Microcosm wetlands for wastewater treatment with different hydraulic loading rates and macrophytes

Constructed wetlands (CW) usually require large land areas for treating wastewater. This study evaluated the feasibility of applying CW with less land requirement by operating a group of microcosm wetlands at a hydraulic retention time (HRT) of less than 4 d in southern Taiwan. An artificial wastewater, simulating municipal wastewater containing 200 mg L(-1) of chemical oxygen demand (COD), 20 mg L(-1) of NH4+-N (AN), and 20 mg L(-1) of PO4(3-)-P (OP), was the inflow source. Three emergent plants [reed, Phragmites australis (Cav.) Trin. ex Steud.; water primrose, Ludwigia octovalvis (Jacq.) P.H. Raven; and dayflower, Commelina communis L.] and two floating plants [water spinach, Ipomoea aquatica Forssk.; and water lettuce, Pistia stratiotes L.] plants were tested. The planted systems showed more nutrient removal than unplanted systems; however, the type of macrophytes in CW did not make a major difference in treatment. At the HRTs of 2 to 4 d, the planted system maintained greater than 72,80, and 46% removal for COD, AN, and OP, respectively. For AN and OP removal, the highest efficiencies occurred at the HRT of 3 d, whereas maximum removal rates for AN and OP occurred at the HRT of 2 d. Both removal rates and efficiencies were reduced drastically at the HRT of 1 d. Removals of COD, OP, and AN followed first-order reactions within the HRTs of 1 to 4 d. The efficient removals of these constituents obtained with HRT between 2 and 4 d indicated the possibility of using a CW system for wastewater treatment with less land requirement.     

PERFORMANCE VARIATIONS OF COD AND NITROGEN REMOVAL BY VEGETATED SUBMERGED BED WETLANDS1

ABSTRACT: Vegetated submerged bed wetlands can supplement treatment of onsite wastewater systems. This study evaluated vegetation, media, and seasonal impacts on system performance in six meso scale rock plant filters with and without narrow leaf cattails (Typha augustifolia). Daily chemical oxygen demand (COD) reductions in planted cells averaged 85 percent and weekly total nitrogen (TN) reductions averaged 50 percent. Planted cells had 17 percent greater COD reduction and 76 percent greater TN reduction than unplanted cells, both significant differences. Media type affected COD reduction, particularly in unplanted cells. COD treatment in planted cells was highest for fine crushed limestone (87±13 percent) and least variable for coarse river gravel (85±11 percent). No significant difference in TN reduction was observed for different media types (48 to 51 percent range). Seasonal influences on treatment included a significant decrease during late fall and early spring and a significant increase with temperature. After a step increase in organic loading, treatment efficiency decreased sharply but returned to prior levels after an adaptation period of about one month. Planted cells not only exhibited higher treatment efficiency but also had a retarded organic matter breakthrough, appearing after three to seven times the period for a bromide tracer. This supports a hypothesis that retardation of contaminant movement through the treatment cells results in enhanced removal. These results support the use of rock plant filters, but demonstrate the need to account for performance variations in system design. (KEY TERMS: constructed wetlands; seasonal effects; subsurface flow; Typha augustifolia; onsite wastewater treatment; water quality.)     

Nitrogen and phosphorus removal from domestic strength synthetic wastewater using an alternating pumped flow sequencing batch biofilm reactor

Nutrient removal from domestic strength synthetic wastewater by an alternating pumped flow sequencing batch biofilm reactor (APFSBBR) was investigated in this laboratory study. The APFSBBR comprised two reactor tanks (Reactors 1 and 2) with two identical biofilm modules of vertical tubular plastic media with a high specific surface area, one in each tank. The APFSBBR was operated in cycles of four phases: fill, anaerobic, aerobic, and draw. During the fill phase, Reactor 1 was half-filled with domestic strength synthetic wastewater. During the subsequent anaerobic phase, most of the phosphorus release took place from the submerged biofilm in this reactor. In the aerobic phase, the wastewater was circulated by pumps between Reactors 1 and 2, resulting in denitrification at the start of the aerobic phase due to low oxygen concentrations, followed by nitrification and luxury uptake of phosphorus when oxygen concentrations increased. During the draw phase, Reactor 2 was half-emptied of the treated water. At the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) loading rates on the total biofilm area of 3.20 g COD, 0.33 g TN, and 0.06 g TP m(-2) d(-1), the removal efficiencies were 97, 85, and 92% for COD, TN, and TP, respectively.     

