Pilot-scale Wetland Research Articles

Influence of sediment quality and microbial community on the functioning capacity of a constructed wetland treating alkaline leachate after 5.5 years in operation

Constructed wetlands (CWs) have been demonstrated as a cost-effective alternative to chemical treatment systems for mine waters, with the microbial communities attributed to promoting carbonation and aiding pH neutralization. However, few data are available for the long-term use of CWs treating alkaline leachates nor the activity of microbes within them. To investigate the feasibility of CW to buffer alkaline pH, a pilot-scale wetland was implemented in 2015 to treat alkaline bauxite residue leachate. After 5.5 years, samples of supernatant water and sediment were taken at 0.5 m increments along the 11 m long wetland. Waters were analysed for pH, EC and metal(loid) content, while sediment was subjected to physico-chemical assessment and element fractionation. Microbial biomass and community were assessed by phospholipid fatty acid analysis (PLFA) and functionality by the Rapid Automated Bacterial Impedance Technique (RABIT).Evidence presented demonstrates that the CW operating for 66 months effectively treats bauxite residue leachate, with reduced influent pH from 11.5 to 7.8. Trace element analysis revealed effective reduction in Al (94.9 %), As (86.7 %) and V (57.6 %) with substrate analysis revealing a frontloading of elevated pH and trace element content in the first 5 m of the wetland. Sediment Al, As and V were present mostly (>94 % of total) in recalcitrant forms. Sediment Na was mostly soluble (48–62 %), but soils were not sodic (ESP < 15 %). Investigations into the microbial community revealed greatest biomass was in the first 5 m of the wetland, where pH, EC and metal contents were greatest. Microbial respiration using endemic Phragmites australis as a substrate demonstrates an ability to cycle recalcitrant carbon sources within a CW system. These novel microbial findings highlight the need for further investigation into the microbial communities in alkaline CWs.

Pilot-Scale Hybrid Wetland System for the Final Treatment of Dairy Wastewater

Pilot-Scale Hybrid Wetland System for the Final Treatment of Dairy Wastewater

Application of algae to free surface wetlands for effluent reuse

AbstractThe main goal of this study is to assess the role of Algae in the treatment of wastewater and its capability to improve the performance of the free surface wetland as a green solution. It offers a non‐conventional water resource that participate in solving the water scarcity issue in Egypt. This study was carried out in Lake Manzala Water Research Station which is located at the tail end of Bahr El Baqar Drain in Northern Delta in ‏Egypt. A pilot scale wetland consisting of four parallel basins under natural climatic conditions were used for the experiment. The first cell was cultivated with Reeds (traditional plant used in wetlands), while the algae were cultivated in the three other basins. Three different microalgae and algae species (Chlorella, Spirulina and Azolla) were experimented and compared to assess for the finest removal efficiency for different contaminants as BOD, COD, TN, TP, TC, FC and heavy metals. A tailor‐made module was developed with Excel Visual Basic Application programming language to compare the efficiencies of the different treatment systems. Results showed that BOD and COD best removal results were reached by Chlorella with 88% and 84% removal efficiencies respectively. Results also showed that Azolla is the most efficient treatment media for drainage water containing high concentrations of TN while Spirulina was found to be the most efficient in extracting the heavy metals such as Aluminum (Al), Iron (Fe) and Manganese (Mn).

Two-stage constructed wetland systems for polluted surface water treatment

Two pilot scale wetland systems were studied for the removal of organics, nitrogen, phosphorus and coliform from polluted surface water. Each system consisted of two units: a vertical flow (VF) wetland packed with construction materials gravel, brick or organic sugarcane bagasse, followed by a surface flow (SF) or floating treatment (FT) wetland. All wetland units were planted with Phragmites. The wetland systems were operated under constant and shock hydraulic load (HL) periods. Input COD, N, P loadings ranged between 61 and 2181, 7–1040, 2–194 g/m2d, respectively across first stages of each system. Mean removal percentages ranged between 39 and 97, 11–83, 20–100% and 4–85, 16–86, 1.4–100% across first and second stage wetlands, respectively. Mass balance analyses revealed ≤7% N and ≤14% P accumulation in plants; as such, microbial and adsorption kinetics controlled removal dynamics. Nitrification was the limiting nitrogen removal factor in first stage wetlands; organic carbon was supplied by the employed media. Aerobic organics removal and nitrification were diminished during initial stage of shock load periods. In contrast, second stage SF and FT wetlands showed stable removal performances under similar conditions. Resuspension of settled particles decreased removal performance in second stage wetlands, as shock periods progressed toward final stage. Coliform mortality was increased in second stage wetlands. Physico-chemical properties of brick materials in construction material based VF wetland and hanging root volume inside the water column of FT wetland supplemented removal performance. In general, this study provides evidence on potential application of constructed wetlands for polluted surface water treatment.

