Improvement of biodegradation in compact co-current biotrickling filter by high recycle liquid flow rate: Performance and biodegradation kinetics of ammonia removal

As a microbial-environmental-control-type deodorizing system, we have developed a compact biotrickling filter system for small-scale livestock farms. The performance of the compact co-current biotrickling filter operated at high recycle liquid flow rates was systematically examined. In particular, we studied improvements in the nitrification ability of the system due to the resultant enhancement of absorption and dissolution of NH₃ and absorption of O₂ with the high flow rates of recycle liquid flowing downward co-currently with gas flow. At the empty bed residence time of 50 s, almost complete removal of NH₃ was obtained with recycle liquid flow rates of 103 and 205 L m⁻³ day⁻¹ for 20 days while the inlet NH₃ concentration was increased from 200 to 500 ppm. With a recycle liquid flow rate of 411 L m⁻³ day⁻¹ the removal efficiency remained above 95% for 57 days while the inlet NH₃ concentration was increased from 200 to 700 ppm. The biodegradation kinetics for NH₃ removal was successfully analyzed using the Haldane substrate inhibition kinetics. The present data and kinetic analyses showed that the substrate inhibition was suppressed and the biodegradation of ammonia in the compact biotrickling filter could be improved by the high recycle liquid flow rate.     

Performance of the Columbia,Missouri, treatment wetland

Constructed treatment wetlands have served the City of Columbia, MO, for fourteen years. Four free water surface wetland units in series, comprised of 23 cells, are an addition to the activated sludge wastewater treatment plant, for the purpose of added biochemical oxygen demand (BOD) and total suspended solids (TSS) control. The system operates year-round, and supplies water to the Eagle Bluffs Conservation Area for wetland maintenance. The cattail wetlands processed an average of 57,000 m³/d, at a water depth of 20 cm. The resulting detention time was approximately 2 days, and the hydraulic loading was 13 cm/d. Water temperatures were warm leaving the treatment plant and in the wetlands in winter, because of the short detention. The period of record average carbonaceous biochemical oxygen demand (CBOD) leaving the wetlands was 5.0 mg/L, and the TSS was 14.7 mg/L. Dissolved oxygen was depressed in summer, likely because of the high sediment demand. Nutrient concentrations were only minimally reduced, total nitrogen (TN) by 22% and total phosphorus (TP) by 6%. However, load reductions were maximal, 98 t/yr for nitrogen, and 3.6 t/yr for phosphorus. Fecal coliforms were reduced by 98%, and E. coli by 95%. First order rate coefficients were high for CBOD (64 m/yr), nitrate (61 m/yr) and organic nitrogen (42 m/yr), but relatively low for ammonia (8 m/yr) and phosphorus (5.7 m/yr). Nitrogen removal was strongly affected by vegetative uptake. Sediment accretion in the wetland inlets was substantial, at 1.6 cm/yr in the inlets to the upstream wetland units. Muskrats caused vegetation damage, and waterfowl use was high in winter, causing TSS excursions.     

Effects of vegetation,limestone and aeration on nitritation,anammox and denitrification in wetland treatment systems

Integration of partial nitrification (nitritation) and anaerobic ammonium oxidation (anammox) in constructed wetlands creates a sustainable design for nitrogen removal. Three wetland treatment systems were operated with synthetic wastewater (60 mg NH₃–N L^?1) in a batch mode of fill – 1-week reaction – drain. Each treatment system had a surface flow wetland (unplanted, planted, and planted plus aerated, respectively) with a rooting substrate of sandy loam and limestone pellets, followed by an unplanted subsurface flow wetland. Meanwhile, three surface flow wetlands with a substrate of sandy loam and pavestone were operated in parallel to the former surface flow wetlands. Influent and effluent were monitored weekly for five cycles. Aeration reduced nitrogen removal due to hindered nitrate reduction. Vegetation maintained pH near neutral and moderate dissolved oxygen, significantly improved ammonia removal by anammox, and had higher TN removal due to coexistence of anammox and denitrification in anaerobic biofilm layers. Nitrite production was at a peak at the residence time of 4–5 d. Relative to pavestone, limestone increased the nitrite mass production peak by 97%. The subsurface flow wetlands removed nitrogen via nitritation and anammox, having an anammox activity of up to 2.4 g N m^?3 d^?1 over a startup operation of two months.     

