Comparison of nutrient cycling in a surface-flow constructed wetland and in a facultative pond treating secondary effluent.

There is a growing interest in the possibilities offered by combinations of waste stabilisation ponds (WSP) and constructed wetlands (CW). The purpose of our study was to compare treatment performances and nutrient cycling in a surface-flow wetland (SFW) and in a WSP treating secondary effluent. In the period between 2000 and 2003, a pilot SFW and a pilot WSP were constructed at the outlet of the wastewater treatment plant and their performance monitored while both were active under the same conditions. The SFW was planted with Phragmites australis and Eichhornia crassipes, while in the WSP development of algae was spontaneous. Performance efficiency was monitored by means of evaluation of physical and chemical parameters in water, by measurement of plant productivity and by analysis of N and P contents in biomass. The SFW with macrophytes proved more efficient in decreasing the suspended solids (64.6%), settleable solids (91.8%), organic N (59.3%), total N (38%), COD (67.2%) and BOD5 (72.1%) than the WSP. The WSP with algae was more efficient in treatment of ammonia nitrogen (48.9%) and ortho-phosphate (43.9%). The results of this study provide data that are of help in optimising combinations of SFW and WSP.     

Feasibility of a constructed wetland and wastewater stabilisation pond system as a sewage reclamation system for agricultural reuse in a decentralised rural area.

The performance of a constructed wetland (CW) and wastewater stabilisation pond (WSP) system for sewage reclamation and paddy rice irrigation in a decentralised rural area was examined using a feasibility study. The CW was satisfactory for sewage treatment, with good removal efficiency even in the winter period, but the effluent concentration was relatively high in the winter period owing to the high influent concentration. The CW effluent was further treated in a WSP and the WSP effluent was considered safe for crop irrigation with respect to sewage-borne pathogens. Reclaimed water irrigation did not adversely affect the yield of rice; on the contrary, it resulted in an approximately 50% greater yield than in controls. The chemical characteristics of the soil did not change significantly during the experimental period of irrigation with reclaimed water. In the winter, CW effluent could be stored and treated in a WSP until the spring; the water could then be discharged or reused for supplemental irrigation during the typical Korean spring drought. Overall, sewage treatment and agronomic reuse using a CW-WSP system could be a practical integrated sewage management measure for protecting receiving water bodies and overcoming water shortages in decentralised rural areas.     

多级人工湿地-塘组合系统对微污染水体污染物去除效果的实验研究

采用多级人工湿地-塘组合系统处理微污染水体,考察水力停留时间的变化条件下系统对COD、TP、浊度、氨氮等去除效果的影响.实验结果表明:在水力停留时间为5d时,COD、TP、浊度、氨氮去除率分别为62%、75%、80%、60%,多级人工湿地-塘组合系统能够有效的去除微污染水体污染物质.     

Domestic wastewater treatment by a constructed wetland system planted with rice

The experiments were conducted in four concrete laboratory scale free water surface constructed wetland units 1 m wide, 1.5 m long and 0.8 m deep. Paddy field soil was added to a depth of 0.4 m and rice seedlings (Oryza sativa L.) were transplanted into the units at a density of 25 plants/m(2). Domestic wastewater collected from Chiang Mai University was applied into each unit via two different modes to evaluate suitable conditions for wastewater treatment and rice yield. In the first experiment, the wastewater was fed intermittently (7 h/day) with a hydraulic loading rate of 2, 4, 6 and 8 cm/day. The maximum removal efficiencies for chemical oxygen demand, biological oxygen demand, total kjedahl nitrogen and suspended solids were only 49.1, 58.7, 64.0 and 59.4%, respectively, due to the short hydraulic retention time for the biodegradation of organic substances. In the second experiment, the wastewater in each unit was inundated to a depth of 15 cm for 10, 15, 20 and 25 days in each unit and then drained and re-flooded. Removal efficiencies of chemical oxygen demand, biological oxygen demand, total kjedahl nitrogen and suspended solids were greater than in the first experiment especially at the 25 day retention time and except for suspended solids met the Thai national effluent standard. The study revealed that apart from wastewater treatment, wastewater can replace natural water to grow rice in the dry season or throughout the year. Moreover, nutrients in wastewater can be a substitute for chemical fertilizers. Rice grain production was 4,700 kg/ha and only 6% less than the production from the conventional paddy field.     

Effects of effluent recirculation in vertical-flow constructed wetland on treatment efficiency of livestock wastewater.