Effectiveness of vertical subsurface wetlands for iron and manganese removal from wastewater in drinking water treatment plants

Population growth and urbanization pose a greater pressure for the treatment of drinking water. Additionally, different treatment units, such as decanters and filters, accumulate high concentrations of iron (Fe) and manganese (Mn), which in many cases can be discharged into the environment without any treatment when maintenance is performed. Therefore, this paper evaluates the effectiveness of vertical subsurface wetlands for Fe and Mn removal from wastewater in drinking water treatment plants, taking a pilot scale wetland with an ascending gravel bed with two types of plants: C. esculenta and P. australis in El Hormiguero (Cali, Colombia), as an example. The pilot system had three upstream vertical wetlands, two of them planted and the third one without a plant used as a control. The wetlands were arranged in parallel and each formed by three gravel beds of different diameter. The results showed no significant difference for the percentage of removal in the three wetlands for turbidity (98 %), Fe (90 %), dissolved Fe (97 %) and Mn (98 %). The dissolved oxygen presented a significant difference between the planted wetlands and the control. C. esculenta had the highest concentration of Fe in the root with (103.5 ± 20.8) µg/g ; while P. australis had the highest average of Fe concentrations in leaves and stem with (45.7 ± 24) µg/g and (41.4 ± 9.1) µg/g, respectively. It is concluded that subsurface wetlands can be an interesting alternative for wastewater treatment in the maintenance of drinking water treatment plants. However, more research is needed for the use of vegetation or some technologies for the removal or reduction of the pollutant load in wetlands, since each drinking water treatment plant will require a treatment system for wastewater, which in turn requires a wastewater treatment system as well.

Modeling the relationship of aeration, oxygen transfer and treatment performance in aerated horizontal flow treatment wetlands

Mechanical aeration is commonly used to improve the overall treatment efficacy of constructed wetlands. However, the quantitative relationships of air flow rate (AFR), water temperature, field oxygen transfer and treatment performance have not been analyzed in detail until today. In this study, a reactive transport model based on dual–permeability flow and biokinetic formulations of the Constructed Wetland Model No. 1 (CWM1) was developed and extented to 1) simulate oxygen transfer and treatment performance for organic carbon and nitrogen of two pilot–scale horizontal flow (HF) aerated wetlands (Test and Control) treating domestic sewage, and, 2) to investigate the dependence of oxygen transfer and treatment performance on AFR and water temperature. Both pilot–scale wetlands exhibited preferential flow patters and high treatment performance for chemical oxygen demand (COD) and NH4–N at AFRs of 128–700 L m−2 h−1. A reduction of the AFR in the Test system from 128 to 72 L h−1 m−2 substantially inhibited NH4–N removal. Conservative tracer transport as well as reactive transport of dissolved oxygen (DO), soluble and total chemical oxygen demand (CODs, CODt), NH4–N and NOx–N measured in pilot–scale experiments were simulated with acceptable accuracy (E1¯=0.39±0.26). An equation to estimate the volumetric oxygen transfer coefficient was found to be: kLa,20=0.511ln(AFR). Simulated treatment performance depended on kLa,20 in a non–linear manner. A local sensitivity analysis of the calibrated parameters revealed porosity, hydraulic permeability and dispersion length of the fast flow field as well as kLa,20 as most important. An optimal AFR for a spatially and temporally continuous aeration pattern for treatment wetlands treating similar influent was estimated to 150–200 L h−1 m−2. This study provides insights into aeration mechanisms of aerated treatment wetlands and highlights the benefits of process modeling for in–depth system analysis.

