Evaluation of 2- and 3-stage combinations of vertical and horizontal flow constructed wetlands for treating greenhouse wastewater

The adsorption characteristics of various filter media and treatment efficiency of small pilot-scale constructed wetlands (CWs) were investigated in order to design optimum CWs for treating greenhouse wastewater. Calcite was the best filter medium for the adsorption of ammonium nitrogen and phosphorus under various temperature and pH conditions. However, removal efficiency of calcite for total nitrogen (T-N) removal was low due primarily to high nitrate levels. Thus, several hybrid CWs (containing calcite as filter media) consisting of combinations of vertical flow (VF) and horizontal flow (HF) beds were evaluated for improving efficiency for T-N removal. Both 2- and 3-stage combinations of the VF and HF beds were tested. The optimum hybrid CWs was demonstrated to be a 3-stage combination of horizontal flow (HF)–vertical flow (VF)–horizontal flow (HF), which provided suitable conditions for both nitrification and denitrification, which improved removal of T-N in wastewater containing nitrate. In the HF–VF–HF 3-stage hybrid CWs, the reduction in chemical oxygen demand (COD), T-N, and total phosphorus (T-P) in the effluent were 95.1, 68.4 and 94.3%, respectively. The removal of COD, T-N and T-P in 3-stage HF–VF–HF CWs was rapid in order of VF (second stage) ≫ HF (first stage) ≫ HF (third stage), VF (second stage) ≫ HF (third stage) > HF (first stage) and VF (second stage) ≫ HF (first stage) ≫ HF (third stage), respectively.     

Releasing behavior of copper in recirculated bioreactor landfill

The purpose of this study was to determine the releasing behavior of copper in municipal solid waste (MSW) in landfill with respect to refuse and leachate as an inseparable system. Two simulated bioreactor landfills, one with leachate recirculation and the other without, were operated in room temperature for 320 days. Copper in refuse showed behaviors of staggered migration and retention, which corresponded with the degradation process of landfill obviously. The significant different amounts of Cu²⁺ leached out from refuse into leachate of two landfills were 24.74 mg and 118.53 mg after 320 days’ operation, respectively. It also reflected the releasing behavior of copper in landfill refuse at different stage accordingly. The results confirmed that the refuse in landfill had high potential of secondary pollution after closure.     

Ethanol addition as a strategy for start-up and acclimation of an AnSBBR for the treatment of landfill leachate

This study evaluated the ethanol addition as a strategy for start-up and acclimation of a pilot scale (1300 L) anaerobic sequencing batch biofilm reactor (AnSBBR) for the treatment of municipal landfill leachate with seasonal biodegradability variations. The treatment was carried out at ambient temperature (23.8 ± 2.1 °C) in the landfill area. In a first attempt, the leachate collected directly from landfill showed to be predominantly recalcitrant to anaerobic treatment and the acclimation was not possible. In a second attempt, adding ethanol to leachate, the reactor was successfully acclimated. After acclimation, without ethanol addition, the COD_Total influent ranged from 4970 to 13040 mg L^?1 and the removal efficiencies ranged from 12.1% to 70.7%. A final test was carried out increasing the ammonia and free-ammonia concentration from 2486 mgN L^?1 and 184 mgN L^?1 to 4519 mgN L^?1 and 634 mgN L^?1, respectively, with no expressive inhibition verified. The start-up strategy was found to be feasible, providing the acclimation of the biomass in the AnSBBR, and maintaining the biomass active even when the leachate was recalcitrant.     

Operation of partial nitrification to nitrite of landfill leachate and its performance with respect to different oxygen conditions

The coupled system of partial nitrification and anaerobic ammonium oxidation (Anammox) is efficient in nitrogen removal from wastewater. In this study, the effect of different oxygen concentrations on partial nitrification performance with a sequencing batch reactor (SBR) was investigated. Results indicate that, partial nitrification of landfill leachate could be successfully achieved under the 1.0–2.0 mg L⁻¹ dissolved oxygen (DO) condition after 118 d long-term operation, and that the effluent is suitable for an Anammox reactor. Further decreasing or increasing the DO concentration, however, would lead to a decay of nitrification performance. Additionally, the MLSS concentration in the reactor increased with increasing DO concentration. Respirometric assays suggest that low DO conditions (<2 mg L⁻¹) favor the ammonia-oxidizing bacteria (AOB) and significantly inhibit nitrite oxidizing bacteria (NOB) and aerobic heterotrophic bacteria (AHB); whereas high DO conditions (>3 mg L⁻¹) allow AHB to dominate and significantly inhibit AOB. Therefore, the optimal condition for partial nitrification of landfill leachate is 1.0–2.0 mg L⁻¹ DO concentration.     

