Vertical-flow Wetland Research Articles

English

The efficiency of a scale model vertical flow wetland (VFW) and aerobic wetland system in treating acid mine drainage was monitored over a two year period. The vertical flow system was constructed using a mixture of mushroom compost and limestone and the aerobic wetland was a cattail (Typha latifolia) dominated system constructed with mushroom compost as the planting medium. Water samples were collected weekly and analyzed for pH, acidity, alkalinity, iron, manganese, iron and manganese oxidizing bacteria. There was nearly a three unit increase in pH (3.73-6.65) along with a 83% reduction in acidity from an average of 300 mg/L to 50mg/L (83%) and corresponding net alkaline discharge of between 40-9 mg/l. The average iron concentrations were reduced from 32 to 4 mg/l (88%), but only an average of 2 mg/L (11%) of manganese was removed with all manganese reductions occurring in the aerobic wetland. The efficiency of the system varied seasonally, as well as between years, and the reductions in iron and manganese concentrations were correlated with bacterial activity within the systems. The majority of reduction in acidity in the VFW occurred within the upper 45 cm of the substrate, whereas alkaline addition and metal removal occurred between 45 and 90 cm of substrate depth. The efficiency of the systems decreased in the second year of operation. The efficiency of the scale model was similar to systems currently treating acid mine drainage in northwestern Pennsylvania.

Phosphorus Removal in Different Constructed Wetlands

To make the constructed wetlands more acceptable for sewage treatment, these systems need to guarantee high purification rates for both organic substances as well as plant nutrients (N, P). However, in most constructed wetlands, the P elimination rate remains relatively low. By comparing the purification rates for P (and P fractions in soil after fractionated extraction) among different systems, it was determined that the addition of iron filings to the filter material is more effective in ensuring a sustainable high removal capacity than the use of Ca-rich soils. Long-term studies on a horizontal flow wetland (HFW) show that an iron-rich soil filter with Phragmites australis removes 97% of P from sewage even after nine years at pH values of between 4.6 and 4.9. About 60% of the P is bound to Fe (or Al) in a predominately amorphous form. In a vertical flow wetland (VFW), the P removal rate remains much lower (27%) at pH values of between 5.8 and 6.4. About 30% of the P is bound to iron, 30% to Ca and 20% as refractory P. Altogether, HFWs seem to be more effective in P elimination than VFWs because of the longer flowing distance and treatment time. Removal of plants from the soil filter leads to a significant decrease of 50% in the P elimination rate. This result indirectly shows the role of plants in microbiological P transformation processes and in the direct elimination of P by binding it to humic substances.

Mature experimental constructed wetlands treating urban water receiving high metal loads.

The aim was to assess over 2 years the treatment efficiencies of vertical-flow wetland filters containing macrophytes and granular media of different adsorption capacities. Different concentrations of lead and copper sulfate (constant for 1 year each) were added to urban beck inflow water in order to simulate pretreated (pH adjustment assumed) mine wastewater. After 1 year of operation, the inflow concentrations for lead and copper were increased from 1.30 to 2.98 and from 0.98 to 1.93 mg/L, respectively. However, the metal mass load rates (mg/m(2)/d) were increased by a factor of approximately 4.9 for lead and 4.3 for copper. No breakthrough of metals was recorded. Lead and copper accumulated in the biomass of the litter zone and rhizomes of the macrophytes. Furthermore, microbiological activity decreased during the second year of operation. Bioindicators such as ciliated protozoa and zooplankton decreased sharply in numbers but diatoms increased. In conclusion, the use of macrophytes and adsorption media did not significantly enhance the filtration of lead and copper. Particulate lead is removed by filtration processes including straining. Furthermore, some expensive and time-consuming water quality variables can be predicted with less expensive ones such as temperature in order to reduce sampling costs.

