Hybrid Constructed Wetland System Research Articles

Influence of hydraulic loading rate, simulated storm events and seasonality on the treatment performance of an experimental three-stage hybrid constructed wetland system

An experimental hybrid system based on an anaerobic reactor followed by three stages of different constructed wetland configurations was evaluated when operating under a high hydraulic loading rate (HLR=0.27md−1, considering the area of the VF beds) for one year, which corresponds to four times the nominal hydraulic loading rate, with the purpose of reducing the specific area required. Moreover, in order to assess its buffer capacity, a major storm event was simulated by increasing the HLR 10 times during 1h. A tracer experiment was also performed to determine the experimental hydraulic retention time (HRT). The system consisted of a hydrolytic upflow sludge blanket (HUSB) reactor followed by two alternating 1.5m2 vertical subsurface flow, a 2m2 horizontal subsurface flow and a 2m2 free water surface constructed wetlands operating in series. The system achieved very high values of removal of solids, organic matter and nutrients (82, 93, 96 and 75% for COD, BOD5, TSS and NH4-N, respectively). Removal of PO4-P and SO42− were though fairly low, of 11 and 10%, respectively. There was a seasonal effect in the system for parameters whose removal highly depends on biodegradation, being enhanced under warmer conditions (98 and 92% removal of BOD5 and NH4-N in summer vs. 87 and 67% removal of BOD5 and NH4-N in winter). The experimental HRT of the entire system was of about 38h, which is greater than the theoretical HRT (28h). During the simulation of the storm event removal efficiencies did not vary significantly from the ones obtained under normal conditions (average of 83, 99 and 80% for COD, TSS and NH4-N removal, respectively). The system showed a very good buffer capacity coping with sharp fluctuations in flow to be treated, showing to be an adequate solution for wastewater treatment in small communities. The specific area requirement under the long-term operation showed to be as low as 2m2/PE.

Evaluation of Horizontal–Vertical Subsurface Hybrid Constructed Wetlands for Tertiary Treatment of Conventional Treatment Facilities Effluents in Developing Countries

In this study, four large pilot-scale horizontal–vertical hybrid constructed wetlands (CWs) were constructed for the tertiary treatment of effluent of North Wastewater Treatment Plant in Isfahan, Iran. The plant effluent did not meet the regulation limits of wastewater reuse for various applications (e.g., irrigation of food and non-food crops, forests and green areas, groundwater recharge, and urban reuse applications). So the hybrid CW system was set up to provide a suitable effluent for this purpose. Each hybrid unit consisted of a 100-m2 horizontal flow (HF) and a 32-m2 vertical flow (VF) subsurface CW operating in series. Three emergent plants consisting of Phragmites australis, Typha latifolia, and Arundo donax were planted in the CWs and one unit left unplanted. The filling material was fine grain from 3–7 mm. The average organic load and the average hydraulic loading rate (HLR) of the system were 15 g biochemical oxygen demand (BOD5) m−1 day−1 and 5.3 cm day−1, respectively. The k-C* first-order model constant was computed for seven physical, chemical, and microbiological parameters—BOD5, chemical oxygen demand (COD), total suspended solids (TSS), NO3-N, NH4-N, total phosphorus (TP), and fecal coliforms—based on the influent/effluent concentration data for estimation of required surface area of full-scale CWs in the future. The results of 12-month sampling showed that the hybrid HF-VF CWs are highly efficient in removing of the BOD5 (85 % medium), COD (80 % medium), TSS (79 % medium), NH4-N (78 % medium), TP (74 % medium), and fecal coliforms (99 % medium). Also, there were no significant differences between various planted hybrid CWs in removal efficiency and first-order model constant for BOD5, COD, TSS, and coliforms, nor were there significant differences between planted and unplanted CWs for these parameters. But, for nutrients, the removal efficiencies of planted CWs were higher than those of control CW during the operation time. Among the CWs, the Phragmites showed the best efficiency for removal of nutrients followed by Arundo. It was observed that the removal efficiencies in HFCWs were higher than those in VFCWs due to longer hydraulic retention time (HRT), but for coliform removal, the VFCWs showed a higher efficiency. The effluent quality met the requirements for its reuse in various applications, but bacterial contents were equal to levels that permit the reuse of effluent in the non-food crop, forest and other green area irrigation, groundwater recharge, and some urban applications with restricted public exposure. The results of this pilot-scale research study showed that the performance of a single HFCW was probably not sufficient to achieve a suitable water quality for reuse of effluents and the hybrid CWs are more efficient and feasible systems for this purpose.