Fate and distribution of arsenic in laboratory-scale subsurface horizontal-flow constructed wetlands treating an artificial wastewater

Knowledge regarding the fate, accumulation and distribution of arsenic inside constructed wetlands is still insufficient. Based on a complete mass balance analysis, the aim of this study was to investigate the fate and distribution of As in distinct wetland compartments and different segments along the wetland gradient. Experiments were carried out in laboratory-scale wetland systems, two planted with Juncus effusus and one unplanted, using an As-containing artificial wastewater. The obtained results revealed that the planted wetlands have a substantially higher As-mass retention capacity (59–61% of the total As inflow) than wetlands without plantation (only 44%). However, different loads of organic carbon within the inflowing artificial wastewater showed no remarkable influence on As-mass retention in the planted wetlands. Nearly 47–52% of the total inflowing As mass was found to be retained within the first half of the planted wetlands and this retention decreased step by step along the flow path. In contrast, only 28% of the total inflowing As mass was retained within the first half of the unplanted wetland. In general, a different fate and distribution of As was observed inside the planted and unplanted wetlands. Higher As concentrations were exhibited by the plant roots (51.5–161.5 mg As kg^?1 dry wt.) compared to the shoots (1.1–6.4 mg As kg^?1 dry wt.). Analysis of the total As-mass balance in the planted wetlands revealed that nearly 44–49% of the total inflowing As was recovered or concentrated within the plant roots, only 1% was sequestered within the plant shoots, 7–10% were entrapped or deposited within the gravel bed sediments, 2–3% were retained in the standing pore water, 39–41% were flushed out as outflow and the remaining 1–2% is still considered to be unaccountable. Total As accumulation in the plant shoots made a small contribution to the mass balance, and plant root biomass was found to be the most important compartment for As retention. In contrast, nearly 11% of the total inflowing As were found in the sediment, 2% in the standing pore water, 57% in the outflow and a substantially higher portion (nearly 30%) remained unaccountable in the unplanted bed, which might be released as volatile As compounds or lost from the system due to various unknown reasons. The results indicate that plants have a remarkable effect on As retention and stability of already retained As; hence planted wetlands might be a suitable option for treating As-contaminated wastewater.     

Treatment of high-strength wastewater in tropical constructed wetlands planted with Sesbania sesban: Horizontal subsurface flow versus vertical downflow

Treatment of various types of wastewaters is an urgent problem in densely populated areas of many tropical countries. We studied the potential of using Sesbania sesban, an N₂-fixing shrub, in constructed wetland systems for the treatment of high-strength wastewater. A replicated horizontal subsurface flow system and a saturated vertical downflow system was established with planted and unplanted beds to assess the effects of system design and presence of plants on treatment performance. The systems were loaded with a mixture of domestic and pig farm wastewater at three hydraulic loading rates of 80, 160 and 320 mm d^?1. The S. sesban plants grew very well in the constructed wetland systems and produced 17.2–20.2 kg dry matter m^?2 year^?1 with a high nitrogen content. Mass removal rates and removal rate constants increased with loading rate, but at 320 mm d^?1 the effluent quality was unacceptable and hydraulic problems appeared. Mass removal rates and removal rate constants were much higher than reported in other studies probably because of the high-strength wastewater, the high loading rates and the tropical conditions. Planted systems removed pollutants much more efficiently than the unplanted controls. Direct plant uptake constituted only up to 8% of the total-N removal and 2% of the P removal at the lowest loading rate, and was quantitatively of low importance compared to other removal processes. The significant effects of plants were therefore related more to their indirect effects on the removal processes. This study for the first time documents that S. sesban can be used in constructed wetland systems for the treatment of polluted water while at the same time producing a valuable N rich biomass that can be used for animal fodder or soil amendment.     

