Performance evaluation and effects of hydraulic retention time and mass loading rate on treatment of woodwaste leachate in surface-flow constructed wetlands

Four surface-flow mesocosm wetlands were operated at different hydraulic retention times during two periods to treat diluted woodwaste leachate that was acidic, of very high oxygen demand, and toxic. Temperature, dissolved oxygen, and redox potential decreased with increasing water depth. However, there was no significant vertical variation in microbial biomass. No significant development in biomass of planktonic microorganisms was found over 6 weeks of initial operation. It took <1–6 weeks for maturation of the biofilm on submerged plant surfaces and the sedimentary microbial community. Mass reduction efficiencies of chemical oxygen demand, and tannin and lignin increased significantly with hydraulic retention time when 10% leachate was fed with tap water. When a more recalcitrant influent was fed, there was a slight increase of reduction efficiency with increasing hydraulic retention time. Reduction rates increased linearly with mass loading rates up to 0.4 kg m⁻³ d⁻¹ chemical oxygen demand and 0.13 kg m⁻³ d⁻¹ tannin and lignin. Precipitation and evapotranspiration had profound impacts on the overall performance and its variability. Mass balance-based operating data of wetlands with a mature microbial community are required for proper performance assessment.     

An ecological study of the rare rotifer species Trochosphaera solstitialis (Thorpe 1893) and the first report of the male

An ecological study of the rotifer species Trochosphaera solstitialis (Thorpe, 1893) was conducted for a period of eight months in a temporary pond in eastern Texas, U.S.A. The pond was found to be environmentally stressed and contained large amounts of decomposing vegetation. Physico-chemical factors contributing to the stressed conditions were low dissolved oxygen concentrations, low pH values, high ammonia concentrations, and high color values caused by large concentrations of iron, tannin and lignin. Large concentrations of iron, tannin, and lignin seem to be highly correlated with T. solstitialis populations. Physicochemical conditions probably eliminated predators of the rotifer, such as fish. Males of T. solstitialis were observed which never left the body cavity of the female. Males probably do not feed with an apparent rudimentary digestive system.     

Long term performance of a constructed wetland for landfill leachate treatment

The constructed wetland (CW) was developed as a pilot integrated system for the capital city's old sanitary landfill site. It consisted of three interconnected beds, two of vertical flow and one of horizontal flow stage. The CW covered 311 m² with an intermittent hydraulic load of 0.5 cm d⁻¹, filled with sand media and planted with reeds and cattails. The performance efficiency of the CW systems was evaluated for 7 years through physical and chemical parameters. Some monitored parameters varied noticeable. The efficiency for COD was 50%, BOD₅ (59%), ammonia nitrogen (51%), nitrate (negative), total phosphorus (P) (53%), sulfates (negative), sulfides (49%), chlorides (35%), and Fe (84%). The average concentrations of suspended solids, COD, BOD₅, nitrate, total P, sulfates, sulfides, and Fe were below limits after treatment. The ratio between N and P showed a limited level of P for biological processes. The performance of the system did not vary significantly with regard to temperature, however, it varied with precipitation. The results showed that the CW system, as a tertiary system or as an independent system, could be a low-cost alternative for the treatment of leachate from old landfill sites.     

Recycling of aquaculture wastewater using charcoal based constructed wetlands

Abstract

The competitive demand for water makes it a scarce resource for agricultural use. This necessitates wastewater reuse for irrigation and any other agricultural purpose, especially in developing countries where treatment of wastewaters is not a priority. The aim of this study was to evaluate the performance of a charcoal-based constructed wetland (CBCW) in treating aquaculture wastewater. Aquaculture wastewater from a Research Fishpond Farm was treated in a CBCW planted with Sacciolepsis africana and Commelina cyannae for 5?days retention time. Raw wastewater and the treated wastewater from the constructed wetland (CW) was sampled and the physicochemical parameters determined. The performance of the CW in treating aquaculture wastewater was conducted. The result showed that the CBCW was capable of removing 50% TSS, 88% COD, 93% BOD_5, and 100% nitrate nitrogen. The pH and DO of the wastewater before treatment and after treatment ranged from 6.68 to 6.91 and 4.13 to 6.30?mg/l, respectively. Thus, CWs have great potential for the treatment of aquaculture wastewater and prevention of environmental degradation through wastewater treatment, thereby solving the problem of water scarcity for agriculture for optimum food production.     

