Effect of recirculation on organic matter removal in a hybrid constructed wetland system

This research project aimed to determine the technologically feasible and applicable wastewater treatment systems which will be constructed to solve environmental problems caused by small communities in Turkey. Pilot-scale treatment of a small community's wastewater was performed over a period of more than 2 years in order to show applicability of these systems. The present study involves removal of organic matter and suspended solids in serially operated horizontal (HFCW) and vertical (VFCW) sub-surface flow constructed wetlands. The pilot-scale wetland was constructed downstream of anaerobic reactors at the campus of TUBITAK-MRC. Anaerobically pretreated wastewater was introduced into this hybrid two-stage sub-surface flow wetland system (TSCW). Wastewater was first introduced into the horizontal sub-surface flow system and then the vertical flow system before being discharged. Recirculation of the effluent was tested in the system. When the recirculation ratio was 100%, average removal efficiencies for TSCW were 91 +/- 4% for COD, 83 +/- 10% for BOD and 96 +/- 3% for suspended solids with average effluent concentrations of 9 +/- 5 mg/L COD, 6 +/- 3 mg/L BOD and 1 mg/L for suspended solids. Comparing non-recirculation and recirculation periods, the lowest effluent concentrations were obtained with a 100% recirculation ratio. The effluent concentrations met the Turkish regulations for discharge limits of COD, BOD and TSS in each case. The study showed that a hybrid constructed wetland system with recirculation is a very effective method of obtaining very low effluent organic matter and suspended solids concentrations downstream of anaerobic pretreatment of domestic wastewaters in small communities.     

Modelling and evaluation of nitrogen removal performance in subsurface flow and free water surface constructed wetlands.

With the aim of protecting drinking water sources in rural regions, pilot-scale subsurface water flow (SSF) and free water surface flow (FWS) constructed wetland systems were evaluated for removal efficiencies of nitrogenous pollutants in tertiary stage treated wastewaters (effluent from the Pasak?y biological nutrient removal plant). Five different hydraulic application rates and emergent (Canna, Cyperus, Typhia sp., Phragmites sp., Juncus, Poaceae, Paspalum and Iris) and floating (Pistia, Salvina and Lemna) plant species were assayed. The average annual NH4-N, NO3-N and organic-N treatment efficiencies were 81, 40 and 74% in SSFs and 76, 59 and 75% in FWSs, respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. Nitrification, denitrification and ammonification rate constants (k20) values in SSF and FWS systems were 0.898 d-1 and 0.541 d(-1), 0.486 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908, respectively. Results show that the first-order plug flow model clearly estimates slightly higher or lower values than observed when compared with the other model.     

Nitrogen management in reservoir catchments through constructed wetland systems.

In this study, nitrogen removal was investigated in pilot-scale subsurface flow (SSF) and in free water surface flow (FWS) constructed wetlands installed in the campus of TUBITAK-Marmara Research Center, Gebze, near Istanbul, Turkey. The main purposes of this study are to apply constructed wetlands for the protection of water reservoirs and to reuse wastewater. Experiments were carried out at continuous flow reactors. The effects of the type of plants on the removal were investigated by using emergent (Canna, Cyperus, Typhia spp., Phragmites spp., Juncus, Poaceae, Paspalum and Iris.), submerged (Elodea, Egeria) and floating (Pistia, Salvina and Lemna) marsh plants at different conditions. During the study period HLRs were 30, 50, 70, 80 and 120 L m(2)d(-1) respectively. The average annual NH4-N, NO(3)-N, organic N and TN treatment efficiencies in SSF and FWS wetlands are 81% and 68%, 37% and 49%, 75% and 68%, 47% and 53%, respectively. Nitrification, denitrification and ammonification rate constant (k20) values in SSF and FNS systems have been found as 0.898 d(-1) and 0.541 d(-1), 0.488 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908 respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances.     

A pollutant removal prediction tool for stormwater derived diffuse pollution.

This report describes the development of a methodology to theoretically assess the effectiveness of structural BMPs with regard to their treatment of selected stormwater pollutants (metals, polyaromatic hydrocarbons and herbicides). The result is a prioritisation, in terms of pollutant removal efficiency, of 15 different BMPs which can inform stormwater managers and other stakeholders of the best available options for the treatment of urban runoff pollutants of particular environmental concern. Regardless of the selected pollutant, infiltration basins and sub-surface flow constructed wetlands are predicted to perform most efficiently with lagoons, porous asphalt and sedimentation tanks being the least effective systems for the removal of pollutants. The limitations of the approach in terms of the variabilities in BMP designs and applications are considered.     

