Horizontal Flow Bed Research Articles

What can we learn from old wetlands? Lessons that have been learned and some that may have been forgotten over the past 20 years

The bulk of research, development, and application of constructed wetland systems (CWSs) have taken place in the past 20 years. There are now thousands of these systems being used in Europe.Many are used for individual houses or small groups of houses, but themost common use is for treating the domestic sewage from villages to achieve secondary treatment. There are also larger systems for tertiary and storm sewage overflow treatment. The processes have spread out from domestic wastewater treatment into many other areas, such as mine water treatment and industrial effluent treatment. Development has been more rapid than is usual for wastewater treatment processes, and the processes are now regarded as conventional. One of the reasons is that the processes are seen as both “green” and cost-effective. Another reason for the rapid development of CWSs is that there has been very close national and international cooperation. This chapter describes the stepwise development of treatment applications from the simple horizontal flow beds for biochemical oxygen demandmeasured over 5 days and total suspended solids removal in the mid-1980s, moving on to vertical flow beds capable of nitrification in the early 1990s. The development of hybrid systems capable of the previous treatment applications plus denitrification in the late 1990s will be described together with themain advances.

Combinations of Horizontal and Vertical Flow Constructed Wetlands to Improve Nitrogen Removal

Nitrogen removal in wetlands is achieved through two pathways: (a) N cycling and (b) storage. N cycling is a permanent removal pathway. There has been an increasing interest in the development of technologies to alleviate permanent nitrogen removal limitation in constructed wetlands by ensuring prevalence of conditions enhancing N cycling. The purpose of this study is to review an emerging technology of vegetated submerged bed constructed wetland system aimed at improving nitrogen removal in wetlands through rational system design. The design and performance of this system type is evaluated. The oxygen transfer capacity and nitrogen removal mechanisms on system performance are evaluated. Constructed wetland combinations most commonly consist of vertical flow (VF) and horizontal flow (HF) beds where VF and HF are aimed at nitrification and denitrification, respectively. Nitrate nitrogen accumulation is the most limiting factor in typical VF based systems.

Modelling pollutant removal in a pilot-scale two-stage subsurface flow constructed wetlands

The hydraulic behaviour and effluent pollutant concentrations in a pilot-scale two-stage subsurface flow constructed wetland for treatment of municipal wastewater have been simulated. The experimental pilot plant is located in San Michele di Ganzaria (Eastern Sicily) and consists of four lines of two-stage subsurface flow constructed wetlands for secondary or tertiary treatment of municipal wastewater. The first stage, for each line, consists of a horizontal flow bed, while in the second stage a vertical flow bed operates for two lines and a horizontal flow bed for the other two. Phragmites sp. was used as vegetation in two lines while the other two lines are without plants. The HYDRUS-2D software was applied to describe flow and single-solute transport, while the multi-component reactive transport module CW2D was used to model the transformation and elimination processes of organic matter, nitrogen and phosphorus. Tracer studies and chemical wastewater analyses were carried out to calibrate and validate the transport model. In general, the simulation results obtained show a good match with the measured data for water flow, tracer experiments and pollutant removal processes.

Evaluation of a hybrid constructed wetland for treating domestic sewage from individual housing units surrounding agricultural villages in South Korea

The treatment efficiency of 2- and 3-stage constructed wetlands (CWs) was evaluated for treating domestic sewage from houses surrounding agricultural villages. The optimum depth of filter media was 90 cm. The optimum volume ratio of vertical flow (VF) and horizontal flow (HF) beds was 1:2, and the optimum filter medium was broken stone in the VF-HF 2-stage hybrid CWs. Based on the above optimum conditions, removal efficiency of biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), total nitrogen (T-N), and total phosphorus (T-P) were 99, 98, 99, 68, and 72%, respectively. However to utilize constructed wetlands (CWs) for treating domestic sewage for an individual house, would require downsizing of the 2-stage hybrid CWs. In addition, the low removal efficiency of T-N and T-P in 2-stage hybrid CWs would require improvements necessary to meet acceptable water quality discharge standards. Thus, to reduce the CWs' area and improve the T-N and T-P removal efficiencies, VF-HF 2-stage hybrid CW was modified into VF/HF(I)-HF(II) and VF/HF(I)-HF(III) 3-stage hybrid CW. The optimum reduced size of 3-stage hybrid CW was the VF/HF(I)-HF(II) configuration which also increased T-N removal. Using this system, removal efficiency of BOD, COD, SS, T-N, and T-P were 99, 98, 99, 83, and 75%, respectively. In VF/HF(I)-HF(II) CW, the removal velocity of BOD, COD and SS was rapid on the order of VF (1st stage) >> HF(II) (3rd stage) > or = HF(I) (2nd stage), VF (1st stage) >> HF(II) (3rd stage) > HF(I) (2nd stage) and VF (1st stage) >> HF(I) (2nd stage) > HF(II) (3rd stage), respectively. The removal velocity of T-N and T-P in VF/HF(I)-HF(II) CWs was rapid on the order of HF(I) (2nd stage) > HF(II) (3rd stage) > or = VF (1st stage) and VF (1st stage) > HF(I) (2nd stage) > HF(II) (3rd stage), respectively.

