Horizontal Flow Bed Research Articles

Studies of Wastewater Management through Microbiology of Constructed Wetland

Constructed wetlands are distinguished by certain environmental factors that let many physical and biological processes to occur simultaneously. This is the outcome of a particular habitat that supports the development of microbes and hydrophytes, which are plants that can live in aquatic and semiaquatic environments and are capable of anaerobic, anaerobic, and aerobic environments. Their combined activity amplifies the processes of oxidation and reduction, which are in charge of eliminating and holding onto contaminants. Sorption, sedimentation, and absorption all aid in these processes. Treatment wetland systems have been employed in community management for more than 50 years because of these benefits. Constructed wetlands are becoming more and more popular for treating or pre-treating many kinds of industrial wastewater because of their benefits, cheap operating costs, and high removal efficiency. The paper examines how these facilities are being used worldwide to treat industrial wastewater. With a focus on particular and distinctive pollutants from industries, the conditions of usage and efficacy of pollutants removal from wastewater that degrades quickly and slowly were described. The article addressed the use of subsurface horizontal flow beds for the treatment of wastewater from various industrial processes, including the manufacturing of paper, oil, and coffee, as well as the food sector, which includes wineries and distilleries. Constructed wetlands are used in Poland to treat wastewater and milk processing sludge on a pilot size or to dewater sewage sludge generated in municipal wastewater treatment plants that handle household sewage with around 40% of wastewater from the dairy and fish industries. Constructed wetlands provide the so-called ecosystem function in addition to an adequate degree of treatment in every instance.

Evaluation of Hybrid Constructed Wetland Performance and Reuse of Treated Wastewater in Agricultural Irrigation

Agriculture is being negatively affected by the decrease in precipitation that has been observed over the last few years. Even in the Czech Republic, farmers are being urged to irrigate their fields despite the fact that sources of water for irrigation are rapidly being depleted. This problem might be partially solved via the reuse of treated wastewater in certain agricultural sectors. However, the public perception of the reuse of wastewater remains negative primarily due to unknown risks to the environment and public health. To overcome this barrier, a semi-operated irrigation field was established at Kostelec nad Ohří in the Central Bohemian region of the Czech Republic and planted with common garden crops such as tomatoes (Lycopersicon esculentum), potatoes (Solanum tuberosum) and lettuces (Lactuca sativa L.) irrigated with two different water sources, i.e., treated wastewater from a local nature-based treatment system, a hybrid constructed wetland (HCW), and local fresh water from well. The HCW was put into operation in 2017 and was reconstructed in 2018 and includes both horizontal and vertical flow beds; the trial irrigation field was added in the same year. The reconstruction of the facility significantly enhanced the removal efficiency with respect to all monitored parameters, e.g., biochemical oxygen demand (BOD5), chemical oxygen demand (COD), N–NH4+, total N and the suspended solids (TSS), except for total P. The HCW also ensured the significant removal of several observed pathogenic microorganisms (E. coli, intestinal enterococci and thermotolerant coliforms). During the 2018 and 2019 growing seasons, we observed the significantly enhanced growth of the crops irrigated with wastewater from the HCW due to the fertilizing effect. The risks associated with the contamination of crops irrigated with treated water are not negligible and it is necessary to pay sufficient attention to them, especially when introducing irrigation with wastewater into practice.

Reliability and Efficiency of Pollutant Removal in Four-Stage Constructed Wetland of SSVF-SSHF-SSHF-SSVF Type

The present paper reports pollutant removal efficiencies and reliability for a four-stage hybrid constructed wetland (HCW) consisting of the following sequence of subsurface (SS), vertical flow (VF) and horizontal flow (HF) beds: SSVF-SSHF-SSHF-SSVF. The experiments were carried out over a period of three years, with sampling done in each season: winter, spring, summer and autumn. Grab samples of wastewater collected from different stages of treatment were tested for total suspended solids (TSS), BOD5, COD, total nitrogen (TN) and total phosphorus (TP). The wetland was found to have a very high efficiency of removal of suspended solids and organics, with relatively little seasonal variability. The three-year average TSS removal efficiency was approximately 92.7%. The effectiveness of elimination of organic compounds was very high throughout the study period at 96.6% BOD5 and 95% COD. The effluent from the four-stage system had significantly lower contents of TN and TP compared to the wastewater discharged from the first two beds of this facility.

