Total Hydraulic Retention Time Research Articles

Hydrogen production from cassava processing wastewater in an anaerobic fixed bed reactor with bamboo as a support material

Attempting to associate waste treatment to the production of clean and renewable energy, this research sought to evaluate the biological production of hydrogen using wastewater from the cassava starch treatment industry, generated during the processes of extraction and purification of starch. This experiment was carried out in a continuous anaerobic reactor with a working volume of 3L, with bamboo stems as the support medium. The system was operated at a temperature of 36°C, an initial pH of 6.0 and under variations of organic load. The highest rate of hydrogen production, of 1.1 L.d-1.L-1, was obtained with application of an organic loading rate of 35 g.L-1.d-1, in terms of total sugar content and hydraulic retention time of 3h, with a prevalence of butyric and acetic acids as final products of the fermentation process. Low C/N ratios contributed to the excessive growth of the biomass, causing a reduction of up to 35% in hydrogen production, low percentages of H2 and high concentrations of CO2in the biogas.

Semiconducting polyurethane/polypyrrole/polyaniline for microorganism immobilization and wastewater treatment in anaerobic/aerobic sequential packed bed reactors

ABSTRACTThe development of new materials for microorganism immobilization is very important in wastewater treatment. In this work polyurethane (PU) foams were modified polymerizing pyrrole and aniline onto their surface by chemical oxidization to obtain polyurethane/polypyrrole (PU/PPy), polyurethane/polyaniline (PU/PANI), and PU/(PPy‐co‐PANI) supports which were used to immobilize microorganisms for municipal wastewater treatment in batch mode and continuous flow using two sequential (anaerobic/aerobic) packed bed reactors (PBR) varying the total hydraulic retention time (HRT). The supports were characterized by Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) and tested in chemical oxygen demand (COD) removal during treatment of a municipal wastewater. It was observed from SEM analysis that globular nanostructures of PPy and PPy‐co‐PANI were formed onto the PU surface with average diameters between 100 and 300 nm, which are typical of aqueous polymerization of pyrrole monomer; however irregular nanostructures were observed when PANI was homopolymerized onto the PU foam. Batch wastewater treatment after 14 days showed COD removal efficiencies of 77%, 69%, 78%, and 80% for PU foam, PU/PPy, PU/PANI, and PU/(PPy‐co‐PANI), respectively; which was explained as a function of polymers morphology deposited onto the PU foam surface. Also it was observed from the sequential PBR that for 24 h and 36 h of HRT, 80 and 90% of COD removal can be achieved; respectively.© 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42242.

The energy-saving anaerobic baffled reactor membrane bioreactor (EABR-MBR) system for recycling wastewater from a high-rise building.

A novel energy-saving anaerobic baffled reactor-membrane bioreactor (EABR-MBR) system has been developed as a compact biological treatment system for reuse of water from a high-rise building. The anaerobic baffled reactor (ABR) compartment had five baffles and served as the anaerobic degradation zone, followed by the aerobic MBR compartment. The total operating hydraulic retention time (HRT) of the EABR-MBR system was 3 hours (2 hours for ABR compartment and very short HRT of 1 hour for aerobic MBR compartment). The wastewater came from the Charoen Wisawakam building. The results showed that treated effluent quality was quite good and highly promising for water reuse purposes. The average flux of the membrane was kept at 30 l/(m2h). The EABR-MBR system could remove chemical oxygen demand, total nitrogen and total phosphorus from building wastewater by more than 90%. Moreover, it was found that phosphorus concentration was rising in the ABR compartment due to the phosphorus release phenomenon, and then the concentration decreased rapidly in the aerobic MBR compartment due to the phosphorus uptake phenomenon. This implies that phosphorus-accumulating organisms inside the EABR-MBR system are responsible for biological phosphorus removal. The research suggests that the EABR-MBR system can be a promising system for water reuse and reclamation for high-rise building application in the near future.