Metal Removal from Water Discharges by a Constructed Treatment Wetland

A full‐scale constructed wetland treatment system consisting of four pairs of wetland cells (3.2 ha total area) with water flowing through a pair of cells in series prior to discharge was investigated. A retention basin provided stable water flow to the system. Water retention time in the wetland system was approximately 48 hours, and the wetland cells operated at circumneutral pH. Vegetation development within the cells has been excellent. Copper removal efficiency was greater than 75 % from the start‐up of the system, while mercury efficiency improved with maturation of the treatment cells. Sampling of the water course through the wetlands conducted during the fourth year of operation validated continued performance, and assessed the fate of a larger suite of metals present in the water. Copper and mercury removal efficiencies were still very high, both in excess of 80 % removal from the water after passage through the wetland system. Mercury removal continued along the entire water course through the system, while copper was removed almost immediately upon entering the wetland cells. Lead removal from the water by the system was 83 %, zinc removal was 60 %, and nickel was generally unaffected. Organic carbon in the water was also increased by the system and reduced the bioavailability of some metals. Operation and maintenance of the system continued to be minimal, and mainly consisted of checking for growth of the vegetation and free flow of the water through the system. The system was entirely passive, relying on gravity as the power source of water flow. No reportable permit exceedances have been experienced since the wetland began treating an outfall discharge.     

一株脱氮细菌鉴定及其效果研究

针对传统人工湿地治理污染河湖水工艺中存在的脱氮效率低、环境安全性差等问题，从污水处理厂生化池污泥中分离纯化获得菌株TY（CGMCC1.18865，该菌种已于2020年在中国普通微生物菌种保藏中心入库），通过配水试验，验证菌株脱氮特性，并进一步以火山岩为填料，采用湿地模拟系统装置对比附配TY菌的湿地系统与传统湿地系统对污染水体的脱氮效果的差异；通过16S rRNA基因序列分析，鉴定获得的菌株TY，同时对其表现出的反硝化作用进行分析研究。结果表明：分离获得的TY菌株为假单胞菌属（Pseudomonas sp.），配水试验中对氨氮和总氮的去除率分别为84.2%和93.6%。通过对模拟湿地系统出水氨氮、总氮和化学需氧量（COD）监测，发现30 d平均去除率分别可提升至94.3%、88.0%和82.3%，较传统湿地分别提高27.9%、28.8%和7.3%。研究表明，TY菌脱氮过程中有少量的硝态氮和亚硝态氮的积累，可降低对环境的不利影响、有利于脱氮反应连续进行，从而提高人工湿地脱氮效率，具有进一步探究的前景。     

Comparison of horizontal and vertical constructed wetland systems for landfill leachate treatment

The main purpose of this study was to treat organic pollution, ammonia and heavy metals present in landfill leachate by the use of constructed wetland systems and to quantify the effect of feeding mode. The effect of different bedding material (gravel and zeolite surface) was also investigated. A pilot-scale study was conducted on subsurface flow constructed wetland systems operated in vertical and horizontal mode. Two vertical systems differed from each other with their bedding material. The systems were planted with cattail (Typha latifolia) and operated identically at a flow rate of 10 l/day and hydraulic retention times of 11.8 and 12.5 day in vertical 1, vertical 2 and horizontal systems, respectively. Concentration based average removal efficiencies for VF1, VF2 and HF were NH₄–N, 62.3%, 48.9% and 38.3%; COD, 27.3%, 30.6% and 35.7%; PO₄–P, 52.6%, 51.9% and 46.7%; Fe(III), 21%, 40% and 17%, respectively. Better NH₄–N removal performance was observed in the vertical system with zeolite layer than that of the vertical 2 and horizontal system. In contrast, horizontal system was more effective in COD removal.     