Organofosfatlı Pestisitlerin Pilot Ölçekli Sulak Alan Reaktörlerinde Gideriminin İncelenmesi

Modern tarımın yaygınlaşmasıyla birlikte dünyada pestisit kullanımı artmıştır. Birçok ülkede olduğu gibi ülkemizde de aşırı ve bilinçsizce pestisit kullanımı sonucunda su ve toprak ortamında giderek artan miktarlarda pestisit kirlenmesi görülmektedir. Meriç- Ergene Havzası’nda bulunan ve etrafında yoğun bir şekilde çeltik tarımı yapılan Meriç Deltası sulak alanları da bu kirlenmenin görüldüğü bölgelerden biridir. Bu çalışma kapsamında, Meriç Deltası sulak alanlarından numuneler alınarak organofosfatlı pestisitlerin akıbeti incelenmiştir. Sulak alanları temsil etmesi amacıyla pilot ölçekli reaktörle çalışılmış, seçilen 4 organofosfatlı pestisit (Chlorpyrifos, Dichlorvos, Fenthion, Diazinon) için biyolojik ayrışma ve adsorpsiyon deneyleri yapılmıştır. Pilot ölçekli sistemde, seçilen pestisitlerin yarı ömürleri belirlenmiş ve bitki ve sediment üzerine adsorpsiyon miktarları ölçülmüştür. Aynı zamanda pestisitlerin yeraltı suyuna sızma potansiyelleri GUS (“Groundwater Ubiquity Score” / “Yeraltı Suyunda Mevcudiyet Katsayısı”) kullanılarak hesaplanmıştır. Elde edilen sonuçlar serbest yüzey akışlı yapay sulak alan sistemlerinin organofosfatlı pestisitlerin giderimindeki etkinliğini ortaya koymuştur. Bu çalışmadan elde edilen sonuçlar, organofosfatlı pestisitlerin giderimi için önerilen yapay sulak alanların tasarımı için yol gösterici niteliktedir.

Screening of 19 Salix clones in effective phytofiltration potentials of manganese, zinc and copper in pilot-scale wetlands

Willows (Salix spp.) have been regarded as one of interesting plants for phytofiltration of water contaminated with trace metals. In this paper, the clonal differences in tolerance and phytofiltration capacity of mixed metals (Mn, Zn, and Cu) were evaluated in greenhouse pilot-scale wetlands with a floating-support culture system. The results showed that broad clonal variations of biomass accumulation in response to mixed metals ranging from growth inhibition to stimulation. Clones differed in tolerance to multi-metals by tolerance index (TI) based on shoot and root biomass. We also found that wide variations in uptake and accumulation of three metals, which was related to species/clones and metal species. The willows showed high Mn and Zn translocation capacity from roots to leaves suitable for phytoextraction. In contrast, all clones had poor Cu translocation capacity, and Cu mainly retained in roots suitable for rhizofiltration. Among all Salix clones, clones SM30 and J903 had large phytofiltration potential for three metals with their high tolerance.

Natural pyrite to enhance simultaneous long-term nitrogen and phosphorus removal in constructed wetland: Three years of pilot study

The searches for suitable substrates with high capacity for phosphorus (P) removal and promoting denitrification for enhancing nitrogen (N) removal have been a key work in constructed wetlands (CWs) research in the past several decades. But few substrates enhancing simultaneous long-term N and P removal in CWs have been found before. In this study, two subsurface flow pilot-scale wetlands using natural pyrite and limestone as substrates were constructed. After 3 year of operation, we found that pyrite had no negative effects on growth of reeds, removals of chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N), but enhanced long-term total nitrogen (TN) and total phosphorus (TP) removals in constructed wetland. In the three years, the average TP and TN removals of pyrite constructed wetland (PCW) were 87.7 ± 14.2% with 0.25 ± 0.20 mg/L of average effluent TP and 69.4 ± 21.4% with 4.0 ± 3.2 mg/L of average effluent TN, respectively. The main P form in the PCW was (Fe + Al)-bound P. The mechanisms of the PCW with enhanced simultaneous long-term N and P removals were anaerobic and aerobic oxidations of pyrite. The main bacteria were Anaeromyxobacter (4.9%), Ramlibacter (4.8%), Defluviicoccus (4.2%), Azoarcus (3.7%), Geobacter (3.4%), and they were highly related to anaerobic and aerobic oxidation of pyrite in the PCW.