Nutrient retention function of a stream wetland complex—A high-frequency monitoring approach

The ability of riverine ecosystems to retain nutrients depends on different hydrological, chemical and biological conditions including exchange processes between streams and wetlands. We investigated nutrient retention in a stream wetland complex on the time scale of daily hydrological exchange between both systems. Daily mass balances of NO₃-N, NH₄-N, TP and SRP were calculated with data obtained by two automated measurement stations in a stream reach upstream and downstream of a wetland. The pattern of hydrological exchange between stream and wetland was used to classify characteristic hydrological periods like floods, base and low flows. The nutrient retention function of the stream wetland complex varied considerably during phases of similar hydrologic conditions. Despite re-wetting measures in the wetland, an overall net export of all nutrients except for NH₄-N characterised the whole growing season. Nitrate retention occurred during summer flood (retention in the wetland, 23 kg NO₃-N d^?1, 17% of the input load) and low flow (retention in the stream, 1 kg NO₃-N d^?1, 2% of the input load). TP retention during summer could be assigned to sedimentation (0.7 kg TP d^?1, 7% during flooding in the wetland, 0.2 kg TP d^?1, 4% during low flow in the stream). SRP retention was only intermittent. We concluded that the nutrient retention of streams and wetlands can only be optimised by restoration measures that regard both systems as one functional unit in terms of nutrient retention.     

An integrated constructed wetland to treat contaminants and nutrients from dairy farmyard dirty water

Water pollution by agriculture can include inappropriately managed dairy farmyard dirty water. In Ireland, dairy farmyard dirty water includes farmyard runoff, parlour washings, and silage/farmyard manure effluents. The objectives of this study were to determine (i) the quality and quantity of dirty water generated at a farm-scale and (ii) the seasonal effectiveness of a constructed wetland to treat farmyard dirty water. The wetland system was 4800 m² in area and treated dirty water from a 42-cow organic dairy unit with an open yard area of 2031 m². Monthly dirty water inflow rate to the wetland ranged between 3.6 and 18.5 m³ d⁻¹. Farmyard dirty water accounted for 27% of hydrological inputs to the wetland, whereas rainfall on wetland, along with wetland bank inflows accounted for 45 and 28%, respectively. Farmyard dirty water quality and quantity did not vary with season. Yearly mass loads discharged to the wetland were 47 ± 10 kg yr⁻¹ of soluble reactive phosphorus (SRP), 128 ± 35 kg yr⁻¹ of NH₄⁺, 5484 ± 1433 kg yr⁻¹ of organic material as measured by five-day biological oxygen demand (BOD₅), and 1570 ± 465 kg yr⁻¹ of total suspended solids (TSS). Phosphorus retention by the wetland varied with season (5–84%) with least amounts being retained during winter.     

A comparative study of surface and subsurface flow constructed wetlands for treatment of combined sewer overflows: A greenhouse experiment

The use of surface flow (SFCWs) and subsurface flow constructed wetlands (SFCWs) for the treatment of combined sewer overflows was assessed at pilot scale. Synthetic wastewater was applied in three batches with decreasing concentrations to mimic concentration profiles that are obtained in the field during overflow events. Three simulated combined sewer overflows were applied on each wetland. Composite water samples (60 in total) were taken for a period of 8 days to study the removal of total nitrogen (Ntot), NH₄–N, NO₃–N, total COD (CODtot) and total phosphorus. Redox potential, which was monitored at various locations along the wetlands, was more negative in the SSFCWs. In general, removal occurred faster in the SSFCWs and the final concentrations were lower. The removal of Ntot was only 36.6 ± 3.3% in the SFCWs due to nitrification-limiting conditions. The conditions in the SSFCWs, in contrast, seemed to promote Ntot removal (removal efficiency 96.7 ± 1.9%). The removal of P was hampered in both wetland types by reducing conditions. P that was initially removed was released again from the substrates later on. First-order removal rate constants were derived for the removal of both CODtot (SSFCWs: 1.1 ± 0.3 m d^?1; SFCWs: 0.17 ± 0.06 m d^?1) and Ntot (SSFCWs: 0.4 ± 0.1 m d^?1; SFCWs: 1.7 ± 0.5 m d^?1).     

