The potential use of constructed wetlands in a recirculating aquaculture system for shrimp culture

A pilot-scale constructed wetland unit, consisting of free water surface (FWS) and subsurface flow (SF) constructed wetlands arranged in series, was integrated into an outdoor recirculating aquaculture system (RAS) for culturing Pacific white shrimp (Litopenaeus vannamei). This study evaluated the performance of the wetland unit in treating the recirculating wastewater and examined the effect of improvement in water quality of the culture tank on the growth and survival of shrimp postlarvae. During an 80-day culture period, the wetland unit operated at a mean hydraulic loading rate of 0.3 m/day and effectively reduced the influent concentrations of 5-day biochemical oxygen demand (BOD5, 24%), suspended solids (SS, 71%), chlorophyll a (chl-a, 88%), total ammonium (TAN, 57%), nitrite nitrogen (NO2-N, 90%) and nitrate nitrogen (NO3-N, 68%). Phosphate (PO4-P) reduction was the least efficient (5.4%). The concentrations of SS, Chl-a, turbidity and NO3-N in the culture tank water in RAS were significantly (P相似文献   

复合人工湿地对城市受污染河水的净化效果

采用2种复合人工湿地系统处理昆明市城市河流污水,为期1年的运行结果表明:2种复合人工湿地系统对城市河流污水具有良好的污染物去除性能,TN、TP、COD和SS的月平均去除率分别达到50%、85%、85%和80%以上;2种复合人工湿地系统具有良好的耐冲击性,季节变化对出水水质不存在显著影响。其中,垂直上行流复合人工湿地系统性能更优于垂直上行流与水平流复合人工湿地系统;强降雨会对复合人工湿地出水水质造成一定的影响。     

椰糠填料用于人工湿地处理制胶废水

以椰糠作为湿地工作层主要填料,采用复合垂直流人工湿地处理海南天然橡胶加工业低浓度废水。结果表明,在144 mm/d水力负荷条件下,椰糠填料人工湿地对废水中的COD、BOD5、NH3-H及TP的去除率分别达到68.99%、66.49%、59.55%和75.22%,显著高于无椰糠对照组。当水力负荷提高至216 mm/d,系统运行稳定,出水水质仍能达到污水排放标准(GB 8978-1996)和《农业灌溉水质标准》(GB5084-92)。     

Seasonal performance of an outdoor constructed wetland for graywater treatment in a temperate climate

The seasonal treatment efficiency of a pilot-scale constructed wetland system located outdoors in a semi-arid, temperate climate was evaluated for graywater in a comprehensive, 1-year study. The system consisted of two wetland beds in series--a free water surface bed followed by a subsurface flow bed. Water quality monitoring evaluated organics, solids, nutrients, microbials, and surfactants. The results showed that the wetland substantially reduced graywater constituents during fall, spring, and summer, including biochemical oxygen demand (BOD) (92%), total nitrogen (85%), total phosphorus (78%), total suspended solids (TSS) (73%), linear alkylbenzene sulfonate (LAS) surfactants (94%), and E. coli (1.7 orders of magnitude). Except for TSS, lower removals of graywater constituents were noted in winter--BOD (78%), total nitrogen (64%), total phosphorus (65%), LAS (87%), and E. coli (1.0 order), indicating that, although wetland treatment slowed during the winter, the system remained active, even when the average water temperature was 5.2 +/- 4.5 degrees C.     

Constructed wetlands as a component of the agricultural landscape: mitigation of herbicides in simulated runoff from upland drainage areas

Constructed wetlands are a recommended practice for buffering pollutant source areas and receiving waters. A wetland consisting of a sediment trap and two treatment cells was constructed in a Mississippi Delta lake watershed. A 3-h simulated runoff event was initiated (2003) to evaluate fate and transport of atrazine and fluometuron through the wetland. Water samples were collected during a runoff simulation and then afterward at selected intervals for 21 d, and analyzed for the herbicides. Breakthrough patterns for herbicide concentrations in water samples during the first 20 h after simulated runoff showed peak concentrations in the first 6 h, with gradual tailing as the herbicide pulse was diluted in the second, excavated (deeper) cell. Atrazine and fluometuron concentrations in the first (shallower, non-excavated) cell averaged 12- and 20-fold greater, respectively, than those in the second cell following simulated runoff, indicating entrapment in the first cell. Atrazine and fluometuron concentrations in the shallower cell decreased 32% and 22%, respectively, 9 d following simulated runoff, indicating either degradation or sorption to soil or wetland flora. In the excavated cell, concentrations were even lower, and atrazine declined more rapidly than fluometuron. Results indicate constructed wetlands can improve downstream water quality though sequestration or processing of pollutants.     