Kinetic coefficients for the domestic wastewater treatment using hybrid activated sludge process

In this study, the performance of a novel configuration of the hybrid growth bioreactor in pilot-plant scale (containing of anoxic, aerobic and sedimentation sections) was investigated for Isfahan municipal wastewater treatment plants. The bioreactor performance was evaluated after primary sedimentation tanks under the inlet COD concentration of 0.27±0.02 g/L, at different suspended biomass concentrations of about 3, 4, and 5 as g/L and different total hydraulic retention times 4, 8, and 12 h. An industrial moving bed packing with protected specific surface area of 350 m2/m3 was used in the bioreactor with a 30% of filling ratio. The modified Stover–Kincannon and Grau models are applied to predict the bio kinetic coefficients of COD removal. According to the results obtained, the substrate removal rate constant (ks) for Grau model was in the range of 8.23–10.96 (1/d), and the saturation constant (KB) value and the maximum total substrate utilization rate (Umax) for modified Stover–Kincannon were in the range of 57.4–87.7 (g/L d) and 62.6–91.4 (g/L d), respectively. Also, the results showed that the bioreactor follows the models with 98–99% correlation coefficients.

Settling basin design in a constructed wetland using TSS removal efficiency and hydraulic retention time

Using total suspended solid (TSS) removal efficiency and hydraulic retention time (HRT) as design parameters a design guideline of a settling basin in a constructed wetland (CW) was suggested; as well as management of sediment and particle in the settling basin. The CW was designed to treat the piggery wastewater effluent from a wastewater treatment plant during dry days and stormwater runoff from the surrounding paved area during wet days. The first settling basin (FSB) in the CW was theoretically designed with a total storage volume (TSV) of 453m3 and HRT of 5.5hr. The amount of sediment and particles settled at the FSB was high due to the sedimentation and interception of plants in the CW. Dredging of sediments was performed when the retention rate at the FSB decreased to approximately 80%. Findings showed that the mean flow rate was 21.8m3/hr less than the designed flow rate of 82.8m3/hr indicating that the FSB was oversize and operated with longer HRT (20.7hr) compared to the design HRT. An empirical model to estimate the length of the settling basin in the CW was developed as a function of HRT and desired TSS removal efficiency. Using the minimum tolerable TSS removal efficiency of 30%, the length of the FSB was estimated to be 31.2m with 11.8hr HRT.

Color, organic matter and sulfate removal from textile effluents by anaerobic and aerobic processes.

An upflow anaerobic sludge blanket (UASB)-submerged aerated biofilter (SAB) system was evaluated to remove color and chemical oxygen demand (COD) from real textile effluent. The system was operated for 335 days in three phases (P-1, P-2, P-3) with total hydraulic retention time varying from 21 h to 14 h. The results showed that high sulfate levels (>300 mg SO4(2-)/L) impaired the dye reduction. The best color removal efficiencies of 30% and 96% for the UASB and the reactor system, respectively, were obtained in P-1; the SAB higher efficiency was associated with adsorption. The best COD removal efficiency of 71% for the reactor system was obtained in P-2. Precipitation of some material composed mostly of sulfur (98%) and some metals occurred in the UASB. However, the precipitated sulfur was again oxidized in the SAB. The system also showed an effective toxicity reduction in tests (Daphnia magna) with the treated effluent.

Development of the anaerobic baffled reactor-membrane bioreactor (ABR-MBR) as a biological nutrient removal system for high-rise building wastewater recycling

A novel anaerobic baffled reactor-membrane bioreactor (ABR-MBR) system has been developed as a compact combined biological treatment system and membrane separation unit for wastewater recycling from high-rise buildings. Here, the anaerobic baffled reactor (ABR) compartment had five baffles and served as anaerobic degradation zone, followed by the aerobic membrane bioreactor (MBR) compartment for further aerobic degradation of organic residues. The total operating hydraulic retention time (HRT) of the ABR-MBR system was 3 h (2 h for ABR compartment and 1 h for aerobic MBR compartment). The wastewater used in the study came from Charoen Wisawakam Building, Faculty of Engineering, Chulalongkorn University, located in Bangkok city, Thailand. The results showed that treated effluent quality was quite good and highly promising for water reuse purposes. The average permeate flux of the membrane was kept at 30 L/m2-h. The ABR-MBR system could remove more than 90% COD, total nitrogen, and total phosphorus from building wastewater at total operating HRT of only 3 h. Specific phosphorus uptake rate obtained in the aerobic MBR compartment is calculated to be 4.82 mgP/gMLSS h. Moreover, a rapid phosphorus uptake phenomenon in the MBR compartment implies that PAOs biomass seems to respond for biological phosphorus removal by the ABR-MBR system. The research suggests that the ABR-MBR system can be a promising system for water reuse and reclamation for high-rise buildings in the near future.