Factors influencing the efficiency of constructed wetlands used for the treatment of intensive trout farm effluent

In this paper the factors influencing treatment performance of subsurface flow constructed wetlands (SSF wetlands) treating aquaculture effluents were identified and quantified. The financial impact of advanced aquaculture effluent treatment with SSF wetlands was calculated.It is the first long-term, commercial-scale trial of SSF wetland treatment for effluents from intensive trout farming, a highly diluted effluent at very high flow rates (mean total phosphorous concentration 0.34 mg L^?1 at 14.3 L s^?1). The 12-month survey provided the opportunity to generate calculation fundamentals for the commercial application of SSF wetlands for aquaculture. Treatment efficiencies of up to 75–86% for total ammonia nitrogen (TAN), biological oxygen demand (BOD₅) and total suspended solids (TSS) were achieved. The daily area retention rate per square meter wetland area was between 2.1 and 4.5 g for TAN and between 30 and 98 g for TSS.The performance of the six wetland cells comprising three replicated hydraulic loading groups (14.5, 6.9, 3.3 m³ m^?2 day^?1) was monitored, offering the possibility to identify factors influencing treatment efficiency through multifactor analysis. These factors turned out to be nutrient inflow concentration, hydraulic loading rate and accumulation of TSS within the wetland bed, the only time-dependent factor. Factors such as vegetation period and fish harvesting were shown to be of significant but negligible importance.Inflow nutrient concentration is determined by production intensity, husbandry conditions, feed quality and any pre-treatment of effluent. Hydraulic load is determined by the space and budget available for SSF construction. TSS accumulation in the wetland is influenced by pre-treatment of the solid fraction prior to the wetland and determines the wetland service lifetime.From these factors the expenses of commercial wetland application can be estimated, leading to a cost increase around €0.20 kg^?1 fish produced (less than 10% of production costs) and therefore confirm the commercial feasibility of SSF wetland treatment.     

Liquid chromatography–tandem mass spectrometry method for the simultaneous quantitative determination of the organophosphorus pesticides dimethoate,fenthion, diazinon and chlorpyrifos in human blood

Simultaneous determination of the organophosphorus pesticides dimethoate, fenthion, diazinon and chlorpyrifos in human blood by HPLC–tandem mass spectrometry was developed and validated. The pesticides were extracted by a simple one-step protein precipitation procedure. Chromatography was performed on a Luna C₁₈ (30 mm × 2.0 mm, 3 μm) column, using a step-gradient at a flow rate of 0.4 ml/min. The assay was linear from 0.5 to 100 ng/ml (r² > 0.992, n = 24) for all pesticides. The inter- and intra-day accuracy and precision for the method was 96.6–106.1% and <10%, respectively. The lower limit of quantification was 0.5 ng/ml. In conclusion, the method described displays analytical performance characteristics that are suitable for the quantification of these pesticides in cases of acute poisoning.     

Performance evaluation of constructed wetlands in a tropical region

Five emergent plant species were compared for their effectiveness in treating contaminants in a wetland system constructed on a military base in El Salvador. The system consisted of the subsurface flow (SSF), open water (OW) and free surface flow (SF) wetlands with a combined flow capacity of up to 151.4 m³ d^?1. Reliability and consistent performance in extreme conditions, such as those occurring during the tropical dry or wet seasons were important evaluation criteria. The discontinuous flow patterns typical of tropical climates necessitated the use of water balance calculations using climatic data such as rainfall and evapotranspiration. System characterization was achieved by computation of daily input and output mass loading rates for each individual constituent. Results suggest that Phragmites and Brachiaria were the most effective plants in SSF wetland. Brachiaria provided the added benefit of serving as a source of fodder and proved proficient, with N and P uptakes of 1.5–3.14% and 0.17–0.25% per dry plants’ biomass, respectively. Typha yielded the highest dry season removal efficiency within the SF (BOD₅: 80.78 ± 9.35%, COD: 65.18 ± 19.6%, TN: 58.59 ± 19.3%, oil and grease: 78.34 ± 10.55%, total dissolved phosphorus: 66.5 ± 20.7%). Phragmites–Typha treatment subset performed better year-round than either Thalia–Thalia or Brachiaria–Cyperus. Evaluated plants were capable of surviving and proliferating in extreme tropical climates.     