Performance comparison of experimental constructed wetlands with different filter media and macrophytes treating industrial wastewater contaminated with lead and copper

The aim of this study was to investigate the treatment efficiency of passive vertical-flow wetland filters containing different macrophytes ( Phragmites and/or Typha) and granular media with different adsorption capacities. Gravel, sand, granular activated carbon, charcoal and Filtralite (light expanded clay) were used as filter media. Different concentrations of lead and copper sulfate were added to polluted urban stream inflow water to simulate pretreated mine wastewater. The relationships between growth media, microbial and plant communities as well as the reduction of predominantly lead, copper and five-day biochemical oxygen demand (BOD 5) were investigated. An analysis of variance showed that concentration reductions ( mg l −1) of lead, copper and BOD 5 were significantly similar for the six experimental wetlands. Microbial diversity was low due to metal pollution and similar for all filters. There appears to be no additional benefit in using adsorption media and macrophytes to enhance biomass performance during the first 10 months of operation.

Removal of hydrogen sulphide BOD from brackish water using vertical flow wetlands in a Caribbean environment

Wastewater from a 550-inhabitant community had been treated and discarded using an anaerobic filter. Due to seawater intrusion in the aquifer that supplies the water, high concentrations of hydrogen sulphide were detected in the effluent. A vertical flow wetland was designed in 1998 for treating this effluent. Four parallel reed beds with a total area of 556 m2 were constructed. During the first months of operation, a mean BOD5 removal efficiency of 91% was obtained, with loads to the wetland system up to 4 g/m2/d of grease and oils (G&O). In 1999, problems of soil clogging were found due to high G&O content in the wastewater, with loads up to 15 g/m2/d of G&O, which highly influenced the hydraulic conductivity of the beds, generating the clogging problems. The low hydraulic conductivity and the high effluent G&O content, caused low BOD5 and COD removal efficiencies. As G&O accumulated in the soil, the removal efficiencies decreased. Despite the clogging problems, there has been a high sulphide removal throughout the system operation. The wetlands removed sulphides successfully, under loads up to 20 g S=/m2/d. Four native species of macrophytes were planted: Paspalum penisetum, Typha sp, Conocarpres erectus and Scirpus lacustris. All of them but Typha sp. were established in the system.

Use of constructed wetlands for acid mine drainage abatement and stream restoration

Constructed wetlands have been used for over two decades for the treatment of acid mine drainage (AMD). Through a variety of physical, chemical, biological processes, these wetlands are effective in reducing acidity and removing up to 99% of iron and aluminium from AMD, but they only remove 20-30% of the manganese loading. The Slippery Rock Creek watershed in northwestern, Pennsylvania has been adversely impacted by acid mine drainage (AMD) for over 100 years with 74 mine discharges contributing a total of 1,228.8 kg, 282 kg and 69 kg/day of sulfuric acid, iron and aluminium, respectively to receiving streams. In the Slippery Rock Creek Watershed, aerobic and vertical flow wetlands, along with limestone drains and vertical flow limestone beds help to restore acid mine drainage impacted streams. Since 1995, the construction of seven passive treatment systems currently contribute 192.8 kg of alkalinity and remove 39% of the acid loading to a 4.83 km section of Slippery Rock Creek. When the eight passive treatment currently under construction are in operation, it is anticipated that there will be an additional 34.7% reduction in acidic loading to streams within the watershed. The cost of restoring all streams currently impacted by acid mine drainage within the Slippery Rock Creek watershed is currently estimated at $8,929,500.

Removal of nutrients from combined sewer overflows and lake water in a vertical-flow constructed wetland system

Lake Utterslev is situated in a densely built-up area of Copenhagen, and is heavily eutrophicated from combined sewer overflows. At the same time the lake suffers from lack of water. Therefore, a 5,000 m2 vertical flow wetland system was constructed in 1998 to reduce the phosphorus discharge from combined sewer overflows without reducing the water supply to the lake. During dry periods the constructed wetland is used to remove phosphorus from the lake water. The system is designed as a 90 m diameter circular bed with a bed depth of c. 2 m. The system is isolated from the surroundings by a polyethylene membrane. The bed medium consists of a mixture of gravel and crushed marble, which has a high binding capacity for phosphorus. The bed is located within the natural littoral zone of the lake and is planted with common reed (Phragmites australis). The constructed wetland is intermittently loaded with combined sewer overflow water or lake water and, after percolation through the bed medium, the water is collected in a network of drainage pipes at the bottom of the bed and pumped to the lake. The fully automated loading cycle results in alternating wet and dry periods. During the initial two years of operation, the phosphorus removal for combined sewer overflows has been consistently high (94-99% of inflow concentrations). When loaded with lake water, the phosphorus removal has been high during summer (71-97%) and lower during winter (53-75%) partly because of lower inlet concentrations. Effluent phosphorus concentrations are consistently low (0.03-0.04 mg/L). Ammonium nitrogen is nitrified in the constructed wetland, and total suspended solids and COD are generally reduced to concentrations below 5 mg/L and 25 mg/L, respectively. The study documents that a subsurface flow constructed wetland system can be designed and operated to effectively remove phosphorus and other pollutants from combined sewer overflows and eutrophicated lake water.