Experimental study of a novel hybrid constructed wetland for water reuse and its application in Southern China

A new type of hybrid constructed wetland (CW), consisting of both vertical-baffled flow wetland (VBFW) and horizontal subsurface flow wetland (HSFW), has been deployed in Southern China to naturally accelerate the removal of organic matter and nitrogen. The hybrid CW system is characterised by a combination of continuous baffled flow vertical wetland and 'S' pattern horizontal subsurface flow wetland with natural aeration ditches to increase the concentration of dissolved oxygen in the HSFW bed. An internal circulatory system from the HSFW effluent back to the VBFW may optionally be operated to enhance the biological denitrification effect. Cyperus alternifolius is the main macrophyte in the wetland bed. The performance of the hybrid CW was studied with a pilot-scale system and three full-scale systems for municipal sewage treatment in Southern China. The results suggest that this new hybrid CW can achieve removal efficiencies of chemical oxygen demand, suspended solids, ammonia nitrogen, total nitrogen, and total phosphorus of better than 83.6, 95.0, 71.7, 64.5 and 68.1% respectively, with a specific wetland bed area of 0.70-0.93 m(2) PE(-1). The mean effluent concentrations of these parameters would meet the regulatory discharge limits for wastewater treatment systems (GB18918, 2002) and reuse in the context of agricultural irrigation solutions in China.     

Twenty years experience with constructed wetland systems in Denmark--what did we learn?

Full scale constructed wetland systems for wastewater treatment have been in operation in Denmark since 1983, mainly for the treatment of domestic sewage from small villages. The systems are constructed as soil-based horizontal subsurface flow systems but, because of low soil hydraulic conductivity, surface runoff is evident in most of the systems. Two decades of experience show that soil-based systems are generally efficient in removing suspended solids and BOD, but the removal of nitrogen and phosphorus is lower (typically 30-50%) and the systems do not nitrify ammonium. Contrary to earlier claims, the reeds do not increase the hydraulic conductivity of cohesive soils as much as necessary to secure sub-surface flow. Operation needs of soil-based reed beds are low and normally restricted to emptying of the sedimentation tank, cleaning of the distribution system and mowing of the grass around the system. The dead plant material and accumulated litter on the surface of the systems improve performance after the initial years. A significant number of systems have been shut down or extended with other technologies in order to meet new effluent standards, particularly demands for nitrification. New constructed wetland systems are either compact vertical flow systems which provide good nitrification, willow systems with no discharge or restored wetland systems for nitrate removal. If efficient removal of phosphorus is required, this is achieved by chemical precipitation in the sedimentation tank.     

水平潜流人工湿地脱氮除磷研究进展

总结了水平潜流人工湿地的脱氮除磷机理,分析了进水水质、植物、基质、温度和水力停留时间这5种影响处理效果的主要因素,从不同角度论述了提高脱氮除磷效果所采取的措施,并探讨了水平潜流人工湿地存在的局限性和发展趋势。     

Optimal performance of an immersed membrane bioreactor equipped with a draft tube for domestic wastewater reclamation.

One of the options to prevent membrane fouling is to implement air lifting that can improve the cake removal from the membrane surface. This study presents the results of tests that were carried out at the Institutes for Desert Research, Kiryat Sde-Boker, Israel, and focused on the influence of hydrodynamic conditions on fouling in a pilot-scale immersed membrane bioreactor (IMBR) using a hollow fiber membrane module of ZW-10 (Zenon Environmental, Canada) under ambient conditions. In this system, the cross-flow velocities across the membrane surface were induced by one conical and four cylindrical draft-tubes. The relationship between the crossflow velocity and the aeration intensity, the influence of the crossflow on fouling rate under various hydrodynamic conditions were investigated and optimal operating conditions were obtained. Optimal operating conditions were reached during the long-term experiment period (70 days) for the treatment of domestic wastewater. The system was stable without external chemical cleaning. The results showed that the permeate was of high quality, and the removal of COD and BOD was 94.0% and 98.8%, respectively.The crossflow near the membrane surface reveals a major contribution for minimizing membrane fouling, and could offer guidelines for future design of similar systems.     