EMMC process for combined removal of organics, nitrogen and an odor producing substance

In order to improve the process performance regarding the removal of organics, nitrogen, and an odor-causing compound (sulfide) contained in domestic wastewater, an entrapped-mixed-microbial cell (EMMC) with and without humic substances for both fixed and moving carrier reactors and conventional suspended growth culture (i.e. conventional activated sludge process) were investigated simultaneously. Both synthetic (simulated to the organics concentration of general domestic sewage) and actual domestic wastewater were investigated under operational conditions of 12 h of hydraulic retention time (HRT) with 1 h of aeration and 1 h of non-aeration, and 6 h of HRT with continuous aeration, at a room temperature of 25 +/- 2 degrees C. It was found that entrapping humic substances in the EMMC carriers had no impact on the removal of organics, nitrogen, and the odor-producing compound. Additionally, the performance of the EMMC moving carrier system for the removal of these pollutants is similar to that of the EMMC fixed carrier system. In general, the EMMC associated systems which provide high solids retention time achieve a better removal of chemical oxygen demand (COD), nitrogen, and the odor-producing substance than the suspended growth system for both HRTs of 6 h (continuous aeration) and 12 h (1 h of aeration and 1 h of non-aeration). Both the fixed and moving carrier EMMC processes, therefore, have the potential for improvement or replacement of the existing conventional activated sludge process with regard to improving the effluent qualities (such as COD, nitrogen and odor-producing compound) for reuse/disposal.     

BATCH REACTOR UNVEGETATED WETLAND PERFORMANCE IN TREATING DAIRY WASTEWATER1

ABSTRACT: Wetlands that treat holding pond effluent can be designed to utilize the pond storage capacity to allow flexibility in system management. Management of a wetland as a sequencing batch reactor can simplify operation and control detention times, but little performance data on such systems are available. The objective of this study was to evaluate the batch reactor wetland concept by quantifying removal of chemical oxygen demand (COD), total suspended sediments (TSS), total nitrogen (TN), ammonium (NH₄), nitrate (NO₃), total phosphorus (TP), and orthophosphate (PO₄) and by assessing the suitability of first‐order kinetics. Weekly samples were collected following batch loadings of wetland cells with high concentration or low concentration dairy holding pond wastewater during both fall and spring seasons. During three‐week batch periods without plants, overall mass removal averaged 54 percent for COD, 58 percent for TSS, 90 percent for TN, 72 percent for NH₄, ‐54 percent for NO₃, 38 percent for TP, and ‐8 percent for PO₄. Best fit, first‐order kinetic rate constant (k) and background concentration (C*) for COD varied by season, with k = 0.024/d and C*= 0 mg/l in fall and k = 0.056/d and C*= 200 mg/l in spring. Ammonium exhibited a consistent C*= 0 mg/l but had variable rate constants of k = 0.121/d for low concentration treatments and k = 0.079/d for high concentration treatments. Using first‐order kinetics was also appropriate for TN, with k = 0.061/d and C*= 0 mg/l for all loadings and seasons, but was not consistently appropriate for TP or PO₄. These results support the use of first‐order kinetics to describe treatment in batch reactor wastewater treatment wetlands without vegetation, perhaps during the establishment phase or in open water zones of vegetated wetlands. Further work is needed to assess the effects of vegetation.     

SBR中好氧颗粒污泥的培养

采用竖式SBR作为反应器，利用城市污水处理厂剩余污泥作为接种污泥，通过不间断运行培养出好氧颗粒污泥。实验结果表明，采用非限量曝气模式好氧颗粒污泥降解模拟污水的效果较好，其COD去除率可达98％以上。曝气量对好氧颗粒污泥的形成和稳定具有重要影响，当气速为26．5m／h时，好氧颗粒污泥的性状和处理有机废水效果最佳。同时好氧颗粒污泥对pH值的变化不明显，当pH为5—8范围内，其COD去除率都可达到85％以上。但是未经驯化的好氧颗粒污泥对对硝基苯酚和对氯苯酚两种芳香类有机物较敏感，而对硝基苯酚对其毒性更大。当对硝基苯酚和。对氯苯酚浓度为10mg／L时，其COD去除率仅为42．5％和52％。     