Development of a conceptual model for vertical flow wetland metabolism

Four parallel vertical constructed wetlands, with a total area of 556 m2, are used to treat domestic wastewater, coming from a community of 550 inhabitants. The system includes pre-treatment with an anaerobic filter and post-treatment with chlorine, before discharging the effluent to the ocean. Four native species of macrophytes were planted: Paspalum penisetum, Typha sp, Conocarpres erectus and Scirpus lacustris. In situ measurements of gas content were performed for each bed during an operation cycle. After a feeding discharge, an unaltered sample of sand from each bed was taken, and a respirometric test was implemented to measure the metabolic activity in terms of oxygen consumption kinetics, CO2 production and organic matter degradation. The results were used to develop a conceptual model of the microbiologic metabolism for the process of organic matter removal from wastewater. Sorption in the bed is the main mechanism for organic matter removal from the wastewater, with subsequent biological oxidation during the resting period. The degradation rate for dissolved organic matter is found to be dependent on its concentration and on oxygen content in the gaseous phase. During the days of major activity, the oxygen content was not fully recovered when a new discharge occurred, finding anaerobic activity within the bed.

Nutrient removal efficiency and resource economics of vertical flow and horizontal flow constructed wetlands

In order to reduce the very high costs of sewage disposal in the new federal states of Germany, more decentralized purification systems need to be established. To attain higher surface water quality, and thereby the acceptance of such systems by governmental authorities, good removal rates for organic substances and also for nutrients (N, P) are necessary. Constructed wetlands for wastewater treatment (reed-bed systems) in Germany and in the USA have been used successfully. This study compares the purification performances of constructed horizontal flow wetlands (HFW) and vertical flow wetlands (VFW), including: (1) a small horizontal flow wetland (HFW); (2) a sloped HFW; (3) a larger HFW; (4) a stratified vertical flow wetland (VFW); and (5) an unstratified VFW. It is shown that both the horizontal flow and vertical flow systems can remove more than 90% of organic load and of total N and P, if there is an effective precleaning step, and if the specific treatment area is great enough (>50 m 2/m 3 per d). HFWs have an advantage in long-term removal of P because it is bound to organic substances to a high degree. Decentral and semicentral natural treatment systems also save material (76%) and energy (83%) for their function compared with central technical systems.

Treatment of acid mine drainage by four vertical flow wetlands in Pennsylvania

Acid mine drainage (AMD) is a serious problem in many watersheds where coal is mined. Passive treatments, such as wetlands and anoxic limestone drains (ALDs), have been developed, but these technologies show varying treatment efficiencies. A new passive treatment technique is a vertical flow wetland or successive alkalinity producing system (SAPS). Four SAPS in Pennsylvania were studied to determine changes in water chemistry from inflow to outflow. The Howe Bridge SAPS removed about 130 mg l −1 (40%) of the inflow acidity concentration and about 100 mg l −1 (60%) iron (Fe). The Filson 1 SAPS removed 68 mg l −1 (26%) acidity, 20 mg l −1 (83%) Fe and 6 mg l −1 (35%) aluminium (Al). The Sommerville SAPS removed 112 mg l −1 (31%) acidity, exported Fe, and removed 13 mg l −1 (30%) Al. The McKinley SAPS removed 54 mg l −1 (91%) acidity and 5 mg l −1 (90%) Fe. Acid removal rates at our four sites were 17 (HB), 52 (Filson1), 18 (Sommerville) and 11 (McKinley) g of acid per m 2 of surface wetland area per day (g/m 2 d −1 ). Calcium (Ca) concentrations in the SAPS effluents were increased between 8 and 57 mg l −1 at these sites. Equilibrators, which were inserted into compost layers to evaluate redox conditions at our sites, showed that reducing conditions were generally found at 60 cm compost depths and oxidized conditions were found at 30 cm compost depths. Deeply oxidized zones substantiated observations that channel flow was occurring through some parts of the compost. The Howe Bridge site has not declined in treatment efficiency over a six year treatment life. The SAPS construction costs were equal to about seven years of NaOH chemical treatment costs and 30 years of lime treatment costs. So, if the SAPS treatment longevity is seven years or greater and comparable effluent water quality was achieved, the SAPS construction was cost effective compared to NaOH chemical treatment. Construction recommendations for SAPS include a minimum of 50 cm of compost thickness, periodic replacement or addition of fresh compost material, and increasing the number of drainage pipes underlying the limestone.

