Performance of hybrid constructed wetland systems for treating septic tank effluent

The integrated wetland systems were constructed by combining horizontal-flow and vertical-flow bed, and their purification efficiencies for septic tank effluent were detected when the hydraulic retention time （HRT） was 1 d, 3 d, 5 d under different seasons. The results showed that the removal efficiencies of the organics, phosphorus were steady in the hybrid systems, but the removal efficiency of total nitrogen was not steady due to high total nitrogen concentration in the septic tank effluent. The average removal rates of COD （chemical oxygen demand） were 89%, 87%, 83%, and 86% in summer, autumn, winter and spring, respectively, and it was up to 88%, 85%, 73%, and 74% for BOD5 （5 d biochemical oxygen demand） removal rate in four seasons. The average removal rates of TP （total phosphorous） could reach up to 97%, 98%, 95%, 98% in four seasons, but the removal rate of TN （total nitrogen） was very low. The results of this study also indicated that the capability of purification was the worst in winter. Cultivating with plants could improve the treated effluent quality fTom the hybrid systems. The results of the operation of the horizontal-flow and vertical-flow cells （hybrid systems） showed that the removal efficiencies of the organics, TP and TN in horizontal-flow and vertical-flow cells were improved significantly with the extension of HRT under the same season. The removal rate of 3 d HRT was obviously higher than that of 1 d HRT, and the removal rate of 5 d HRT was better than that of 3 d HRT, but the removal efficiency was not very obvious with the increment of HRT. Therefore, 3 d HRT might be recommended in the actual operation of the hybrid systems for economic and technical reasons.

Research on Nitrogen Removal and Microorganism in a Subsurface Flow Constructed Wetland System in Sihong County

Experiments in monitoring the removal of organic material and nitrogen and determining the amounts of mi- croorganism at different sites in the subsurface flow constructed wetland in Sihong county were performed. The results show that the removal of CODCr agrees with the kinetic equation of a first order reaction. The removal of pollutants varies with different seasons. The removal rates of CODCr, NH3-N, TN in the spring are 15%–23% higher than those in the autumn. The amount of ammonifier is larger than that of denitrifying bacteria and the amount of denitrifying bacte- ria is larger than that of nitrosomonas. The amount of bacteria around the plant roots is larger than that on the surface of the packing medium. No apparent change is observed for the amount of denitrifying bacteria and nitrosomonas between spring and autumn.

Experiences with Constructed Wetland Systems in Korea

In spite of the low temperature during the winter season and the high land environment, the wetland treatment system is gaining popularity in Korea because of its lower construction cost and simplicity in operation and maintenance. Many different types of wetland treatment systems have been built during the last 10 years, among which the free water surface wetland has been predominant. Most of the large-scale systems are government projects for improving the water quality of the streams flowing into the estuary dikes and reservoirs. The covering plants used in this system are different in different areas but cattails and reeds or their combinations are common. Constructed wetlands in Korea can be characterized by their shallow depths and short hydraulic residence times. There is no established flow pattern and configuration rules for constructing wetlands, but many efforts have been made with a view to improving their ecological function. Flow control is the most difficult problem in designing a riverbed or riparian wetland. There have been scores of flow rate control devices developed for wetlands, but none of them guarantee wetlands’ safety against flooding. In earlier wetland construction, the building materials were mainly soil. Recently, strong and durable building materials such as rocks, gravel beds, concrete and steel are used at vulnerable places to protect them from erosion. Our investigation indicated that the wetland system would be an appropriate technology because it is not only cheaper to construct, but also requires less maintenance work. However, we suffer from the reduced effectiveness in performance during the winter. We need to evaluate the partial treatment accomplished during 6 to 7 months per year.