Establishment and convergence of photosynthetic microbial biomats in shallow unit process open-water wetlands

The widespread adoption of engineered wetlands designed for water treatment is hindered by uncertainties in system reliability, resilience and management associated with coupled biological and physical processes. To better understand how shallow unit process open-water wetlands self-colonize and evolve, we analyzed the composition of the microbial community in benthic biomats from system establishment through approximately 3 years of operation. Our analysis was conducted across three parallel demonstration-scale (7500 m2) cells located within the Prado Constructed Wetlands in Southern California. They received water from the Santa Ana River (5.9 ± 0.2 mg/L NO3-N), a water body where the flow is dominated by municipal wastewater effluent from May to November. Phylogenetic inquiry and microscopy confirmed that diatoms and an associated aerobic bacterial community facilitated early colonization. After approximately nine months of operation, coinciding with late summer, an anaerobic community emerged with the capability for nitrate attenuation. Varying the hydraulic residence time (HRT) from 1 to 4 days the subsequent year resulted in modest ecological changes across the three parallel cells that were most evident in the outlet regions of the cells. The community that established at this time was comparatively stable for the remaining years of operation and converged with one that had previously formed approximately 550 km (350 miles) away in a pilot-scale (400 m2) wetland in Northern California. That system received denitrified (20.7 ± 0.7 mg/L NO3-N), secondary treated municipal wastewater for 5 years of operation. Establishment of a core microbiome between the two systems revealed a strong overlap of both aerobic and anaerobic taxa with approximately 50% of the analyzed bacterial sequences shared between the two sites. Additionally the same species of diatom, Stauirsa construens var. venter, was prolific in both systems as the putative dominant primary producer. Our results indicate that despite differences in scale, geographic location and source waters, the shallow open-water wetland design can select for a rapid convergence of microbial structure and functionality associated with the self-colonizing benthic biomat. This resulting biomat matures over the first growing season with operational parameters such as HRT further exerting a modest selective bias on community succession.

Mineral Processing Residue Use as Substrate in a Modular Engineered Wetland for Wastewater Treatment

Safeguarding the water quality of Poyang Lake, China’s largest freshwater lake, is essential for long-term regional water resource sustainability. The use of locally-available mineral processing residues as reactive substrate in engineered wetlands may provide a cost-effective treatment alternative for mixed agricultural and domestic wastewaters entering Poyang Lake. In this study, Chinese iron- and steel-making slags and a titanium mineral processing residue with high nutrient removal capacity were identified in laboratory experiments. A pilot-scale modular wetland system consisting of free water surface, and vertical and horizontal subsurface flow units, all planted with locally-available vegetation, was constructed at the Poyang Lake Modelling Experiment and Research Base in Jiangxi Province. Assessment of nutrient removal efficiency and effluent water quality was undertaken to inform upscaling and optimization of the modular unit process wetland design. The pilot-scale wetland system removed 55% of inorganic N in influent wastewater and was particularly effective in P attenuation, removing 81% of total P. The environmentally-acceptable pH of wetland system effluents, along with low concentrations of dissolved metals and the absence of potential for either N- or Si-limitation, indicated that the modular wetland system examined was potentially suitable for treatment of mixed wastewater entering Poyang Lake. The use of the selected mineral processing residues as reactive substrate in engineered wetland systems enhanced pollutant removal processes in the modular engineered wetland system, effectively attenuating pollutants in mixed wastewater.

Effect of key design parameters on bacteria community and effluent pollutant concentrations in constructed wetlands using mathematical models.

