Nitrogen removal from secondary effluent by using integrated constructed wetland system

The treatment capacity of an integrated constructed wetland system (CWS) that was designed to reduce nitrogen (N) from secondary effluent was explored. The integrated CWS consisted of vertical-flow constructed wetland, floating bed and sand filter. The vertical-flow wetland was filled with gravel, steel slag and peat from the bottom to the top. Vetiver zizanioides was selected to grow in the vertical-flow constructed wetland and Coix lacrymajobi L. was grown in the floating bed. The results showed that the integrated CWS displayed superior removal efficiency for nitrate nitrogen (NO₃⁻-N), ammonia nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂⁻-N), and total nitrogen (TN). The average NO₃⁻-N, NO₂⁻-N, NH₄⁺-N and TN removal efficiencies of the integrated CWS were 98.83%, 95.60%, 98.05% and 92.41%, respectively, during the whole experimental operation. The integrated CWS may have a good potential for removing N from secondary effluent.     

Hydraulic residence time computation for constructed wetland design

Hydraulic residence time (HRT) is one of the key design parameters controlling the removal efficiency of contaminants and nutrients in stormwater and wastewater wetlands. The paper presents a new approach to the estimation of HRT using the variable residence time (VART) model. The VART model is employed to simulate the major processes (including advection, dispersion, and transient storage of contaminants/nutrients in vegetated zones) affecting HRT and thereby to produce a hydraulic residence time distribution (HRTD) for a design wetland. The HRTD in combination with a moment-based method is then utilized to find a mean design HRT for the design wetland. Methods for estimation of parameters governing the HRTD are proposed. The new approach to HRT computation is demonstrated through a case study for the Tres Rios Demonstration (TRD) Wetlands in Arizona, USA. Modeling results show that the design HRTs for the Hayfield wetland (H1) and the Cobble wetlands (C1 and C2) are 4.04, 4.66, and 2.65 days, respectively. The computed HRTs agree well with those reported by previous studies, confirming the efficacy of the new approach to hydraulic design of constructed wetlands.     

Influence of bed media characteristics on ammonia and nitrate removal in shallow horizontal subsurface flow constructed wetlands

Two bed media were tested (gravel and Filtralite) in shallow horizontal subsurface flow (HSSF) constructed wetlands in order to evaluate the removal of ammonia and nitrate for different types of wastewater (acetate-based and domestic wastewater) and different COD/N ratios. The use of Filtralite allowed both higher mass removal rates (1.1 g NH₄–N m⁻² d⁻¹ and 3 g NO₃–N m⁻² d⁻¹) and removal efficiencies (>62% for ammonia, 90–100% for nitrate), in less than 2 weeks, when compared to the ones observed with gravel. The COD/N ratio seems to have no significant influence on nitrate removal and the removal of both ammonia and nitrate seems to have involved not only the conventional pathways of nitrification–denitrification. The nitrogen loading rate of both ammonia (0.8–2.4 g NH₄–N m⁻² d⁻¹) and nitrate (0.6–3.2 g NO₃–N m⁻² d⁻¹) seem to have influenced the respective removal rates.     

Potential for total nitrogen removal by combining vertical flow and horizontal flow constructed wetlands: A full-scale experiment study

To improve total nitrogen removal, a full-scale experimental study was conducted on a hybrid constructed wetlands plant designed for 100 person equivalents. The plant was composed of a first stage of vertical filters (fed with raw wastewater), followed by a second stage of horizontal filters. It was monitored over one year, measuring hydraulic conditions, physico-chemical conditions, gas emission, oxygen levels in the gas phase as well as regular treatment performance by 24-h composite samples. Different vertical filter configurations (media depth, intermediate and passive aeration system) were tested as well as two horizontal filter designs. Nitrogen removal is discussed in terms of the efficiency of each stage in relation to the season and the load applied. This study indicates limits for systems configuration and suggests some design avenues for hybrid systems to reach high and regular levels of nitrogen removal with reasonable surface area per person.     