Phosphorus mass load and outflow concentration relationships in stormwater treatment areas for Everglades restoration

Mass loading and outflow phosphorus (P) relationships were investigated for four stormwater treatment area (STA) wetlands in south Florida. These systems, ranging in size from 350 to 2670 ha, were constructed by the South Florida Water Management District (SFWMD) for Everglades restoration, and approaches currently are being investigated for optimizing their design and management. We analyzed 2–7 years of P removal data from 10 independent STA process trains using system classifications based on dominant vegetation type, which was either emergent aquatic vegetation (EAV) or submerged aquatic vegetation (SAV), and prior land use, which was either recently farmed (RF) or historic wetland (HW). We found that a 1–2 year history of mass loading rates (MLR) at or below ∼1.3 g P/m²/year in STA process trains provided a high likelihood of achieving outflow total P (TP) concentrations less than ∼30 μg/L. Statistical analyses revealed that P removal performance of SAV and EAV-HW systems was generally superior to that of EAV-RF systems. These performance differences were corroborated with data from seven other non-STA Florida-based treatment wetlands. Furthermore, in the subset of SAV and continuously flooded EAV-HW data with P MLRs at or below ∼2 g/m²/year, outflow P concentrations were consistently between 10 and 20 μg/L, mass removal efficiencies were consistently above 85%, and the wetlands demonstrated a substantial resilience to small-to-moderate pulsed inflow P loads. Despite 16 occurrences in these full-scale STA data of annual flow-weighted mean outflow P concentrations between 10 and 20 μg/L, no significant MLR–P relationships were identified for targeting specific P concentrations in this range.     

Water quality performance of treatment wetlands in the Imperial Valley,California

Two demonstration treatment wetland systems were studied for over four years. Both consisted of sedimentation basins, followed by wetland cells. The Imperial, CA system had four wetland cells totaling 4.7 ha, 25% vegetated with bulrushes (Schoenoplectus californicus), and the Brawley, CA system had two wetland cells totaling 1.8 ha, also 25% vegetated with bulrushes. Imperial received irrigation runoff water at 30 cm/day, and Brawley received New River water at 11 cm/day, both with moderately high levels of nutrients, sediments and pathogens. The systems seeped 40–60% of the incoming water. The hydraulic efficiencies of the systems were high because of compartmentalization and high aspect ratios. Concentration reductions of TN, TP and TSS were 50%, 39%, and 97% at Imperial, and 73%, 50% and 96% at Brawley. Imperial achieved about 1.5 log₁₀ reductions in total coliforms, fecal coliforms and Escherichia coli, while Brawley achieved about 2.7 log₁₀ reductions. The sedimentation basins settled most of the incoming TSS, as well as the algal solids that were generated in the basins. Algal uptake removed nutrients in the basins, which were supersaturated with oxygen. The wetlands were effective in denitrification, and trapped the remaining and generated TSS. Removal rate constants, corrected for infiltration, were at the high end of those reported for other wetlands.     

Nitrate-nitrogen retention in wetlands in the Mississippi River Basin

Nitrate-nitrogen retention as a result of river water diversions is compared in experimental wetland basins in Ohio for 18 wetland-years (9 years × 2 wetland basins) and a large wetland complex in Louisiana (1 wetland basin × 4 years). The Ohio wetlands had an average nitrate-nitrogen retention of 39 g-N m⁻² year⁻¹, while the Louisiana wetland had a slightly higher retention of 46 g-N m⁻² year⁻¹ for a similar loading rate area. When annual nitrate retention data from these sites are combined with 26 additional wetland-years of data from other wetland sites in the Basin Mississippi River (Ohio, Illinois, and Louisiana), a robust regression model of nitrate retention versus nitrate loading is developed. The model provides an estimate of 22,000 km² of wetland creation and restoration needed in the Mississippi River Basin to remove 40% of the nitrogen estimated to discharge into the Gulf of Mexico from the river basin. This estimated wetland restoration is 65 times the published net gain of wetlands in the entire USA over the past 10 years as enforced by the Clean Water Act and is four times the cumulative total of the USDA Wetland Reserve Program wetland protection and restoration activity for the entire USA.     