Constructed wetlands are currently recognized as an effective environmental biotechnology for wastewater treatment, but the influence of their design parameters on internal functioning and contaminant removal efficiency is still under discussion. In this work, the effect of aspect ratio and water depth on bacteria communities as well as treatment efficiency of horizontal subsurface flow constructed wetlands (HSSF) under the Mediterranean climate was evaluated, using a mathematical model. For this purpose, experimental results from four pilot-scale wetlands of equal surface area but different aspect ratios and water depth were used. The HSSF system was fed with municipal wastewater. The experimental data were simulated using the BIO_PORE model, developed in the COMSOL Multiphysics™ platform. Simulations with the BIO_PORE model fitted well to the experimental results, showing a higher removal efficiency for the shallower HSSF for COD (93.7% removal efficiency) and ammonia nitrogen (73.8%). The aspect ratio had a weak relationship with the bacteria distribution and the removal efficiency. In contrast, the water depth was a factor. The results of the present study confirm a previous hypothesis in which depth has an important impact on the biochemical reactions causing contaminants transformation and degradation.

Geological study for a wetland restoration: the case of the drained Mouria Lake (W. Peloponnese).

The Μouria Lake was drained for cultivation during late 1960’s. A 0.5-ha large pilot-scale wetland is now constructed in order to study the sedimentological lakerestoration aspects. The uppermost horizons (up to 3 m thick) consist of fine sediments (mud, silt, clay) of fluvial origin, deposited in a lacustrine environment and constituting the lagoonal bottom material, which extents all over the area ever covered by the original Mouria Lake. A sand layer (3 m beneath the current surface) constitutes the substrate of the lagoonal bottom revealing a higher energy deposition environment in comparison to the overlying fine sediments. High pH and electric conductivity values reveal strong alkaline environment and high content of dissolved solids, respectively. The sediments reveal high CEC, as a result of high clay minerals content. Other main mineral phases that occur include quartz, feldspars and calcite. The weathering of marginal rocks is the major factor controlling the mineralogical-geochemical composition of the sediments. The strong alkaline features of the sediments inhibit trace element mobilization. Continuous monitoring of the chemical composition is necessary in order to predict and prevent a possible mobilization of hazardous trace elements and the subsequent release to the environment.

Escherichia coli O157:H7 attachment and persistence within root biofilm of common treatment wetlands plants

Pathogen retention and subsequent release within the rhizosphere of wastewater treatment wetlands may be a concern for human health. To address this concern, the enteric pathogen Escherichia coli O157:H7 with a DsRed plasmid insertion was used as a model pathogenic organism in an open-air chemostat reactor with constant flow of simulated wastewater. Colonization and persistence of the organism was tracked on roots of two obligate wetland plant species, Carex utriculata and Schoenoplectus acutus, originally grown in pilot scale wetland reactors. Teflon nylon string, clean and with existing indigenous biofilm, was used as an inert surface control. Epifluorescence microscopy and qPCR were used to verify E. coli O157:H7 abundance for up to 1 week. Initial attachment was seen on all surfaces, with colonization decreasing through 1 week. qPCR showed preferential association of the pathogen with roots over the nylon. There was a significant difference between plant type; S. acutus showed significantly higher numbers compared to C. utriculata. E. coli O157:H7 binding and persistence on root surfaces may be a means of survival in treatment wetlands.

Dynamics of Bacterial Community Abundance and Structure in Horizontal Subsurface Flow Wetland Mesocosms Treating Municipal Wastewater

Dynamics of bacterial community abundance and structure of a newly established horizontal subsurface flow (HSSF) pilot-scale wetland were studied using high-throughput sequencing and quantitative polymerase chain reaction (PCR) methods. Bacterial community abundance increased rapidly within one month and stabilised thereafter in three replicate HSSF constructed wetland (CW) mesocosms. The most dominant phylum was Proteobacteria, followed by Bacteroidetes in wetland media biofilms and Firmicutes in influent wastewater. CW bacterial community diversity increased over time and was positively related to the wastewater treatment efficiency. Increase in the abundance of total bacteria in the community was accompanied with the abundance of denitrifying bacteria that promoted nitrate and nitrite removal from the wastewater. During the 150-day study period, similar patterns of bacterial community successions were observed in replicate HSSF CW mesocosms. The data indicate that successions in the bacterial community in HSSF CW are shaped by biotic interactions, with a significant contribution made by external abiotic factors such as influent chemical parameters. Network analysis of the bacterial community revealed that organic matter and nitrogen removal in HSSF CW could be, in large part, allocated to a small subset of tightly interconnected bacterial species. The diversity of bacterial community and abundance of denitrifiers were good predictors of the removal efficiency of ammonia, nitrate and total organic C in HSSF CW mesocosms, while the removal of the seven-day biochemical oxygen demand (BOD7) was best predicted by the abundance of a small set of bacterial phylotypes. The results suggest that nitrogen removal in HSSF CW consist of two main pathways. The first is heterotrophic nitrification, which is coupled with aerobic denitrification and mediated by mixotrophic nitrite-oxidizers. The second pathway is anaerobic denitrification, which leads to gaseous intermediates and loss of nitrogen as N2.