The use of multi-criteria analysis for selection of technology for a household WWTP compatible with sustainable development / Zastosowanie analizy wielokryterialnej do wyboru rozwiązania technologicznego przydomowej oczyszczalni ścieków zgodnego z ideą zrównoważonego rozwoju

Abstract This paper presents the use of multi-criteria analysis as a tool that helps choosing an adequate technology for a household wastewater treatment plant. In the process of selection the criteria of sustainable development were taken into account. Five municipal mechanical-biological treatment plants were chosen for the comparative multi-criteria analysis. Different treatment technologies, such as sand filter, activated sludge, trickling filter, a hybrid system - activated sludge/trickling filter and a hybrid constructed wetland system VF-HF type (vertical and horizontal fl ow) were taken into account. The plants’ capacities were 1 m3∙d-1 (PE=8) and they all meet the environmental regulations. Additionally, a solution with a drainage system was included into the analysis. On the basis of multi-criteria analysis it was found that the preferred wastewater treatment technologies, consistent with the principles of sustainable development, were a sand filter and a hybrid constructed wetland type VF-HF. A drainage system was chosen as the best solution due to the economic criteria, however, taking into consideration the primary (ecological) criterion, employment of such systems on a larger scale disagree with the principles of sustainable development. It was found that activated sludge is the least favourable technology. The analysis showed that this technology is not compatible with the principles of sustainable development, due to a lack of proper technological stability and low reliability.

Effluent quality and reuse potential of domestic wastewater treated in a pilot-scale hybrid constructed wetland system

The study investigates treatment and reuse potential of domestic wastewater of a small community of about 30 people sequentially by anaerobic pretreatment followed by horizontal (HSSF-CW) and vertical (VSSF-CW) sub-surface flow constructed wetlands operated in series. The organic and suspended solids load to the hybrid wetland system was decreased by anaerobic pretreatment. HSSF-CW mainly removed organic matter and supported denitrification whereas VSSF-CW mainly obtained nitrification and phosphorus removal. Recirculation of the effluent increased particularly total nitrogen removal in the wetland system. The study involves evaluation of the whole system in terms of effluent quality. It was achieved on average >95% organic matter and >90% nitrogen removal in the hybrid constructed wetland system with anaerobic pretreatment at a specific wetland surface area of only about 1 m2 per person. Average mass removal rates were 21.17 gCOD/m2day, 5.58 gBOD5/m2day, 2.78 gTKN/m2day, 1.35 gTN/m2day, 0.44 gTP/m2day and 5.21 gTSS/m2day throughout the total duration of the operation. Consequently, the effluent met the regulations for discharge limits for organic matter and suspended solids. COD and TN concentrations decreased to below 20 mg/L in the effluent. It was also shown that effluent of the system could be reused for irrigation if it is disinfected properly.

Full-scale hybrid constructed wetlands incorporated with an initial anaerobic stage for domestic wastewater treatment in a drinking water catchment area