Pilot-scale temperate-climate treatment of domestic wastewater with a staged anaerobic fluidized membrane bioreactor (SAF-MBR)

A pilot-scale staged anaerobic fluidized membrane bioreactor (SAF-MBR) was operated continuously for 485 days, without chemical cleaning of membranes, treating primary-settled domestic wastewater with wastewater temperature between 8 and 30°C and total hydraulic retention time (HRT) between 4.6 and 6.8h. Average chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) removals averaged 81% and 85%, respectively, during the first winter at 8-15°C before full acclimation had occurred. However, subsequently when fully acclimated, summer and winter COD removals of 94% and 90% and BOD5 removals of 98% and 90%, respectively, were obtained with average effluent COD never higher than 23 mg/L nor BOD5 higher than 9 mg/L. Operational energy requirement of 0.23 kW h/m(3) could be met with primary and secondary methane production, and could be reduced further through hydraulic change. Biosolids production in all seasons averaged 0.051 g volatile suspended solids per g COD removed.

Combined mesophilic anaerobic and thermophilic aerobic digestion process for high-strength food wastewater to increase removal efficiency and reduce sludge discharge.

In this study, a process that combines the mesophilic anaerobic digestion (MAD) process with thermophilic aerobic digestion (TAD) for high-strength food wastewater (FWW) treatment was developed to examine the removal of organic matter and methane production. All effluent discharged from the MAD process was separated into solid and liquid portions. The liquid part was discarded and the sludge part was passed to the TAD process for further degradation. Then, the digested sludge from the TAD process was recycled back to the MAD unit to achieve low sludge discharge from the combined process. The reactor combination was operated in two phases: during Phase I, 40 d of total hydraulic retention time (HRT) was applied; during Phase II, 20 d was applied. HRT of the TAD process was fixed at 5 d. For a comparison, a control process (single-stage MAD) was operated with the same HRTs of the combined process. Our results indicated that the combined process showed over 90% total solids, volatile solids and chemical oxygen demand removal efficiencies. In addition, the combined process showed a significantly higher methane production rate than that of the control process. Consequently, the experimental data demonstrated that the combined MAD-TAD process was successfully employed for high-strength FWW treatment with highly efficient organic matter reduction and methane production.

Treatment of coal gasification wastewater by a two-phase anaerobic digestion

Coal gasification wastewater (CGW) is a refractory wastewater, whose anaerobic treatment has been a severe problem due to its toxicity and poor biodegradability. Using a two-stage anaerobic digestion as a control, the two-phase anaerobic digestion of real CGW was investigated. After 210 d of operation, the maximum removal efficiencies of COD and total phenols (TP) reached 50–60% and 55–60%, respectively, in the two-phase anaerobic digestion at total hydraulic retention time (HRT) of 48 h; the corresponding efficiencies were at low levels of 40–45% and 42–50%, respectively, in the two-stage anaerobic digestion. COD and TP removal efficiencies increased to 69.7 and 65.9%, when 50% of the effluent was recirculated to the hydrolytic acidogenic reactor. Phenol utilization rate and specific methanogenic activity (SMA) were decreased to 57.6 mg phenol/(gVSS d) and 394.3 mg COD-CH4/(gVSS d), respectively, as the HRT in the hydrolytic acidogenic reactor was reduced to 18 h. After the two-phase anaerobic digestion, the wastewater concentrations of the aerobic effluent COD could reach below 150 mg/l when compared to 237.2 mg/l if two-stage anaerobic digestion was done and 328.5 mg/l if sole aerobic pretreatment was done. The results suggested that the two-phase anaerobic digestion improved significantly both anaerobic and aerobic biodegradation of real CGW.

Cost-effectiveness analysis of TOC removal from slaughterhouse wastewater using combined anaerobic–aerobic and UV/H2O2 processes

The objective of this study is to evaluate the operating costs of treating slaughterhouse wastewater (SWW) using combined biological and advanced oxidation processes (AOPs). This study compares the performance and the treatment capability of an anaerobic baffled reactor (ABR), an aerated completely mixed activated sludge reactor (AS), and a UV/H2O2 process, as well as their combination for the removal of the total organic carbon (TOC). Overall efficiencies are found to be up to 75.22, 89.47, 94.53, 96.10, 96.36, and 99.98% for the UV/H2O2, ABR, AS, combined AS–ABR, combined ABR–AS, and combined ABR–AS–UV/H2O2 processes, respectively. Due to the consumption of electrical energy and reagents, operating costs are calculated at optimal conditions of each process. A cost-effectiveness analysis (CEA) is performed at optimal conditions for the SWW treatment by optimizing the total electricity cost, H2O2 consumption, and hydraulic retention time (HRT). The combined ABR–AS–UV/H2O2 processes have an optimal TOC removal of 92.46% at an HRT of 41 h, a cost of $1.25/kg of TOC removed, and $11.60/m3 of treated SWW. This process reaches a maximum TOC removal of 99% in 76.5 h with an estimated cost of $2.19/kg TOC removal and $21.65/m3 treated SWW, equivalent to $6.79/m3 day.