시설하우스 폐양액 처리를 위한 소형 인공습지의 최적 조합방법, 여재깊이 및 폐양액 부하량

시설하우스 폐양액 처리를 위한 소형 폐양액처리장치 개발을 위해 소형 폐양액처리장치를 VF-HF, VF-VF, HF-VF 및 HF-HF 조합형으로 구분하여 조합방법별, 여재깊이별 및 폐양액 부하량별로 각각 최적 조건을 조사하였으며, 개발된 시설하우스 폐양액처리장치의 적용성을 검증하기 위해 상기 최적조건하에서 실제 오이, 파프리카 및 딸기 시설하우스에서 배출되는 폐양액의 수처리효율을 조사하였다. 여재 깊이에 따른 오염물질의 수처리 효율은 BOD, COD, SS, T-N 및 T-P 모두에서 깊이가 깊어짐에 따라 수처리효율이 점점 증가하였으며,여재깊이70 cm에서 모든 조합의 BOD, COD 및 SS의 처리효율은 각각 87, 84 및 82% 이상으로 조합방법에 따라 큰 차이 없이 안정적인 수처리 효율을 보였다. T-N 및 T-P의 경우 HF-HF 및 HF-VF 조합형의 처리효율이 타 조합방법에 비해 약간 높았다. 폐양액 부하량에 따른 BOD, COD, SS, T-N 및 T-P의 처리효율은 <TEX>$150L\;m^{-2}\;day^{-1}{\approx}300L\;m^{-2}\;day^{-1}</TEX><TEX>></TEX><TEX>450L\;m^{-2}\;day^{-1}$</TEX>순으로 폐양액의 부하량이 증가함에 따라 수처리 효율이 점점 감소하였다.모든 폐양액 부하량에서의 오염물질 처리효율은HF-VF 및 HF-HF 조합형이 다른 조합형에 비해 높았으며, 특히 총 질소의 경우 HF-HF 조합형이 가장 높은 처리효율을 보였다. 장치의 최적 여재깊이는 70 cm이상이었고, 최적 폐양액 부하이상의 결과를 미루어 볼 때 시설하우스 소형 폐양액처리량은 <TEX>$300L\;m^{-2}\;day^{-1}$</TEX>이하이었으며, 최적 조합방법은HF-HF 조합형이었다. To obtain optimum configuration, depth and load of constructed wetlands(CWs) for treating of hydroponic waste solution(HWS) which was produced in greenhouses, the study was conducted with 4 kinds of combined systems such as Vertical flow(VF)-Horizontal flow(HF), VF-VF, HF-VF and HF-HF CWs. In four configurations of CWs, the treatment efficiency of pollutants from HWS under depth of HF and VF beds, HWS loading and HWSs were investigated. Removal rate of pollutants under different depth of VF and HF in 2-stage hybrid CWs was in the order of 50 cm < 70 cm regardless of CWs configuration. Removal rate of pollutants under HWS loading in 2-stage hybrid CWs was in the order of <TEX>$150L\;m^{-2}\;day^{-1}{\fallingdotseq}300L\;m^{-2}\;day^{-1}\;</TEX><TEX>></TEX><TEX>\;450L\;m^{-2}\;day^{-1}$</TEX>. The optimum depth and HWS loading were 70 cm and <TEX>$300L\;m^{-2}\;day^{-1}$</TEX> in four configurations of CWs, respectively. Using this optimum condition, for various HWSs (cucumber, paprika and strawberry HWS), removal rate of pollutants in HF-HF CWs was higher than that in HF-VF CWs. Optimum configuration of 2-stage hybrid CWs for treating hydroponic waste solution in greenhouses was found out to be HF-HF CWs. Therefore, under the optimum conditions, removal rate of BOD, COD, SS, T-N and T-P in HF-HF CWs were 84, 81, 84, 51 and 93%, respectively.