CONSTRUCTED WETLAND CONTROL OF BOD LEVELS IN AIRPORT RUNOFF

A surface water treatment system consisting of an aeration reservoir and pond (holding capacities 45,000 and 19,000 m³) and a network of 12 horizontal subsurface flow gravel-filled constructed wetland cells of different sizes (total surface area 2.08 ha) and planted with Phragmites australis, was commissioned at Heathrow Airport, London, United Kingdom, in the winter of 2002. Ongoing monitoring of the treatment system has shown significant reductions in the biochemical oxygen demand (BOD₅) throughout the system with levels decreasing by up to 76.7% across the constructed wetland cells following high anti- and de-icing fluid applications. However, continued exposure to BOD₅ concentrations exceeding the design target has resulted in anaerobic conditions in the wetland. The addition of nutrients to the treatment system has resulted in improved removal efficiency for elevated BOD₅ loadings in the aerated reservoir from 25.5% to 47.5%, The addition of different nutrient dosing regimes to complementary pilot-scale planted and unplanted vertical flow columns showed average but statistically insignificant BOD₅ removal percentage increases from 61.9 ± 21.1% to 70.8 ± 26.5%, respectively, in planted columns over a 7-day period. There is an overall improvement in the performance of the system, but operational reviews are continuing.     

Operational factors and nutrient effects on activated sludge treatment of Pinus radiata kraft mill wastewater

The biodegradability of Pinus radiata bleached kraft mill wastewater by an activated sludge treatment during a period of 280 days was evaluated. The effect of varying hydraulic retention time (HRT) in the range of 48 to 4.5 h and nitrogen (N) and phosphorus (P) addition on removal of biological oxygen demand (BOD5), chemical oxygen demand (COD), suspended solids (TSS and VSS), total phenolic compounds, tannin and lignin and reduction of toxicity was investigated. Removal of BOD5 was higher than 90% when HRT varied from 16 to 6 h, but decreased when HRT was less than 6 h. Similar performance was observed for COD removal, which was about 60% when HRT was varied from 16 to 6 h. Removal of total phenolic compounds and tannin and lignin was seriously affected by HRT. N and P addition to maintaining a ratio of 100:5:0.3 provided optimal BOD5, COD and suspended solids removal when HRT varied from 16 to 7 h, and no toxicity (using Daphnia) was detected in the treated effluent. When HRT was less than 6 h, the system showed destabilisation and pH, COD, BOD5 and suspended solids removal decreased.     

Removal of polycyclic aromatic hydrocarbons and linear alkylbenzene sulfonates from domestic wastewater in pilot constructed wetlands and a gravel filter

Removal efficiencies of polycyclic aromatic compounds (PAHs) and linear alkyl benzene sulfonates (LAS) were evaluated in a pilot-scale constructed wetland (CW) system combining a free water surface wetland, a subsurface wetland and a gravel filter in parallel. The effect of parameters such as temperature and mass loading rate was also examined. The subsurface constructed wetland system was found to have the overall best performance on pollutants removal. In particular, the average removal of PAHs and LAS was 79.2% and 55.5% for the SSF (Subsurface Flow) constructed wetland, 68.2% and 30.0% for the FWS (Free Water Surface) constructed wetland and 73.3% and 40.9% for the gravel filter, respectively. Removal efficiency and the estimated first-order volumetric removal rate constant (k_v) for both PAHs and LAS decreased with increasing water temperature. The experimental results suggest that the absorption in solid media is the main mechanism for xenobiotics removal in constructed wetlands and that the overall performance of the SSF wetland is significantly better than the FWS wetland or the gravel filter.     

Modeling the hydraulic effect of transverse deep zones on the performance of short-circuiting constructed treatment wetlands

Short-circuiting, which occurs when a large fraction of water traveling through a system exits well before the residence time, reduces the performance of constructed treatment wetlands. Recent field and laboratory observations have shown that short-circuiting within vegetated marsh areas results from narrow, continuous fast flowpaths that experience longitudinal dispersion but do not exchange fluid with slow flowing regions of dense vegetation on either side. Based on these observations, this paper develops an analytic stream tube model with dispersion to represent flow through the marsh areas of a short-circuiting constructed treatment wetland under steady flow conditions. The model also includes transverse deep zones, which rapidly dissipate fast flowpath momentum and introduce lateral mixing through wind-driven circulation. Modeled results reveal that a transverse deep zone that replaces a portion of a wetland marsh can offset the adverse impact of short-circuiting flowpaths through two separate mechanisms. First, lateral mixing can dilute the water that has traveled through a fast flowpath. Second, deep zones reduce the probability that fast flowpaths align throughout the entire wetland. The model results suggest that deep zones may improve wetland performance when properly sized and located, even when they do not directly contribute to contaminant removal.     