Emissions of greenhouse gases from ponds constructed for nitrogen removal

Methane and carbon dioxide emission from three constructed ponds were monitored during an annual cycle. Water temperature was a good predictor of methane emission in all three ponds. In the most intensively studied pond, nitrate concentration in the bottom water could further explain the amount of methane emitted. When water temperature exceeded 15 °C between 1 and 54 mg, CH₄ m⁻² h⁻¹ was emitted on all occasions, while at temperatures below 10 °C, less than 0.6 mg CH₄ m⁻² h⁻¹ was emitted. The flux of carbon dioxide differed between the ponds and no consistent patterns were found. In a laboratory study at 20 °C, we showed that high, but naturally occurring, nitrate concentrations (8 and 16 mg NO₃⁻–N l⁻¹) constrained the production of methane compared to the treatment with no nitrate addition. Nitrous oxide production was positively correlated with nitrate concentration. Carbon dioxide production was highest at the highest nitrate concentration, which indicates that increased nitrate loading on ponds and wetlands will stimulate organic matter decomposition rates. Our conclusion is that these ponds constructed for nitrate removal emit greenhouse gases comparable to lakes in the temperate region.     

The layer effect in nutrient removal by two indigenous plant species in horizontal flow constructed wetlands

A layer effect study was conducted to investigate the transformation of nitrogenous pollutants in two batch subsurface horizontal constructed wetlands. Artificial drainage water containing a low concentration of chemical oxygen demand (COD_Cr), but high concentration of ammonia and nitrate, was treated in two batch wetland cuboids. The nitrogen removal rates were found to be significantly affected by the characters of the layer as well as the biomass and roots of different plant species (P < 0.05). Correlations between pH, oxidation-reduction potential, and retention time indicated that nitrogen removal rates under study conditions mainly depended on the location of the layer and the plant species in the constructed wetland.     

Statistical modelling of organic matter and emerging pollutants removal in constructed wetlands

Multiple regression models, clustering tree diagrams, regression trees (CHAID) and redundancy analysis (RDA) were applied to the study of the removal of organic matter and pharmaceuticals and personal care products (PPCPs) from urban wastewater by means of constructed wetlands (CWs). These four statistical analyses pointed out the importance of physico-chemical parameters, plant presence and chemical structure in the elimination of most pollutants. Temperature, pH values, dissolved oxygen concentration, redox potential and conductivity were related to the removal of the studied substances. Plant presence (Typha angustifolia and Phragmites australis) enhanced the removal of organic matter and some PPCPs. Multiple regression equations and CHAID trees provided numerical estimations of pollutant removal efficiencies in CWs. These models were validated and they could be a useful and interesting tool for the quick estimation of removal efficiencies in already working CWs and for the design of new systems which must fulfil certain quality requirements.     

抚仙湖窑泥沟人工湿地的除磷效果研究

为了减缓和控制抚仙湖局部湖湾水体富营养化趋势,在抚仙湖北岸建设了净化面积1 hm²的人工湿地.综合利用生物氧化塘、水平潜流人工湿地和表面流人工湿地治理技术,对入湖河道窑泥沟污水中磷的去除效果进行了试验研究.结果表明,该人工湿地系统对磷具有较强的去除能力.总磷去除率在57.7%～81.10%之间,平均去除率为54.9%.单位面积磷滞留量平均为26 mg·m^-2·d^-1,其中,湿地植物同化作用磷滞留量为26.1 mg·m^-2·d^-1,约占磷滞留总量的10%,大部分磷去除是通过基质吸附和沉降作用,但主要湿地植物水芹的季节变化对相应功能区的除磷效果会产生一定影响.试验期间,各功能区单位面积磷滞留量依次为水平潜流人工湿地＞生物氧化塘＞沉淀池＞表面流人工湿地.     

风车草和香根草在人工湿地中迁移养分能力的比较研究

为研究风车草（Cyperus alternifolius）和香根草（Vetiveria zizanioides）迁移养分的能力,建立17.0 m²风车草潜流式人工湿地和13.3 m²香根草潜流式人工湿地处理猪场废水,在四个季节末测定植物生物量和组织氮、磷、铜、锌含量.结果表明,香根草地下部生物量大于风车草,地上部生物量则是风车草大于香根草.风车草年地上部收获量为3406.47 g·m^-2,比香根草的1483.88 g·m^-2高2.3倍;风车草的氮含量为22.69 mg·g^-1,比香根草的15.44 mg·g^-1高7.25 mg·g^-1;风车草的磷含量为6.09 mg·g^-1,比香根草的5.47 mg·g^-1高0.62 mg·g^-1.植株含铜、锌量风车草略比香根草高.风车草每年迁移N 68.72 g·m^-2和P 18.49 g·m^-2,香根草迁移N 8.93 g·m^-2和P 3.69 g·m^-2.风车草人工湿地每年由植物迁移的氮、磷、铜、锌比香根草高4～7倍.     