Model-based operational guidelines of a bioprocess for biological nitrogen removal and complete stabilisation of anaerobically digested sewage sludge

The concept of one-stage reactor system for biological nitrogen removal over nitrite of ammonium high loaded sidestreams is going to be applied to remove nitrogen from anaerobically digested sewage sludge and to achieve its complete stabilisation. Dealing with sludge, the organic matter needed to denitrify is present in the inflow as particulate substrate, which requires a hydrolysis step. The latter implies high anoxic hydraulic retention time (HRT). During both aerobic and anoxic phases, ammonium is released which implies the need to enlarge aerobic HRT. Both effects lead to a total HRT higher than those for nitrification-denitrification of wastewater with soluble substrate. The purpose of this paper is to define, by computer simulation, a set of theoretical criteria, which will be applied later to the operation of a pilot-scale post-aeration reactor to be located in a Spanish WWTP. These criteria will be defined by simulating the reactor performance under different operating conditions. As a conclusion, some operation guidelines have been established for the above-mentioned scenario in terms of aerobic and anoxic retention time, dissolved oxygen concentration and effluent requirements (NH(4)(+), NO(2)(-) and NO(3)(-)).

Effect of temperature on the treatment of domestic wastewater with a staged anaerobic fluidized membrane bioreactor

A laboratory staged anaerobic fluidized membrane bioreactor (SAF-MBR) system was applied to the treatment of primary clarifier effluent from a domestic wastewater treatment plant with temperature decreasing from 25 to 10 °C. At all temperatures and with a total hydraulic retention time of 2.3 h, overall chemical oxygen demand (COD) and biochemical oxygen demand (BOD5) removals were 89% and 94% or higher, with permeate COD and BOD5 of 30 and 7 mg/L or lower, respectively. No noticeable negative effects of low temperature on organic removal were found, although a slight increase to 3 mg/L in volatile fatty acids concentrations in the effluent was observed. Biosolids production was 0.01-0.03 kg volatile suspended solids/kg COD, which is far less than that with aerobic processes. Although the rate of trans-membrane pressure at the membrane flux of 9 L/m(2)/h increased as temperature decreased, the SAF-MBR was operated for longer than 200 d before chemical cleaning was needed. Electrical energy potential from combustion of the total methane production (gaseous and dissolved) was more than that required for system operation.

Application of a constructed wetland system for polluted stream remediation

Summary In 2010, the multi-function Kaoping River Rail Bridge Constructed Wetland (KRRBW) was constructed to improve the stream water quality and rehabilitate the ecosystem of the surrounding environment of Dashu Region, Kaohsiung, Taiwan. The KRRBW consists of five wetland basins with a total water surface area of 15 ha, a total hydraulic retention time (HRT) of 10.1 days at a averaged flow rate of 14 740 m 3 /day, and an averaged water depth of 1.1 m. The influent of KRRBW coming from the local drainage systems containing untreated domestic, agricultural, and industrial wastewaters. Based on the quarterly investigation results of water samples taken in 2011–2012, the overall removal efficiencies were 91% for biochemical oxygen demand (BOD), 75% for total nitrogen (TN), 96% for total phosphorus (TP), and 99% for total coliforms (TC). The calculated first-order decay rates for BOD, TN, TP, NH 3 –N, and TC ranged from 0.14 (TN) to 0.42 (TC) 1/day. This indicates that the KRRBW was able to remove organics, TC, and nutrients effectively. The high ammonia/nitrate removal efficiency indicates that nitrification and denitrification processes occurred simultaneously in the wetland system, and the detected nitrite concentration confirmed the occurrence of denitrification/nitrification. Results from sediment analyses reveal that the sediment contained high concentrations of organics (sediment oxygen demand = 1.9–5.2 g O 2 /m 2 day), nutrients (up to 15.8 g total nitrogen/kg of sediment and 1.48 g total phosphorus/kg of sediment), and metals (up to 547 mg/kg of Zn and 97 mg/kg of Cu). Appropriate wetland management strategies need to be developed to prevent the release of contaminants into the wetland system. The wetland system caused the variations in the microbial diversities and dominant microbial bacteria. Results show the dominant nitrogen utilization bacteria including Denitratisoma oestradiolicum , Nitrosospira sp., Nitrosovibrio sp., D . oestradiolicum , Alcaligenes sp., Steroidobacter denitrificans , Hydrocarboniphaga effuse were responsible for nitrogen removal, and the dominant carbon degrading bacteria ( Stenotrophomonas maltophilia , H. effuse , Alcaligenes sp., Pseudomonas sp., Fusibacter sp., Chlofoflex i, Guggenheimella bovis , Bacillus pumilus ) were responsible for carbon reduction. The denaturing gradient gel electrophoresis (DGGE) and nucleotide sequence techniques provide a guide for microbial ecology evaluation, which can be used as an indication of contaminants removal. Results from this study show that constructed wetlands have the potential to be developed into an environmentally acceptable river water quality improvement and wastewater polishment alternative for practical application.

