Free Water Surface Constructed Wetlands Research Articles

Fuzzy logic models for BOD removal prediction in free-water surface constructed wetlands

Fuzzy logic-based methods have been recently applied to environmental problems, demonstrating appropriateness to address imprecise data. A methodology, based on fuzzy inference systems (FIS) is presented, in an effort to assess organic matter removal efficiency in free-water surface (FWS) constructed wetlands (CWs). A fuzzy model was developed and is validated using experimental data collected in a two-year period in five pilot-scale FWS CW units. The CWs differed in plan view shape, soil type of the substrate material and plant species, and operated under four different hydraulic residence times (HRTs) at various ambient conditions. Model predictions showed good agreement with the experimental data. An effort was also made to collect data from the literature and verify the model using independent data from various other CWs of different settings and operating conditions. The proposed methodology seems to be a satisfactory modeling tool to be used in predicting FWS CW performance.

The use of free water surface constructed wetland to treat the eutrophicated waters of lake L’Albufera de Valencia (Spain)

Three free water surface constructed wetlands (FWSCWs) have been built in the border of the Lake L’Albufera de Valencia (Valencia, Spain). This lake is the emblematic element of one of the most important wetlands in Spain, L’Albufera de Valencia Natural Park, and it is highly eutrophicated. The function of the set of CWs (9ha) is treating the eutrophic water from the lake with the objective of reducing the phytoplankton population and nutrients. The treatment wetlands named as FG and fp are comprised of three basins in a series, while the last, F4, consists of a single cell. During the first 2 years of operation, the inflow from lake was gradually increased from 0.01m3s−1 (April 2009) to 0.13m3s−1 (December 2010) with the goal of establishing the maximum hydraulic loading rate (HLR) and finding the highest removal efficiency. Input concentrations of different water quality variables studied showed a high variability. The inflow contained 8.80–94mgl−1 TSS, 0.16–1.13mgl−1 TP, 1–17.30mgl−1 TN, 0.13–13.10mg Nl−1 DIN, 0.10–11.50mg NO3−-Nl−1, and 3.34–257.03μgl−1 Chl a. The best removal results for these parameters were obtained in the FG wetland, where the average mass removal efficiencies were 75% TSS, 65% TP, 52% TN, 61% DIN, 58% NO3−-N, and 46% Chl a. In the set of constructed wetlands the removal rates increased with the hydraulic load rate for TSS and TP but neither for nitrogen species nor Chl a; for these variables the input concentrations are a key factor in removal. For instance, mean removal rate for nitrate is 101mg Nm−2d−1 but values higher than 400mg Nm−2d−1 were obtained when input concentrations were about 7mg NO3−-Nl−1. Values of first-order constant aerial rate (kA) have been obtained for all variables. The corresponding values for nitrogen species and total phosphorus are higher than obtained in previous studies but the value kA value for TSS is low (94.9myear−1) owing to the eutrophic characteristics of water and a kA value for phytoplankton-Chl a of 65.1myear−1 is introduced. The management of CWs implies the harvest of vegetation, not for remove nitrogen because nitrification–denitrification processes reduce the 83.3% of TN that enters, but for the phosphorus, limiting nutrient in the Lake L’Albufera, that now is accumulated in plants and soils but could be sent back in several years.