This study involves sequential treatment of domestic wastewater by anaerobic reactors followed by horizontal (HSSF-CW) and vertical (VSSF-CW) subsurface flow-constructed wetlands. Two full-scale systems constructed in two villages were operated in order to treat domestic wastewaters of about 2,000 and 500 inhabitants. Anaerobic treatment of domestic wastewater served as a pretreatment step before the constructed wetland (CW) systems. Anaerobic pretreatment was performed by an upflow anaerobic sludge bed reactor or an anaerobic baffled reactor. Anaerobically pretreated wastewater was first introduced into parallel HSSF-CWs and then parallel VSSF-CWs before being discharged. Efficient treatment of wastewaters of the two villages was particularly important since they are located in the watershed of a drinking water reservoir. The treatment efficiencies of systems were 88 and 83% for chemical oxygen demand, 89 and 81% for BOD5, 57 and 39% for total nitrogen, 55 and 53% for total phosphorus, 94 and 90% for total suspended solids removal on average, respectively, in Balcik and Orucoglu villages. The effluent concentrations met the discharge limits. The study showed that hybrid CW system with anaerobic pretreatment is an effective method to treat domestic wastewaters of small communities with populations below 2,000.

Community Based Sewage Treatment through Hybrid Constructed Wetlands System for Improved Heath & Hygiene and for Enhanced Agriculture Productivity / Livelihood Generation in Rural Water Scarce Environments-Pakistan

World over, fresh water scarcity problems are growing in scope & complexity to multiple factors, like population growth, climatic impacts, excessive water uses pattern in agriculture. A substantial quantum of treated wastewater , can be made available through constructed wetlands, which can supplement the fresh water scarcity. Almost, 80 % of the total generated raw sewage is being discharged into water bodies or being used for agriculture purposes, specially for vegetable farming, which contributes towards fresh water sources and food chain contamination. Centralized mechanical types of wastewater treatment plants are in use which is capital and recurring costs intensive. Resultantly, due to lack of sufficient recurring finances and energy shortages, these sewage treatment plants become non-operational and un-manageable. Moreover, huge centralized sewage treatment plants are difficult to manage due to longer chain of wastewater collection system and inflexibility of reuse of treated water in the areas of its generation. Therefore, keeping in view these obvious impediments, it was envisaged to plan & implement community based constructed wetlands system for sewage treatment, based on bio and phyto-remediation processes at village Chattal, district Chakwal (an arid area) which is functioning well and being sustained from selling the treated water to farmers and harvesting the various aquatic plants. Temporal analysis was carried out for verification of treatment system efficiency, whereby, monthly wastewater samples were collected at Inlet point (treated water reservoir) and got analyzed for Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD) from PCRWR-Islamabad. Analysis report showed significant reduction of COD & BOD i.e. 86.1% & 91.4% respectively which are under permissible limits of Pak-EPA. Aesthetic value of treated water is remarkably improved after treatment as turbidity reduced from 15 NTU to 2 NTU. Detailed Health survey was carried out at village Chattal, to ascertain, the intervention efficiency. The result showed significant reduction in diarrheal & Hepatitis diseases i.e. 92.5% & 40% respectively and substantial improvements was observed in socio-economic, biodiversity and health & environment conditions of the rural population of village Chattal. Pakistan- the study area. This model will prove to be equally good in the rural environments of developing countries, especially in South Asia and Africa.

Temperature influence on nitrogen removal in a hybrid constructed wetland system in Northern Italy

The objective of this research was to investigate the efficiency and seasonal performance of a full-scale hybrid constructed wetland system (HCW) in reducing total nitrogen (TN), ammonia nitrogen (NH4-N) and nitrate nitrogen (NO3-N). HCW with a total area of about 130m2 and hydraulic load of 2m3/day was composed of three subsurface flow vertical systems (VF), working in parallel and one horizontal (HF) connected in series. The system was loaded daily with synthetic wastewater having an average concentration of TN of 250mg/L (about 125mg/L of NH4-N and 125mg/L of NO3-N). Water samples were collected and analyzed from May to July 2011 and from January 2012 to July 2012. Variations were observed in nutrient removal performance related to temperature.During the whole monitoring period median reduction efficiency (RE) in the HCW was TN 95%, NH4-N 95% and NO3-N 93%, although three sub-periods characterized by different performances have been observed. During the first period (from May to July 2011) the RE was positive for the three nitrogen forms considered, whereas from January to the end of March 2012 the RE was lower, particularly for TN and NO3-N. From April 2012, when the temperature rose above 14.8°C, there was an increase in the performance that reached the 2011 values.Internal production of NO3-N was observed, mainly in the VF systems between January and March 2012. The median removals of mass pollutants per m2 of HCW per day were TN 3.1g/m2/d, NH4-N 1.5g/m2/d, NO3-N 1.5g/m2/d. Segmented regression analysis identified a breakpoint at 14.2°C for wastewater temperature that caused variations in TN and NO3-N concentration reduction performances. According to this approach the abatement was always positively correlated with temperature, but different regression slopes were obtained below and above the breakpoint. In particular, with lower temperature the abatement of NO3-N and TN increased by 1.7 and 2.0% per °C of temperature increase; with temperature higher than 14.2°C the increase in abatement due to increased temperature was sharper, especially for NO3-N.