Kinetics of pollutants removal in vertical and horizontal flow constructed wetlands in temperate climate

This paper reports a comparative study on kinetics of organic matter expressed as BOD5 and nitrogen removal in constructed wetlands operated in Poland. Analyzed data were collected at eight wetland systems, composed of subsurface flow beds: horizontal flow (HF) and vertical flow (VF), in different number and sequences. The analysis involved particularly mass removal rates (MRR) and first-order removal rate coefficients of BOD5 and total nitrogen (kA and kv for VF and HF filters, respectively, and k20 as a parameter averaged for a temperature of 20 °C). It was found that the higher the load of pollutants applied to the beds, the higher MRR values were obtained. The average k-rates in analyzed systems were mostly lower than those reported in the literature, especially in the case of total nitrogen. Its removal obtained in horizontal flow beds was kv = 0.002–0.042 d−1, while in vertical flow systems kA varied from 0.007 m d−1 to 0.0037 m d−1. According to data given by previous studies, first-order reaction rates for nitrogen removal varied in range from kv = 0.048 d−1 to kv = 0.19 d−1 and kA from 0.007 to 0.1 m d−1 in HF and VF beds, respectively. Regarding BOD5 shown in literature, removal rate kv for HF beds varied from 0.071 to 6.11 d−1, and kA for VF beds varied from 0.019 to 1.0 m d−1, while in this study lower k-rates were obtained: kv = 0.005–0.085 d−1 and kA = 0.015–0.130 m d−1. Relatively long monitoring period, for some of constructed wetland up to 16 years, resulted in good data set and enables creation of the graphs, which could be helpful in evaluation and designing of constructed wetlands for PE bigger than 50, in moderate climate conditions.

Seasonal changes of contamination removal in constructed wetlands systems

The investigation was carried out at two different hybrid constructed wetlands, whichtreated municipal sewage after mechanical treatment from small villages in PomeranianRegion, In all facilities first step of biological treatment were horizontal flow beds, Themain difference concerns configuration of the facilities and sewage distributions systemsinto vertical flow beds, The measurement period was divided into vegetation (from Aprilto October) and outside vegetation seasons (from November to March) for all analysedfacilities.The results allowed for estimation of efficiency removal of different contaminations inboth measurements seasons. Comparison of the amount of sewage and loads ofcontamination inflowing and outflowing from the facilities are presented. Achievedresults make it possible to estimate the rate of organic matter decomposition and nitrogenremoval in vegetation and outside vegetation seasons.

Modeling of Pollutants Removal in Subsurface Vertical Flow and Horizontal Flow Constructed Wetlands

Reject water is a by-product of every municipal and agro-industrial wastewater treatment plant (WWTP) applying sewage sludge stabilization. It is usually returned without pre-treatment to the biological part of WWTP, having a negative impact on the nitrogen removal process. The current models of pollutants removal in constructed wetlands concern municipal and industrial wastewater, whereas there is no such model for reject water. In the presented study, the results of treatment of reject water from dairy WWTP in subsurface vertical flow (SS VF) and subsurface horizontal flow (SS HF) beds were presented. During a one-year research period, SS VF bed reached 50.7% efficiency of TN removal and 73.8% of NH4+-N, while SS HF bed effectiveness was at 41.4% and 62.0%, respectively. In the case of BOD5 (biochemical oxygen demand), COD (chemical oxygen demand), NH4+-N, and TN (total nitrogen), the P-k-C* model was applied. Multi-model nonlinear segmented regression analysis was performed. Final mathematical models with estimates of parameters determining the treatment effectiveness were obtained. Treatment efficiency increased up to the specific temperature, then it was constant. The results obtained in this work suggest that it may be possible to describe pollutant removal behavior using simplified models. In the case of TP (total phosphorus) removal, distribution tests along with a t-test were performed. All models predict better treatment efficiency in SS VF bed, except for TP.