비점오염물질 저감을 위한 주암호 생태습지의 수생태학적 효율 평가

비점오염원 저감을 위해 설치된 주암호 생태습지의 수질정화효율을 평가하기 위하여 시스템별 및 시기별 오염물질의 함량과 처리효율을 조사하였다. 유입원수의 BOD, COD, SS, T-N 및 T-P의 함량은 각각 0.20~0.91, 1.24~8.00, 0.6~8.6, 0.04~2.50 및 <TEX>$0.001{\sim}0.685mg\;L^{-1}$</TEX> 범위로 나타났다. 주암호 생태습지 유입수의 대부분이 현행 오염물질 수질기준을 초과하지 않은 상태로 유입되었지만 비점오염원이 많이 유입되는 특정 시기 (장마철)에는 높은 오염물질 함량을 나타내었다. 시기별로는 전반적으로 여름철에 유입원수의 영양염류의 유입이 다른 시기에 비해 높은 경향이었다. 전반적으로 C 시스템이 오염물질의 처리효율이 가장 높은 경향이었다. A 시스템의 습지들은 대부분 겨풀이 우점하고 있었으며 B 시스템의 습지들은 겨풀과 연꽃이 우점하고 있었다. C 시스템의 습지들은 겨풀, 수련 및 부들이 우점하고 있었다. 주암호 생태습지는 오염물질의 처리능이 전반적으로 안정화 상태에 도달하지 못한 것으로 판단되며, 특히 겨풀 및 물 참새피 등 식물교란종의 습지 내 침투로 인하여 습지의 수질정화효율이 전반적으로 낮았다. 따라서 본 연구결과로부터 조성초기 인공습지는 식생의 발달 여부가 수질의 안정화와 습지의 수생태학적 역할을 증대시키는데 중요한 역할을 하는 것으로 판단된다. To reduce non-point source pollutants in Juam Lake eco-wetlands, purification efficiencies of pollutants were investigated at three different systems. The constructed wetlands (CWs) consisted of A system, B system and C system. A system consisted of <TEX>$1^{st}$</TEX> free water surface (FWS) CW, <TEX>$2^{nd}$</TEX> FWS CW, <TEX>$3^{rd}$</TEX> FWS CW, <TEX>$4^{th}$</TEX> subsurface flow (SSF) CW and <TEX>$5^{th}$</TEX> SSF CW. B system consisted of <TEX>$1^{st}$</TEX> FWS CW, <TEX>$2^{nd}$</TEX> FWS CW, <TEX>$3^{rd}$</TEX> FWS CW, <TEX>$4^{th}$</TEX> FWS CW and <TEX>$5^{th}$</TEX> SSF CW. C system consisted of <TEX>$1^{st}$</TEX> FWS CW, <TEX>$2^{nd}$</TEX> FWS CW, <TEX>$3^{rd}$</TEX> FWS CW, <TEX>$4^{th}$</TEX> FWS CW and <TEX>$5^{th}$</TEX> SSF CW. The concentrations of BOD, COD, SS, T-N and T-P in inflow ranged 0.20 ~ 0.91, 1.24 ~ 8.00, 0.60 ~ 8.60, 0.04 ~ 2.50 and <TEX>$0.001{\sim}0.685mg\;L^{-1}$</TEX> from March to October in 2011, respectively. Removal rates of BOD, SS, T-N and T-P were high in Autumn, Spring, Spring and Summer, respectively. In A system, <TEX>$1^{st}$</TEX> FWS CW, <TEX>$2^{nd}$</TEX> FWS CW and <TEX>$3^{rd}$</TEX> FWS CW were dominated by Leersia oryzoides. In B system, <TEX>$1^{st}$</TEX> FWS CW, <TEX>$3^{rd}$</TEX> FWS CW and <TEX>$4^{th}$</TEX> FWS CW were dominated by Leersia oryzoides. In C system, <TEX>$2^{nd}$</TEX> FWS CW and <TEX>$3^{rd}$</TEX> FWS CW were dominated by Nymphaea teragona.