Efficiency and effectiveness of systems for the treatment of domestic wastewater based on subsurface flow constructed wetlands in Jarabacoa, Dominican Republic

Constructed wetlands(CwW)are well known nature-based systems for water treatment.This study evaluated the efficiency and effectiveness of seven domestic wastewater treatment systems based on horizontal flow CWs in Jarabacoa,the Dominican Republic.The results showed that the CWs were efficient in reducing the degree of contamination of wastewater to levels below the Dominican wastewater discharge standards for parameters such as the 5-day biochemical oxygen demand(BOD5)and chemical oxygen demand,but not for the removal of phosphorus and fecal coliforms.In addition,a horizontal flow subsurface wetland in the peri-urban area El Dorado was evaluated in terms of the performance of wastewater treatment in tropical climatic conditions.The concentrations of heavy metals,such as zinc,copper,chromium,and iron,were found to decrease in the effluent of the wetland,and the concentrations for nickel and manganese tended to increase.The levels of heavy metals in the effluent were lower than the limit values of the Dominican wastewater discharge standards.The construction cost of these facilities was around 200 USD per population equivalent,similar to the cost in other countries in the same region.This study suggested some solutions to the improved performance of CWs:selection of a microbial flora that guarantees the reduction of nitrates and nitrites to molecular nitrogen,use of endemic plants that bioaccumulate heavy metals,combination of constructed wetlands with filtration on activated carbon,and inclusion of water purification processes that allow to evaluate the reuse of treated water.

The Role of Coix lacryma-jobi Linn. in Wastewater Treatment System of Constructed Wetland

The dynamic of growth and nutrient （N and P） absorption of Coix lacryma-jobi Linn.in constructed wetland （CW）,as well as the effect of constructed wetland harvest on N,P absorption in eutrophic water were studied.The results revealed that,in Summer and Autumn,especially in August,C.lacryma-jobi could obtain higher biomass and N,P accumulations,thereby achieving the most efficient purification; from the breeding value point of view,N,P contents could be improved by the appropriate increase of harvest times of C.lacryma-jobi,while too many harvest times was inappropriate to the wastewater purification by C.lacryma-jobi and the nutrients accumulation.So,C.lacryma-jobi should be harvested completely in August during its growth period,and twice-3 times of harvests was appropriate.

Removal,distribution and plant uptake of perfluorooctane sulfonate(PFOS)in a simulated constructed wetland system

A vertical-flow constructed wetland(VFCW)was used to treat simulated domestic sewage containing perfluorooctane sulfonate(PFOS).The removal rate of PFOS in the domestic sewage was 93%–98%,through soil adsorption and plant uptake,suggesting that VFCWs can remove PFOS efficiently from wastewater.The removal of PFOS in the VFCW was dependent on soil adsorption and plant uptake;moreover,the percentage of soil adsorption was 61%–89%,and was higher than that of the plants uptake(5%–31%).The absorption capacity of Eichhornia crassipes(E.crassipes)(1186.71 mg/kg)was higher than that of Cyperus alternifolius(C.alternifolius)(162.77 mg/kg)under 10 mg/L PFOS,and the transfer factor of PFOS in E.crassipes and C.alternifolius was 0.04 and 0.58,respectively,indicating that PFOS is not easily translocated to leaves from roots of wetland plants;moreover,uptake of PFOS by E.crassipes was more than that of C.alternifolius because the biomass of E.crassipes was more than that of C.alternifolius and the roots of E.crassipes can take up PFOS directly from wastewater while C.alternifolius needs to do so via its roots in the soil.The concentration of 10 mg/L PFOS had an obvious inhibitory effect on the removal rate of total nitrogen,total phosphorus,chemical oxygen demand,and ammonia nitrogen in the VFCW,which decreased by 15%,10%,10%and 12%,respectively.Dosing with PFOS in the wastewater reduced the bacterial richness but increased the diversity in soil because PFOS stimulated the growth of PFOS-tolerant strains.