Study on purification mechanism in soil penetration facility for effluents from urban area and control strategies.

In this study, demonstration experiments for removal of pollutants from road surface runoff during storm events were carried out under natural conditions in an outdoor pilot-scale soil penetration facility. In general, soil retains suspended matter and removes dissolved matter by adsorption. However, issues such as reduced purification capacity resulting from clogging and recovery of purification capacity during periods of intermittent supply of the storm water affect the removal efficiency of pollutants. Therefore, this study aimed at clarifying purification mechanisms during storm events and understanding how the structural characteristics of the soil penetration facility affect purification capacity based on long-term continuous measurements. In addition, modeling the purification mechanism under changing characteristics of rainfall in the long-term was undertaken.     

Regeneration of barium carbonate from barium sulphide in a pilot-scale bubbling column reactor and utilization for acid mine drainage

Batch regeneration of barium carbonate (BaCO(3)) from barium sulphide (BaS) slurries by passing CO(2) gas into a pilot-scale bubbling column reactor under ambient conditions was used to assess the technical feasibility of BaCO(3) recovery in the Alkali Barium Calcium (ABC) desalination process and its use for sulphate removal from high sulphate Acid Mine Drainage (AMD). The effect of key process parameters, such as BaS slurry concentration and CO(2) flow rate on the carbonation, as well as the extent of sulphate removal from AMD using the recovered BaCO(3) were investigated. It was observed that the carbonation reaction rate for BaCO(3) regeneration in a bubbling column reactor significantly increased with increase in carbon dioxide (CO(2)) flow rate whereas the BaS slurry content within the range 5-10% slurry content did not significantly affect the carbonation rate. The CO(2) flow rate also had an impact on the BaCO(3) morphology. The BaCO(3) recovered from the pilot-scale bubbling column reactor demonstrated effective sulphate removal ability during AMD treatment compared with commercial BaCO(3).     

Nitrogen dynamics in a constructed wetland system treating landfill leachate.

A pilot scale treatment system was established in 2002 at the Laflèche Landfill in Eastern Ontario, Canada. The system consists of a series of treatment steps: a stabilisation basin (10,000 m3), a woodland peat trickling filter (5,200 m2), a subsurface flow constructed wetland planted in Phragmites sp. (2,600 m2), a surface flow constructed wetland planted in Typha sp. (3,600 m2) and a polishing pond (3,600 m2). The system operates from May to December with leachate being recycled within the landfill during the winter months. Hydraulic loading was increased three-fold over four operating seasons with nitrogen and organic mass loading increasing six-fold. Excellent removal efficiencies were observed with 93% BOD5, 90% TKN and 97% NH4-N removed under the highest loading conditions. Almost complete denitrification was observed throughout the treatment system with NO3-N concentrations never exceeding 5mg L(-1). The peat filter reached treatment capacity at a hydraulic loading of 4cm d(-1) and organic loading rate of 42 kg BOD ha(-1) d(-1), which is consistent with design criteria for vertical flow wetland systems and intermittent sand filters, The first order plug flow kinetic model was effective at describing TKN and ammonium removal in the SSF and FWS wetlands when background concentrations were taken into account. Ammonium removal k-values were consistent with the literature at 52.6 and 57.7 yr(-1) for the SSF and FWS wetlands, respectively, while TKN k-values at 6.9 and 7.7 yr(-1) were almost an order of magnitude lower than literature values, suggesting that leachate TKN could contain refractory organics not found in domestic wastewater.     

Experience in non-conventional wastewater treatment techniques used in the Czech Republic.

Among the most common non-conventional wastewater treatment techniques used in the Czech Republic are waste stabilisation ponds (WSP), subsurface horizontal flow constructed wetlands (CW) and vertical flow groundfilters (GF). These extensive systems can be advantageously used for treatment of waters coming from sewerages where the ballast weighting commonly makes more than half of dry-weather flow. The monitoring was focused at 14 different extensive systems. Organics removal efficiencies were favourable (CW-82%; GF-88%); in the case of WSP only 57% due to the algal bloom. Total nitrogen removal efficiencies were 43 and 47% for WSP and GF; in the case of CW only 32% due to often occurring anaerobic conditions in filter beds. Total phosphorus removal efficiencies were 37, 35 and 22% for WSP, GF and CW, respectively. Often occurring problems are the ice-blockage of surface aerators at WSP during wintertimes, the pond duckweed-cover or the algal bloom at WSP during summers; a gradual colmatage of filter systems; and the oxygen deficiency in beds of subsurface horizontal flow constructed wetlands. Czech legal regulations do not allow treated wastewater disposal into underground waters. There is only an exception for individual family houses. Up to now, knowledge gained by monitoring of a village (which uses the infiltration upon a permission issued according to earlier legal regulations) have not shown an unacceptable groundwater quality deterioration into the infiltration areas.     