Emerging organic contaminant removal in a full-scale hybrid constructed wetland system for wastewater treatment and reuse

A full-scale hybrid constructed wetland (CW) system based on three stages of different wetlands configurations showed to be a very robust ecotechnology for domestic wastewater treatment and reuse in small communities. It consisted of a 317-m2 vertical subsurface flow (VF), a 229-m2 horizontal subsurface flow (HF), and a 240-m2 free water surface (FWS) CWs operating in series. VF and HF wetlands were planted with Phragmites australis and the FWS contained a mixture of plant species. An excellent overall treatment performance was exhibited on the elimination of conventional water quality parameters (98–99% average removal efficiency for TSS, BOD5 and NH4–N; n=8), and its final effluent proved to comply with existing Spanish regulations for various reuse applications. The removal of studied emerging contaminants, which included various pharmaceuticals, personal care products and endocrine disruptors, was also very high (above 80% for all compounds), being compound dependent (n=8). The high rates were achieved due to high temperatures as well as the differing existing physico-chemical conditions occurring at different CW configurations, which would allow for the combination and synergy of various abiotic/biotic removal mechanisms to occur (e.g. biodegradation, sorption, volatilization, hydrolysis, photodegradation). While aerobic metabolic pathways and solids retention are enhanced in the VF bed, other removal mechanisms such as anaerobic biodegradation and sorption would predominate in the HF bed. At last, photodegradation through direct sunlight exposure, and less importantly, sorption onto organic matter, seem to take an active part in organic contaminant removal in the FWS wetland.

Evaluation of a hybrid constructed wetland system for treating urban stormwater runoff

This study developed hybrid constructed wetlands (CWs) for treatment of urban stormwater runoff pollutants. Hybrid CWs applied at narrow sections in urban areas are typically small and modular in type. Several treatment mechanisms were occurring in the hybrid system to treat high level of pollutant mass loading from urban stormwater runoff. A small scale hybrid CW comprised of a sedimentation tank, free water surface (FWS) CW, and horizontal sub-surface flow (HSSF) CW, was studied. A total of 10 test runs were simulated in the hybrid CW since July 2011–November 2012. Based on the results, almost 51–78% reduction in pollutants such as TSS, COD, TN, TP, and total heavy metals (Fe, Cu, and Zn) was achieved after passing the first and second units of the hybrid CW (i.e. sedimentation tank and FWS CW). Finally, additional 9–25% reduction of these pollutants was obtained as they went through the HSSF CW. Using normalized pollutant concentration with respect to the facility length, the appropriate size of hybrid CWs was determined to be at least 2 m. Comparing the removal efficiencies of the two types of hybrid CW system (i.e. reed and iris combination in Type A; and reed and cattail combination in Type B) similar results were obtained.