Productivity and chemical properties of Salix viminalis in a horizontal subsurface flow constructed wetland during long-term operation

The paper presents the results of a study of selected parameters of common osier (Salix viminalis) biomass sampled annually, over a 12-year period, from a constructed wetland wastewater treatment plant. The focus of the study was on parameters that were relevant to biomass energy management. The study was conducted in a constructed wetland wastewater treatment plant consisting of one horizontal flow bed with a total area of 186 m2, planted with osier willows. The following biomass parameters were analysed: biomass yield, volume, humidity, ash content, higher and lower heating values, and contents of N, P, K in different parts of plant stems. The study showed that osier biomass harvested from the investigated constructed wetland system could be used as an energy source in thermochemical processes. The higher and lower heating values were similar to those obtained by other authors (18.13 and 17.38 MJ·kg−1, respectively). The energy yield (17.49 MJ·m−2) and energy density (3486–5411 MJ·m−3) were also calculated. Young shoot parts had higher ash and micronutrient contents and lower energy parameters than old parts.

The use of constructed wetlands for the treatment of industrial wastewater

Abstract Constructed wetlands are characterized by specific conditions enabling simultaneous various physical and biochemical processes. This is the result of specific environment for the growth of microorganisms and hydrophytes (aquatic and semiaquatic plants) which are capable of living in aerobic, anaerobic and facultative anaerobic conditions. Their interaction contributes to the intensification of oxidation and reduction responsible for the removal and retention of pollutants. These processes are supported by sorption, sedimentation and assimilation. Thanks to these advantages, treatment wetland systems have been used in communal management for over 50 years. In recent years, thanks to its advantages, low operational costs and high removal efficiency, there is growing interest in the use of constructed wetlands for the treatment or pre-treatment of various types of industrial wastewater. The study analyzes current use of these facilities for the treatment of industrial wastewater in the world. The conditions of use and efficiency of pollutants removal from readily and slowly biodegradable wastewater, with special emphasis on specific and characteristic pollutants of particular industries were presented. The use of subsurface horizontal flow beds for the treatment of industrial wastewater, among others from crude oil processing, paper production, food industry including wineries and distillery, olive oil production and coffee processing was described. In Poland constructed wetlands are used for the treatment of sewage and sludge from milk processing in pilot scale or for dewatering of sewage sludge produced in municipal wastewater treatment plant treating domestic sewage with approximately 40% share of wastewater from dairy and fish industry. In all cases, constructed wetlands provided an appropriate level of treatment and in addition the so-called ecosystem service.

Performance evaluation of hybrid treatment wetland for six years of operation in cold climate.

In Hokkaido, northern Japan, there are 12 hybrid subsurface constructed wetlands (HSCWs) and most of them are treating high concentrated organic wastewater. One of these systems is an HSCW situated in Embetsu, northern Hokkaido, and it has been in operation since November of 2006 to treat dairy milking parlor wastewater. The system is composed of two vertical flow beds and a horizontal flow bed. The influent and the effluent flow rates and pollutant concentrations and loads were extremely variable. Throughout its 6years of operation, most of the pollutant removals were decently high. Removal efficiencies for COD, BOD5, and SS were ranging in the 90%. Removal efficiencies for TN, NH4-N, and BOD5 were improving because of the development of the soil ecosystem and the Phragmites australis community. However, the removal efficiencies of TP were decreasing, presumably because of the declining adsorption ability. The accumulation of TP in the first and the second vertical beds had reached its plateau. Vertical beds had high removal efficiencies for TN, COD, BOD5, and SS. These high removal efficiencies of the first vertical bed may be caused from the efficient removal of solid material that is deposited as an organic layer of the first vertical bed. High NH4-N removal efficiencies exerted by the second vertical bed may be due to the recycling of wastewater. In conclusion, the HSCW was working excellently for its 6years of operation, and it could be concluded that it has not reached its life yet.