Significance of Primary Treatment Selection in the Efficiency of Wastewater Treatment in Constructed Wetlands (CWs)

This research explores strategies to enhance the efficiency of secondary treatment in Vertical Flow Constructed Wetlands (CW) in Montenegro. The focus is on selecting appropriate primary treatment methods alongside three distinct substrate types to improve wastewater treatment efficacy. The study examines the combination of two primary treatments with different substrate types in constructed wetlands (CW1, CW2, and CW3). The primary treatments include the existing wastewater treatment plant (WWTP) in Podgorica, involving coarse material removal through screens, inert material separation in aerated sand traps, and sediment and suspended matter removal in primary sedimentation tanks. The Extreme Separator (ExSep) was employed to evaluate its efficacy as a primary treatment method. The research demonstrates that the efficiency of CW can be significantly enhanced by selecting suitable primary treatment methods and substrates in Podgorica’s conditions. The most promising results were achieved by combining ExSep as a primary treatment with secondary treatment in CW-3. The removal efficiencies after CW3 for COD, BOD, and TSS exceeded 89%, 93%, and 91%, respectively. The outcomes underscore the significance of primary treatment in mitigating pollutant loads before discharge into the constructed wetlands, emphasizing potential areas for further optimization in wastewater treatment practices to enhance environmental sustainability and water quality management.

Performance assessment and microbial diversity of two pilot scale multi-stage sub-surface flow constructed wetland systems

This study assessed the performance and diversity of microbial communities in multi-stage sub-surface flow constructed wetland systems（CWs）. Our aim was to assess the impact of configuration on treatment performance and microbial diversity in the systems. Results indicate that at loading rates up to 100 g BOD5/（m2·day）, similar treatment performances can be achieved using either a 3 or 4 stage configuration. In the case of phosphorus（P）, the impact of configuration was less obvious and a minimum of 80% P removal can be expected for loadings up to 10 g P/（m2·day） based on the performance results obtained within the first16 months of operation. Microbial analysis showed an increased bacterial diversity in stage four compared to the first stage. These results indicate that the design and configuration of multi-stage constructed wetland systems may have an impact on the treatment performance and the composition of the microbial community in the systems, and such knowledge can be used to improve their design and performance.

Electricity generation during wastewater treatment by a microbial fuel cell coupled with constructed wetland

A membrane-less constructed wetland microbial fuel cell （CW-MFC） is constructed and operated under continuous flow with a hydraulic retention time （HRT） of 2 d. Fed with glucose, the CW-MFC generates a stable current density of over 2 A/m3 with a resistor of 1 kΩ and has a chemical oxygen demand （COD） removal efficiency of more than 90% after the startup of 2 to 3 d. A series of systems with the electrode spacings of 10, 20, 30 and 40 cm are compared. It is found that the container with the electrode spacing of 20 cm gains the highest voltage of 560 mV, the highest power density of 0. 149 W/m 3, and the highest Coulombic efficiency of 0.313%. It also has the highest COD removal efficiency of 94. 9%. In addition, the dissolved oxygen （DO） concentrations are observed as the lowest level in the middle of all the CW-MFC reactors. The results show that the more COD is removed, the greater power is generated, and the relatively higher Coulombic efficiency will be achieved. The present study indicates that the CW-MFC process can be used as a cost-effective and environmentally friendly wastewater treatment with simultaneous power generation.

Research Progress on Application of Constructed Wetland in Wastewater Treatment in China

Constructed wetlands as a wastewater eco-treatment technology has devel-oped for decades. Combining wastewater-treatment with water recycle in an efficient way, it plays an important role in water body restoration and ecological construction. Constructed wetlands with unique advantages have attracted intensive attention since it developed, and have been widely used in treatment of domestic sewage, industrial wastewater, and mine wastewater. In this paper, we summarized the clas-sification, composition, combination, operation mode and pol utant removal mecha-nism of constructed wetlands, as wel as the research progress on the application of constructed wetland in wastewater treatment at home and abroad. In addition, in view of the problems of using constructed wetlands to treat wastewater in China, corresponding solutions were put forward, including setting up system construction standards for constructed wetlands, developing the regulatory and enhancing tech-niques of nitrogen and phosphorus removal, and taking advantage of the unique features of constructed wetlands to improve and restore ecological environment.