Enhancing the treatment efficiency of livestock wastewater by effluent recirculation is investigated in a pilot-scale vertical-flow constructed wetland. The wetland system is composed of downflow and upflow stages, on which narrow-leaf Phragmites communis and common reed Phragmites typhia are planted, respectively; each stage has a dimension of 4 m(2) (2 m x 2 m). Wastewater from the facultative pond is fed into the system intermittently at a flow rate of 0.4 m(3)/d. Recirculation rates of 0, 25%, 50%0, 100% and 150% are adopted to evaluate the effect of the recirculation rate on pollutants removal. This shows that with effluent recirculation the average removal efficiencies of NH4-N, BOD5 and SS obviously increase to 61.7%, 81.3%, and 77.1%, respectively, in comparison with the values of 35.6%o, 50.2%, and 49.3% without effluent recirculation. But the improvement of TP removal is slight, only from 42.3% to 48.9%. The variations of NH4-N, DO and oxidation-reduction potential (ORP) of inflow and outflow reveal that the adoption of effluent recirculation is beneficial to the formation of oxide environment in wetland. The exponential relationships with excellent correlation coefficients (R(2) > 0.93) are found between the removal rates of NH4-N and BOD5 and the recirculation rates. With recirculation the pH value of the outflow decreases as the alkalinity is consumed by the gradually enhanced nitrification process. When recirculation rate is kept constant at 100%, the ambient temperature appears to affect NH4-N removal, but does not have significant influence on BOD5 removal.     

Comparison of maturation ponds and constructed wetlands as the final stage of an advanced pond system.

The treatment performance of a maturation pond (MP), the typical final polishing stage of an Advanced Pond System (APS), is compared with that of a surface-flow constructed wetland (CW) over 19 months. Both received approximately 67 mm d-1 of wastewater after passage through upstream stages of the APS. The MP, with greater sunlight exposure, had higher algal biomass (and associated suspended solids) than the CW, showed higher dissolved oxygen (DO) concentrations and greater diurnal variation in DO and pH. Neither polishing stages reduced nutrients markedly, with the CW exporting slightly more NH(3)-N and DRP, and less NO(3)-N than the MP. Disinfection was more efficient in the MP (geometric mean 1 log load removal, 12 MPN (100ml)-1) compared to the CW (0.47 log load removal, 53 MPN (100ml)-1). Incorporation of a final rock filter (28% of area) reduced median solids levels to < 10 g m(-3) in both the MP and CW. A hybrid between MPs and CWs with alternating zones of open-water (for enhanced disinfection and zooplankton grazing of algal solids) and wetland vegetation (promoting sedimentation and denitrification, and providing refugia for zooplankton) may provide more consistent effluent quality that either stage alone.     

Influence of biofilm on removal of surrogate faecal microbes in a constructed wetland and maturation pond.

The effect of biofilm on the attenuation of pathogen-sized particles from wastewater was compared for biofilms cultivated in a surface flow constructed wetland (SFW) and maturation pond (MP) The fate of fluorescently labelled microspheres (FLM) as surrogates for viruses (0.1 microm), bacteria (1 microm) and parasitic protozoa (4.5 microm dia) was investigated in microcosms in the presence or absence of biofilms. Rates of FLM removal from suspension were higher in the presence of biofilms for all particle sizes (kd 0.02-0.11 h(-1)) in MP and SFW microcosms with removal efficiency related to particle size and biofilm thickness and structure. Greater removal of 0.1 microm (79-81%), 1 microm FLM (92-96%) and 4.5 microm FLM (up to 98%) from suspension were found for microcosms containing thicker (autotrophic) biofilms grown in the MP or open water zone of the SFW. Lower removal of 43% (0.1 microm), 59% (1 microm) and 84% (4.5 microm) occurred in microcosms containing thinner heterotrophic biofilms from SFW vegetated zones. Providing surfaces for attachment of photosynthetic biofilms offers potential to enhance pathogen removal in open water systems. In vegetated systems, linkage to more oxic openwater zones may allow thicker and 'stickier' epiphytic biofilms to develop, improving pathogen interception and removal.     

Reuse of a dyehouse effluent after being treated with the combined catalytic wet peroxide oxidation process and the aerated constructed wetland.

A catalytic wet peroxide oxidation process was combined with the aerated constructed wetland in order to treat the raw dyehouse wastewater to in acceptable level for reuse as washing process water. More than 90% of BOD and CODs could be removed with the wet peroxide oxidation reactor and the remaining pollutants in the treated water were transformed into biodegradable ones which could have been successfully treated at the following aerated constructed wetland. The highest values of BOD5, CODMn, CODCr, SS and T-N in the treated water were 1.6, 1.8, 2.1, 0.5 and 12.8 mg/L, respectively. These values were low enough for the treated water to be reused at the washing process.     

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.     

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.     