Behaviour of heavy metals during tertiary bio-filtration.

More stringent water quality parameters in the Annex of the Water Framework Directive 2000/60/EC led to the introduction of "Maximum Tolerable Risk concentrations" (MTR-values) in the national legislation in The Netherlands (Vierde Nota Waterhuishouding). The MTR-values give limitations for the concentrations of e.g. heavy metals (HM's) but also for nutrients: Ntot < 2.2 mg/l, Ptot <0.15 mg/l. Investigations of HM removal during denitrifying flocculation filtration are conducted on the effluent of a typical modern Dutch WWTP. Because of low concentrations of HM's in the feed water, a cocktail of copper, nickel and zinc chloride (approximately equal 150-200 microg/l) is dosed before filtration. Preliminary jar tests and filtration tests with media filtration in pilot-scale and lab-scale are conducted. The results show high removal of nickel and zinc during jar tests with dosing of powdered activated carbon. During filtration tests at pilot-scale the bounded fraction of copper and zinc is highly removed. All three HM's are removed in the lab-scale activated carbon filter. After dosing, nickel is found mainly in the dissolved form, but it is removed in the lab-scale activated carbon filter. The removal of HM's via adsorption subsequently leads to a discussion on the toxicity of HM's and their bio-availability.     

Effects of sorption, sulphate reduction, and Phragmites australis on the removal of heavy metals in subsurface flow constructed wetland microcosms.

The removal of Co, Ni, Cu and Zn from synthetic industrial wastewater was studied in subsurface flow constructed wetland microcosms filled with gravel or a gravel/straw mixture. Half of the microcosms were planted with Phragmites australis and half were left unplanted. All microcosms received low-strength wastewater (1 mg L(-1) of Co, Ni, and Zn, 0.5 mg L(-1) Cu, 2,000mg L(-1) SO4) during seven 14-day incubation batches. The pore water was regularly monitored at two depths for heavy metals, sulphate, organic carbon and redox potential. Sorption properties of gravel and straw were assessed in a separate experiment. A second series of seven incubation batches with high-strength wastewater (10 mg L(-1) of each metal, 2,000 mg L(-1) SO4) was then applied to saturate the substrate. Glucose was added to the gravel microcosms together with the high-strength wastewater. Sorption processes were responsible for metal removal during start-up, with the highest removal efficiencies in the gravel microcosms. The lower initial efficiencies in the gravel/straw microcosms were presumably caused by the decomposition of straw. However, after establishment of anaerobic conditions (Eh approximately -200 mV), precipitation as metal sulphides provided an additional removal pathway in the gravel/straw microcosms. The addition of glucose to gravel microcosms enhanced sulphate reduction and metal removal, although Phragmites australis negatively affected these processes in the top-layer of all microcosms.     

Nitrogen removal of high strength wastewater via nitritation/denitritation using a sequencing batch reactor.

The sequencing batch reactor (SBR) process concept was applied to achieve efficient ammonium removal via nitrite under both laboratory and pilot-scale conditions. Both sets of experimental results show that without pH control or carbon addition the nitritation process consistently converted approximately 50% of the ammonium from biosolids dewatering liquids to nitrite with hydraulic retention times (HRT) as short as 10 h. The results from the pilot-scale study also indicate that the selective oxidation of ammonium to nitrite is a reliable process as the accumulation of nitrate was never an issue during a 330-day trial. The SBR process concept was extended to achieve complete nitrogen removal through nitritation and denitritation in the laboratory scale. The experimental results indicate that a total reduction of 96-98% of the ammonium nitrogen from biosolids dewatering liquids (influent concentration typically 1,200 g m(-3)) was achieved with a short HRT of 1.1 d and a removal rate of 1.05 kgNm(-3)d(-1). This process concept was tested at pilot scale where the nitritation process could be started up without temperature control in a short period of time. Nitrogen removal rates up to 1.2 kgNm(-3)d(-1) at an HRT of 0.88 d have been obtained. COD to nitrogen ratios required in the pilot plant were consistently in the range 1.6-1.9 kgCOD kg(-1)N removed.     