Performance of a constructed wetland-pond system for treatment and reuse of wastewater from campus buildings.

A constructed wetland-pond system consisting of two free-water-surface-flow (FWS) wetland cells, a scenic pond, and a slag filter in series was used for reclamation of septic tank effluent from a campus building. The results show that FWS wetlands effectively removed major pollutants under a hydraulic loading rate between 2.1 and 4.2 cm/d, with average efficiencies ranging from 74 to 78% for total suspended solids, 73 to 88% for 5-day biochemical oxygen demand, 42 to 49% for total nitrogen, 34 to 70% for total phosphorous, 64 to 79% for total coliforms, and 90 to 99.9% for Escherichia coli. After passing through the scenic pond and slag filter, the reclaimed water was used for landscape irrigation. There were a variety of ornamental plants and aquatic animals established in the second FWS cell and scenic pond with good water quality, thus enhancing landscape and ecology amenity in campuses.     

Abundance and removal of antibiotic resistance genes (ARGs) in the rearing environments of intensive shrimp aquaculture in South China

Although research regarding antibiotic resistance genes (ARGs) in aquaculture environments has gained increasing scientific interest, further studies are required to understand the abundances and removal mechanisms of ARGs during the entire rearing period of shrimp aquaculture. Thus, in this study, abundances, distributions and removal rates of ARGs in different environmental compartments of intensive shrimp farms in South China were investigated during the entire rearing period. The results indicated that sul1 and cmlA were the predominant ARGs in the water and sediment samples. Additionally, the total abundance of ARGs was higher in shrimp pond water than in the source water and farm effluent. Moreover, sediment samples indicated significantly higher ARG abundances than water samples from the shrimp ponds (P?<?0.05). Environmental factors were found to significantly affect the distribution of ARGs in shrimp rearing environments. Furthermore, stable ponds aided the removal of ARGs from shrimp pond water. This study accounted for temporal variations in ARG abundances as well as removal of ARGs in different environmental compartments during the entire shrimp rearing period. However, additional research is required to optimize the water treatment process for removal of ARGs from the aquaculture.     

Influence of vegetation in mitigation of methyl parathion runoff

A pesticide runoff event was simulated on two 10 m x 50 m constructed wetlands (one non-vegetated, one vegetated) to evaluate the fate of methyl parathion (MeP) (Penncap-M). Water, sediment, and plant samples were collected at five sites downstream of the inflow for 120 d. Semi-permeable membrane devices (SPMDs) were deployed at each wetland outflow to determine exiting pesticide load. MeP was detected in water at all locations of the non-vegetated wetland (50 m), 30 min post-exposure. MeP was detected 20 m from the vegetated wetland inflow 30 min post-exposure, while after 10d it was detected only at 10 m. MeP was measured only in SPMDs deployed in non-vegetated wetland cells, suggesting detectable levels were not present near the vegetated wetland outflow. Furthermore, mass balance calculations indicated vegetated wetlands were more effective in reducing aqueous loadings of MeP introduced into the wetland systems. This demonstrates the importance of vegetation as sorption sites for pesticides in constructed wetlands.     

Pilot-scale constructed wetlands for petroleum-contaminated groundwater.

A pilot study was conducted to determine the feasibility of using constructed treatment wetlands to remediate recovered groundwater from the subsurface of a former refinery site. The pilot system consisted of four subsurface flow treatment cells operated in an upward vertical flow mode and equipped with subsurface aeration lines. The treatment system showed minimal capability for methyl-tert-butyl ether removal, but did effectively remove total petroleum hydrocarbons-deisel range organics and total benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes (total BTEX). Effluent benzene concentrations were less than 0.05 mg/L in 70% of the samples from a treatment cell using subsurface aeration and a wetland sod amendment. Based on 1 year of operating data, cumulative mass removal approached 80% for benzene and 88% for total BTEX.     