비점오염원 처리를 위한 자유수면형 인공습지에서 수생식물의 영양염류 흡수특성 평가

본 연구는 비점오염원 처리를 위한 자유수면형 인공습지인 복내 바이오파크 인공습지에서 수생식물에 의한 영양염류의 흡수특성을 평가하고자 하였다. 복내 바이오파크 인공습지내 주요 우점종은 달뿌리풀, 수련, 부들, 갈대 및 줄이었으며 최대건물생산량을 보인 8월의 주요 우점식생의 한 주당 건물생산량은 부들(54.27 g/plant) > 달뿌리풀(44.30 g/plant) <TEX>${\geqq}$</TEX> 갈대(39.60 g/plant) <TEX>${\geqq}$</TEX> 줄(37.80 g/plant) <TEX>${\fallingdotseq}$</TEX> 수련(36.75 g/plant) 순으로 높았다. 복내 바이오파크 인공습지내 수생식물의 질소 함량은 지상부의 경우 달뿌리풀, 수련, 부들, 갈대 및 줄이 각각 1.80~2.06%, 1.94~2.14%, 2.07~2.57%, 2.20~2.33% 및 2.20~2.33% 범위로 부들이 다른 수생식물에 비해 약간 높았으나 시기별로 큰 차이 없었으며 지하부의 질소 함�c도 이와 유사한 경향이었다. 복내 바이오파크 인공습지내수생식물의 인 함량은 지상부에서는 달뿌리풀(9400~9900 mg/kg 범위) 및 지하부에서는 줄(4964~6452 mg/kg 범위)이 다른 수생식물에 비해 약간 높았으나 시기에 따른 수생식물의 인 함량은 큰 차이 없이 비슷하였다. 복내 바이오파크 인공습지내 수생식물의 최대 질소 흡수량은 8월에 달뿌리 풀이 773 mg/plant, 수련이 625 mg/plant, 부들이 1206 mg/plant, 갈대가 754 mg/plant 및 줄이 768 mg/plant 이었다. 수생식물의 최대 인 흡수량은 8월에 달뿌리풀이 397 mg/plant, 수련이 177 mg/plant, 부들이 411 mg/plant, 갈대가 261 mg/plant 및 줄이 229 mg/plant이었다. 복내 바이오파크 인공습지내 수생식물 중 부들의 영양염류 흡수량이 가장 많았다. 이상의 결과는 향후 비점오염원 처리를 위한 인공습지 시공시 습지특성에 맞는 최적의 수생식물을 선정하는데 활용될 수 있을 것이다. BACKGROUND: Generally, water plants may play an important role in nutrients(N, P) removal in constructed wetlands(CWs). Previous studies considered nutrients uptake by water plants in various CWs for treating point source pollution. On the other hand, few studies considered nutrients uptake by water plants in free water surface(FWS) CWs for treating non-point source pollution. METHODS AND RESULTS: To investigate characteristics of nutrient uptake by water plants in FWS CWs, dry weights, nutrients content and nutrients uptake by water plants were investigated from April, 2008 to October, 2008. Dominance plants were Phragmites japonica STEUD (PHRJA), Nymphaea tetragona ANGUSTA(NTMTE), Typha orientalis PRESL(TYHOR), Phragmites communis TRINIUS(PHRCO) and Zizanis latifolia TURCZ(ZIZLA) in FWS CWs. The dry weights of water plants in August were higher in the order of TYHOR(54.27 g/plant) > PHRJA(44.30 g/plant) <TEX>${\geqq}$</TEX> PHRCO(39.60 g/plant) <TEX>${\geqq}$</TEX> ZIZLA(37.80 g/plant) <TEX>${\fallingdotseq}$</TEX> NTMTE(36.75 g/plant). The T-N and T-P contents by water plants were not significantly differences regardless of cultivation period. The maximum amount of T-N uptake by water plants in August were 773 mg/plant for PHRJA, 625 mg/plant for NTMTE, 1206 mg/plant for TYHOR, 754 mg/plant for PHRCO and 768 mg/plant for ZIZLA. The maximum amounts of T-P uptake by PHRJA, NTMTE, TYHOR, PHRCO and ZIZLA were 397, 177, 411, 261 and 229 mg/plant in August, respectively. CONCLUSION(s): The results of this study suggest that optimum water plant was Typha orientalis PRESL in free water surface constructed wetlands.

Genetic potential for N 2O emissions from the sediment of a free water surface constructed wetland

Removal of nitrogen is a key aspect in the functioning of constructed wetlands. However, incomplete denitrification may result in the net emission of the greenhouse gas nitrous oxide (N 2O) resulting in an undesired effect of a system supposed to provide an ecosystem service. In this work we evaluated the genetic potential for N 2O emissions in relation to the presence or absence of Phragmites and Typha in a free water surface constructed wetland (FWS-CW), since vegetation, through the increase in organic matter due to litter degradation, may significantly affect the denitrification capacity in planted areas. Quantitative real-time PCR analyses of genes in the denitrification pathway indicating capacity to produce or reduce N 2O were conducted at periods of different water discharge. Genetic potential for N 2O emissions was estimated from the relative abundances of all denitrification genes and nitrous oxide reductase encoding genes ( nosZ). nosZ abundance was invariably lower than the other denitrifying genes (down to 100 fold), and differences increased significantly during periods of high nitrate loads in the CW suggesting a higher genetic potential for N 2O emissions. This situation coincided with lower nitrogen removal efficiencies in the treatment cell. The presence and the type of vegetation, mainly due to changes in the sediment carbon and nitrogen content, correlated negatively to the ratio between nitrate and nitrite reducers and positively to the ratio between nitrite and nitrous oxide reducers. These results suggest that the potential for nitrous oxide emissions is higher in vegetated sediments.

Investigating the effectiveness of aquatic plants (Echinocloa L and Cyperus L ) in removing nutrients from wastewater: The case of Chemelil constructed wetland- Kenya

This study focused on the effectiveness of wetland plants: Echinocloa pyramidalis (L) andCyperus papyrus (L) in purifying wastewater from sugar factory stabilization pond effluent. This study was performed in a pilot-scale Free Water Surface Constructed Wetland (FWSCW) system in Chemelil sugar factory, Kenya. Four of the eight constructed wetlands (CWs) were planted with C. papyrus and the other half with E. pyramidalis.Water samples and plant specimen were taken fortnightly at inlets and outlets of the cells and analysed for total phosphates and total nitrates. The data was analysed by use of Microsoft excel and SPSS computer packages. Water analysis recorded a reduction in the nutrient levels between the inlet pond nine and the final outlet channel to River Nyando. The plants grown in the wetland experienced a reduction in the level of total foliar nitrogen and phosphorous, indicating that though the nutrients were being removed from the wetland, the same were not those assimilated by the plants either. The control plants had higher folia phosphorous and nitrogen, an indication that the system of the constructed wetland was able to eliminate the nutrients effectively from the plants. Key words: Wastewater, eutrophication, assimilation, Echinocloa pyramidalis, Cyperus papyrus, sugar factory. wastewater.