Alkalinity generation and metals retention in a successive alkalinity producing system

Alkalinity generation and metals retention were evaluated during the initial year of operation of a treatment wetland, consisting of four 185 m2 inseries cells comprised of alternating vertical-flow anaerobic substrate wetlands (VFs) and surface-flow aerobic settling ponds (SFs). The substrate in the VFs consists of spent mushroom substrate (SMS) and limestone gravel, supplemented with hydrated fly ash in a 20∶10∶1 ratio by volume. Approximately 15±4 L/min of acid mine drainage (AMD) from an abandoned underground coal mine in southeastern Oklahoma, USA, was directed to the system in October 1998 (mean influent water quality: 660 mg L−1 net acidity as CaCO3 eq., pH 3.4, 215 mg L−1 total Fe, 36 mg L−1 Al, 14 mg L−1 Mn, and 1000 mg L−1 SO4 −2). Flow through the first VF resulted in substantial increases in alkalinity, decreased metal concentrations and circumneutral pH. 258±84 mg L−1 of alkalinity was produced in the first VF by a combination of processes. Final discharge waters were net alkaline on all sampling dates (mean net alkalinity=136 mg L−1). Total Fe and Al concentrations decreased significantly from 216±45 to 44±28 mg L−1 and 36±6.9 to 1.29±4.4 mg L−1, respectively. Manganese concentrations did not change significantly in the first two cells, but decreased significantly in the second two cells. Mean acidity removal rates in the first VF (51 g m−2 day−1) were similar to those previously reported.

Nutrient Removal in a Vertical Upflow Wetland in Piracicaba, Brazil

Vertical upflow wetland systems have shown high nutrient removal efficiencies. The removal of nutrients (N and P) from wastewater was investigated in a vertical upflow wetland system in Piracicaba, Brazil. The concentration removal was 93% for phosphate, 78% for nitrate and 50% for ammonia. Effective phosphate removal was observed in the top soil layer which has a high surface adsorption area. Nitrate was removed satisfactory at low loading rates due to plant uptake and denitrification. Removal of ammonia was concentration dependent and decreased at high inflow concentrations. Spatial sampling through the bed showed that the treatment efficiency was not uniform. The possibility of the recycling of nutrients as a soil improver or animal feed is an important feature of this type of vertical flow wetland system.

Treatment of Potato Processing Wastewater with Engineered Natural Systems

A full-scale integrated natural system has been used to treat high strength potato processing water for 2 years. The integrated natural system consists of free water surface and vertical flow wetlands, and a facultative storage lagoon. Influent wastewater averages 2800 mg/L COD, 150 mg/L TN and 350 mg/L TSS. Approximately 5300 m3/d of wastewater flows through the treatment system annually. The treatment objective is a 53% reduction in total nitrogen. The wastewater application permit requires an annual nitrogen load of 500 kg/ha yr on 213 hectares of land used to grow alfalfa and other fodder crops. Free water surface wetlands are used for sedimentation, mineralization of organic matter, and denitrification. Vertical flow wetlands oxidize organic matter and nitrogen. A lagoon provides storage during the winter when irrigation is not possible and functions as a facultative lagoon. Free water surface wetlands were planted with Typha latifolia and Scirpus validus in fall 1995. Wastewater application began in July of 1996. In the summer months COD removal has been greater than 95% through the free water surface wetlands and vertical flow wetlands. The removal rate decreased to about 75% in the winter. Average summer water temperatures are 18°C; average winter water temperatures are 3°C. Ammonia removal through the vertical flow wetlands averages 85% during the summer and 30-50% removal during the winter. Addition of exogenous carbon to the free water surface wetlands resulted in 95% removal of NO3-N. Use of natural systems have proved to be a cost effective treatment alternative for high strength industrial wastewater.