Ecological effects of cow manure compost on soils contaminated by landfill leachate

The experiment was conducted to evaluate the effect of cow manure compost (CMC) application on leaching toxicity of leachate polluted soils by using Tetrahymena pyriformis (TP). Soils treated with various levels of leachate (0, 12.5 ml, 25 ml, 37.5 ml, and 50 ml leachate per 300 g soil) were amended with 0, 25 g and 50 g CMC, respectively. The results showed CMC application resulted in 7–18% lower leaching toxicity while excessive CMC has no significant benefit for decreasing leaching toxicity further. The alleviating effect of CMC on biotoxicity of soil extract was mainly attributed to either pH increase, high content of P and organic matter, or promotion on soil microbial metabolism and especially pH played an important role in alleviating effect. And the observations indicated that death rate (DR) of TP was more sensitive to leachate level respect to other biological parameters above and TP was effective as the test organism for leaching toxicity. Further studies are needed to unambiguously determine in-deep mechanism of toxicity impacts on TP posed by leachate pollutants.     

Treatment of high-strength wastewater in tropical vertical flow constructed wetlands planted with Typha angustifolia and Cyperus involucratus

The ability of vertical flow (VF) constructed wetland systems to treat high-strength (ca. 300 mg L^?1 of COD and ca. 300 mg L^?1 total-nitrogen) wastewater under tropical climatic conditions was studied during a 5-month period. Nine 0.8-m diameter experimental VF units (depth 0.6 m) were used: three units were planted with Typha angustifolia L., another three units were planted with Cyperus involucratus Rottb and three units were unplanted. Each set of units were operated at hydraulic loading rates (HLRs) of 20, 50 and 80 mm d^?1. Cyperus produced more shoots and biomass than the Typha, which was probably stressed because of lack of water. The high evapotranspirative water loss from the Cyperus systems resulted in higher effluent concentrations of COD and total-P, but the mass removal of COD did not differ significantly between planted and unplanted systems. Average mass removal rates of COD, TKN and total-P at a HLR of 80 mm d^?1 were 17.8, 15.4 and 0.69 g m^?2 d^?1. The first-order removal rate constants at a HLR of 80 mm d^?1 for COD, TKN and total-P were 49.8, 30.1 and 13.5 m year^?1, respectively, which is in the higher range of k-values reported in the literature. The oxygen transfer rates were ca. 80 g m^?2 d^?1 in the planted systems as opposed to ca. 60 g m^?2 d^?1 in the unplanted systems. The number of Nitrosomonas was two to three orders of magnitude higher in the planted systems compared to the unplanted systems. Planted systems thus had significantly higher removal rates of nitrogen and phosphorus, higher oxygen transfer rates, and higher quantities of ammonia-oxidizing bacteria. None of the systems did, however, fully nitrify the wastewater, even at low loading rates. The vertical filters did not provide sufficient contact time between the wastewater and the biofilm on the gravel medium of the filters probably because of the shallow bed depth (0.6 m) and the coarse texture of the gravel. It is concluded that vertical flow constructed wetland systems have a high capacity to treat high-strength wastewater in tropical climates. The gravel and sand matrix of the vertical filter must, however, be designed in a way so that the pulse-loaded wastewater can pass through the filter medium at a speed that will allow the water to drain before the next dose arrives whilst at the same time holding the water back long enough to allow sufficient contact with the biofilm on the filter medium.     

Denitrification capacity in response to increasing nitrate loads and decreasing organic carbon contents in injected leachate of a simulated landfill reactor

Ex situ nitrification followed by denitrification inside the landfill has been recommended to remove ammonia from leachate. The effects of increasing nitrate load and decreasing organic carbon content in the injected leachate on the denitrifying capacity of municipal solid waste (MSW) were investigated. Results showed that MSW possesses a high denitrification capacity. Nitrate reduction could be initiated within 48 h after the first addition of nitrate. Nitrate reduction rate increased with the increasing nitrate loading concentration. When the nitrate loading concentration was increased to 850 mg L^?1, nitrate reduction rate reached up to 35 mg L^?1 h^?1. Nitrite accumulation could be found after the addition of nitrate in each test. However, the maximum nitrite accumulation efficiency declined with increased nitrate load. Organic carbon played an important role in the reduction of nitrate, and both endogenous and exogenous organic materials could act as electron donors.     