温度和基质对人工湿地脱氮除磷效果的影响

构建由潜流人工湿地和表流人工湿地串联而成的复合人工湿地系统,研究了复合人工湿地脱氮除磷效果以及温度和基质对人工湿地脱氮除磷效果的影响。结果表明,复合人工湿地TP、氨氮平均去除率为33.64%、57.24%;水温降低会导致人工湿地氮磷去除率下降;基质为粗砂的潜流人工湿地脱氮除磷能力大于基质为砾石的潜流人工湿地。     

Landfill leachate treatment by an experimental subsurface flow constructed wetland in tropical climate countries.

Municipal leachate was treated in an experimental unit of constructed wetlands of subsurface flow type. The parameters studied were organics (BOD and COD), solids and heavy metals (Zn, Ni, Cu, Cr and Pb). Using two types of emergent plants of Scirpus globulosus and Eriocaulon sexangulare, more than 80% removal was achieved for all the parameters. E. sexangulare removed organics and heavy metals better than Scirpus globulosus. A higher concentration of heavy metals in the influent did not change the removal efficiency.     

High-rate stormwater clarification with polymeric flocculant addition.

Treatment of urban stormwater by clarification, with flocculant addition, was studied in Toronto, Canada using a pilot-scale clarifier with removable lamellar plates. Almost 90 stormwater runoff events were characterised at the study site and found fairly polluted. The previous research phase indicated good treatability of this stormwater by lamellar clarification with flocculant addition (total suspended solids, TSS, removal of 84%, at a surface load of 15 m/h), but there were concerns about cleaning plates after storm events. With the aid of numerical modelling, hydraulic improvements to the clarifier inlet zone were retrofitted in 2004 and permitted the removal of the lamellar pack without a loss in treatment efficiency. In the modified clarifier, a cationic polymeric flocculant dosage of 4 mg/L with conventional clarification provided a TSS removal of 77%, at surface loads up to 43 m/h. The use of the polymer did not increase the acute toxicity of the treated effluent. The clarifier sludge was severely polluted by several heavy metals and would require special disposal. The treatment process tested could be well applied in projects requiring intensive stormwater treatment at compact sites.     

Heavy metal-binding proteins from metal-stimulated bacteria as a novel adsorbent for metal removal technology.

Water pollution with toxic heavy metals is of growing concern because heavy metals could bring about serious problems for not only ecosystems in the water environment but also human health. Some metal removal technologies have been in practical use, but much energy and troublesome treatments for chemical wastes are required to operate these conventional technologies. In this study, heavy metal-binding proteins (HMBPs) were obtained from metal-stimulated activated sludge culture with affinity chromatography using copper ion as a ligand. Two-dimensional electrophoresis revealed that a number of proteins in activated sludge culture were recovered as HMBPs for copper ion. N-termini of five HMBPs were determined, and two of them were found to be newly discovered proteins for which no amino acid sequences in protein databases were retrieved at more than 80% identities. Metal-coordinating amino acids occupied 38% of residues in one of the N-terminal sequences of the newly discovered HMBPs. Since these HMBPs were expected to be stable under conditions of water and wastewater treatments, it would be possible to utilize HMBPs as novel adsorbents for heavy metal removal if mass volume of HMBPs can be obtained with protein cloning techniques.     

Performance of Pilot-scale Constructed Floating Wetlands in the Removal of Nutrients and Pesticides

Aiming to evaluate the efficacy of constructed floating wetlands (CFW) in removing agrochemicals (nutrients and pesticides), a series of experiments were run continuously for a 16-week period in pilot-scale CFW systems to study the effect of two aquatic plant species (duckweed and water hyacinth) and climatic parameters. The CFW systems were loaded daily with agricultural polluted water containing a fertilizer and five pesticides, whose concentrations and removal efficiencies were measured in the experiments. Average nutrient and pesticide reductions varied from 27.4% to 83.6% and from 12.4% to 42.7%, respectively. The two plants performed almost equally well. High temperatures and increased solar radiation significantly contributed to increased removal performance. The results suggest the use of CFW systems as effective and low-cost agricultural pollution control technologies.