香根草人工湿地处理生活污水的试验研究

通过建立香根草人工湿地系统,研究该系统对生活污水的COD、TP、TN的处理效果以及系统的耐污性。在水力停留时间(HRT)为6h的条件下,COD、TP、TN的去除率分别为63.5%、88.3%、72.4%。研究表明,香根草人工湿地系统对城镇生活污水具有较好的净化效果,且系统在该试验条件下耐污性良好。     

Use of constructed wetland systems with Arundo and Sarcocornia for polishing high salinity tannery wastewater

Treatment of tannery wastewater is problematic due to high and variable concentrations of complex pollutants often combined with high salinity levels. Two series of horizontal subsurface flow constructed wetlands (CWs) planted with Arundo donax and Sarcocornia fruticosa were set up after a conventional biological treatment system operating at a tannery site. The aim of the CWs was polishing organics and nitrogen from the high salinity effluent (2.2-6.6?g Cl(-)?L(-1)). Both plant species established and grew well in the CW. Arundo, however, had more vigorous growth and a higher capacity to take up nutrients. The CWs were efficient in removing COD and BOD(5) with removal efficiencies varying between 51 and 80% for COD (inlet: 68-425?mg?L(-1)) and between 53 and 90% for BOD(5) (inlet: 16-220?mg?L(-1)). Mass removal rates were up to 615?kg COD ha(-1)?d(-1) and 363 BOD(5) kg?ha(-1)?d(-1). Removal efficiencies were 40-93% for total P, 31-89% for NH(4)(+) and 41-90% for Total Kjeldahl Nitrogen. CW systems planted with salt tolerant plant species are a promising solution for polishing saline secondary effluent from the tannery industry to levels fulfilling the discharge standards.     

化学强化SBR工艺生物脱氮除磷试验研究

本文以脱氮为优势条件进行了SBR工艺生物脱氮试验,确定了脱氮模式的运行工艺参数,即瞬时进水-曝气3h-缺氧2h-沉淀闲置1h-出水。SBR在此模式下运行,COD、NH3-N、TN的去除率分别为90％、95％、60％以上。系统对TP的去除也比较稳定,进水TP为6．57—10．4mg／L时,出水为1．68—4．23mg／L。对SBR脱氮后出水投加AlCl3进行化学除磷,试验发现,投加量为20mg／L时出水,TP均能达到《城镇污水处理厂污染物排放标准》（GB18918—2002）一级标准的B标准。     

Effects of feeding time and organic loading in an anaerobic sequencing batch biofilm reactor (ASBBR) treating diluted whey

An investigation was carried out on the performance of an anaerobic sequencing batch biofilm reactor (ASBBR) treating diluted cheese whey when submitted to different feed strategies and volumetric organic loads (VOL). Polyurethane foam cubes were used as support for biomass immobilization and stirring was provided by helix impellers. The reactor with a working volume of 3 L treated 2 L of wastewater in 8-h cycles at 500 rpm and 30 degrees C. The organic loads applied were 2, 4, 8 and 12 g COD L(-1) d(-1), obtained by increasing the feed concentration. Alkalinity was supplemented at a ratio of 50% NaHCO(3)/COD. For each organic load applied three feed strategies were tested: (a) batch operation with 8-h cycle; (b) 2-h fed-batch operation followed by 6-h batch; and (c) 4-h fed-batch followed by 4-h batch. The 2-h fed-batch operation followed by 6-h batch presented the best results for the organic loads of 2 and 4 g COD L(-1) d(-1), whereas the 4-h fed-batch operation followed by 4-h batch presented results slightly inferior for the same organic loads and the best results at organic loads of 8 and 12 g COD L(-1) d(-1). The concentration of total volatile acids varied with fill time. For the higher fill times maximum concentrations were obtained at the end of the cycle. Moreover, no significant difference was detected in the maximum concentration of total volatile acids for any of the investigated conditions. However, the maximum values of propionic acid tended to decrease with increasing fill time considering the same organic load. Microbiological analyses revealed the presence of Methanosaeta-like structures and methanogenic hydrogenotrophic-like fluorescent bacilli. No Methanosarcina-like structures were observed in the samples.     