Water-Nutrient-food Nexus The Role of Green Algae for Sustainable Food Production in Urban Wetlands Through Untreated Wastewater

The nutrients in domestic wastewater are increasingly being regarded as a valuable resource for energy and nutrient recovery for an Eco-city. The nutrient stream can be used safely for food production through ecological engineering interventions (introduction of green algae in urban wetlands). Effects of wastewater on growth yield and microbial contamination on hydroponic tomato ( Lycopersicon esculentum ) was studied in pilot scale wetland for 6 month under the presence of green algae ( Euglena sp. ) with different chlorophyll a concentration. Domestic wastewater (BOD 205 mg.L -1 , TN 29 mg.L -1 and TP 8 mg.L -1 ) with loading rate of 0.9 L.m -2 .d -1 was used for each wetland. The wastewater did not affect fruit pH, increased their size up to 1.7 ± 0.31 cm in diameter, and weight up to 69.3 ± 6.0 g. Microbial contamination (Total coliforms (TC) and Fecal coliforms (FC)) on fruit surface significantly decreased (p < 0.05) with the increasing algal concentration up to 240 μg.L -1 . Inactivation of bacterial contamination (TC and FC) under the presence of algae associated with high dissolved oxygen concentration (9.7 ± 1.1 mg.L -1 ) and pH increases (8.2 ± 0.8) attributes in wetland. In summary, tomato production in urban wetlands under the presence of green algae enhances the importance of safe and sustainable food production through untreated wastewater.

Water residence time and pesticide removal in pilot-scale wetlands

The use of agricultural pesticides may lead to environmental contamination. Constructed wetlands (CWs) are often recommended for decreasing non-point source pollution by pesticides. The aim of this study was to evaluate the influences of water residence time (WRT) on the effectiveness of two CWs for decreasing pollution in drainage water at the pilot scale. Thus, two successive charge/discharge steps were conducted successively with high and low flows before conducting a step with no flow. For both pilot experiments, the measured effectiveness was between 22 and 100% of the applied quantities of the five pesticides. These results were correlated with the physicochemical properties of the pesticides, particularly their adsorption and desorption capacities. In addition, the pilot scale wetlands were less effective during short WRT (from 15.2 to 100%) than during long WRT (from 17.8 to 100%), despite the greater remobilisation observed during the discharge steps with low flows. After stopping flow, the DT50 values of the pesticides in the aqueous phase were less than 4 days in the two pilot wetlands, likely due to their rapid transfer to the solid phase (soil or straw). In addition, the DT50 values measured in the solid phases ranged from 3.8 days to more than one year. Thus, the WRT must be optimised in the CW by maintaining vegetation or installing weirs, to favour retention processes (sorption, sedimentation) during the drainage periods (October to May). Next, the pesticides stored in the solid phase could be subjected to degradation processes, particularly when moisture, residence times and temperature conditions are favourable (summer).

Removal of organic pollutants from oak leachate in pilot scale wetland systems: How efficient are aeration and vegetation treatments?