Influence of recirculation over COD and N-NH4 removals from landfill leachate by horizontal flow constructed treatment wetland

Abstract

Treatment of landfill leachate is a challenge due to its complex chemical composition and high recalcitrance and because of high costs for conventional wastewater treatment. In our study, leachate from the Quitaúna Landfill, Sao Paulo Metropolitan Region, Brazil, was treated at a laboratory scale with a horizontal subsurface flow constructed treatment wetland (HF-CTW) operating under a recirculation regime. Two units planted with Heliconia psittacorum (HP) and Cyperus papyrus (CP), and one unplanted control unit were assessed. With a recirculation regime over 21?days, the planted units removed 40% of chemical oxygen demand (COD) while the control unit removed only 29%. True color removal efficiencies were 2, 22, and 23% for the control, HP, and CP HF-CTWs, respectively. The ammonium nitrogen removal efficiencies for a 21-day hydraulic retention time (HRT) were 63–81% for planted units and 72% for the control. The increase of the HRT from 7 to 21?days led to the enhancement of ammonium nitrogen removal but did not affect the COD and total nitrogen removals. This phenomenon is a consequence of leachate’s low biodegradability. The present study shows the importance of the HRT and plant presence for landfill leachate treatment using HF-CTWs.     

Predicting Biogeochemical Calcium Precipitation in Landfill Leachate Collection Systems

Clogging of leachate collection systems within municipal solid waste landfills can result in greater potential for contaminants to breach the landfill barrier system. The primary cause of clogging is calcium carbonate (CaCO_3(s)) precipitation from leachate and its accumulation within the pore space of the drainage medium. CaCO_3(s) precipitation is caused by the anaerobic fermentation of volatile fatty acids (VFAs), which adds carbonate to and raises the pH of the leachate. An important relationship in modeling clogging in leachate collections systems is a yield coefficient that relates microbial fermentation of VFAs to precipitation of calcium carbonate. This paper develops a new, mechanistically based yield coefficient, called the carbonic acid yield coefficient (Y_H), which relates the carbonic acid (H₂CO₃) produced from microbial fermentation of acetate, propionate, and butyrate to calcium precipitation. The empirical values of Y_H were computed from the changes in acetate, propionate, butyrate, and calcium concentrations in leachate as it permeated through gravel-size material. The theoretical and empirical results show that the primary driver of CaCO_3(s) precipitation is acetate fermentation. Additionally, other non-calcium cations (e.g., iron and magnesium) precipitated with carbonate (CO_2-) when present in the leachate. A common yield between total cations bound to CO₃ ^2- and H₂CO₃ produced, called the calcium carbonate yield coefficient (Y_c), can reconcile the empirical yield coefficient for synthetic and actual leachates.     

Leachate treatment and greenhouse gas emission in subsurface horizontal flow constructed wetland

Organic and nitrogen removal efficiencies in subsurface horizontal flow wetland system (HSF) with cattail (Typha augustifolia) treating young and partially stabilized solid waste leachate were investigated. Hydraulic loading rate (HLR) in the system was varied at 0.01, 0.028 and 0.056 m³/m² d which is equivalent to hydraulic retention time (HRT) of 28, 10 and 5 d. Average BOD removals in the system were 98% and 71% when applied to young and partially stabilized leachate at HLR of 0.01 m³/m² d. In term of total kjeldahl nitrogen, average removal efficiencies were 43% and 46%. High nitrogen in the stabilized leachate adversely affected the treatment performance and vegetation in the system. Nitrogen transforming bacteria were found varied along the treatment pathway. Methane emission rate was found to be highest at the inlet zone during young leachate treatment at 79–712 mg/m² d whereas CO₂ emission ranged from 26–3266 mg/m² d. The emission of N₂O was not detected.     