Wastewater Treatment by Tropical Plants in Vertical-flow Constructed Wetlands

A subsurface vertical-flow laboratory scale wetland system was designed to investigate the wastewater treatment efficiency by Vetiveria zizanioides Nash, a common grass in Thailand. Diluted pig farm wastewater was fed intermittently. The removal efficiencies in terms of organic carbon, nitrogen and suspended solids were satisfactory under hydraulic and organic loading rates of 36 mm/d and 55 kgCOD/ha.d, respectively. A comparison of the performance of the systems with Vetiveria zizanioides Nash and Cyperus flabelliformis Rottb. to treat domestic wastewater was made. It was found that both plants are suitable for wastewater treatment by vertical-flow constructed wetlands in tropical areas under hydraulic and organic loading rates within 121 mm/d and 198 kgCOD/ha.d, respectively.

Treatment of potato processing wastewater with engineered natural systems

A full-scale integrated natural system has been used to treat high strength potato processing water for 2 years. The integrated natural system consists of free water surface and vertical flow wetlands, and a facultative storage lagoon. Influent wastewater averages 2800 mg/L COD, 150 mg/L TN and 350 mg/L TSS. Approximately 5300 m3/d of wastewater flows through the treatment system annually. The treatment objective is a 53% reduction in total nitrogen. The wastewater application permit requires an annual nitrogen load of 500 kg/ha yr on 213 hectares of land used to grow alfalfa and other fodder crops. Free water surface wetlands are used for sedimentation, mineralization of organic matter, and denitrification. Vertical flow wetlands oxidize organic matter and nitrogen. A lagoon provides storage during the winter when irrigation is not possible and functions as a facultative lagoon. Free water surface wetlands were planted with Typha latifolia and Scirpus validus in fall 1995. Wastewater application began in July of 1996. In the summer months COD removal has been greater than 95% through the free water surface wetlands and vertical flow wetlands. The removal rate decreased to about 75% in the winter. Average summer water temperatures are 18°C; average winter water temperatures are 3°C. Ammonia removal through the vertical flow wetlands averages 85% during the summer and 30–50% removal during the winter. Addition of exogenous carbon to the free water surface wetlands resulted in 95% removal of N03-N. Use of natural systems have proved to be a cost effective treatment alternative for high strength industrial wastewater.

Aquaculture sludge removal and stabilization within created wetlands

The objective of this research was to investigate treatment of the concentrated solids discharge produced during clarifier backwash within an aquaculture facility. Solids removal and stabilization were investigated within two types of created wetlands where water flowed either: (1) vertically, down through a porous substrate; or (2) horizontally, over soil and through plant hedges. Six 3.7×1.2×0.8-m (L×W×H) wetland cells were used to provide three replicates for both types of wetland. Approximately equal numbers of vetiver grass (Vetiveria zizanioides) tillers were planted on both wetlands types in November of 1994. Sludge (7500 mg l−1 solids) was loaded onto both wetland types six times day−1, with no scheduled drying cycle, from 12 May 1995 until 28 February 1996. Sludge was applied at a rate of about 1.35 cm day−1, or about 30 kg dry solids m−2 year−1. Results from this short study indicated that the vertical flow and horizontal flow wetlands, respectively, removed 98 and 96% TSS, 91 and 72% total COD, and 81 and 30% dissolved COD. Both types of wetland cells removed most (82–93%) of the total kjeldahl nitrogen, phosphorus, and dissolved phosphate. Measurements of sludge depths and TVS at the end of the study indicated considerable mineralization occurred in the wetlands; stored sludge at the end of the study had 50% less TVS than untreated sludge.