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

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

A potential new process for improving nitrogen removal in constructed wetlands—Promoting coexistence of partial-nitrification and ANAMMOX

Conventional nitrification by vertical flow constructed wetlands beds and denitrification by horizontal flow constructed wetlands beds were considered as the main ways to remove nitrogen in constructed wetlands. However, recent evidences showed that there are other microbial pathways for nitrogen removal which are based on partial-nitrification of ammonium to nitrite with combining anaerobic ammonium oxidation (ANAMMOX). The full-scale experiments, lasting 100 days in Evieu, east of France, showed that with appropriate design and modification, for example dividing the depth of 80 cm conventional vertical flow beds into a 25 cm unsaturated layer and a 55 cm saturated layer, this new model cannot only get a better performance in removal efficiency of total nitrogen, but also achieved a promoted growth of ANAMMOX bacteria which will function to further remove the ammonium in horizontal flow beds. With fluorescent in situ hybridization (FISH) analysis, aerobic ammonia oxidizing bacteria (AOB) in conventional vertical flow CWs and ANAMMOX bacteria in the interface between unsaturated–saturated layer of amelioration vertical flow CWs and the followed horizontal flow CWs were tested. This paper described the design, the performance and the results. Comparison experiments with conventional process of nitrification–denitrification beds were also done at the same times; results indicated that the two processes carried on are completely different pathways. Results of experiments, nitrogen balance and FISH analysis proved that the process of partial-nitrification with ANAMMOX can be realized in constructed wetlands and can obtain higher removal efficiency of total nitrogen than conventional methods.

Pollutants removal effectiveness in hydrophyte filters with sequential vertical and horizontal flow

The performance of constructed wetland composed of sequential reed beds with vertical and horizontal flow of sewage was evaluated, basing on results of concentrations of organic matter, suspended solids and nutrients in inflow and in outflow as well as after subsequent stages of treatment in period 2001–2003. It was proved that dominant role in organic substances removal reaching 98.0% plays vertical flow filter. The removal of phosphorus took place in horizontal flow constructed wetland with efficiency of 36.5%, in vertical flow bed with efficiency 32.9%. Additionally applied adsorption filter removed the rest of phosphorus compounds to the value below 1mg d−1.Horizontal flow bed secured efficient nitrification of ammonia nitrogen average equal to 81.1% during vegetation season and 93.9% in outside vegetation season. The efficient the denitrification process took place only in 2001 year in horizontal flow constructed wetland with efficiency equal to 0.5g N day−1 (below project assumptions). In the further time of exploitation colmotation of filling material occurred due to excess load of contaminants from illegal discharge of sewage from individual farms.

Nitrogen and bacterial removal in constructed wetlands treating domestic waste water

The current study was carried out to compare the performances of two combined systems at pilot scale: the first one is composed of a vertical flow bed planted with Phragmites and a horizontal flow bed planted with Typha. The second combined system is an unplanted one. Each vertical flow bed, placed in the upstream of the horizontal flow bed is fed intermittently with a flow rate of 0.144 m 3 per day corresponding to an hydraulic application rate of a 0.24 m 3/m 2/day. Such parameters as Kjeldahl nitrogen, ammonia, and nitrate, nitrite, total and faecal coliform in the influent and effluent of the wetland system are examined, and their removal rates are determined. Nitrogen removal in planted system was greater than in unplanted one especially for nitrogen Kjeldahl (27 and 5%) and nitrogen ammonia (19 and 6%). Whereas, removal of nitrate-nitrite in planted system is less than in unplanted one (4 and 13%). However, bacterial removal in both planted and unplanted system was similar.

Using a compact combined constructed wetland system to treat agricultural wastewater with high nitrogen

The objectives of this study were to find appropriate conditions for nitrogen removal by a compact combined constructed wetland system and to evaluate the removal rate constant in a tropical climate. This study will present suitable operating conditions for a combined system to treat pig farm wastewater containing high ammonia-nitrogen. Four laboratory-scale combined constructed wetland units (0.5 x 1.0 x 1.0 m3): vertical flow vegetated bed over horizontal flow sand bed, were operated under an average temperature of 24 degrees C. Pig farm wastewater with COD and NH4-N concentration of 1034 and 448 mg/L in average was fed to the system at different HLR from 2 to 8 cm/day. The performance of the system when operated with a vertical flow bed followed by a horizontal flow bed or vice versa did not show a significant difference but under high HLR, nitrogen removal efficiencies were clearly reduced. Nitrobacter and Nitrosomonas were found in a large number in vertical flow beds and the same for denitrifier bacteria in a horizontal flow beds. Removal rate constants for nitrification (kNH4+ -N) were 0.0413 m/d for H-Vmode and 0.0339 m/d for V-H mode. Removal rate constants for denitrification (kNOx-N) were 0.0979 m/d for H-Vmode and 0.0399 m/d for V-H mode, respectively.