This study investigated the effects of aeration and/or vegetation in experimental constructed wetlands (CWs) as mesocosms on the removal of pollutants in oak wood leachate. Twelve outdoor wetland mesocosms, with randomized replicated treatment combinations of vegetation (Phragmites australis) and aeration was monitored during the second and third year after construction. The investigation included control tanks with no aeration and no vegetation. The parameters monitored were polyphenols (PPs), chemical oxygen demand (COD) and water colour. The reduction of COD after 28 days was approx. 50% and more than 50% of PPs, whereas only 40% of the water colour was removed. Aeration increased the effect of both COD and PP removal. The vegetation treatment had a small but significant effect on removal of COD. The vegetation + aeration treatment, as well as aeration alone, increased the removal efficiency of COD from 9.5 g m−3 d−1 in the control to 11 g m−3 d−1. The results suggest that CWs can be used to treat stormwater contaminated by oak wood leachate. Further, it is suggested that the main processes for removal of pollutants in the leachate occur in the open-water habitat and that the hydraulic retention time is more important for removal than aeration and vegetation related processes.

Sunlight inactivation of fecal indicator bacteria in open-water unit process treatment wetlands: Modeling endogenous and exogenous inactivation rates

A pilot-scale open-water unit process wetland was monitored for one year and found to be effective in enhancing sunlight inactivation of fecal indicator bacteria (FIB). The removal of Escherichia coli and enterococci in the open-water wetland receiving non-disinfected secondary municipal wastewater reached 3 logs and 2 logs in summer time, respectively. Pigmented enterococci were shown to be significantly more resistant to sunlight inactivation than non-pigmented enterococci. A model was developed to predict the inactivation of E. coli, and pigmented and non-pigmented enterococci that accounts for endogenous and exogenous sunlight inactivation mechanisms and dark processes. Endogenous inactivation rates were modeled using the sum of UVA and UVB irradiance. Exogenous inactivation was only significant for enterococci, and was modeled as a function of steady-state singlet oxygen concentration. The rate constants were determined from lab experiments and an empirical correction factor was used to account for differences between lab and field conditions. The model was used to predict removal rate constants for FIB in the pilot-scale wetland; considering the variability of the monitoring data, there was general agreement between the modeled values and those determined from measurements. Using the model, we estimate that open-water wetlands at 40° latitude with practical sizes can achieve 3-log (99.9%) removal of E. coli and non-pigmented enterococci throughout the year [5.5 ha and 7.0 ha per million gallons of wastewater effluent per day (MGD), respectively]. Differences in sunlight inactivation rates observed between pigmented and non-pigmented enterococci, as well as between lab-cultured and indigenous wastewater bacteria highlight the challenges of using FIB as model organisms for actual pathogens in natural sunlit environments.

Nitrate removal in shallow, open-water treatment wetlands.

The diffuse biomat formed on the bottom of shallow, open-water unit process wetland cells contains suboxic zones that provide conditions conducive to NO3(-) removal via microbial denitrification, as well as anaerobic ammonium oxidation (anammox). To assess these processes, nitrogen cycling was evaluated over a 3-year period in a pilot-scale wetland cell receiving nitrified municipal wastewater effluent. NO3(-) removal varied seasonally, with approximately two-thirds of the NO3(-) entering the cell removed on an annual basis. Microcosm studies indicated that NO3(-) removal was mainly attributable to denitrification within the diffuse biomat (i.e., 80 ± 20%), with accretion of assimilated nitrogen accounting for less than 3% of the NO3(-) removed. The importance of denitrification to NO3(-) removal was supported by the presence of denitrifying genes (nirS and nirK) within the biomat. While modest when compared to the presence of denitrifying genes, a higher abundance of the anammox-specific gene hydrazine synthase (hzs) at the biomat bottom than at the biomat surface, the simultaneous presence of NH4(+) and NO3(-) within the biomat, and NH4(+) removal coupled to NO2(-) and NO3(-) removal in microcosm studies, suggested that anammox may have been responsible for some NO3(-) removal, following reduction of NO3(-) to NO2(-) within the biomat. The annual temperature-corrected areal first-order NO3(-) removal rate (k20 = 59.4 ± 6.2 m yr(-1)) was higher than values reported for more than 75% of vegetated wetlands that treated water in which NO3(-) was the primary nitrogen species (e.g., nitrified secondary wastewater effluent and agricultural runoff). The inclusion of open-water cells, originally designed for the removal of trace organic contaminants and pathogens, in unit-process wetlands may enhance NO3(-) removal as compared to existing vegetated wetland systems.