Performance evaluation of a newly developed flow diverted bed system for stream restoration

The flow diverted bed (FDB) system was developed to improve the stream water quality. This system (Run 2) had two wetlands where the flow from the upper layer (aerobic) in the first wetland could be redirected to the lower layer (anaerobic) in the second wetland by the flow diverter, and vice versa. In addition, the yellow-soil media placed at the bottom layer allowed a larger influx in the lower layer and had a sorption capacity of phosphate ions. The removal efficiencies of COD and TN at Run 2 [hydraulic loading rate (HLR) = 177 cm/d] was 1.7–3.6 times higher than that at Run 1 (HLR = 192 cm/d) without the diverter. The values of void fraction, dimensionless variance, dispersion number, Peclet number and velocity for this system were found to be 0.6637, 0.2847, 0.1717, 5.8241, and 53.2 m/d, respectively. The reducing trend of each pollutant was exponentially decreased along the overall length of this system. Also, the transport was dominated by convection (plug flow) rather than dispersion (complete mix). The volumetric removal rate constants for COD, SS, TKN, TN, and TP were found to be 4.854, 7.988, 1.388, 1.625, and 1.767 d⁻¹ via the first-order rate model. Consequently, the flow diverter and yellow-soil media in this system played an important role in enhancing the treatability of pollutants and operating at a higher HLR.     

Analysis of polychlorinated biphenyls in human serum by gas chromatography–mass selective detection operating at high ion source temperature

Optimization of analytical instrumentation is essential when analyses of persistent organic pollutants in human serum are performed at ultra-trace levels. This research describes the analysis of polychlorinated biphenyls (PCBs) in serum using gas chromatography coupled with a mass selective detector (GC/MSD) in the selected ion monitoring (SIM) mode. We selected PCB-58 and PCB-186 as internal standards (ISs) for the method development, and newborn calf serum (NCS) was chosen as the matrix. The matrix was fortified with PCB congeners and extracted by an automated solid phase extraction system using C18 sorbent. The extracts were analyzed at two ion source temperatures, 230 and 300 °C. The use of high ion source temperature increased the abundances of high-mass ions, and the response factors in SIM mode for PCBs. An excellent linearity from 0.5 to 100 ng/ml at ion source temperature of 300 °C was demonstrated, with a calculated detection limit of 0.1 ng/g serum. Seven replicate fortifications of newborn calf serum, at three spiking levels of 1, 10, and 50 ng/g of serum, gave mean recoveries of 110%, 85%, and 98%, with average relative standard deviation (RSD) values of 5.4%, 7.3%, and 4.7%, respectively.     

Management scenario evaluation for a large treatment wetland using a spatio-temporal phosphorus transport and cycling model

This paper describes the development of a two-dimensional, spatially distributed model to simulate coupled hydrologic and phosphorus (P) biogeochemical processes in a 147-ha cell of a 1544-ha stormwater treatment wetland designed to help protect the greater Everglades, FL, USA. The model was used to assess the effects of a suite of feasible management alternatives on the long-term ability of the wetland to sustain total P (TP) removal. The spatial and temporal dynamics of TP retention were simulated under historical (1995–2000) conditions, and under assumptions of removal of short-circuiting channels and ditches, changes in external hydraulic and TP loading, and long-term (>20 years) impacts on soil and water column TP dynamics under current and reduced load conditions. Internal hydrology and transport processes were calibrated against measured tracer concentrations, and subsequently validated against outflow discharge and spatial chloride concentration data. Cycling of P was simulated as first-order uptake and release, with different uptake coefficients for open water/sparse submerged aquatic vegetation (SAV) areas (0.2 day^?1) and dense SAV areas (0.4 day^?1), and a much lower, uniform release coefficient (1.97 × 10^?4 day^?1). The calibration and validation of the P model showed good agreement with field measurements of water column TP concentrations measured at the wetland outlet (calibration RMSE = 10.5 μg L^?1; validation RMSE = 15.6 μg L^?1). Under simulated conditions of preferential channels eliminated, average annual TP treatment effectiveness increased by 25%. When inflow TP loads were assumed to be eliminated after 6 years of loading, the release of accumulated soil P sustained predicted annual average outlet concentrations above 6.7 μg L^?1 for 18 years, decreasing at a rate of 0.16 μg L^?1 yr^?1. Sensitivity analyses indicate that the most critical model input factors include flow resistance parameters, initial soil TP content, and P cycling parameters compared to initial water level, initial TP concentration in water column, ET and transport parameters.     