Control Effect of Floating Plants Constructed Wetland to Nitrogen and Phosphorus Pollution from Rice Field Drainage

[Objective] The control effect of floating plants constructed wetland to nitrogen and phosphorus pollution from rice field drainage was studied.[Method] Firstly,the characteristic of floating plants and the purification principle of pollutants were introduced,and then purification effect was analyzed through controlling nitrogen and phosphorus pollution from rice field drainage by floating plants constructed wetland.[Result] By means of floating plants constructed wetland,the average removal rate of total nitrogen(TN) from double-season early and late rice field drainage reached 52.17% and 62.23%,respectively,while that of total phosphorus(TP) was 45.69% and 74.37%,respectively,with better removal effect.Meanwhile,floating plants have ecological and ornamental value to some extent.[Conclusion] Floating plants constructed wetland could not only control nitrogen and phosphorus pollution in field drainage effectively but also keep farmland ecosystem in healthy state.

Treatment of Wastewater in Chemistry Laboratory through Flocculent Settling and Constructed Wetlands

The basic chemistry laboratories of three colleges and universities in Guizhou Province were investigated completely,especially the pollution situations of the basic chemistry projects were counted,and the discharge amounts of the poisonous and harmful pollutants in the waste liquid from laboratories were monitored and analyzed.On the basis of the summing-up and analysis of the current research findings,a simple and feasible treatment scheme through flocculating,precipitating and constructed wetlands was designed to control the three kinds of excessive pollutants.

Activities of Urease and Phosphatase in Integrated Vertical Flow Constructed Wetland and Purification Effect of Black and Malodorous River

[Objective]The activities of urease and phosphatase in integrated vertical flow constructed wetland and purification effect of black and malodorous river were studied.[Method]Honeycomb stone and soft filler were used as matrix,the biological grid integrated vertical flow constructed wetland system was built to strengthen treatment for black and malodorous river,and the activities of urease and phosphatase of two fillers in different functional areas of constructed wetland were tested to study the film formation property of two fillers in different functional areas.[Result]Both urease and phosphatase activities on biofilm of soft filler were significantly higher than on biofilm of honeycomb stone filler;indicating that choosing soft filler was more advantageous to the growth of biofilm;and urease activity had significant correlation with total nitrogen removal rate,while phosphatase activity had no significant correlation with total phosphorus removal rate.[Conclusion]This study provided evidences for utilizing the activities of urease and phosphatase to evaluate the purification effect of black and malodorous river and choose appropriate filler.

Design of Constructed Wetland for Treatment of Tailwater from Wastewater Treatment Plant

In this study, the project of constructed wetland for treatment of tailwater from the wastewater treatment plant in Wudang Mountain was taken as an example, and the technological processes, pollution load, wetland bed structure, bed filler, selection of plants and hydraulic conditions of the subsurface flow constructed wetland were discussed. A subsurface flow constructed wetland, which covered an area of 7 227 m^2 was finally designed. It could treat 7 000 m^3 of tailwater from the wastewater treatment plant a day. In addition, the system could reduce the emission of COD, BODs, TN, TP and NH3-N by 25.55, 25.55, 12.78, 1.28 and 17.89 t respectively a day. The outlet water was proved to reach the Standard A of the first class in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant （GB 18918-2002）.

Study on the Floating Plant Climatic Adaptation of Undercurrent Constructed Wetland in North China

[Objective] The aim was to choose appropriate floating plant in the wetland in the north China.[Method] Pistia stratiotes L.,Eichhornia crassipes,and Hydrocharis dubia（Bl.） Backer were planted in the aquatic biological pool of constructed subsurface flow wetland system in the reservoir.Through filed investigation,the growth of the three kinds of plants was studied and their adaptability to the northern climate was concluded.[Result] Judging from the growth speed and state of the three kinds of floating plants,the biological characteristic of Pistia stratiotes L.can perfectly adapt the environment in the pool in the reservoir,followed by the Eichhornia crassipes.The growth state of the Hydrocharis dubia（Bl.） Backer was the worst one and it can not adapt to the north environment.[Conclusion] It provided references for the choice of artificial floating plant in the north area.

Microbial Distribution in Constructed Wetland of Iris pseudacorus L.