The ammonium nitrogen oxidation process in horizontal subsurface flow constructed wetlands

The ammonium nitrogen oxidation process (ANOP) is the first and most important step for nitrogen removal in constructed wetlands (CWs). The process was investigated by observing the products generated from the ANOP in on-site aerobic systems with selective inhibition of nitrite-oxidizing bacteria (NOB) through appropriate regulation of the pH, temperature and dissolved oxygen concentrations. The effects of season, plant type and density on ANOP were also studied to determine the optimal conditions for the ANOP. Nitrite accumulation was found in the aerobic experiments and greater ammonia-oxidizing bacteria than NOB numbers, showing that partial nitrification to nitrite was occurring in the studied CWs. The nitrogen removal rate was positively linearly correlated with the nitrite accumulation rate, and so the more NH₃-N removed by ANOP, the greater the resulting nitrogen removal. Season and plant density had a significant effect on the ANOP. However, there were no significant differences between the units planted with common reed and cattail.     

Nitrate removal in a first-order stream: reconciling laboratory and field measurements

A combination of laboratory and field experiments were carried out to evaluate nitrate(NO ₃ ^t- ) removal during stream transport in a first-order agricultural drainage stream. Intact stream sediment cores overlain with stream and NO ₃ ^– -amended stream water indicated NO ₃ ^– losses averaging 93 — 353 mg m^–2 day^–1, with NO ₃ ^– concentration exerting a primary control on loss rate. Isotopic data indicated enrichment of NO ₃ ^– - ¹⁵N over time as NO ₃ ^– concentrations decreased, indicating a denitrification loss. Field experiments were designed to evaluate dilution of streamwater with low-NO ₃ ^– groundwater in addition to other NO ₃ ^– removal processes during transport. A series of bromide tracer and NO ₃ ^– - addition experiments were carried out in the field; groundwater dilution dominated the downstream NO ₃ ^– concentration trends, accounting for all observed decreases in NO ₃ ^– concentration. Isotopic data did not point to denitrification downstream as a major NO ₃ ^– removal process. This apparent disparity between simulated laboratory and in-situ stream removal rates appears to be a function of the hydrological processes controlling exchanges between stream bottom sediments and the overlying water. These results suggest that caution must be exercised in extrapolating potentials for NO ₃ ^– removal measured in laboratory experiments to the field, as these rates could be overestimated in some watersheds.     

风车草和香根草在人工湿地中迁移养分能力的比较研究

为研究风车草(Cyperus alternifolius)和香根草(Vetiveria zizanioides)迁移养分的能力,建立17.0m²风车草潜流式人工湿地和13.3 m²香根草潜流式人工湿地处理猪场废水,在四个季节末测定植物生物量和组织氮、磷、铜、锌含量.结果表明,香根草地下部生物量大于风车草,地上部生物量则是风车草大于香根草.风车草年地上部收获量为3406.47 g·m^-2,比香根草的1483.88 g·m^-2高2.3倍;风车草的氮含量为22.69 mg·g^-1,比香根草的15.44 mg·g^-1高7.25 mg·g^-1;风车草的磷含量为6.09 mg·g^-1,比香根草的5.47 mg·g^-1高0.62 mg·g^-1.植株含铜、锌量风车草略比香根草高.风车草每年迁移N 68.72 g·m^-2和P18.49 g·m^-2,香根草迁移N 8.93 g·m^-2和P 3.69 g·m^-2.风车草人工湿地每年由植物迁移的氮、磷、铜、锌比香根草高4～7倍.     

潜流湿地和表面流湿地的净化效果与植物生长比较

分别以砾石和土壤为填料构建成潜流人工湿地和表面流人工湿地,处以较大水力负荷的污水处理。比较了两种湿地对污水的净化效果,结果表明在较大水力负荷条件下两种湿地的净化效果都较差,但潜流湿地对各种污染物的净化能力都优于表面流湿地;土柱法测量了湿地植物的根系生物量,结果显示湿地植物地上部分长势差异不明显,但潜流湿地的根系生物量显著低于表面流湿地的根系生物量(P<0.05)。结合前期实验结果得出湿地净化效果不仅与湿地植物根系生物量有相关关系,还与其他因素有一定的相关关系。     