Phosphorus removal from agricultural runoff by constructed wetland

A free-water surface wetland covering an area of 2800 m² was operated from March 2002 to June 2004 for agricultural runoff treatment in the Dianchi Valley in China. In the wetland were grown Zizania Caduciflora Turez Hand-mazt and Phragmites australis (Cav.) Trin.ex Steud. The instantaneous inflow rate was measured and the integrated flux was recorded by an ultrasonic flow instrument all year round. The average inflow rate, hydraulic loading rate (HLR) and hydraulic retention time (HRT) were kept at 242 m³ d^?1, 12.7 cm d^?1 and 2.0 d, respectively. The annual average total phosphorus (TP) in the inflow was 0.87 mg L^?1, and the corresponding removal efficiency was calculated to be 59.0%. Biannual plant uptake and removal by harvesting and seed transport was the main pathway for TP removal, while the influent TP load was 12.9 g m^?2 year^?1. Hydraulic retention time had a significant positive correlation with the removal of P (r² = 0.88). Water temperature, inflow phosphorus load, inflow and hydraulic load rates were positively correlated with the removal of P. Inflow phosphorus concentrations were negatively correlated with the removal of P. It is shown that the free-water surface wetland was an effective and economical system for agricultural runoff treatment in lake regions.     

The role of plants in the removal of nutrients at a constructed wetland treating agricultural (dairy) wastewater,Ontario, Canada

The South Nation River Watershed, in eastern Ontario, Canada, is an agricultural watershed impacted by excess nutrient loading primarily from agricultural activities. A constructed wetland for the treatment of agricultural wastewater from a 150-cow dairy operation in this watershed was monitored in its eighth operating season to evaluate the proportion of total nitrogen (TN) (approximated by total Kjeldahl nitrogen (TKN) due to low NO₃⁻) and total phosphorus (TP) removal that could be attributed to storage in Typha latifolia L. and Typha angustifolia L., which dominate this system. Nutrient loading rates were high, with 16.2 kg ha⁻¹ d⁻¹ N and 3.4 kg ha⁻¹ d⁻¹ P entering the wetland and loading the first wetland cell. Plant uptake accounted for 0.7% of TKN removal when the vegetated free water surface cells were considered together. However, separately, in the second wetland cell with lower N and P loading rates, plants accounted for 9% of TKN, 21% of NH₄⁺ and 5% of TP removal. Plant uptake was significant to overall removal given wetland age and nutrient loading. Nutrient storage during the growing season at this constructed wetland helped reduce the nutrient load entering the watershed, already stressed by intensive local agriculture.     

Feasibility of using constructed treatment wetlands for municipal wastewater treatment in the Bogotá Savannah,Colombia

The main water bodies in the Bogotá Savannah have been seriously polluted due to the mismanagement of domestic, agricultural, and industrial wastewater. While there are a number of wastewater treatment facilities in the region, most do not function properly. There is a great need for inexpensive and sustainable wastewater treatment systems that are not technologically sophisticated and that do not require intensive management. The main goal of this study was to quantify the performance and sustainability of treatment wetlands and existing wastewater treatment systems in this region. Using data from the literature, a treatment wetland model was developed, which focused on pollutant removal. The modeled performance was compared to a system of waste stabilization ponds and a sequencing batch reactor. The three systems were subject to cost analysis and an emergy evaluation, leading to the assessment of indicators of cost-benefit for comparison. The economic analysis suggested that the net annual cost of the treatment wetland was US$ 14,672, compared to US$ 14,201 for the stabilization ponds and US$ 54,887 for the batch reactor. The emergy evaluations show that the ponds have the lowest annual emergy flow (6.65 + 16 sej/yr), followed by the constructed wetland (2.88E+17 sej/yr) and the batch reactor (8.86E+17 sej/yr). These results were combined to estimate treatment ratios (contaminants removed per lifetime cost, and contaminants removed per total emergy), cost ratios (cost per volume of water, annual cost per capita, and construction cost per capita), and emergy ratios (treatment yield, renewable emergy, lifetime emprice, construction emprice, non-renewable emergy, empower density, environmental loading, total emergy per volume of water, and emergy per capita).