Operation strategy of a sequencing batch reactor for simultaneous removal of wastewater organic matter and nutrients

The Sequencing Batch Reactor (SBR) system employing activated sludge process is an alternative wastewater treatment technology. A cycle of the conventional SBR system generally consists of five periods, with complete aeration during the React period to oxidize the organic matter and nitrify the ammonium-nitrogen of wastewater. Laboratory-scale reactors were used to evaluate the feasibility of incorporating alternative aerobic-anoxic-aerobic stages within the React period for simultaneous removal of organic matter, N and P. Two cycles of SBR process per day were maintained.Under the operation strategy of 0.75-h fill, 8-h react (with continuous aeration), 3.25-h settle, draw and idle periods, the treatment performance became consistent after running the system for two to four cycles (1–2 days). The percentages of both BOD₅ and COD removal were around 94% from Cycle 2 onwards, the BOD₅ content dropped from initial 251 mg L⁻¹ to less than 14 mg L⁻¹ in the final effluent. A steady nitrification (about 97%) was obtained from Cycle 4 onwards, with 1 mg NH₄⁺-N L⁻¹ and 25 mg NO₃⁻-N L⁻¹ present in the final effluent. This suggested that the time required for SBR system to acclimate and reach an equilibrium state was relatively short when compared with the time needed for continuous flow activated sludge system. The findings also show that 4-h aeration during the react period was long enough to achieve more than 90% nitrification. With the incorporation of a 3-h anoxic stage after the initial 4-h aeration of the react period, a satisfactory denitrification process was observed, with nitrate level dropped from 27 to around 8 mg L⁻¹ within 3 h. The second aeration stage did not cause significant change in wastewater nitrogen content. The wastewater phosphate content declined rapidly during the initial 4-h aeration and P-release was not observed during the anoxic stage. A slight reduction of P was found in the second aeration stage suggesting that more P-uptake occurred in this stage. A 12-h cyclic SBR system with the incorporation of 4-h aerobic, 3-h anoxic and final 1-h aerobic stages into the 8-h react period was demonstrated to be able to remove C, N and P simultaneously.     

Ammonia emissions from surface flow and subsurface flow constructed wetlands treating dairy wastewater

Agricultural wastewater treatment is important for maintaining water quality, and constructed wetlands (CW) can be an effective treatment option. However, some of the N that is removed during treatment can be volatilized to the atmosphere as ammonia (NH(3)). This removal pathway is not preferred because it negatively impacts air quality. The objective of this study was to assess NH(3) volatilization from surface flow (SF) and subsurface flow (SSF) CWs. Six CWs (3 SF and 3 SSF; 6.6 m(2) each) were loaded with dairy wastewater ( approximately 300 mg L(-1) total ammoniacal nitrogen, TAN = NH(3)-N + NH(4)(+)-N) in Nova Scotia, Canada. From June through September 2006, volatilization of NH(3) during 12 or 24 h periods was measured using steady-state chambers. No differences (p > 0.1) between daytime and nighttime fluxes were observed, presumably due in part to the constant airflow inside the chambers. Changes in emission rates and variability within and between wetland types coincided with changes in the vegetative canopy (Typha latifolia L.) and temperature. In SSF wetlands, the headspace depth also appeared to affect emissions. Overall, NH(3) emissions from SF wetlands were significantly higher than from SSF wetlands. The maximum flux densities were 974 and 289 mg NH(3)-N m(-2) d(-1) for SF and SSF wetlands, respectively. Both wetland types had similar TAN mass removal. On average, volatilization contributed 9 to 44% of TAN removal in SF and 1 to 18% in SSF wetlands. Results suggest volatilization plays a larger role in N removal from SF wetlands.     

Para-chlorophenol containing synthetic wastewater treatment in an activated sludge unit: effects of hydraulic residence time

Due to the toxic nature of chlorophenol compounds present in some chemical industry effluents, biological treatment of such wastewaters is usually realized with low treatment efficiencies. Para-chlorophenol (4-chlorophenol, 4-CP) containing synthetic wastewater was treated in an activated sludge unit at different hydraulic residence times (HRT) varying between 5 and 30 h while the feed COD (2500 mg l(-1)), 4-CP (500 mg l(-1)) and sludge age (SRT, 10 days) were constant. Effects of HRT variations on COD, 4-CP, toxicity removals and on settling characteristics of the sludge were investigated. Percent COD removals increased and the effluent COD concentrations decreased when HRT increased from 5 to 15 h and remained almost constant for larger HRT levels. Nearly, 91% COD and 99% 4-CP removals were obtained at HRT levels above 15 h. Because of the highly concentrated microbial population at HRT levels of above 15 h, low effluent (reactor) 4-CP concentrations and almost complete toxicity removals were obtained. High biomass concentrations obtained at HRT levels above 15 h were due to low 4-CP contents in the aeration tank yielding negligible inhibition effects and low maintenance requirements. The sludge volume index (SVI) decreased with increasing HRT up to 15 h due to high biomass concentrations at high HRT levels resulting in well settling sludge with low SVI values. Hydraulic residence times above 15 h resulted in more than 90% COD and complete 4-CP and toxicity removals along with well settling sludge.     