用氧化塘—浮石床湿地系统处理暖寒季低污染河水

在滇池流域构建氧化塘-浮石床湿地复合系统对暖季与寒季的城市低污染河水开展了净化效能研究。结果表明:该系统可通过小幅调节流量来有效净化暖季与寒季低污染河水。塘与湿地的水力负荷分别为0.22、0.37m3/(m2.d)时系统对暖季低污染河水具有较高的处理效率,各污染物的平均去除率分别为CODCr75%、TP 93%、TN 64%、NH4+-N 87%。塘与湿地的水力负荷分别为0.17、0.29 m3/(m2.d)时系统对寒季低污染河水具有较优的处理效果:各污染物的平均去除率分别为CODCr72%、TP 89%、TN 53%、NH4+-N 73%。系统出水均符合GB18918-2002的一级A排放标准。系统在暖季对低污染河水中污染物的去除速率明显高于寒季。     

Treatments of oil-refinery and steel-mill wastewaters by mesocosm constructed wetland systems.

In this study, two types of industrial wastewater, oil-refining and steel-milling, were selected for investigating their feasibility of treatment by mesocosm constructed wetland systems. The secondly treated effluents from the wastewater treatment plants were directly discharged into the systems controlled at different flow rates. Three wetland mesocosms were installed in the two industries: mesocosms A and B were in the oil refinery, and mesocosm C was in the steel mill. The substratum media used in wetland systems were sand (mesocosm A) and gravel (mesocosms B and C), while the vegetation types selected were reeds (mesocosms A and B) and mixed species of reeds and cattails (mesocosm C). The flow regimes were controlled as free water surface (FWS) and subsurface flow (SSF) for the sand- and gravel-beds, respectively. According to the experimental results, we found that the system treating oil-refining wastewater performed better than that treating steel-milling wastewater learned by comparing the removal efficiencies of COD, total N and total P. In addition, it was found that for oil-refining wastewater treatments, the SSF wetland system (mesocosm B) performed better than FWS (mesocosm A) wetland system when comparing both of their removal of pollutants and growth of vegetation. Besides, the effluents from these two industrial wetland treatment systems might be reclaimed and reused for boiler water, cooling, cleaning and miscellaneous purposes in industries. Further treatments are required if the constructed wetland effluents are thought about being reused for processing in industries.     

Treatment of high strength wastewater with vertical flow constructed wetland filters.

The aim of the present study was to evaluate the behaviour of vertical flow constructed wetlands to treat high strength wastewater. Influents were obtained mixing tap water with different percentages of MSW landfill leachate (5%, 10% and 20%). Phragmites australis seedlings were used as macrophytes. The reeds were nurtured during three spring months, before the start of the experimental period. Three and four days of detention time were adopted. Influent concentrations of 510-2,050 mg L(-1), 180-740 mg L(-1) and 65-260 mg L(-1) were obtained for COD, N-NH4(+) and N-NO3(-), respectively. The environmental temperature averaged around 31.0 +/- 1.4 degrees C. During the experimental period, all parameters showed an increasing removal efficiency trend. Best results in terms of COD removal were obtained for mixtures at lowest rate of landfill leachate; while, denitrification process showed an opposite behaviour; finally, the removal of ammonia nitrogen appeared to be independent upon influent concentrations. Analysis carried out on the reed tissues showed a theoretic maximum storage of TKN in the leaves of about 55 mg/g dry weight. A leachate percentage of about 35% was derived to be able to fully inhibit the growth of macrophytes.     

大港油田稳定塘废水处理工程出水pH升高原因探析

针对稳定塘处理采油废水过程中pH升高、进而影响出水达标排放的问题,通过现场监测和室内试验考察了预处理工艺及废水自有组分对pH的影响。结果表明,导致体系pH升高的最主要因素是采油废水本身的水质组分。稳定塘中水样的pH与CODCr、VFA负相关,其中与CODCr的相关性达到显著性水平(p0.01),这表明该稳定塘的pH升高是由VFA的散失和部分有机组分的降解共同作用导致的。结果表明,当采用稳定塘或湿地系统对油田废水进行处理时,必须精心设计或加设酸化调节池,使其出水pH能满足达标排放要求。     

The effect of a vertical flow filter bed on a hybrid constructed wetland system.