Nitrogen removal from wastewater in vertical flow constructed wetlands containing LWA/gravel layers and reed vegetation

The influence of light weight aggregates made of fly ash from sewage sludge thermal treatment (FASSTT LWA) on the nitrogen removal efficiency from artificial wastewater in constructed wetlands (CW) with vertical flow reed bed was investigated. Thirty lysimeters with six different double-layer bed constructions (upper layer of FASSTT LWA with thicknesses of: 0 cm, 12 cm, 25 cm, 50 cm, and 100 cm of the total depth of the lysimeter, above a lower gravel layer), either with or without reed plants were operated with wastewater hydraulic loading rate of 4.67 mm/d. During a six-month experiment, high efficiency of ammonia removal was observed. The influence of FASSTT LWA as a bed material and the presence of reed on CW treatment efficiency was determined. The highest total nitrogen removal efficiency, 59.5%, was obtained in the CW with double-layer lysimeters consisting of 25% FASSTT LWA (upper layer), and 75% gravel (lower layer), and planted with reed.     

A hydrologic assessment of the Everglades Nutrient Removal Project, a subtropical constructed wetland in South Florida (USA)

The Everglades Nutrient Removal Project (ENRP), a 1544-ha constructed wetland in south Florida, was intensively monitored throughout its five-year operational history. Water budgets for the ENRP and each of its interior treatment cells were dominated by surface flows (≥85% of inflows; ≥68% of outflows) with smaller contributions from precipitation, evapotranspiration, groundwater flux, and change in storage. The mean water depth, hydraulic loading rate for surface water, and nominal hydraulic retention time for the entire wetland were 0.6 m, 3.1 cm d⁻¹ and 17.7 d, respectively, and were comparable to values anticipated in design. The east flow-way was slightly shallower (0.2 m) and received proportionately more flow (61%) than the west flow-way. The hydrology of other treatment wetlands is often driven by surface flows. All treatment cells in the ENRP were to some extent hydraulically short-circuited. There was net groundwater inflow to the ENRP from Water Conservation Area 1 (WCA-1) resulting from significant head differences between these wetlands. Groundwater outflow to the adjacent farmlands was greatest in Cell 2 and substantially exceeded groundwater inflow. All hydrologic parameters exhibited seasonality to some extent; fluctuation in water depth and groundwater inflows corresponded with the seasonal change in stage in WCA-1. Errors in the ENRP and individual cell water budgets were generally less than 10% and within the range of errors for water budgets from other wetlands.     

Effects of hydraulic loading rate on pollutants removal by a deep subsurface wastewater infiltration system

The subsurface wastewater infiltration (SWI) system proved to be an effective and low-cost technique for decentralized sewage treatment in areas without adequate domestic treatment facilities. Field-scale experiments were conducted through a deep SWI system, with effective depth of 1.5 m, under hydraulic loading rates of 0.040, 0.065, 0.081 and 0.10 m³/m² d. Taking the hydraulic and treatment efficiencies into consideration, the hydraulic loading rate of 0.081 m³/m² d was recommended. Under this condition, NH₃-N, TN, and COD removal efficiencies were 86.2 ± 3.0, 80.7 ± 1.9 and 84.8 ± 2.1%, respectively. In the effluent, NH₃-N concentration declined to 2.3-4.4 mg/L, accounting for 63.2-65.6% of TN. NO₃-N concentration increased from 0.2 to 0.3 mg/L in the influent to 2.0-2.5 mg/L in the effluent. The nitrifying bacteria number declined with increased depth, while the amount of denitrifying bacteria increased. The analysis of results about the nitrifying and denitrifying bacteria distribution indicated that the most effective ranges for nitrification and denitrification process were 0.3-0.7 m and 0.7-1.5 m, respectively.     

Relationships between plant photosynthesis,radial oxygen loss and nutrient removal in constructed wetland microcosms

The objective of this study was to investigate the relationships between root radial oxygen loss (ROL), photosynthesis, and nutrient removal, based on the hypothesis that ROL is primarily an active process which is affected positively by photosynthesis, and is correlated positively with nutrient removal. Four common wetland plants were studied in small-scale monoculture wetlands. Higher ROL coincided with faster growth among the four monocultures. Significant correlation between ROL and photosynthetic rate existed in Cyperus flabelliformis wetland (P < 0.01). Both ROL and photosynthesis represented close correlations with nutrient removal rates in all four monocultures. Significant differences in ROL, photosynthetic rate, removal rates of NH₄⁺, and soluble reactive phosphorus (SRP) were found among the four species. ROL and photosynthetic rates showed single-peak daily and seasonal patterns, with maximum daily values around noon, and with maximum yearly values in summer or autumn for the four monocultures. The results suggest that the ROL of wetland plants is related to active physiological processes. Both ROL and photosynthetic rate are indices which can be used to identify wetland plants with a higher nutrient removal capacity.     