Enzymatic activities in a moving bed membrane bioreactor for real urban wastewater treatment: Effect of operational conditions

The microbial hydrolytic enzymatic activities (acid phosphatase, alkaline phosphatase and glucosidase) in a moving bed membrane bioreactor (MBMBR system) for real urban wastewater treatment were investigated. This study was conducted in both suspended biomass and attached biofilm present in a MBMBR system. For this, four experimental phases with 20% and 35% (v/v) carrier filling ratios (CFRs) were conducted, which combined two mixed liquor total suspended solid (MLTSS) concentrations (c.a. 2500 and 4500mg/L) and two hydraulic retention times (HRTs) (10 and 24h). Hydrolytic activities of acid phosphatase, alkaline phosphatase and α-glucosidase in the mixed liquor (suspended biomass) were higher than in the biofilm (independent of the carrier concentration), during the four experiments, possibly due to better substrate diffusion in the mixed liquor. A redundancy analysis (RDA) was performed to evaluate the relationship between enzymatic activities and chemical oxygen demand (COD), biological oxygen demand at 5 days (BOD5), mixed liquor volatile suspended solid concentration (MLVSS), biofilm total solids (BTS), HRT, pH, CFR and temperature. According to the results obtained with the Monte Carlo permutation test, CFR, MLVSS, BTS, COD, temperature and HRT significantly contributed to the variation of enzymatic activities in the MBMBR.

Reducing the risk of foaming and decreasing viscosity by two-stage anaerobic digestion of sugar beet pressed pulp

Anaerobic digestion (AD) of sugar beet pressed pulp (SBPP) is a promising treatment concept. It produces biogas as a renewable energy source making sugar production more energy efficient and it turns SBPP from a residue into a valuable resource. In this study one- and two-stage mono fermentation at mesophilic conditions in a continuous stirred tank reactor were compared. Also the optimal incubation temperature for the pre-acidification stage was studied. The fastest pre-acidification, with a hydraulic retention time (HRT) of 4days, occurred at a temperature of 55°C. In the methanogenic reactor of the two-stage system stable fermentation at loading rate of 7kgVS/m³d was demonstrated. No artificial pH adjustment was necessary to maintain optimum levels in both the pre-acidification and the methanogenic reactor. The total HRT of the two-stage AD was 36days which is considerably lower compared to the one-stage AD (50days). The frequently observed problem of foaming at high loading rates was less severe in the two-stage reactor. Moreover the viscosity of digestate in the methanogenic stage of the two-stage fermentation was in average tenfold lower than in the one-stage fermentation. This decreases the energy input for the reactor stirring about 80%. The observed advantages make the two-stage process economically attractive, despite higher investments for a two reactor system.

Enhancement of denitrification in a down-flow hanging sponge reactor by effluent recirculation

A down-flow hanging sponge reactor, constructed by connecting three identical units in series, was applied to the treatment of artificial wastewater containing phenol and ammonia under high salinity conditions (10.9 g-Cl(-)/L). The theoretical hydraulic retention time (HRT) of each unit was 4 h (total HRT = 12 h). To enhance denitrification by effluent recirculation, the effluent recirculation ratio was increased in increments ranging from 0.0 to 2.0. The concentration of total ammonia nitrogen (TAN), NO2-N, and NO3-N in the final effluent as a proportion of the TAN in the influent was determined to calculate the unrecovered, or denitrification, proportion. The denitrification proportion of the reactor was equivalent to 19.1 ± 14.1% with no effluent recirculation; however, this was increased to 58.6 ± 6.2% when the effluent recirculation ratio was increased to 1.5. Further increasing the effluent recirculation ratio to 2.0 resulted in a decrease in the denitrification proportion to 50.9 ± 9.3%. Activity assays of nitrification and denitrification, as well as 16S rRNA gene sequence analysis, revealed that denitrification occurred primarily in the upper sections of the reactor, while nitrification increased in the lower sections of the reactor. Gene sequence analysis revealed that denitrification by Azoarcus-like species using phenol as an electron donor was dominant.