Nitrogen removal efficiencies in a free water surface constructed wetland in relation to plant coverage

Vegetation coverage is considered to be a key factor controlling nitrogen removal in wetlands. We describe the use of newly designed stainless steel incubation chambers to detect shifts in the in situ nitrate reduction activities associated to areas covered with common reed ( Phragmites australis) and cattail ( Typha latifolia) in the sediment of a free water surface constructed wetland (FWS-CW). Activities were measured at six different positions and times of the year and were related to physicochemical and hydraulic variables. Mean nitrate + nitrite reduction activities varied from 11.1 to 69.4 mg N/m 2/h and showed a high variability within sediment types. Ammonification rates accounted for roughly 10% of the total nitrate reduction and were especially relevant in vegetated areas. Measured activities were highly above total nitrogen removal efficiencies estimated in the three parallel treatment cells of the Empuriabrava FWS-CW, indicating the potentiality of the system. In situ nitrate reduction activities correlated well with physichochemical characteristics such as pH and temperature. Additionally, differences in the total nitrogen removal efficiencies were detected between the three treatment cells and were related to changes in the water retention time. The plant species effect was detected in treatment cells of comparable hydraulic loads in which vegetation belts dominated by Typha latifolia were shown to have greater nitrogen removal efficiencies.

Characteristics of contaminants in water and sediment of a constructed wetland treating piggery wastewater effluent

Constructed wetland (CW) is the preferred means of controlling water quality because of its natural treatment mechanisms and function as a secondary or tertiary treatment unit. CW is increasingly applied in Korea for secondary effluent of livestock wastewater treatment. This study was conducted to recognize the characteristics of contaminants in the accumulated sediment at the bottom soil layer and to reduce the phosphorus release from sediments of the free water surface CW for the treatment of secondary piggery wastewater effluent from a livestock wastewater treatment facility. The results revealed that the dominant phosphorus existence types at near the inlet of the CW were non-apatite phosphorus (59%) and residual phosphorus (32%) suggesting that most of the particles of the influent are made up of inorganic materials and dead cells. Sediment accumulation is important when determining the long-term maintenance requirements over the lifetime of CW. Continuous monitoring will be performed for a further assessment of the CW system and design.

Pilot-scale studies of domestic wastewater treatment by typical constructed wetlands and their greenhouse gas emissions

Three typical constructed wetlands (CWs) including Vertical Flow (VF), Free Water Surface (FWS), and Subsurface Flow (SF), and combined VF-SF-FWS constructed wetlands were investigated for the treatment of domestic wastewater with low C/N ratio. The performance of nutrient removal and the characteristics of greenhouse gas emissions, such as CH4 and N2O, from these CWs were compared. The results indicated that the four types of CWs had high removal efficiencies for organic matter and suspended solid (SS). The combined wetland also showed a comparatively good performance for nitrogen and phosphorus removal, and the removal efficiencies for total nitrogen (TN) and total phosphorus (TP) were 81.3% and 84.5%, respectively. The combined CWs had a comparative lower global warming potential. The FWS CW had the highest tendency to emit CH4 and led to a higher global warming potential among the four types of CWs, which was about 586 mg CO2/m2·h.

Dynamics of Typha latifolia L. populations in treatment wetlands in Estonia

The aim of this paper is to evaluate and compare broadleaved cattail ( Typha latifolia L.) biomass production and the nitrogen (N) and phosphorus (P) content in phytomass in three treatment wetland systems and to propose suitable areas for treatment wetlands in Estonia for raw material production. The biomass samples (roots/rhizomes, shoots with leaves and spadixes) and litter were collected from 1 m × 1 m plots—15 plots in the Tänassilma semi-natural wetland, 15 plots in the Põltsamaa free water surface (FWS) constructed wetland (CW), and 10 plots in the Häädemeeste FWS CW. The average aboveground biomass of T. latifolia varied from 0.37 to 1.76 kg DW m −2 in autumn and from 0.33 to 1.38 kg DW m −2 in winter. The greatest average nitrogen (22,950 mg N kg −1) concentration was found in spadixes in 2002, and the phosphorus (6500 mg P kg −1) concentration was measured in roots–rhizomes in 2003. Average standing stock of nitrogen and phosphorus was higher in aboveground than belowground phytomass. In FWS CWs with high hydraulic and nutrient loadings, however, the harvesting of aboveground biomass is not an effective means for the removal of nutrients. Cattail biomass is a valuable insulation material, whereas the fibre from spadixes mixed with clay gives elasticity to clay plasters. According to our estimates, about 5412 km 2 could be used for Typha cultivation in Estonia.