Treatment of agricultural wastewater in two experimental combined constructed wetland systems in a tropical climate

Two designs of experimental combined constructed wetland systems were constructed: vegetated (Scirpus grossus Linn) subsurface horizontal flow bed followed by a vegetated vertical flow bed and a vegetated vertical flow bed over an unvegetated horizontal flow sand bed. The systems were used to compare the nitrification/denitrification efficiency in a tropical climate which has temperatures above an average of 25 degrees C throughout the year. The effluent from a biogas digester of pig farm wastewater with TKN and COD concentrations of approximately 400 and 1,000 mg/L was fed every 4 hours intermittently. The effluent was recycled to the system with the ratio of 1:1 and the hydraulic loading rate was increased from 3 to 6 and 12 cm/d including recycled water. At higher hydraulic loading rates, nitrogen COD and BOD removal efficiencies were lower. The SS, TP and fecal coliform bacteria removal efficiencies were not clearly affected by the high hydraulic loading or the different layout of the system. Nitrogen uptake by plants was very low in relation to the nitrogen loading of the systems. In general, the removal efficiencies of both types were comparable but the system with a vertical flow over horizontal flow sand bed is more suitable for sites with limited land area, although its construction can be more difficult than the system with horizontal flow followed by a vertical flow bed.

Constructed wetlands for wastewater treatment in the Czech Republic

The first constructed wetland (CW) for wastewater treatment was built in the Czech Republic in 1989. This recent survey shows that at the end of 1999 101 systems are in operation and several more are under construction. 95 CWs are designed with sub-surface horizontal flow, 6 systems are hybrid with a combination of vertical and horizontal flow beds. Most systems (56) were designed for the treatment of municipal and domestic sewage while 38 CWs were designed for the treatment of wastewater from combined sewer systems. The most commonly used size of vegetated beds is 1,001-2,500 m2 (31 systems) followed by the area between 51-250 m2 (19%). The area of vegetated bed of the largest system is 4,493 m2. Size distribution is quite evenly spread from very small systems (PE = 3 or 4) up to 1,000 PE. However, most systems (44) were sized to treat wastewater from sources between 101 and 500 PE. The most commonly used macrophyte is Common reed (Phragmites australis) which is used in 34 systems as a monotypic stand and in 44 systems in combination with other macrophytes, most frequently with Reed canarygrass (Phalaris arundinacea) (31 systems) and cattails (Typha spp.) (8 systems).

Phosphorus removal from trout farm effluents by constructed wetlands

Freshwater trout farms need a high and continuous clean water flow to keep fish exposed to a non-toxic ammonium concentration. As a result, the concentration of effluents from these farms are even below standard effluent criteria for municipal wastewater effluent for solids, nitrogen and phosphorus. Nevertheless, the mass of pollutants discharged, originating mostly from excreta and undigested fish food, must be reduced by simple and economical treatment processes. We designed and operated a three-stage system aimed at retaining solids by a 60 pm nylon rotating microscreen followed by treatment with a phosphorus-retaining constructed wetland system. Washwater from the microscreen was pumped to a series of two horizontal flow beds of 100 m3 each (0.6 m deep). Coarse (2 mm) and finer (< 2 mm) crushed limestone were used in each bed, respectively, with the first one being planted with reeds (Phragmites australis) and the second one designed to remove even more phosphorus by adsorption and precipitation. Preliminary results indicated that the microscreen captured about 60% of the suspended solids and that greater than 95% of the suspended solids and greater than 80% of the total phosphorus mass loads were retained by the beds. The potential of constructed wetlands as an ecologically attractive and economical method for treating fish farm effluents to reduce solids and phosphorus discharge appears promising.

Design of a Hybrid Reed Bed System to Achieve Complete Nitrification and Denitrification of Domestic Sewage

The design of vertical-flow (VF) reed beds is reviewed and the performance of the few worldwide existing hybrid systems, combining both horizontal- and vertical-flow beds, is assessed. Horizontal-flow (HF) beds are good for suspended solids removal and will remove BOD5 up to a set loading. Vertical-flow beds can achieve BOD5 removal at much higher loading rates and they are capable of complete nitrification as tertiary or secondary treatment systems. It is possible to achieve biological denitrification in horizontal-flow beds. By combining horizontal- and vertical-flow systems in the appropriate process sequence it is thus possible to produce a system which removes BOD5, TSS and achieves complete nitrification as well as substantial removal of nitrate and hence a lowered Total N. The paper discusses the possible process options for combining horizontal- and vertical-flow systems. One example of these systems will be described in more detail. This is a flexible hybrid system being built by Severn Trent Water. Designed to treat the flow for a small village with a population of 129 it will have vertical-flow beds followed by horizontal-flow beds. The design allows for flexibility such that the size of the vertical-flow and horizontal-flow stages can be altered (for experimental purposes) to allow the design arrangement to be stressed and performance evaluated with the intention of defining the optimum loading rates for each of the stages. The same site also has sludge drying reed beds for treating the primary sludge.