Attenuation of emerging organic contaminants in a hybrid constructed wetland system under different hydraulic loading rates and their associated toxicological effects in wastewater

The capacity of a hybrid constructed wetland (CW) system consisting of two vertical flow (VF) CWs working alternatively (3m2), one horizontal flow (HF) CW (2m2) and one surface flow (FWS) CW (2m2) in series to eliminate 13 emerging organic contaminants (EOCs) under three different hydraulic loading rates (HLRs) (0.06, 0.13 and 0.18m d−1 considering the area of the two VF beds) was studied through a continuous injection experiment. General toxicity, dioxin-like activity, antimicrobial activity and estrogenicity were also measured under the highest hydraulic loading rate. The hybrid system was highly efficient on the removal of total injected EOCs (except for antibiotics, 43±32%) at all three HLRs (87±10%). The removal efficiency in the hybrid CW system showed to decrease as the HLR increased for most compounds. The VF wetlands removed most of the injected EOCs more efficiently than the other two CWs, which was attributable to the predominant aerobic degradation pathways of the VF beds (70±21%). General toxicity was reduced up to 90% by the VF beds. Estrogenicity and dioxin-like activity were similarly reduced by the VF and the HF wetlands, whereas antimicrobial activity was mainly removed by the FWS wetland. Bearing this in mind, this injection study has demonstrated that the use of hybrid CW systems is a suitable wastewater technology for removing EOCs and toxicity even at high HLRs.

Three-stage hybrid constructed wetland system for wastewater treatment and reuse in warm climate regions

An experimental hybrid constructed wetland system consisting of 3 stages of different wetland configurations (i.e. two vertical flow beds (1.5m2 each) alternating feed-rest cycles followed by a horizontal subsurface flow (2m2) and a free water surface (2m2) wetlands in series) and the quality of its final effluent were evaluated for about one year. Mean overall removal rates were as 97% TSS, 78% COD, 91% BOD5, 94% NH4-N, 46% TN and 4% PO4-P. Vertical flow beds achieved high organic matter retention (77% BOD5) and great nitrification capacity (74% NH4-N removal). Although horizontal and free water surface wetlands accomplished little denitrification, they enabled water disinfection to produce an effluent suitable for various reuse applications. Authors suggest partial bypass from the Imhoff tank to the horizontal subsurface flow wetland so as to provide a carbon source to promote denitrification. The treatment system performed equally well in terms of organic matter and ammonium removal both in warm and cold seasons. However, reduced nitrate retention took place in horizontal and free water surface wetlands in the cold season, presumably due to low denitrification activity at low water temperatures. In general, the three-stage hybrid constructed wetland system has proven to constitute an appropriate ecotechnology for wastewater treatment and reuse in small communities of warm climate areas.

Design and performance of hybrid constructed wetland systems for high-content wastewater treatment in the cold climate of Hokkaido, northern Japan

The performance of six multistage hybrid constructed wetland systems was evaluated. The systems were designed to treat four kinds of high-content wastewater: dairy wastewater (three systems, average inflow content 2,400-5,000 mg·COD l(-1), 3-6 years of operation); pig farm wastewater, including liquid food washing wastewater (one system, 9,500 mg·COD l(-1), 3 years); potato starch processing wastewater (one system, 20,000-60,000 mg·COD l(-1), 3 years); and wastewater containing pig farm swine urine (one system, 6,600 mg·COD l(-1), 2.8 years) (COD = chemical oxygen demand). The systems contained three or four vertical (V) flow beds with self-priming siphons and surface partitions and no or one horizontal (H) flow bed (three to five beds). In some V flow beds, treated effluents were recirculated (Vr) through the inlet to improve performance. Mean annual temperature was 5-8 °C at all locations. To overcome clogging due to the high load in a cold climate, we applied a safety bypass structure and floating cover material to the V flow beds. Calculated average oxygen transfer rates (OTRs) increased proportionally with the influent load, and the OTR value was Vr > V> H. The relations of load-OTR, COD-ammonium, and a Arrhenius temperature-dependent equation enable the basic design of a reed bed system.