Diversity of the nitrite reductase gene nirS in the sediment of a free-water surface constructed wetland.

The diversity of the nitrite reductase gene nirS was studied in the bulk sediment of a free-water surface constructed wetland (FWS-CW) located next to the Empuriabrava wastewater treatment plant (WWTP), in Castelló d'Empúries (Girona, NE Spain). The study period extended from the inception of the treatment wetland, in June 1998, until March 1999 and comprised periods of relatively high nitrate and ammonium concentrations at the influent and low nitrate-removal efficiencies. To evaluate nirS diversity, partial gene sequences were obtained by cloning of the respective PCR products. Rarefaction curves based on DOTUR analyses of the deduced amino-acid sequences predicted a greater diversity of nirS genes in samples containing higher ammonium concentrations. Estimated Shannon-Weaver indices of the four cloned samples showed a positive relationship with the N-NH4 +/N-NO3 - ratios measured at the FWS-CW inlet. Identities between the deduced amino-acid sequences and those previously deposited in public databases ranged from 72 to 97%. Phylogenetic analysis based on these deduced sequences grouped 165 nirS clones in seven main clusters according to high similarity indices. Up to 60% of the clones clustered together in a highly homogeneous group with little homologies to any sequence retrieved from cultured representatives. Moreover, prevailing environmental conditions appeared to select for particular denitrifying populations, e.g., with respect to ammonium load and nitrogen removal efficiencies. This observation is of particular interest for the management of treatment wetlands, in which only slight variations in the theoretical denitrification potential of the system can occur.

Treatment of landfill leachate in on-site lagoons and constructed wetlands

On-site “high-tech” leachate treatment systems are often avoided due to large construction and operation costs. Alternative integrated methods need to be examined. This paper describes a biological treatment system, capturing leachate from a municipal sanitary waste (MSW) landfill on-site. The area has a typical cool temperate continental climate. The treatment system is built in a ravine and has been operating since July 1993. The average flow is estimated to be 120 m3 d−1. The low-strength leachate is first treated in a 400 m3 anaerobic pond. Stage 2 is a 4000 m3 aerated lagoon with 3 AIRE-O2 aspirator propeller aerators/mixers. Oxidation of organic matter, NH4-N and Fe take place in this lagoon. Stage 3 is two parallel constructed wetlands (CWs) with horizontal subsurface flow, each with an area of 400 m2. The filters consist of (i) washed gravel and (ii) Light Expanded Clay Aggregates, LECA (size range 10-20 mm). The CWs were planted with Phragmites australis and Typha latifólia. Stage 4 is a 2000 m2 free water surface CW, planted with Scirpus and Typha. The integrated system has no moving parts, except for the aerators. The overall removal of organic matter, N, P, Fe and pathogenes is promising (70-95%). The paper presents combinations with the use of conventional and natural systems in MSW landfill leachate treatment.

Treatment of landfill leachate in on-site lagoons and constructed wetlands

On-site “high-tech” leachate treatment systems are often avoided due to large construction and operation costs. Alternative integrated methods need to be examined. This paper describes a biological treatment system, capturing leachate from a municipal sanitary waste (MSW) landfill on-site. The area has a typical cool temperate continental climate. The treatment system is built in a ravine and has been operating since July 1993. The average flow is estimated to be 120 m3 d−1. The low-strength leachate is first treated in a 400 m3 anaerobic pond. Stage 2 is a 4000 m3 aerated lagoon with 3 AIRE-O2 aspirator propeller aerators/mixers. Oxidation of organic matter, NH4−N and Fe take place in this lagoon. Stage 3 is two parallel constructed wetlands (CWs) with horizontal subsurface flow, each with an area of 400 m2. The filters consist of (i) washed gravel and (ii) Light Expanded Clay Aggregates, LECA (size range 10–20 mm). The CWs were planted with Phragmites australis and Typha latifólia. Stage 4 is a 2000 m2 free water surface CW, planted with Scirpus and Typha. The integrated system has no moving parts, except for the aerators. The overall removal of organic matter, N, P, Fe and pathogenes is promising (70–95%). The paper presents combinations with the use of conventional and natural systems in MSW landfill leachate treatment.