Wastewater treatment by tropical plants in vertical-flow constructed wetlands

A subsurface vertical-flow laboratory scale wetland system was designed to investigate the wastewater treatment efficiency by Vetiveria zizanioides Nash, a common grass in Thailand. Diluted pig farm wastewater was fed intermittently. The removal efficiencies in terms of organic carbon, nitrogen and suspended solids were satisfactory under hydraulic and organic loading rates of 36 mm/d and 55 kgCOD/ha.d, respectively.A comparison of the performance of the systems with Vetiveria zizanioides Nash and Cyperus flabettiformis Rottb. to treat domestic wastewater was made. It was found that both plants are suitable for wastewater treatment by vertical-flow constructed wetlands in tropical areas under hydraulic and organic loading rates within 121 mm/d and 198 kgCOD/ha.d, respectively.

A model of factors controlling orthophosphate removal in planted vertical flow wetlands

Orthophosphate removal from wastewater by planted vertical-flow wetlands (VFWs) occurs through three parallel paths, with reaction rates of: sorption to substratum>biofilm assimilation⪢macrophyte uptake. Short term (one or two loadings) plant removal of phosphorus (P) is small but irreversible, whereas P removed by substratum sorption, or non-reactive P (NRP) formation, can be returned as reactive phosphorus (RP). The quantity of P removed by the three paths is substratum>macrophyte ⪢biofilm, in the short term, but macrophyte>substratum⪢biofilm, over months. Rhizosphere hydrology restricts P removal, the rate is limited by mass transfer without liquid mixing, but trebled by mixing. Evapotranspirational mixing alone is small and erratic. In small, above-ground, systems environmental temperature changes cause daily mixing, but prevailing soil temperature gradients limit below-ground mixing. A planted wetland, conceptual model, explains: (1) retention times: determined by initial RP removal rates, and operationally dependent on RP concentration and mixing. Aqueous phase cycling reduces retention times several fold; (2) minimum outflow concentrations: controlled by the gravel–PO 4 sorption equilibrium; (3) sustainable annual P removal: the quantity harvested in the macrophytes. Substratum Fe(III) oxide–hydroxide sorption provides additional assimilation for some years. Specific, model derived, VFW design and operation recommendations are made.

Integrated natural systems for treating potato processing wastewater

Potato processing wastewater contains high concentrations of COD, TSS and TKN. A combination of surface flow wetlands, intermittent vertical flow wetlands, ponds and land application has been used for treatment. This engineered natural system balances irrigation requirements, nitrogen supply and seasonal growth patterns to provide effective year-round operation. A first pilot wetland was operated to determine operability, effectiveness, and plant survival at high COD and nitrogen concentrations. A second pilot system of four wetlands in series was operated to obtain design and operating information. Two surface flow wetlands provided TSS and COD reduction, and ammonified the organic nitrogen. Subsequently, nitrification occurred in the vertical flow wetlands, followed by denitrification in a surface flow wetland. The design target was a balanced nitrogen and irrigation supply for application to crops. Winter storage was used to match the crop application period to the growing season. Both pilot projects met design objectives, and a full-scale system has begun operation.

Deterministic and stochastic aspects of constructed wetland performance and design

Potato processing wastewater contains high concentrations of COD, TSS and TKN. A combination of surface flow wetlands, intermittent vertical flow wetlands, ponds and land application has been used for treatment. This engineered natural system balances irrigation requirements, nitrogen supply and seasonal growth patterns to provide effective year-round operation. A first pilot wetland was operated to determine operability, effectiveness, and plant survival at high COD and nitrogen concentrations. A second pilot system of four wetlands in series was operated to obtain design and operating information. Two surface flow wetlands provided TSS and COD reduction, and ammonified the organic nitrogen. Subsequently, nitrification occurred in the vertical flow wetlands, followed by denitrification in a surface flow wetland. The design target was a balanced nitrogen and irrigation supply for application to crops. Winter storage as used to match the crop application period to the growing season. Both pilot projects met design objectives, and a full scale system has begun operation.