2种人工湿地的水力停留时间及净化效果

以复合垂直流人工湿地(IVCW)和水平潜流人工湿地(HSCW)为研究对象,研究了2种湿地运行的季节性最佳水力停留时间(HRT)参数,并监测了2种湿地在最佳HRT参数下运行时对污水的净化效果。结果显示:(1)在IVCW中,最佳HRT在春、秋季为8～10 h;夏季为6 h;冬季为12 h。在HSCW中,最佳HRT在春、秋季为10～12 h;夏季为6～8h;冬季为24～36 h。(2)2种湿地对COD的去除率均无显著的季节性差异;湿地进水中NH4+-N/TN比值与TN去除率显著负相关;不同季节下IVCW对TN的去除效果均高于HSCW。(3)水温对TN、TP去除率的影响在IVCW中比HSCW中的明显;水温高时,2种湿地中的TN去除率较高,IVCW中的TP去除率也较高,但HSCW中的TP去除率则较低,它们间均未达到显著的相关性。     

Modeling the impact of potential wetlands on phosphorus retention in a Swedish catchment

In southern Sweden, wetlands are constructed to remove nitrogen (N) in agricultural catchments. The possible effects of such wetlands on riverine phosphorus (P) were also estimated using input-output data from three well-monitored wetlands. This was done to formulate a simple model for removal of P that is dependent on inflow characteristics. Next, the N- and P-reducing effects of wetlands were modeled on a catchment scale (1900 km2) using the HBV-NP model and various assumptions about the wetland area and location. All three wetlands functioned as sinks for total P (tot-P) and for total suspended solids (TSS) with a removal of 10% to 31% and 28% to 50%, respectively. Mean P-removal rates of 17-49 kg ha(-1) yr(-1) were well simulated with the model. Catchment scale simulations indicated that wetlands were more efficient (in percentage of load) as traps for P than for N and that this may motivate the construction of wetlands for P removal far upstream from the catchment outlet.     

Slaughterhouse wastewater treatment in a full-scale system with constructed wetlands.

This work evaluated the performance of a full-scale system with wetlands for slaughterhouse (abattoir) effluent treatment in the State of Hidalgo, México. The treatment system consisted of a primary sedimentation tank, an anaerobic lagoon, and a constructed subsurface-flow wetland, in series. The wetland accounted for almost 30% of the removal of organic matter. In general, the treatment system achieved satisfactory pollutant removals, but the final effluent could not meet the Mexican environmental regulations for fecal coliform counts, five-day biochemical oxygen demand (BOD5), and total suspended solids (TSS). Overall, removal levels were 91%, 89%, and 85% for BOD5, chemical oxygen demand, and TSS, respectively. However, BOD5 in the final effluent (137 mg/L) was higher than the maximum level of 30 mg/L allowed by the regulatory agency. Although organic nitrogen removal levels were approximately 80%, the nitrogen persisted in oxidation state -3 as ammonia-nitrogen, the removal of which was only 9% in the wetland stage. On average, phosphorus removal was null, and, on occasion, the phosphorus concentration in the treated effluent was higher than that of the influent. Coliform reductions in the overall system were high (on the order of 5 logs on average), whereas the coliform removal in the wetland was between 2 to 3.5 logs. The treatment system was also effective at removing pathogens (Vibrio cholerae, Salmonella, and Shigella). Further laboratory tests with the wetland effluent suggest that post treatment in a sand filter stage followed by disinfection with sodium hypochlorite (NaOCl) could help meet the Mexican discharge regulations, particularly the criteria for coliforms and total BOD5.     

Microbial source tracking of Escherichia coli in a constructed wetland.