A novel biofilm carrier for pollutant removal in a constructed wetland based on waste rubber tire chips

The increasing number of waste tires has posed a serious threat to environmental protection and public health efforts in recent years. Waste rubber tire chips (WRTCs) are introduced as a novel media and biofilm carrier of subsurface flow (SSF) constructed wetland (CW), which is combined with free water surface (FWS) CW to form a hybrid experimental system. Two parallel hybrid CW systems are used: a control CW system uses a SSF CW with a gravel bed while WRTC is the SSF media for the other hybrid CW system. Comparing the experimental results of hybrid CWs with those of WRTC bed and gravel bed reveals that withered vegetation does not significantly influence the biochemical oxygen demand (BOD) removal performances for individual CWs or hybrid CW systems. However, withered vegetation deteriorates the removal performance of ammonia-nitrogen (NH3-N). Regrowing vegetation restores the CW ability of gravel SSF CW to remove NH3-N. The original vegetation of WRTC SSF CW, reeds, is dead in the winter. Some new superior vegetations, barnyard grass and globose bead hat-sedge make a removal performance comparable to that of gravel bed SSF CW. Owing to some steel belts connected to WRTC, iron ions are naturally released into the SSF CW and increase nitrate average removal rates of gravel bed SSF CW, −13.1%, to that of WRTC bed SSF CW, 62.2%. The hybrid CW with WRTC SSF CW is nearly twice the nitrate removal rate of the hybrid CW system with gravel SSF CW. As for total phosphorus (TP) removal performance, the average removal rates are 10.0% and 39.9% for gravel SSF CW and WRTC SSF CW, respectively. Moreover, the TP average removal rate of WRTC hybrid CW, 53.4%, is superior to that of gravel hybrid CW, 27.2%.

Effects of load fluctuations on treatment potential of a hybrid sub-surface flow constructed wetland treating milking parlor waste water

A hybrid sub-surface constructed wetland (CW) system consisting of 2 gravel filled vertical sub-surface (VFa & VFb) beds, each 160 m2 in size planted with Phragmites australis and a sand filled horizontal sub-surface (HF) bed, 336 m2 in size, planted with rice was operated from 2007 to 2010 for treating milking parlor waste water in Hokkaido, Japan. Hybrid CW system received huge fluctuations in average yearly inlet loads for TSS (526.0–1259mgL−1 & 2.7–9.0gm−2d−1), BOD5 (1,080–2,114mgL−1 & 8.4–14.4gm−2d−1), COD(1,962–7,085mgL−1 & 14.5–50.0gm−2d−1), TN (116.0–243.0mgL−1 & 0.8–1.6gm−2d−1), NH4-N (54.0–90.0mgL−1 & 0.40–0.64gm−2d−1), TC (1,022–2,215mgL−1 & 6.0–15.1gm−2d−1), TP (15.3–41.7mgL−1 & 0.11–0.28gm−2d−1) during study period. Average yearly purification and removal rates were least fluctuated for TSS (95.7–99.4%); moderately for BOD5 (86.1–95.7%), COD(87.5–96.1%) and TC (79.5–91.3%); highly for TN (72.6–90.6%), NH4-N (62.9–85.3%) and TP (64.8–87.2%). A sharp decrease in TP purification and removal rates were observed in 2008 due to sharp decrease in influent TP concentration in 2008 compared to 2007. OTR values for VF(a), VF(b), HF bed and total system were observed as 21.7, 19.3, 4.8 and 12.3gO2m−2d−1 respectively. Average k value of hybrid CW system for BOD5, TN, NH4-N and TP during study period were 7.0±1.8, 7.4±3.3, 5.6±4.1 and 4.9±2.0myr−1 respectively.Average concentration of TSS, TP, TN and NH4-N in the final effluent for all years were below the discharge limit value of: 150mgL−1 for TSS; 8mgL−1 for TP, 60mgL−1 for TN and NH4-N. However, average BOD5 and COD concentrations could not meet the discharge limit value of 120mgL−1 during 2007 and 2008.