Nitrogen transformation in the hybrid bioreactor landfill

The hybrid bioreactor landfill was promising in solid waste management. In the work, the nitrogen removal and nitrogen transformation in hybrid bioreactor landfill with sequencing of facultative anaerobic and aerobic conditions was explored. The result showed that the combination of facultative anaerobic and aerobic conditions in the hybrid bioreactor landfill was indeed effective in eliminating ammonia both from the leachate and the refuse thoroughly. About 72% of nitrogen was reduced from the landfilled fresh refuse through the operation of 357 days. At the end of the experiment, the concentrations of COD, ammonia, nitrate and TN in the leachate decreased to 399.2 mg l^?1, 20.6 mg N l^?1, 3.7 mg N l^?1 and 25.3 mg N l^?1, respectively.     

Electricity from landfill leachate using microbial fuel cells: Comparison with a biological aerated filter

Four experimental columns were employed in this study to investigate their performance under wastewater treatment conditions. One column was set-up as a biological aerated filter and the remaining three were set-up as microbial fuel cells (MFCs), two of which were connected to an external load whereas the third was left open circuit. The performance of the columns under several flow rates and leachate strengths was studied in terms of BOD₅ removal efficiencies and electricity generation, when a fixed resistive load was connected. Results obtained demonstrated that it is possible to generate electricity and simultaneously treat landfill leachate in MFC columns. Energy generation in MFC columns improved with increasing flow rates from 24 to 192 mL/h, while BOD₅ removal efficiency levels reached a maximum at 48 mL/h and dropped to relatively low values at higher flow rates. The maximum removal efficiencies were obtained at a loading rate of 0.81 kg BOD₅/m³ d for columns C1, C2 and C4 and 1.81 kg BOD₅/m³ d for column C3. Electrical output levels and BOD₅ concentrations at the MFC columns showed a linear relationship, which allows the system to be used as a BOD₅ sensor. Part of the BOD removal was not associated with power generation and was attributed to the presence of alternative end terminal electron acceptors and volatilisation. The MFC columns could reach the same or even higher removal efficiencies than those from the biological aerated filter with the advantage of producing energy and saving cost of aeration. To the best of the authors’ knowledge, this is the first study that compares the MFC technology with other conventional treatment systems for removing pollutants from wastewater.     

Nitrogen and phosphate mass balance in a sub-surface flow constructed wetland for treating municipal wastewater

This paper reports on the feasibility of using sub-surface horizontal flow constructed wetlands to treat municipal wastewater in Hong Kong. Two different hydraulic retention times (10-day and 5-day) and different types of treatments (with and without vegetation) were investigated. Better performance in the planted treatments was obtained in both hydraulic retention time treatments. Nutrients were better removed in treatments with plants (DOC 68% and 72%; NH₄-N 92% and 95%; TKN 65% and 62%; PO₄-P 79% and 72%; TP 67% and 52% for 10-day HRT; 5-day HRT treatments). In the unplanted treatments, negative values were achieved in the removal of phosphate in wastewater and the presence of plants could further polish the wastewater so phosphate concentrations decreased in the planted treatments. The effluent concentrations in the planted treatments meet the Inland Water A effluent standard, and they can be used in recreation park in Hong Kong (1 mg L⁻¹ of NO_x; 15 mg L⁻¹ of NH₃; 1 mg L⁻¹ of TP).     

Long-term phosphorus and nitrogen removal processes and preferential flow paths in Northern constructed peatlands

Four treatment peatlands were studied in Northern Finland in order to determine peat P, Al and Fe concentration distributions and to find removal parameters for nutrient modelling. The sites had been under loading for 10–16 years. About 20 peat samples for analyses of oxalate-extractable and total P, Al and Fe were collected from the depth 0–10 cm in each peatland. The peat P concentration ranged from 0.097 mg g^?1 to 14 mg g^?1 being 1.7 mg g^?1on average. P accumulated in preferential flow path areas. Although P concentrations were locally high, DSSP (the index of potential soil P release from peat to water) was very low in all studied peatlands, indicating that peat was not saturated by phosphorus. The results indicate that Al-based precipitation chemicals increase substantially P retention capacity of peatland and maintain a stabile P reduction in spite of varying P loads. The results also show long-term phosphorus accumulation in peatlands polishing municipal wastewater from activated sludge treatment. The regression analyses showed that k-value for N removal depends on N loading and hydraulic loading. The first-order area model together with regression analysis of the rate constant result in a good agreement between observed and calculated nitrogen concentration. The NH₄-N loading to the peatland should be below 0.10 mg m² d^?1 in order to achieve a high reduction of 70%.     