Data from 18 sampling wells in Kodij?rve horizontal subsurface flow (HSSF) constructed wetland (CW) (South Estonia) is presented and differences in purification efficiencies inside the HSSF CW are calculated. Temporarily anaerobic conditions in the Kodij?rve HSSF system did not allow efficient removal of BOD7, NH4-N, Ntot and Ptot. In 2002 a vertical subsurface flow filter was constructed to enhance aeration. The design of the system was based simply on the oxygen demand of the wastewater and on the aeration potential of vertical flow wetlands. The vertical flow system has shown satisfactory results. The purification efficiency of BOD7 in the Kodij?rve CW has improved significantly and there has been a slight increase in purification efficiencies of NH4-N and Ntot. On the ohther hand, the removal efficiency of Ptot has decreased significantly. Although, the mass loading rates have increased, mass removal rates of all four parameters have improved significantly. Nevertheless, optimization of the constructed wetland system is essential in order to meet effluent standards during wintertime.     

Wastewater reuse in central Asia: implications for the design of pond systems.

The paper examines the potential of waste stabilisation ponds to provide water for reuse in extreme continental climates such as those of central Asia, where precipitation is low and summer evaporation rates are high. A simple model is used to predict water availability, BOD and faecal coliform removal for different configurations and operating regimes. The results show a significant proportion of flows could be saved for irrigation or river and aquifer replenishment: if current standard designs can be modified for these climates, the outcome is likely to be both more robust and more flexible in terms of types of reuse. The paper concludes with three case studies of evaporation pond systems in Kazakhstan, assessing their potential for conversion to full biological treatment systems for water conservation and reuse.     

潜流人工湿地处理城市污水氮和有机物的研究

在自行建造的模拟人工湿地装置上,通过改变水位来控制小型潜流人工湿地DO浓度,从而提高处理效率。试验中两种水位变化的运行都降低了人工湿地的氮和有机物,特别是对氮有较好的去除效果。第1阶段水位小幅度变化,出水DO浓度主要在2～4mg/L之间,COD、BOD5、TN、TKN去除率分别在85%～93%,91%～95%,65%～75%和75%～85%之间;第2阶段水位大幅度变化,出水DO浓度主要在1～4mg/L之间,COD、BOD5、TN、TKN去除率分别在80%～88%,85%～90%,70%～80%和80%～90%之间。     

Optimal maintenance of constructed wetlands using an environmental decision support system.

Constructed wetlands (CWs) are artificial wastewater treatment systems appropriate for small communities because of their affordability, operability and reliability. These qualities are true whenever CWs are designed and constructed properly, and as long as the necessary operation and maintenance procedures are carried out correctly. Experience shows that the operation and maintenance procedures, and the frequencies with which these procedures are carried out, differ from one CW to another. With this in mind, and along with a projected increase in CWs in Catalonia, the Catalan Water Agency (Agència Catalana de l'Aigua) has developed an Environmental Decision Support System (EDSS) which proposes guidelines for monitoring and maintenance, according to the characteristics of each CW. This EDSS was developed following a methodology based on five steps: (i) problem analysis; (ii) collecting data and knowledge acquisition; (iii) model selection; (iv) model implementation and (v) validation. This paper describes the methodology followed to build the decision support system and presents some examples of the information provided by this EDSS.     

The effect of the redox-potential on the retention of phosphorus in a small constructed wetland.

Building wetlands in small arable streams is a popular supplement to best management practice on arable fields. Particle bound phosphorus settles in the small constructed wetlands (CWs), receiving agricultural diffuse pollution. The sorption behavior of phosphorus is, however, redox-sensitive, and bound phosphorus may be remobilized in periods with low redox potential. This paper investigates changes in the redox potential in the free water of wetland Berg (Norway) during a three-year period, and how these redox changes affect the total phosphorus (TP) and total reactive phosphorus (TRP) retention. Despite eutrophic conditions in the wetland, the redox potential was never negative, and usually higher than 400 mV, indicating aerobic conditions. The relative retention was 440% and 43% for TP and TRP, respectively. The specific retention was 100 g TP and 43 g TRPm(-2) yr(-1). Loss of phosphorus was only observed during less than 19% of the total period of time. The net loss was less than 5% of the specific retention. The high positive redox potential probably conserves the redox-sensitive phosphorus in the wetland sediment as long as water fows through the CW.     

Performance of a pilot-scale high rate algal pond system treating abattoir wastewater in rural South Australia: nitrification and denitrification.

As part of a study examining the efficacy of high-rate algal pond treatment of high-strength abattoir wastewater, the impact of pond configuration and loading rate on nitrification was determined. The extent of nitrification in all ponds was consistent with mass balance estimates of oxygen demand and availability. Deeper ponds were more stable nitrifying systems, with shallow ponds displaying greater variation in response to changes in nitrogen loading. In a separate experiment the pond system was modified by covering a part of an in-series HRAP to exclude light, providing conditions suitable for denitrification. Specific denitrification rates were often within the range typical for endogenous carbon sources, with mass balance calculations indicating removals of up to 95%.