Little information has been gathered on the effect of avian species on the microbial water quality in constructed wetlands. To address this concern, fecal pollution from nonpoint and point sources was evaluated in a constructed wetland in Tolleson, Arizona. Antibiotic resistance profiling and biochemical fingerprinting were performed on 325 Escherichia coli isolates, collected from key points in the wetlands. Multivariate statistical analysis was used to interpret the data for samples collected on October 3 and December 12, 2000, and January 16, 2001. It was found that the passerine population was the major source of the Escherichia coli in the water samples collected in the wetlands on October 3 and December 12, 2000, whereas the regrowth in the treated municipal wastewater was the main source on January 16, 2001. This information is useful in providing data for operators in the monitoring of wetlands created for wastewater treatment and wildlife habitat.     

Increasing hydraulic residence time in constructed stormwater treatment wetlands with designed bottom topography.

The treatment efficiency of wetlands depends primarily on the residence time of the polluted storm water (Walker, 1998). Because of this, increasing hydraulic residence times (HRTs) at various flow levels will increase the treatment efficiency of constructed wetlands. In this research, the effects of characteristic bottom topographic features that increase HRT were explored through the use of a two-dimensional hydrodynamic model. Based on numerical simulations of rectangular test wetlands, relationships were made between topographic features and their effects on HRT. Results from the simulations showed that creating baffled wetlands with multiple vertical-scale topography can markedly increase HRT, as is illustrated in a design example. When compared (using the hydrodynamic model) with a wetland having no bottom topography, the design example wetland increased HRT by 113% for the low-flow (142 L/sec) peak flood, and 39% for the 2-year flood event (1700 L/sec).     

Possible use of constructed wetland to remove selenocyanate,arsenic, and boron from electric utility wastewater

Wetland microcosms were used to evaluate the ability of constructed wetlands to remove extremely high concentrations of selenocyanate (SeCN-), arsenic (As), and boron (B) from wastewater generated by a coal gasification plant in Indiana. The wetland microcosms significantly reduced the concentrations of selenium (Se), As, B, and cyanide (CN) in the wastewater by 64%, 47%, 31%, and 30%, respectively. In terms of the mass of each contaminant, 79%, 67%, 57%, and 54% of the Se, As, B, and CN, respectively, loaded into the microcosms were removed from the wastewater. The primary sink for the retention of contaminants within the microcosms was the sediment, which accounted for 63%, 51%, and 36% of the Se, As, and B, respectively. Accumulation in plant tissues accounted for only 2-4%, while 3% of the Se was removed by biological volatilization to the atmosphere. Of the 14 plant species tested, cattail, Thalia, and rabbitfoot grass were highly tolerant of the contaminants and exhibited no growth retardation. Environmental toxicity testing with fathead minnow (Pimephales promelas) larvae confirmed that the water treated by the wetland microcosms was less toxic than untreated water. The data from the wetland microcosms support the view that constructed wetlands could be used to successfully reduce the toxicity of aqueous effluent contaminated with extremely high concentrations of SeCN-, As, and B, and that a pilot-scale wetland should therefore be constructed to test this in the field. Cattail, Thalia, and rabbitfoot grass would be suitable plant species to establish in such wetlands.     

垂直潜流人工湿地有机物积累及去向初步分析

为防治湿地堵塞、改善湿地处理效果,初步探讨了湿地中有机物的积累规律,并估算湿地中有机物不同去除途径的贡献率。结果表明,垂直潜流人工湿地中基质间积累的有机物主要是不可溶有机物,且粒径主要集中在5.00μm以上,分析是不同粒径有机物凝聚积累的缘故;垂向沿程基质间有机物的积累量受进水水力负荷影响明显;进入垂直潜流人工湿地中的有机物绝大部分都被生物(植物和微生物)吸收和利用而得以去除,该途径贡献率可达99.9%以上。     

Heavy metals in coastal wetland sediments of the Pearl River Estuary, China

Sediment quality in coastal wetlands of the Pearl River Estuary was concerned since the wetlands were used for land reclamation, aquaculture and wildlife protection, and meanwhile served as one of the main ultimate sinks for large amount of heavy metals discharged from the rapidly developing Pearl River Delta. Total concentrations of heavy metal, such as Zn, Ni, Cr, Cu, Pb, and Cd, and their chemical speciation were investigated. Results showed that the sediments were significantly contaminated by Cd, Zn and Ni with concentration ranges of 2.79-4.65, 239.4-345.7 and 24.8-122.1mg/kg, respectively. A major portion (34.6-46.8%) of Pb, Cd, and Zn was strongly associated with exchangeable fractions, while Cu, Ni and Cr were predominantly associated with organic fractions, residual, and Fe-Mn oxide. Cd and Zn would be the main potential risk and the sediment quality is no longer meeting the demand of the current wetland utilization strategies.     