Characteristics of simultaneous organic and nutrient removal in a pilot-scale vertical submerged membrane bioreactor (VSMBR) treating municipal wastewater at various temperatures

A pilot-scale vertical submerged membrane bioreactor (VSMBR) with anoxic and oxic zones in one reactor was operated in an attempt to reduce the problems concerning effective removal of organic matter and nutrients from municipal wastewater. Source water with total chemical oxygen demand (TCOD)/total nitrogen (TN) ratio of 5.5 was treated at various temperatures (13–25 °C) over an interval of about 1 year. As a result, total suspended solid (TSS) and TCOD were removed by 100% and higher than 98%, respectively. Moreover, the average removal efficiencies of TN and total phosphorus (TP) were found to be 74% and 78% at 8 h-hydraulic retention time (HRT) and 60-days sludge retention time (SRT). Under these conditions, the specific removal rates (SRR) of TN and TP were found to be 0.093 kg N m⁻³ day⁻¹ and 0.008 kg P m⁻³ day⁻¹, and the daily production of excess sludge (DPES), 0.058 kg TSS day⁻¹.     

Experimental assessment of the influence of beam hardening filters on image quality and patient dose in volumetric 64-slice X-ray CT scanners

Beam hardening filters have long been employed in X-ray Computed Tomography (CT) to preferentially absorb soft and low-energy X-rays having no or little contribution to image formation, thus allowing the reduction of patient dose and beam hardening artefacts. In this work, we studied the influence of additional copper (Cu) and aluminium (Al) flat filters on patient dose and image quality and seek an optimum filter thickness for the GE LightSpeed VCT 64-slice CT scanner using experimental phantom measurements. Different thicknesses of Cu and Al filters (0.5–1.6 mm Cu, 0.5–4 mm Al) were installed on the scanner’s collimator. A planar phantom consisting of 13 slabs of Cu having different thicknesses was designed and scanned to assess the impact of beam filtration on contrast in the intensity domain (CT detector’s output). To assess image contrast and image noise, a cylindrical phantom consisting of a polyethylene cylinder having 16 holes filled with different concentrations of K₂HPO₄ solution mimicking different tissue types was used. The GE performance and the standard head CT dose index (CTDI) phantoms were also used to assess image resolution characterized by the modulation transfer function (MTF) and patient dose defined by the weighted CTDI. A 100 mm pencil ionization chamber was used for CTDI measurement. Finally, an optimum filter thickness was determined from an objective figure of merit (FOM) metric. The results show that the contrast is somewhat compromised with filter thickness in both the planar and cylindrical phantoms. The contrast of the K₂HPO₄ solutions in the cylindrical phantom was degraded by up to 10% for a 0.68 mm Cu filter and 6% for a 4.14 mm Al filter. It was shown that additional filters increase image noise which impaired the detectability of low density K₂HPO₄ solutions. It was found that with a 0.48 mm Cu filter the 50% MTF value is shifted by about 0.77 lp/cm compared to the case where the filter is not used. An added Cu filter with approximately 0.5 mm thickness accounts for 50% reduction in radiation-absorbed dose as measured by the weighted CTDI. The FOM results indicate that with an additional filter of 0.5 mm Cu or minimum 4 mm Al, a good compromise between image quality and patient dose is achieved for CT images acquired at tube voltages of 120 and 140 kVp. The results seem to indicate that an optimum filter for high kVp acquisitions, routinely used in cardiovascular imaging, should be 0.5 mm copper or 4 mm aluminium minimum.     