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.

Removal of persistent organic pollutants from landfill leachates treated in three constructed wetland systems

The objective of the study was assessment of occurrence and removal of two groups of persistent organic pollutants: polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in landfill leachate (LL) treated in three constructed wetland systems (CWs) of different construction and flow regime. Two subsurface flow systems (SSF) were analyzed: one with horizontal flow and the second one consisting of two vertical flow beds followed by a horizontal flow bed. The third CW was a surface flow (SF) system, consisting of 10 ponds connected in series. The concentrations of 12 PAHs and 7 PCBs were measured in the samples of LL after subsequent treatment stages and in the sediment samples from the SF system as well as in the substrate samples from the SSF flow systems. It was confirmed that the major mechanism of PCB and PAH removal in CW systems was adsorption to the bottom sediments (in the SF system) or substrate of the beds (in the SSF systems) as well as adsorption to suspended solids, followed by sedimentation. The compounds characterized by higher octanol/water partition coefficient were more effectively retained in the sediments. Also removal of these substances occurred in the earlier stages of treatment.

Escherichia coli removal and internal dynamics in subsurface flow ecotechnologies: Effects of design and plants

Subsurface flow ecotechnologies encompass a range of different designs, varying in terms of flow configuration, media type, energy requirements and use of wetland plants. This study compared the removal rates and internal dynamics of Escherichia coli in a range of commonly used and emerging subsurface flow systems designed for secondary treatment of domestic sewage. Fifteen pilot-scale units were loaded with primary treated sewage in Langenreichenbach, Germany and monitored at the inlet, outlet and a several internal sample points between August 2010 and December 2011. The compared systems spanned a range of energetic intensification levels, including passive horizontal flow (HF) beds (25cm versus 50cm deep), moderately-intensified unsaturated pulse-loaded (12 versus 24 times per day) vertical flow (VF) beds (gravel versus sand media), and highly-intensified beds with aeration (HF versus VF) or reciprocating fill and drain hydraulics. Planted (Phragmites australis) and unplanted forms were compared for all designs except for the reciprocating system (unplanted only). In general, there was no significant effect of vegetation on E. coli removal. Despite receiving the highest loading rates (131–146L/m2d), the aerated HF systems and the reciprocating system achieved the highest log concentration reductions (2.8–4.0log10) and the lowest effluent E. coli concentrations (geometric mean less than 1×104MPN/100mL). The gravel-based VF beds had the lowest log concentration reduction (0.8log10) and highest effluent concentrations (6.4–8.9×105MPN/100mL) at a hydraulic loading rate of 96L/m2d. The design type had an extremely significant effect on areal mass removal rates, with the passive HF beds having the lowest removal rates (50cm depth significantly better than 25cm), followed by the unsaturated VF systems (which were not significantly different from one another), while the aerated and reciprocating systems had the highest removal rates. Within the unsaturated VF beds, the use of sand versus gravel substrate, or hourly versus bi-hourly loading regime in the sand-based systems, had no effect on areal load removal. The internal concentration profiles were not significantly different between the unsaturated VF designs, with the exception of the hourly-loaded, planted bed with sand media which had a more rapid rate of concentration reduction with depth. In the HF beds, the internal E. coli concentration reduction was significantly faster in the aerated beds than in the non-aerated beds. Depth and plants had no significant effect on the internal concentration profiles within the non-aerated HF beds. Within the aerated systems, horizontal-flow achieved better E. coli removal than vertical-flow. Subsurface flow ecotechnologies offer great potential as robust and low-maintenance solutions for reducing the pathogen risk associated with domestic wastewater. The intensified systems produced effluent potentially suitable for restricted surface irrigation, at the cost of higher energy consumption, while the effluent from the other design types would require subsurface irrigation or further disinfection prior to reuse.