稳定塘工艺改良与试验研究

笔者从稳定塘结构与净化机理研究,结合厌氧生物膜法、吸附过滤法和稳定塘技术,提出稳定塘工艺改良技术—生物滤塘。本文通过对生物滤塘与传统稳定塘进行对比试验分析,结果表明：当水力停留时间相同时,生物滤塘较传统稳定塘具有较高的COD、NH3-N和TP去除效率,有机负荷调试试验中,当COD浓度达800mg/L时,生物滤塘仍然保持较好的运行状态,COD平均去除率较稳定塘提高了28.8%。     

Performance of an overland flow system for advanced treatment of wastewater plant effluent

Overland flow (OF) systems were evaluated and compared for advanced treatment of municipal and industrial effluents, including nutrients and nondegradable chemical oxygen demand (COD) removal. Three pilot plants were constructed at the Shahin Shahr Wastewater Treatment Plant (WWTP), Isfahan, Iran. Each pilot was assigned a specific wastewater and all were simultaneously operated for 8 months. Treatment of primary effluent, activated sludge secondary effluent, and lagoon effluent of textile wastewater was investigated at application rates (ARs) of 0.15, 0.25, and 0.35m(3)m(-1)h(-1). During 5 months of stable operation after a 3-month acclimation period, mean removals of total 5-day biochemical oxygen demand (TBOD(5)), total COD (TCOD), total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP) and turbidity were 74.5%, 54.8%, 66.2%, 39.4%, 35.8%, and 67.7% for primary effluent; 52.9%, 52.9%, 66.5%, 44.4%, 39.8%, and 50.1% for activated sludge effluent; 65.7%, 58.7%, 70.3%, 41.7%, 41.3%, and 54.9% for textile wastewater lagoon effluent, respectively. The model of Smith and Schroeder, 1985. Field studies of the overland flow process for the treatment of raw and primary treated municipal wastewater. Journal of Water Pollution Control Federation 57, 785-794] was satisfactory for TBOD(5). For all treatment parameters a standard first-order removal model was inadequate to represent the data but a modified first-order model provided a satisfactory fit to the data. Based on the results of this study, it can be concluded that an OF system as advanced treatment had the ability to meet effluent discharge permit limits and was an economical replacement for stabilization ponds and mechanical treatment options.     

Some properties of a sequencing batch reactor for treatment of wastewater containing thiocyanate compounds

Thiocyanate (SCN) compounds in photo-processing wastewater (PPWW) could be treated by an SBR system without any release of thiocyanate to the atmosphere during the aeration step. An SCN loading greater than 84 g m(-3)d(-1) showed negative effects on the growth of bio-sludge and removal efficiencies of the system. The acclimatization period of the system was increased with an increase in SCN concentration or loading. The COD, BOD(5), TKN, and SCN removal efficiencies were 96.0 +/- 1.6%, 72 +/- 2%, 49 +/- 5%, and 82 +/- 3%, respectively, under an SCN loading of up to 84 g m(-3)d(-1). The removal efficiency of the system was repressed by SCN due to the repressed growth rate of nitrification bacteria. However, the removal efficiency could be increased with an increase in HRT or a decrease in SCN loading. Also, increases in HRT or decreases in SCN loading led to increased sludge age or solid retention time (SRT) and decreased the sludge volume index (SVI) value. The SRT and SVI of the system with synthetic wastewater containing 840 mg l(-1) SCN under an HRT of 3 days (SCN loading of 280 g m(-3)d(-1)) were 3.9 +/- 0.7 days and 65 +/- 4 ml g(-1), respectively, while they were 11.2+/-0.8 days and 55 +/- 6 ml g(-1), respectively under an HRT of 10 days (SCN loading of 84 g m(-3)d(-1)).     