Wastewater treatment performance of a vermifilter enhancement by a converter slag–coal cinder filter

The study aimed at investigating rural domestic wastewater treatment performance through vermifilter enhancement by a converter slag–coal cinder filter. The research was carried out by column experiments in a lab scale. Results showed the average removal rate of TCOD, BOD, ammonia nitrogen (NH₄⁺-N) and phosphorus removal by the system were 78.0%, 98.4%, 90.3%, 62.4%, respectively at a hydraulic loading rate of 4 m³ m^?2 day^?1. Vermifiltration was effective for insoluble organic matter and suspended solid removal, and the converter slag–coal cinder filter played an important role in phosphorus removal. The molecular weight of particles in the influent and effluents from every unit of the system were distributed in a wide range between 0.1 kDa and 10,000 kDa with predominance of values between 10 kDa and 300 kDa; the major portion of soluble material are high MW compounds. In addition, the optimal design parameters for vermifiltration and converter slag and coal cinder filters, respectively, were studied in the experiments.     

Interstitial fluid glucose time-lag correction for real-time continuous glucose monitoring

Time lag between subcutaneous interstitial fluid and plasma glucose decreases the accuracy of real-time continuous glucose monitors. However, inverse filters can be designed to correct time lag and attenuate noise enabling the blood–glucose profile to be reconstructed in real time from continuous measurements of the interstitial-fluid glucose. We designed and tested a Wiener filter using a set of 20 sensor-glucose tracings (～30 h each) with a 1-min sample interval. Delays of 10 ± 2 min (mean ± SD) were introduced into each signal with additive Gaussian white noise (SNR = 40 dB). Performance of the filter was compared to conventional causal and non-causal seventh-order finite-impulse response (FIR) filters. Time lags introduced an error of 5.3 ± 2.7%. The error increased in the presence of noise (to 5.7 ± 2.6%) and attempts to remove the noise with conventional low-pass filtering increased the error still further (to 7.0 ± 3.5%). In contrast, the Wiener filter decreased the error attributed to time delay by ～50% in the presence of noise (from 5.7% to 2.60 ± 1.26%) and by ～75% in the absence of noise (5.3% to 1.3 ± 1%). Introducing time-lag correction without increasing sensitivity to noise can increase CGM accuracy.     

Removal of nutrients from wastewater with Canna indica L. under different vertical-flow constructed wetland conditions

Constructed wetlands are becoming increasingly popular worldwide for removing contaminants from domestic wastewater. This study investigated the removal efficiency of nitrogen (N) and phosphorus (P) from wastewater with the simulated vertical-flow constructed wetlands (VFCWs) under three different substrates (i.e., BFAS or blast furnace artificial slag, CBAS or coal burn artificial slag, and MSAS or midsized sand artificial slag), hydraulic loading rates (i.e., 7, 14, and 21 cm d^?1), and wetland operational periods (0.5, 1, and 2 years) as well as with and without planting Canna indica L. The wastewater was collected from the campus of South China Agricultural University, Guangzhou, China. Results show that the percent removal of total P (TP) and ammonium N (NH₄⁺-N) by the substrates was BFAS > CBAS > MSAS due to the high contents of Ca and Al in substrate BFAS. In contrast, the percent removal of total N (TN) by the substrates was CBAS > MSAS > BFAS due to the complicated nitrification/denitrification processes. The percent removal of nutrients by all of the substrates was TP > NH₄⁺-N > TN. About 10% more TN was removed from the wastewater after planting Canna indica L. A lower hydraulic loading rate or longer hydraulic retention time (HRT) resulted in a higher removal of TP, NH₄⁺-N, and TN because of more contacts and interactions among nutrients, substrates, and roots under the longer HRT. Removal of NO₃^?N from the simulated VFCWs is a complex process. A high concentration of NO₃^?N in the effluent was observed under the high hydraulic loading rate because more NH₄⁺-N and oxygen were available for nitrification and a shorter HRT was unfavorable for denitrification. In general, a longer operational period had a highest removal rate for nutrients in the VFCWs.     

Treatment of municipal wastewater using laterite-based constructed soil filter

The present study reports the performance of municipal wastewater treatment plant located at Mumbai, India using laterite soil-based constructed soil filter (CSF) system monitored over 17 months. The results indicated increase in dissolved oxygen levels and reduction of chemical oxygen demand (COD) from 135.4 ± 79.4 to 28.8 ± 19.5 mg/L with first order rate constant (K_d) of 0.23 h^?1. The bio-chemical oxygen demand (BOD) reduced from 92 to less than 10 mg/L with K_d of 0.35 h^?1; suspended solids reduction from mean 188 to 12–18 mg/L and turbidity reduction from mean 140 to 5.0 ± 3.4 NTU. The seasonal data showed 3.2 ± 0.9, 2.8 ± 0.4 and 2.85 ± 1.0 log order removal for total coliform, fecal coliform and heterotrophic plate count, respectively. The unique features of the system include a single unit, low HRT, high hydraulic loading, no chemicals, pretreatment and mechanical aeration, odor free, low energy requirement (0.04 kWh/m³), and green ambience.     