Comparison of vertical and horizontal flow planted and unplanted subsurface flow wetlands treating municipal wastewater

In the search for design criteria for constructed wetlands (CWs) in Nepal a semi-scale experimental setup including horizontal flow (HF) and vertical flow (VF) CWs was developed. This paper compares the performance of HF and VF wetlands, and planted with unplanted beds. The experimental setup consists of two units of HF and VF beds of size 6 m × 2 m × 0.6 m and 6 m × 2 m × 0.8 m (length × width × depth) respectively. For both HF and VF systems, one unit was planted with Phragmites karka (local reed) and one was not planted. The systems were fed with wastewater drawn from the grit chamber of a municipal wastewater treatment plant. The media consisted of river gravel. In the first phase of the experiment the hydraulic loading rate (HLR) was varied in steps; 0.2, 0.08, 0.04 m(3)/m(2)/d and the percent removal increase with decrease in HLR for all beds and parameters except for total phosphorus. In the second phase the loading rate of 0.04 m(3)/m(2)/d was run for 7 months. In both parts of the experiment the planted beds performed better than the unplanted beds and the VF better than the HF beds. To meet Nepalese discharge standards HF beds are sufficient, but to meet stricter requirements a combination of HF and VF beds are recommended.

Partitioning of heavy metals in sub-surface flow treatment wetlands receiving high-strength wastewater

The retention of heavy metals at two pilot-scale treatment wetlands (TWs), consisting of two vertical flow beds (VSSF) followed by a horizontal flow bed (HSSF) was studied. The TWs received high-strength wastewater: reject waters from sewage sludge centrifugation (RW) and landfill leachate (LL). The concentrations of the metals Fe, Mn, Zn, Al, Pb, Cu, Cd, Co, and Ni were measured in treated wastewater, substrate of the beds and in plant material harvested from the beds (separately in above ground (ABG) parts and below ground (BG) parts). The TWs differed in metals retention. In the RW treating TW the metal removal efficiencies varied from 27% for Pb to over 97% for Fe and Al. In the LL treating system the concentrations of most metals decreased after VSSF-1 and VSSF-2 beds; however, in the outflow from the last (HSSF) bed, the concentrations of metals (apart from Al) increased again, probably due to the anaerobic conditions at the bed. A major removal pathway was sedimentation and adsorption onto soil substrate as well as precipitation and co-precipitation. In the LL treating facility the plants contained substantially higher metal concentrations in BG parts, while the upward movement of metals was restricted. In the RW treating facility the BG/ABG ratios were lower, indicating that metals were transported to shoots.

Performance of six multi-stage hybrid wetland systems for treating high-content wastewater in the cold climate of Hokkaido, Japan

The performance of six multi-stage hybrid wetland systems, which were designed and constructed for treating high-content wastewater, was evaluated in the cold climate of Hokkaido, northern Japan. The systems were designed to treat four kinds of wastewater: dairy wastewater (three systems, average inflow 4.9–46.6m3d−1, average inflow content 2400–5000mgCODl−1, 2–5 years of operation); wastewater from a pig farm, including liquid food washing wastewater (one system, 4.1m3d−1, 9500mgCODl−1, 2 years of operation); wastewater from potato starch processing (one system, 5.4–13.3m3d−1, 24,000–54,000mgCODl−1, 2 years of operation); and wastewater containing pig farm swine urine (one system, 16.9m3d−1, 10,100mgCODl−1, 1 year operation). Our systems were composed of three to four vertical (V) flow beds with self-priming siphons and surface partitions and no or one horizontal (H) flow bed (total of three to five beds). In some V flow beds, treated effluents were recirculated (Vr) through the inlet to improve performance, mainly during the growing season. The total bed area was 168–2151m2. 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 (Supersol: lightweight porous glass) to the V flow beds. The safety bypass structure and floating cover material helped to prevent clogging and freezing and maintained dry conditions and abundant growth of reeds and earthworms. The average purification rates were 70–96% for chemical oxygen demand (COD), 39–90% for total nitrogen (TN), 36–82% for NH4–N, and 70–93% for total phosphorous (TP). Calculated average oxygen transfer rates (OTRs) were 16–99gO2m−2d−1. OTRs increased in proportion to influent load, and the OTR value was Vr>V>H. Recirculating the treated effluents was expected to enhance removal of nitrogen in V flow beds mainly by a combination of nitrification and denitrification. By treating higher organic loads per area without clogging, it was possible to minimize the area and cost of treating high-content wastewater. However, more data are needed concerning load and OTR to design a more efficient multi-stage wetland system.