利用人工湿地去除农业径流中农药的研究进展

人工湿地对农业径流污染物去除效果显著,已成为控制农业径流污染的有效措施.本文结合国内外研究,介绍了当前水体农药污染的现状;从物理、化学及生物角度阐述了人工湿地对农药的去除机理和关键过程;归纳总结了人工湿地对农药的去除效率,指出人工湿地对农药的去除效率随农药类型的不同而差异较大:农药的平均去除率,按农药用途分为杀虫剂＞杀菌剂＞除草剂,按农药化学结构分为拟除虫菊酯类>有机磷类>三唑类＞酰胺类＞三嗪类＞脲类;综合考虑,潜流人工湿地在农药去除方面的效果优于表面流人工湿地.在此基础上分析了农药理化性质、人工湿地工艺类型及运行参数、进水中农药浓度、湿地植物等因素对农药在人工湿地中去除的影响.最后指出了当前研究中存在的问题,并提出了研究展望.     

Nitrate removal and DO levels in batch wetland mesocosms: Cattail (Typha spp.) versus bulrush (Scirpus spp.)

Nitrate removal rates and dissolved oxygen (DO) levels were evaluated in small batch-mode wetland mesocosms with two different plant species, cattail (Typha spp.) and bulrush (Scirpus spp.), and associated mineral-dominated sediment collected from a mature treatment wetland. Nitrate loss in both cattail and bulrush mesocosms was first-order in nature. First-order volumetric rate constants (k_V) were 0.30 d⁻¹ for cattail and 0.21 d⁻¹ for bulrush and rates of nitrate loss were significantly different between plant treatments (p < 0.005). On an areal basis, maximum rates of nitrate removal were around 500 mg N/(m² d) early in the experiment when nitrate levels were high (> 15 mg N/L). Areal removal rates were on average 25% higher in cattail versus bulrush mesocosms. DO in mesocosm water was significantly higher in bulrush versus cattail (p < 0.001). DO in bulrush generally ranged between 0.5 and 2 mg/L, while DO in cattail mesocosms was consistently below 0.3 mg/L. Based on cumulative frequency analysis, DO exceeded 1 mg/L around 50% of the time in bulrush, but only 2% of the time in cattail. DO in bulrush exhibited a statistically significant diel cycle with DO peaks in the late afternoon and DO minimums in the early morning hours. Difference in nitrate removal rates between wetland plant treatments may have been due to differing plant carbon quality. Cattail litter, which has been shown in other studies to exhibit superior biodegradability, may have enhanced biological denitrification by fueling heterotrophic microbial activity, which in turn may have depressed DO levels, a prerequisite for denitrification. Our results show that the cattail is more effective than bulrush for treating nitrate-dominant wastewaters.     

Removal of nonionic surfactants from wastewater using a constructed wetland

Removal of nonionic surfactants from municipal wastewater using a constructed wetland with a horizontal subsurface flow was studied in 2009 and 2010. Extraction spectrophotometry with 3′,3″,5′,5″‐tetrabromophenolphthalein ethyl ester and KCl served to determine the analyte concentrations. Triton^® X‐100 was used as a standard to express the nonionic‐surfactant concentrations. Anionic and cationic surfactants were shown not to interfere during the determination. Nonionic surfactants were degraded (to products undeterminable by the method) with a high average efficiency that reached 98.1% in 2009 and 99.1% in 2010, respectively. The average concentration of nonionic surfactants at the inflow was 0.978 mg/l, while it was close to the limit of quantification at the outflow (0.014 mg/l). A significant fraction of nonionic surfactants (38.7%) was already degraded during the pretreatment, and only 14.0% of the nonionic surfactants remained in the interstitial H₂O taken in the vegetation bed at a distance of 1 m from the inflow zone at a 50‐cm depth. Nonionic surfactants were degraded both under aerobic and anaerobic conditions.