Two-Stage Constructed Wetland for Treating Hospital Wastewater in Nepal

To treat the wastewater of a hospital at Dhulikhel/Nepal, a two-stage constructed wetland was built with a settlement tank, a horizontal flow bed as first stage and a vertical flow bed as second stage. The plant is operated without electric power. The aim was the elimination of organic compounds, nitrification and a significant reduction of indicator bacteria. Different phases of operation (high and low water level within the soil profile, serial operation, one stage operation) were investigated, of which the serial operation with high water level in the horizontal flow bed and low water level in the vertical flow bed showed the best elimination performance. The areal removal rate constants (k-values) turned out to be very high (especially of the vertical flow bed) compared with literature values of other subsurface flow constructed wetlands. For the vertical flow bed kCOD was 0.22 m/d and kNH4-N was 0.85 m/d during serial operation. For kNH4-N a strong correlation with the hydraulic loading rate and the COD inlet concentration was found.

A Review of the Design and Performance of Vertical-flow and Hybrid Reed Bed Treatment Systems

The paper reviews the different options for the combination of vertical- and horizontal-flow beds used in hybrid reed bed/wetland systems. The design and performance of these systems are briefly described. The importance of the oxygen transfer capacity of the different arrangements to their performance and their size is discussed. Alternative methods for denitrification are briefly described.

Design of a hybrid reed bed system to achieve complete nitrification and denitrification of domestic sewage

The design of vertical-flow (VF) reed beds is reviewed and the performance of the few worldwide existing hybrid systems, combining both horizontal- and vertical-flow beds, is assessed. Horizontal-flow (HF) beds are good for suspended solids removal and will remove BOD5 up to a set loading. Vertical-flow beds can achieve BOD5 removal at much higher loading rates and they are capable of complete nitrification as tertiary or secondary treatment systems. It is possible to achieve biological denitrification in horizontal-flow beds. By combining horizontal- and vertical-flow systems in the appropriate process sequence it is thus possible to produce a system which removes BOD5, TSS and achieves complete nitrification as well as substantial removal of nitrate and hence a lowered Total N.The paper discusses the possible process options for combining horizontal- and vertical-flow systems. One example of these systems will be described in more detail. This is a flexible hybrid system being built by Severn Trent Water. Designed to treat the flow for a small village with a population of 129 it will have vertical-flow beds followed by horizontal-flow beds. The design allows for flexibility such that the size of the vertical-flow and horizontal-flow stages can be altered (for experimental purposes) to allow the design arrangement to be stressed and performance evaluated with the intention of defining the optimum loading rates for each of the stages.The same site also has sludge drying reed beds for treating the primary sludge.

Two-stage constructed welland for treating hospital wastewater in nepal

To treat the wastewater of a hospital at Dhulikhel/Nepal, a two-stage constructed wetland was built with a settlement tank, a horizontal flow bed as first stage and a vertical flow bed as second stage. The plant is operated without electric power. The aim was the elimination of organic compounds, nitrification and a significant reduction of indicator bacteria. Different phases of operation (high and low water level within the soil profile, serial operation, one stage operation) were investigated, of which the serial operation with high water level in the horizontal flow bed and low water level in the vertical flow bed showed the best elimination performance. The areal removal rate constants (k-values) turned out to be very high (especially of the vertical flow bed) compared with literature values of other subsurface flow constructed wetlands. For the vertical flow bed kCOD was 0.22 m/d and kNH4-N was 0.85 nVd during serial operation. For kNH4-N a strong correlation with the hydraulic loading rate and the COD inlet concentration was found.

Treatment of dairy farm wastewaters in engineered reed bed systems

The objective of an engineered reed bed is to manage the natural growth of the reeds in order to optimise the processing of the wastewater to be purified. Downflow reed beds, with two treatment stages, have been added in front of a previously installed horizontal flow bed on a dairy farm to treat parlour washings and standing yard wastewater. Recent results have shown that the BOD is being reduced from an average of 1006 mg/litre at the inlet to only 57 mg/litre at the exit from the small final lagoon.