인공습지를 이용한 축산폐수처리장에서 수생식물의 생육특성과 영양염류 흡수특성

BACKGROUND: Constructed wetlands for wastewater treatment are vegetated by wetland plants. Wetland plants are an important component of wetlands, and the plants have several roles in relation to the livestock wastewater treatment processes. The objectives of this study were to investigate the growth characteristics and nutrient absorption of water plants in constructed wetlands for treating livestock wastewater. METHODS AND RESULTS: In this study, livestock wastewater treatment plant by constructed wetlands consisted of water plant filtration bed, activated sludge bed, vertical flow(VF), horizontal flow(HF) and HF beds. Phragmites communis TRINIUS(PHRCO) was transplanted in VF bed, Iris pseudoacorus L(IRIPS) was transplanted in HF bed and PHRCO, IRIPS and Typha orientalis PRESEL(THYOR) were transplanted in HF. Growth of water plants in constructed wetlands were the highest in October. The IRIPS growth was higher than other plant as 264 g/plant in October. The absorption of nitrogen and phosphorus by IRIS were 3.38 g/plant and 0.634 g/plant, respectively. The absorption of K, Ca, Mg, Na, Fe, Mn, Cu and Zn by water plants were higher in the order of IRIPS > THYOR > PHRCO. CONCLUSION(S): The absorption of nutrients by water plants were higher on the order of IRIPS > THYOR > PHRCO in constructed wetlands for treating livestock wastewater.

Comparison of nitrogen elimination rates of different constructed wetland designs

In this paper the nitrogen elimination rates of different constructed wetland (CW) designs reported in literature are compared with those obtained for outdoor and indoor 2-stage vertical flow (VF) systems. The outdoor system is located about 150 km west of Vienna. Both stages are planted with Phragmites australis and the system has been operated for 4 years continuously. During this period the average value of the nitrogen elimination rate was 3.30 g N m(-2) d(-1). The indoor system comprises three parallel operated 2-stage VF systems and is located in the technical lab hall at BOKU University. The design of the indoor system resembles the outdoor system. However, there are a few differences: (1) the indoor systems are not planted, and (2) different filter media have been used for the main layer of the first stages. With the indoor system the highest nitrogen elimination rate achieved was 2.24 g N m(-2) d(-1) for the system with zeolite and impounded drainage layer. Similar results have been found in France for treating raw wastewater with VF and horizontal flow (HF) beds in series with nitrogen elimination rates of 1.89 and 2.82 g N m(-2) d(-1) for differently designed HF beds. The highest nitrogen elimination rates of 15.9 g N m(-2) d(-1) reported were for pilot-scale VF CWs treating high-strength synthetic wastewater (total nitrogen of 305 mg L(-1) in the influent) in Thailand. It has been shown that the outdoor two-stage VF CW system has one of the highest nitrogen elimination rates of CWs treating domestic wastewater.

The role of SSVF and SSHF beds in concentrated wastewater treatment, design recommendation

The return flows of reject water from sewage sludge dewatering alter the activated sludge process in a conventional WWTP and increase TN concentration in the final effluent from WWTP. The objective of the investigation carried out was to consider the application of multistage treatment wetland (MTW) for the treatment of reject water from sewage sludge dewatering in a centrifuge (RWC). This paper aims to present the design and performance of each stage of the treatment as well as the efficiency of total MTW. The full scale pilot plant for RWC, consisting of two vertical flow beds (SS VF) working in series, followed by an horizontal flow bed (SS HF), was built in 2008. The applied configuration ensured a very high removal efficiency of principal pollutant (COD - 76.0% and NH4+-N - 93.6%). In the investigated facilities, the SS VF beds ensured an effective removal of nitrogen compounds, especially NH4+-N, whereas the decomposition of hardly degradable Org-N and COD took place in SS HF. This research illustrates that the MTW could be successfully applied for the treatment of RWC.

