they also can be impaired by excessive pollutants from upstream. Nutrients (phosphorus and nitrogen), salinity, and other water quality parameters were measured in five mangrove tidal creeks in different hydrogeomorphic and urbanization settings during high and low tides over a calendar year of wet (June and August 2015) and dry (February and April 2016) seasons in the Greater Naples Bay area in Southwest Florida, USA. Nutrient concentrations (ave. ± std error) in the tidal creeks were 0.055 ± 0.008 mg-P/L for total phosphorus (TP) and 0.610 ± 0.020 mg-N/L for total nitrogen (TN), with an average N:P ratio of 11.4:1. Average wet season TP (0.075 ± 0.010 mg-P/L) was significantly higher than the dry season TP (0.033 ± 0.003 mg-P/L; p < 0.01, f = 15.17, f_crit = 3.89) and the average wet season TN (0.75 ± 0.03 mg-N/L) was significantly higher than dry season TN (0.52 ± 0.02 mg/L; p < 0.01, f = 64.14, f_crit = 3.89), suggesting that urban stormwater runoff is directly or indirectly affecting the nutrient conditions in these mangroves. Significant differences in nutrient concentrations between low tide and high tide were not found for either TP (p = 0.43, f = .63, f_crit = 3.88) or TN (p = 0.20, f = 1.66, f_crit = 3.89). These differences were confirmed by a PCA and cluster analyses, which found differences to be seasonal. We could not conclude from these results whether these five mangrove wetlands were sources nor sinks of nutrients based simply on the measurement of nutrient concentrations. But we illustrated that nutrient concentrations were indicators of the mangroves’ hydrogeomorphic settings, their tidal fluxes from Naples Bay, and the Bay's upstream watersheds, and less by direct urban runoff.     

Bioelectricity production from acidic food waste leachate using microbial fuel cells: Effect of microbial inocula

The effects of three different inocula (domestic wastewater, activated sludge, and anaerobic sludge) on the treatment of acidic food waste leachate in microbial fuel cells (MFCs) were evaluated. A food waste leachate (pH 4.76; 1000 mg chemical oxygen demand (COD)/L) was used as the substrate. The results indicate that the leachate itself can enable electricity production in an MFC, but the co-addition of different inocula significantly reduces the start-up time (approximately 7 days). High COD and volatile fatty acids removal (>87%) were obtained in all MFCs but with only low coulombic efficiencies (CEs) (14–20%). The highest power (432 mW/m³) and CE (20%) were obtained with anaerobic sludge as the co-inoculum. Microbial community analysis (PCR-DGGE) of the established biofilms suggested that the superior performance of the anaerobic sludge-MFC was associated with the enrichment of both fermentative (Clostridium sp. and Bacteroides sp.) and electrogenic bacteria (Magnetospirillum sp. and Geobacter sp.) at the anode.     

Effects of rapid temperature fluctuations prior to breeding on reproductive efficiency in replacement gilts

Rapidly cooling pigs after heat stress (HS) results in a pathophysiological condition, and because rapid temperature fluctuations may be associated with reduced reproductive success in sows, it lends itself to the hypothesis that these conditions may be linked. Objectives were to determine the effects of rapid cooling on thermal response and future reproductive success in pigs. Thirty-six replacement gilts (137.8±0.9 kg BW) were estrus synchronized and then 14.1±0.4 d after estrus confirmation, pigs were exposed to thermoneutral conditions (TN; n=12; 19.7±0.9°C) for 6 h, or HS (36.3±0.5°C) for 3 h, followed by 3 h of rapid cooling (HSRC; n=12; immediate TN exposure and water dousing) or gradual cooling (HSGC; n=12; gradual decrease to TN conditions) repeated over 2 d. Vaginal (T_V) and gastrointestinal tract temperatures (T_GI) were obtained every 15 min, and blood was collected on d 1 and d 2 during the HS and recovery periods at 180 and 60 min, respectively. Pigs were bred 8.3±0.8 d after thermal treatments over 2 d. Reproductive tracts were collected and total fetus number and viability were recorded 28.0±0.8 d after insemination. HS increased T_V and T_GI (P=0.01; 0.98 °C) in HSRC and HSGC compared to TN pigs. During recovery, T_V was reduced from 15 to 105 min (P=0.01; 0.33 °C) in HSRC compared to HSGC pigs, but no overall differences in T_GI were detected (P<0.05; 39.67 °C). Rapid cooling increased (P<0.05) TNFα compared to HSGC and TN pigs during recovery-d 1 (55.2%), HS-d 2 (35.1%), and recovery-d 2 (64.9%). Viable fetuses tended to be reduced (P=0.08; 10.5%) and moribund fetuses tended to be increased (P=0.09; 159.3%) in HSRC compared to HSGC and TN pigs. In summary, rapid cooling prior to breeding may contribute to reduced fetal viability and reproductive success in pigs.     

Characteristics of nitrous oxide (N2O) emission from intermittently aerated sequencing batch reactors (IASBRs) treating slaughterhouse wastewater at low temperature

This study investigated the characteristics of nitrous oxide (N₂O) emission from intermittently aerated sequencing batch reactors (IASBRs) treating high strength slaughterhouse wastewater at 11 °C, where partial nitrification followed by denitrification (PND) was achieved. N₂O generation and emission was examined at three aeration rates of 0.4, 0.6, and 0.8 L air/min in three IASBRs (SBR1, SBR2, and SBR3, respectively). The slaughterhouse wastewater contained chemical oxygen demand (COD) of 6057 ± 172.6 mg/L, total nitrogen (TN) of 576 ± 15.1 mg/L, total phosphorus (TP) of 52 ± 2.7 mg/L and suspended solids (SS) of 1843 ± 280.5 g/L. In the pseudo-steady state, the amount of N₂O emission was up to 5.7–11.0% of incoming TN. The aeration rate negatively affected N₂O emission and the ratio of N₂O emission to incoming TN was reduced by 48.2% when the aeration rate was increased from 0.4 to 0.8 L air/min. Results showed that more N₂O was generated in non-aeration periods than in aeration periods. Lower DO concentrations enhanced N₂O generation in the aeration periods (probably via nitrifier denitrification) while low DO concentrations (lower than 0.2 mg/L) did not affect N₂O generation in the non-aeration periods (probably via heterotrophic denitrification). When PHB was utilized as the organic substrate for denitrification, there was a high N₂O generation potential. It was estimated that 1.8 mg N₂O-N was generated accompanying per mg PHB consumed.     

Nitrogen removal enhanced by shunt distributing wastewater in a subsurface wastewater infiltration system

Three pilot subsurface wastewater infiltration systems filled with the same mixed matrix made of 80% brown soil and cinder at a weight of 20% were constructed in the laboratory. All systems worked successfully in the intermittent feeding mode with total hydraulic loading of 4 m³/(m² d) for over 2 months, with the optimal parameters of shunt ratio of 1:1 and shunt position at the depth of 0.7 m was achieved on the basis of large amounts of experimental data. The experiment results showed that shunt distributing wastewater could significantly improve the nitrogen removal in the subsurface infiltration system and the average removal rates of TN and NH₄-N increased by 10% and 5.67%, respectively. Shunt distributing wastewater had little influence on the removal rates of COD and TP. The results suggested that shunt distributing wastewater was simple and effective for nitrogen removal.