Holocene vegetation and hydrologic changes inferred from molecular vegetation markers in peat,Penido Vello (Galicia,Spain)

Peat molecular chemistry reflects a combination of plant input and decomposition. Both vegetation community and the degree of decomposition of plant remains are highly dependent on depth and fluctuation of the water table and thus peat organic matter (OM) chemistry reflects past hydrological conditions. Changes in hydrology according to the OM composition (by pyrolysis-gas chromatography/mass spectrometry, pyrolysis-GC/MS) in a high-resolution sampled monolith of an 8000 years old peat deposit are presented. Analysis of 18 modern vegetation species resulted in molecular markers for Erica spp., Deschampsia flexuosa, Juncus bulbosus and Carex binervis, in addition to more general markers which enabled differentiation between woody, grass and moss vegetation. Factor analysis of 106 pyrolysis products quantified for all peat samples enabled identification of mineral (Factor 1) and hydrological (Factor 2) conditions of the bog. Depth profiles of vegetation markers showed good agreement with those of the scores of both factors and enabled the identification of 14 relatively wet periods, dating to 1430–1865 AD, 930–1045 AD, 640 AD, 270–385 AD, 190–215 AD, 135 AD, 45 BC–15 AD, 260–140 BC, 640–440 BC, 1055–960 BC, 1505–1260 BC, 2300 BC, 4190–2945 BC and 5700–5205 BC, which show excellent agreement with other palaeoclimatic studies in Europe. The results emphasize the importance of high-resolution sampling, in combination with the use of multiple vegetation markers and other peat OM characteristics for a proper interpretation of a peat record.     

Pre-treatment of hospital wastewater by coagulation–flocculation and flotation

Coagulation–flocculation and flotation processes were evaluated for the pre-treatment of hospital wastewater, including the removal of 13 pharmaceutical and personal care products (PPCPs). Coagulation–flocculation assays were performed in a Jar-Test device and in a continuous pilot-scale plant. Raw hospital wastewater as well as the effluent from the continuous coagulation plant were treated in a flotation cell. Removal of total suspended solids (TSS) during pre-treatment was very effective, reaching an average removal efficiency of 92% in the combined coagulation–flotation process. Musk fragrances were eliminated to a high degree during batch coagulation–flocculation (tonalide: 83.4 ± 14.3%; galaxolide: 79.2 ± 9.9%; celestolide: 77.7 ± 16.8%), presumably due to their strong lipophilic character which promotes the interaction of these compounds with the lipid fraction of solids. For diclofenac (DCF), naproxen (NPX) and ibuprofen (IBP) maximum removals of 46%, 42% and 23%, respectively, were obtained, while the rest of PPCPs were not affected by the physico-chemical treatment. Flotation of raw wastewater led to slightly worse results compared to coagulation–flocculation, although the combined action of both improved the overall efficiency of the process. The proposed pre-treatment strategy for hospital wastewater is useful for assimilating its conventional physico-chemical characteristics to that of municipal wastewater as well as for reducing the load of some PPCPs into the sewer system.     

Synergism of natural and constructed wetlands in Beijing,China

An integrated wetland system (IWS) including constructed wetlands (CWs) and modified natural wetlands (NWs) for wastewater treatment to replenish water to wetlands located at the Beijing Wetland School (BWS) in Beijing, China, is presented in this paper. The synergistic effects of CWs and NWs on treated water quality are investigated. The IWS is proved to be an effective wastewater treatment technique and a better alternative to alleviate the water shortage for conservation of wetlands based on the monitoring data obtained from October 2007 to 2008. The results show that CWs and NWs play different roles in removing contaminants from wastewater. The COD removal efficiency in CWs is higher than that in modified NWs, whereas the modified NWs can compensate for the deficiency of CWs where a stable and sufficient rhizosphere is not fully formed in the start-up period. All removal rates of COD, TN, and TP in CWs and modified NWs vary from 50 to 70%, while the total removal rate of COD, TN, and TP in IWS is about 85–90%. The operational results show that the maximum area loading of organic pollutants in modified NWs (65 kg/ha d) is slightly higher than the empirical one (60 kg/ha d) recommended by USEPA (2000) for free water surface wetlands.