水深对表面流人工湿地污染河水处理系统运行效果的影响

基于中试系统一年的连续运行监测,研究了水深对芦苇表面流人工湿地污染河水处理系统的影响。结果表明,水深对表面流人工湿地污染河水处理系统运行效果有很大影响,在进水COD、氨氮、总氮和总磷等分别为36±4.46、0.92±0.47、6.27±2.01和0.13±0.05 mg/L条件下,水深50 cm时处理效果最好,COD、氨氮、总氮和总磷去除率分别达到42.75%、58.42%、56.94%和43.24%。综合污染物去除效果和人工湿地建设工程量,芦苇表面流人工湿地的水深宜采用50 cm。人工湿地系统中植物光合生理和溶解氧等研究表明,水深主要通过影响植物生长和溶解氧等而影响人工湿地的水质净化效果。     

Long-term efficiency and stability of wetlands for treating wastewater of a lead/zinc mine and the concurrent ecosystem development

A constructed wetland system in Guangdong Province, South of China has been used for treating Pb/Zn mine discharge since 1985. The performance in the purification of the mine discharge and the concurrent ecosystem development within the system during the period of 1985-2000 has been studied. The untreated wastewater contained rather high concentrations of cadmium (Cd) (0.05 mg L(-1)), lead (Pb) (11.5 mg L(-1)), and zinc (Zn) (14.5 mg L(-1)), which greatly exceed the upper limits for industrial wastewater discharge in China. The constructed wetland system effectively removed Cd by 94.00%, Pb by 99.04%, Zn by 97.30%, and total suspended solids (TSS) by 98.95% from the mine discharge over a long period (over 16 years) leading to significant improvement in water quality; it was also found that there were no significantly annual or monthly variations in pH values, As, Cd, Hg, Pb, and Zn concentrations in water collected from the outlet of the wetland. Moreover, diversity and abundance of living organisms, including protozoan, higher plants, terrestrial animals, and birds, increased gradually. The 16-year monitoring results showed a reciprocal relationship, at a certain extent, between restoration of the wetland ecosystem, in other words, the maturity of the wetland, and the long-term efficiency and stability on purifying heavy metal-contaminated wastewater.     

Abundance of Alnus incana ssp. rugosa in Adirondack Mountain shrub wetlands and its influence on inorganic nitrogen

The purpose of this research was to determine the abundance of the nitrogen-fixing shrub, Alnus incana ssp. rugosa (speckled alder), in shrub wetlands of the Adirondack Mountain region of New York State and to determine whether its abundance affects the concentration or accumulation of inorganic nitrogen in wetland substrates. Alder/willow wetlands are the second most common wetland type in the Adirondack region. The Adirondack Park Agency's digital GIS database of wetland types was used to determine the areal extent of alder/willow wetlands in the Adirondacks. Randomly selected wetlands were sampled to determine the size and abundance of alder. Alder densities averaged approximately 7000 stems ha(-1) and alder was present in 75% of the wetlands. As an indication of short-term accumulation of NO(3-) and NH4(+) in wetland substrates, ion exchange resins were used to sample ground water in high and low alder density wetlands as well as from wetlands lacking alder and dominated by conifers. Additionally, NO(3-) and NH(4+) concentrations in ground water samples were measured. NH(4+) accumulation levels from exchange resins were low for all wetland types while groundwater NH(4+) concentration was highest in the low-density alder sites. Wetlands with high alder density had approximately six times higher NO(3-) accumulation than other wetlands. Substrate groundwater NO(3-) concentrations in wetlands of high-density alder exceeded by three times levels in low or no alder wetlands, showing the importance of alder to local N budgets. To assess the recovery of shrub wetlands from acidification, future studies should determine the fate of fixed N in wetland systems.