Biogas production from olive pomace

Biogas production from a slurry obtained by mixing finely ground olive pomace in water was investigated using anaerobic digesters of 1-l working volume at 37°C. A start-up culture was obtained from a local landfill area and was adopted to the slurry within 10 days at this temperature. The biogas generation rates were determined by varying the total solids (TS) concentration in the slurry and the hydraulic retention time (HRT) during semi-continuous digestion. The maximum rate was found to be 0.70 l of biogas per l of digester volume per day, corresponding to a HRT of 20 days and 10% TS with a yield of 0.08 l biogas per g chemical oxygen demand (COD) added to the digester. The methane content of the biogas was in the range of 75–80% for both batch and semi-continuous runs, the remainder being principally carbon dioxide.     

Comparison of plant families in a greenhouse phytoremediation study on an aged polycyclic aromatic hydrocarbon-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous, recalcitrant, and potentially carcinogenic pollutants. Plants and their associated rhizosphere microbes can promote PAH dissipation, offering an economic and ecologically attractive remediation technique. This study focused on the effects of different types of vegetation on PAH removal and on the interaction between the plants and their associated microorganisms. Aged PAH-polluted soil with a total PAH level of 753 mg kg(-1) soil dry weight was planted with 18 plant species representing eight families. The levels of 17 soil PAHs were monitored over 14 mo. The size of soil microbial populations of PAH degraders was also monitored. Planting significantly enhanced the dissipation rates of all PAHs within the first 7 mo, but this effect was not significant after 14 mo. Although the extent of removal of lower-molecular-weight PAHs was similar for planted and unplanted control soils after 14 mo, the total mass of five- and six-ring PAHs removed was significantly greater in planted soils at the 7- and 14-mo sampling points. Poaceae (grasses) were the most effective of the families tested, and perennial ryegrass was the most effective species; after 14 mo, soils planted with perennial ryegrass contained 30% of the initial total PAH concentration (compared with 51% of the initial concentrations in unplanted control soil). Although the presence of some plant species led to higher populations of PAH degraders, there was no correlation across plant species between PAH dissipation and the size of the PAH-degrading population. Research is needed to understand differences among plant families for stimulating PAH dissipation.     

汽车制造厂废水处理工程实例分析

采用二级混凝-气浮-水解酸化-SBR-过滤工艺，对某汽车制造厂的混合废水（包括脱脂废水、电泳废水、磷化废水和生活污水等）进行处理。经过对处理工艺进出水主要水质指标连续1个月的监测，发现COD去除率可达92．5％，SS去除率可达95．2％，NH3-N去除率可达58％，TP去除率可达96．7％，出水水质符合国家《污水综合排放标准》（GB8978—1996）一级排放标准，吨水处理成本为1．6元／t，系统运行稳定，具有明显的经济、环保和社会效益。t     

Performance analysis of on-farm irrigation tanks on agricultural drainage water reuse and treatment

Water reuse and pollutant removal efficiency analysis of the on-farm irrigation tanks (OFTs) was carried out in rice paddy field region of Zhanghe Irrigation District, Southern China through field experiments during the rice growing season of 2009–2011. Water flow measurements indicate that 20.6–68.9% of drainage water captured by OFTs was reused for supplemental irrigation. Rainfall was the most important factor that determines the water reuse efficiency (WRR) of OFTs, since higher rainfall resulted in higher surplus irrigation water draining out of OFTs without reuse, and thus decreased WRR. Fully using the storage capacity for storing return flow, and releasing totally for supplemental irrigation also enhanced WRR of OFTs. Water quality analysis shows that OFTs removed 47.2% of total phosphorous (TP) and 60.8% of total nitrogen (TN) of inflow and have a great effect on increasing sedimentation for return flow as the mean of removal efficiency of pollutant load (REL) for suspended solids (SS) amounted to 68.4%. For water treatment effectiveness of OFTs, high hydraulic retention time (HRT) is most beneficial to increase REL of TN whereas REL of TP is not sensitive to HRT. These results confirm that OFTs can effectively increase agricultural return flow reuse and remove pollutants. As the cascade OFTs irrigation system recycle return flow for several times, the irrigation water demand from outside of region was reduced significantly for rice production. Coupling with the effect of cyclic irrigation on the nutrients recycling by paddy fields, OFTs irrigation system also considerably mitigate the N and P off-site emission. Therefore, it is advisable to integrate the role of OFTs on water reuse and treatment for water saving irrigation and ecological management of paddy fields landscape.