시설하우스 폐양액 주입방법 및 여재 특성에 따른 인공습지에서 수질오염물질의 처리효율

In order to improve T-N and T-P removal in HF (horizontal flow)-HF hybrid constructed wetlands by natural purification method for treating the hydroponic wastewater in greenhouses, the efficiency of water treatment as affected by the injection method of hydroponic wastewater, the addition of special filter media, the particle size of filter media, and the injection ratio of hydroponic wastewater in HF and HF beds were investigated in small-scale HF-HF hydroponic wastewater treatment apparatus. Removal rate of T-P in the water in HF-HF hydroponic wastewater treatment apparatus with calcite as affected by addition method of special filter media was higher than that in HF-HF hydroponic wastewater treatment apparatus with other filter media. Removal rate of BOD, COD, SS, T-N and T-P in the water in mixed filter media with calcite were 86, 84, 87, 50 and 97%, respectively. Removals of pollutants except for T-P in the water were slightly different. Therefore, it should be considered that the removal rate of T-P was good for calcite in HF-HF hydroponic wastewater treatment apparatus. To improve T-N and T-P removal, the optimum particle size of filter media was 1.2 mm, and the optimum injection ratio ( HF bed : HF bed) of hydroponic wastewater was 60:40.

A three-stage experimental constructed wetland for treatment of domestic sewage: First 2 years of operation

Hybrid constructed wetland systems have recently been used to treat wastewaters where high demand for removal of ammonia is required. However, these systems have not been used too often for small on-site treatment systems. This is because in many countries ammonia is not limited in the discharge from small systems. Hybrid systems have a great potential to reduce both ammonia and nitrate concentrations at the same time. In our study we employed a three-stage constructed wetland system consisting of saturated vertical-flow (VF) bed (2.5 m 2, planted with Phragmites australis), free-drained VF bed (1.5 m 2, planted with P. australis) and horizontal-flow (HF) bed (6 m 2, planted with Phalaris arundinacea) in series. All wetlands were originally filled with crushed rock (4–8 mm). However, nitrification was achieved only after the crushed rock was replaced with sand (0–4 mm) in the free-drain wetland. Also, original size of crushed rock proved to be too vulnerable to clogging and therefore, in the first wetlands the upper 40 cm was replaced by coarser fraction of crushed rock (16–32 mm) before the second year of operation started. The system was fed with mechanically pretreated municipal wastewater and the total daily flow was divided into two batches 12 h apart. The evaluation of the results from the period 2007 to 2008 indicated that such a system has a great potential for oxidation of ammonia and reduction of nitrate. The ammonia was substantially reduced in the free-drained VF bed and nitrate was effectively reduced in the final HF bed. The inflow mean NH 4-N concentration of 29.9 mg/l was reduced to 6.5 mg/l with the average removal efficiency of 78.3%. At the same time the average nitrate-N concentration rose from 0.5 to only 2.7 mg/l at the outflow. Removal of BOD 5 and COD amounted to 94.5% and 84.4%, respectively, with respective average outflow concentrations of 10 and 50 mg/l. Phosphorus was removed efficiently despite the fact that the system was not aimed at P removal and therefore no special media were used. Phosphorus removal amounted in 2008 to 65.4%, but the average outflow concentration of 1.8 mg/l is still high. The results of the present study indicate very efficient performance of the hybrid constructed wetlands, but optimal loading parameters still need to be adjusted. The capital cost of the experimental system is comparable to the conventional on-site treatment plant but the operations and maintenance costs are about one third of the conventional plant.