Retention and distribution of Cu, Pb, Cr, and Zn in a full-scale hybrid constructed wetland receiving municipal sewage

This study was conducted to investigate the retention and distribution of Cu, Pb, Cr, and Zn in a hybrid constructed wetland (CW) that consists of both vertical baffled flow wetlands (VBFWs) and horizontal subsurface flow wetlands (HSSFs) with unique flow regimes and oxygen distribution. The heavy metal concentrations in water, sediments, and plant tissues in the hybrid CW were analysed. The removal of heavy metals from the water stream in the monitoring period was not statistically significant. Metal concentrations in the sediments generally decreased along the wastewater treatment process. The reductive anaerobic condition in the VBFW may promote the sulphate reduction and form highly insoluble Cu, Pb, and Zn sulphides, resulting in the higher concentration of the bivalent cations in the VBFW sediments than the corresponding values in the HSSF; however, the aerobic and anoxic environments in the HSSF enhanced the removal of Cr with the co-precipitation of iron and manganese oxides, and their hydroxides. Metal concentrations in plant tissues were not significantly influenced by the concentrations in sediments, while roots contained statistically higher metal concentrations than stems and leaves. The sediments stored 94.01, 86.31, 95.85, and 89.51% of the total Cu, Pb, Cr, and Zn retained in the hybrid CW system, respectively, while only small fractions (<10%) were accumulated in the harvestable macrophyte tissues. It is important to clean not only the accessible sediments in free water surface tank and ponds but also the embedded sediments in vegetated beds for the sustainable removal of heavy metals.

Nutrient Removal from Polluted River Water by Combining Vertical and Horizontal Subsurface Flow Constructed Wetlands

A lab-scale hybrid constructed wetland system was constructed to purify polluted river water. The system was composed of a first stage of the vertical subsurface flow filter, followed by a second stage of horizontal subsurface flow bed. Both beds used furnace slag with a size of 4-60 mm for the main layer. The system was continuously fed. Different depths of unsaturated layer (0 cm, 15 cm and 30 cm) in vertical filter were tested. The unsaturated layer of 30 cm in vertical filter presented the most effective ammonia removal of 89.1%, while lowest NO3--N removal rate of 74.1% for the system. High TN removal efficiencies (77.3%-81.0%) could be observed during operation of three depths. The removals of COD and TP were in the range of 97.1%-98.4% and 76.4%-88.9%, respectively.

A comparative estimate of life cycle greenhouse gas emissions from two types of constructed wetlands in Tianjin, China

Constructed wetlands (CWs) are widely used for wastewater treatment, but may also be sources of greenhouse gas (GHG). This study focuses on comparing the GHG emissions from a vertical flow constructed wetland (VFCW) and a horizontal flow constructed wetland (HFCW) in the city of Tianjin, China. Two methods are used in this paper to estimate the indirect and direct GHG emissions. It is found that the VFCW emits 0.09, 1.34, and 3.31 kg equivalent CO2 (CO2 Eq.) to remove 1.00 m3 wastewater, 1.00 kg COD, and 1.00 kg BOD in the studied life cycle, respectively, in contrast to 0.18, 2.10, and 5.42 kg CO2 Eq. for the HFCW. The results indicate that the adoption of VFCW is a more effective option with respect to GHG emissions when treating the same amount of pollutants. In addition, the operation phase which includes GHG emissions from water treatment process and energy consumption for pump dominates the GHG emissions. For different kinds of GHG from CWs, CO2 dominates the influence on climate change. The CH4 and N2O emissions should also deserve more attention due to their greater global warming potential. This paper further suggests that GHG emissions can be mitigated in the design, construction, and operation stages through some feasible measures. It would reduce GHG emissions in CWs by adopting hybrid CW system (e.g. HF–VF or VF–HF) or choosing suitable plant species which can mitigate GHG emissions. In addition, aeration could contribute to the control of GHG emissions from CWs.

Integrated treatment of combined sewer wastewater and stormwater in a hybrid constructed wetland system in southern Spain and its further reuse