[Objective] The aim was to explore the distributions of main microorganisms in constructed wetland of Iris pseudacorus L.and their function and position in wastewater treatment.[Method]Distributions of main microorganisms in the upstream vertical-flow constructed wetland of Iris pseudacorus was studied by training and observing 4 kinds of microorganisms.[Result]The total number of microorganisms on root surface in unit area was 15.32 times as many as that on filler surfacein,among them bacteria and actinomycete were 17.14 times and 19.84 times as many as those on filler surfacein,respectively.[Conclusion]The distributions of microorganisms are significantly different in different parts of wetland system,obviously on root surface.Bacteria are the main populations of biological wastewater treatment.

Treatment of Domestic Sewage by Channels Constructed Wetland in New Countryside

[Objection] The aim was to study application of channels constructed wetland in treatment of domestic sewages in new countryside. [Method] Supported by construction of new rural areas project in China, we surveyed on new rural areas in Gannan, Jiangxi Province, summarized source, characteristics and treatment of domestic sewage in countryside, and designed channels constructed wetland for sewage treatment. [Result] The technique is proven effective in sewage treatment. After the technique was conducted for a trial run for four months, removal rates of COD, TP and TN averaged 73.07%, 73.25% and 72.36%, respectively. After contin- uous sampling for six times, effluent COD was analyzed 20-35 mg/L, TP was 0.60- 1.19 mg/L and TN was 6.88-11.21 mg/L, better than that of Standard 1B ruled by Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant. [Conclusion] Thanks for low investment, channels constructed wetland can be built by trans- formation of bottom land, proving a good way for treatment of diffuse pollution source and control of water non-point pollution.

Effects of Hydraulic Loading of Vertical Flow Constructed Wetland Clogging

[Objective] The aim was to al eviate the constructed wetland clogging problems and to explore to the effects of hydraulic loading on wetland clogging. [Method] The experiment, through artificial soil columns, simulated vertical flow arti-ficial wetland, set four hydraulic load level at 50, 100, 150 and 200 cm/d, to identify the impact of hydraulic loading on wetland clogging and to explore the factors run-ning threshold. [Result] The results show that the different levels of hydraulic loading have greater impact; in the constructed wetland clogging process under high hy-draulic loading of 200 cm/d, the effective life was only six months, and the single factor can be speculated that the threshold of the hydraulic load should be at 100-150 cm/d; system can last for six months at low hydraulic loading and last for three months at medium hydraulic load. [Conclusion] The research provides references for wetland clogging experiments in future.

Performance of Subsurface Constructed Wetland in River Rehabilitation

[ Objective] This study was to research the treatment effect of different media in undercurrent wetland on contamination, so as to pro- vide reference for rehabitating water body of river along small towns. [ Method ] Three different media of gravel, cobblestone and shale were used to rehabilitate water quality of contaminated river. [ Result ] Gravel, cobblestone and shale all performed well in removing TN, TP and CODw,, in contaminated water, of which gravel stuffed undercurrent wetland run best, averagely removing 49.4% TN, 34.7% and 48. 5% COD~, respectively. [ Conclusion] Undercurrent constructed wetland can effectively improve the water quality of contaminated river, and it is cheaper in cost and simpler in operation, thus suitable for generalizing in small towns of China.

Effect of carbon source on the denitrification in constructed wetlands

The ability of constructed wetlands with different plants in nitrate removal were investigated. The factors promoting the rates of denitrification including organic carbon, nitrate load, plants in wetlands, pH and water temperature in field were systematically investigated. The results showed that the additional carbon source （glucose） can remarkably improve the nitrate removal ability of the constructed wetland. It demonstrated that the nitrate removal rate can increase from 20% to more than 50% in summer and from 10% to 30% in winter, when the nitrate concentration was 30-40 rag/L, the retention time was 24 h and 25 mg/L dissolved organic carbon （DOC） was ploughed into the constructed wetland. However, the nitrite in the constructed wetland accumulated a little with the supply of the additional carbon source in summer and winter, and it increased from 0.15 to 2 mg/L in the effluent. It was also found that the abilities of plant in adjusting pH and temperature can result in an increase of denitrification in wetlands. The seasonal change may also impact the denitrification.