Improving biological phosphorus removal in membrane bioreactors – a pilot study

With increasing water reuse applications and possible stringent regulations of phosphorus content in secondary and tertiary effluent discharge in Florida, USA, alternative technologies beyond conventional treatment processes require implementation to achieve low phosphorus (P) and nitrogen (N) concentrations. A pilot scale membrane bioreactor (MBR) system, operated in Florida, adopted the University of Cape Town (UCT) biological process for the treatment of domestic wastewater. The system operated for 280 days at a wastewater treatment facility with total hydraulic retention time (HRT) of 7 h and sludge retention time (SRT) of 20 days. Operating conditions were controlled to maintain specific dissolved oxygen (DO) concentrations in the reactors, operate at suitable return activated sludge (RAS) rates and to waste from the appropriate reactor. This process favored biological phosphorus removal and achieved 94.1% removal efficiency. Additionally, chemical oxygen demand (COD) and N removal were achieved at 93.9% and 86.6%, respectively. Membrane operation and maintenance did not affect the biological P removal performance but enhanced the process given the different operating requirements compared to that required with the conventional UCT process alone. Conclusively, the result of the pilot study demonstrated improvement in biological phosphorus removal. The UCT-MBR process tested achieved average effluent nitrogen and phosphorus concentrations of 5 mg/L as N and 0.3 mg/L as P.

Two-stage anaerobic fluidized-bed membrane bioreactor treatment of settled domestic wastewater

A two-stage anaerobic fluidized-bed membrane bioreactor (SAF-MBR) system was applied for the treatment of primary-settled domestic wastewater that was further pre-treated by either 10 μm filtration or 1 mm screening. While the different pre-treatment options resulted in different influent qualities, the effluent qualities were quite similar. In both cases at a total hydraulic retention time of 2.3 h and 25 °C, chemical oxygen demand and biochemical oxygen demand (BOD5) removals were 84-91% and 92-94%, with effluent concentrations lower than 25 and 7 mg/L, respectively. With a membrane flux of 6-12 L/m(2)/h, trans-membrane pressure remained below 0.2 bar during 310 d of continuous operation without need for membrane chemical cleaning or backwashing. Biosolids production was estimated to be 0.028-0.049 g volatile suspended solids/g BOD5, which is far less than that with comparable aerobic processes. Electrical energy production from combined heat and power utilization of the total methane produced (gaseous and dissolved) was estimated to be more than sufficient for total system operation.

Nitrogen removal from wastewater plant secondary effluent in a compound natural treatment system

A method for removal of low concentrations of nitrogen in the secondary effluent from a wastewater plant was evaluated. The method can be summarized as follows: Primary Subsurface Vertical Flow Wetland (PSVFW)→Submerged Macrophyte Oxidation Ponds (SMOPs)→Secondary Subsurface Vertical Flow Wetland (SSVFW). Pilot experiments were conducted to assess the efficiency of total nitrogen (TN) removal from secondary effluent from the Chengjiang Wastewater Treatment Plant, China. At a total hydraulic retention time (HRT) of 21.38 days and a hydraulic loading (HL) of 0.024m3m−2d−1, the average TN concentration in the influent decreased from 6.60mgL−1 in the influent to 0.87mgL−1 in the effluent, thus meeting the Class-III surface water standards. PSVFW mediated the ammonification of organic nitrogen (ORG-N) and the nitrification of NH3-N (ammonia), resulting in a TN reduction of 7.58%. In the SMOPs, the concentration of NH3-N was further reduced, and most NO3−-N (nitrate nitrogen) was denitrified under aerobic conditions, resulting in a 63.18% TN reduction. In the SSVFW, the concentrations of the remaining NO3−-N and ORG-N declined even further so that the whole process accounted for an 86.82% TN removal efficiency relative to the influent TN concentrations.