An integrated pilot-scale treatment system consisting of a vertical subsurface flow (317m2), a horizontal subsurface flow (229m2) and a free water surface (240m2) constructed wetlands operating in series for the treatment of a combined sewer effluent was put into operation and monitored over a period of about 1.5 years. The goal of the treatment system was to provide effluents suitable for various water reuse applications. Moreover, the influence of pulses of high flow resulting from several rain events over the treatment performance of the system was evaluated. An intensive sampling campaign was also carried out following an intense storm (45mm in one-hour span) to have a further insight into the characteristics of the inflowing water at the early part of it or so-called ‘first-flush’. Results under dry weather conditions showed a good performance on the removal of BOD5, COD and TSS taking place already in the vertical flow wetland (94, 85 and 90%, respectively). A high removal of total nitrogen occurred also in the vertical flow wetland (66%) suggesting both nitrification and denitrification to take place, presumably due to the existence of both aerobic and anoxic microenvironments within the bed. Removal of Escherichia coli along the treatment system was of almost 5log units. To this respect, the horizontal flow and free water surface wetlands proved to be crucial treatment units to achieve a water quality suitable for further reuse (e.g. recharge of aquifers by percolation through the ground, silviculture and irrigation of green areas non accessible to the public). Although the occurrence of the storm event caused a prompt raise of COD and TSS within the first 30min of rainfall (868 and 764mgL−1, respectively), it was soon followed by a dilution effect. In general the storm events did not jeopardize the correct functioning of the system, proving its robustness for the treatment of a combined sewer effluent.

Variation of dissolved oxygen and redox potential and their correlation with microbial population along a novel horizontal subsurface flow wetland

Aims: This study was conducted to evaluate the performance of a novel horizontal subsurface flow wetland (HSFW) in naturally improving the dissolved oxygen (DO) and the impact on redox condition, microbial activity and the nitrogen removal in the HSFW bed. Materials and methods: The HSFW, equipped with cascaded natural aeration ditches (NADs), was the second stage of a hybrid constructed wetland (CW) after vertical-baffled flow wetland beds. The performances of the HSFW for organics and nitrogen removal in a full-scale hybrid CW system treating municipal wastewater for more than three years have been analysed. The spatial distributions of the oxidation-reduction potential (ORP), DO, microbial population density and specific oxygen uptake rate were determined, and their correlations were analysed in one selected section of the HSFW bed. Results: A 7-m-long shallow NAD increased the DO concentration from 0.28 mg O2 l−1 to 3.80 mg O2 l−1 and the ORP from+37.3 mV to+247.7 mV, creating an aerobic zone with a hydraulic retention time (HRT) of 0.5 h and an anoxic zone of another 0.5 h in series in the subsequent wetland bed. For the whole HSFW with three NADs, the macro aerobic and anoxic environment with a total HRT of 3 h can be created. Conclusions: The unique DO distribution in HSFW may contribute to an optimum environment for partial nitrification and anammox, and obtain a high performance for nitrogen removal. Correlation analysis showed that the microbial activity in the HSFW relied obviously on the redox condition.

Treatment of tannery wastewater in a pilot-scale hybrid constructed wetland system in Bangladesh

This paper reports the pollutant removal performances of a hybrid wetland system in Bangladesh for the treatment of a tannery wastewater. The system consisted of three treatment stages: a subsurface vertical flow (VF) wetland, followed by a horizontal flow (HF) and a VF wetland. The wetlands were planted with common reed (Phragmites australis), but employed different media, including organic coco-peat, cupola slag and pea gravel. In the first stage, experimental results demonstrated significant removal of ammonia (52%), nitrate (54%), BOD (78%), and COD (56%) under high organics loading rate (690gCODm−2d−1); simultaneous nitrification, denitrification, and organics degradation were attributed to the unique characteristics of the coco-peat media, which allowed greater atmospheric oxygen transfer for nitrification and organic degradation, and supply of organic carbon for denitrification. The second stage HF wetland produced an average PO4 removal of 61%, primarily due to adsorption by the iron-rich cupola slag media. In the third treatment stage, which was filled with gravel media, further BOD removal (78%) from the tannery wastewater depleted organic carbon, causing the accumulation of NO3 in the wastewater. Overall, the average percentage removals of NH3–N, NO3–N, BOD, COD, and PO4 were 86%, 50%, 98%, 98% and 87%, respectively, across the whole hybrid system. The results provided a strong evidence to support widespread research and application of the constructed wetland as a low-cost, energy-efficient, wastewater treatment technology in Bangladesh.