An assessment of a natural wetland receiving sewage effluent

An assessment of the performance of a wetland dominated by opportunistic weeds in removing nutrients from a secondary sewage effluent was carried out at Thredbo in Kosciusko National Park. Water quality sampling of the inflow and outflow showed a reduction in turbidity, pH and conductivity with passage through the wetland. Dissolved oxygen levels also decreased. In summer 1982, the phosphorus toad of 1.8 kg P day^-1 was reduced by 44% as wastewater moved through the wetland, and the nitrogen load of 6.4 kg N day^-1 by 65%. Winter retentions were 10% and 14% of inflowing loads, respectively. In 1983 there was a net release of phosphorus and reduced retention of nitrogen. This was regarded as being a result of physical disturbance of the wetland. Vegetation downstream of the effluent inflow was dominated by the opportunistic weeds Epilobium sarmantaceum and Rumex crispus. Upstream, Carex gaudichaudiana and Baeckea gunniana dominated. Marked seasonal changes in vigour and biomass were recorded. Plants, but not sediments, downstream of the inflow contained more nutrients than those upstream. Seed bank analysis showed more seeds downstream than upstream. A moist treatment promoted more seed germination than a flooded treatment. E. sarmantaceum and to a lesser extent R. crispus dominated in each treatment. In an effort to promote greater water retention and replacement of the weed species, channels in the wetland have been blocked with gravel and planted with Phragmites australis and Schoenoplectus validus.     

Repeated batch process for biological treatment of black liquor using brown-rot basidiomycete <Emphasis Type="Italic">Fomitopsis</Emphasis> sp. IMER2

A repeated batch operation is developed for the treatment of alkaline pulp black liquor, through a process of biological acidification precipitation of lignin using brown rot fungus Fomitopsis sp. IMER2. The results showed that COD and color removal of black liquor was dependent on the biomass concentration, pH decrease and initial COD. Based on these results, the repeated batch process was successfully carried out 12 times over 36 days in an air bubble column bioreactor. The average reduction of COD and color was approximately 40% and 70%, respectively.     

人工湿地污水处理工艺设计关键及生态学问题

人工湿地污水处理系统是一种经济高效的污水生态处理技术方式．然而,湿地污水处理技术在性能上仍须有待发展与完善,尤其需要对其处理工艺参数进行不断改进和系统优化．本文针对人工湿地污水处理工程中有关水力停留时间、水传导因素、表面负荷率和工程构筑物设计等技术参数,概括性地剖析、探讨了国内外人工湿地污水处理工艺的设计关键及其主要技术内涵,给出了一些重要的优化模型与最佳数值;与此同时,分析、提出了利用生态学方法克服人工湿地工程运行中所涉及的野生生物管理与蚊蝇控制等问题。     

Tropical wetlands for climate change research, water quality management and conservation education on a university campus in Costa Rica

EARTH University is a small agronomic university with a theme of sustainability in eastern Costa Rica. Several natural and constructed wetlands on its campus are used for research, water quality improvement, and higher education. It has become an important location for research and teaching on humid tropical wetland ecology and management. A 112-ha flow-through Raphia taedigera (Arecaceae) forested wetland is being used for climate change research, focusing on carbon sequestration and methane generation. Methane emissions are measured seasonally and are comparable to rates in tropical wetlands published elsewhere. Carbon sequestration by the wetland appears to be substantially higher than similar flow-through temperate zone wetlands. Treatment wetlands are used on campus to improve water quality of effluents from an animal farm, a dairy plant, a landfill, and a banana paper plant. Water quality was substantially improved in all of these wetlands except the landfill leachate wetland. All of these campus wetlands have been integrated into the four-year education program of EARTH University and 22 undergraduate projects have been completed on wetlands over the past 14 years.     

Increasing ibuprofen degradation in constructed wetlands by bioaugmentation with gravel containing biofilms of an ibuprofen‐degrading Sphingobium yanoikuyae

The aim of this study was to investigate the removal of ibuprofen in laboratory scale constructed wetlands. Four (planted and unplanted) laboratory‐scale horizontal subsurface flow constructed wetlands were supplemented with ibuprofen in order to elucidate (i) the role of plants on ibuprofen removal and (ii) to evaluate the removal performance of a bioaugmented lab scale wetland. The planted systems showed higher ibuprofen removal efficiency than an unplanted one. The system planted with Juncus effusus was found to have a higher removal rate than the system planted with Phalaris arundinacea. The highest removal rate of ibuprofen was found after inoculation of gravel previously loaded with a newly isolated ibuprofen‐degrading bacterium identified as Sphingobium yanoikuyae. This experiment showed that more than 80 days of CW community adaptation for ibuprofen treatment could be superseded by bioaugmentation with this bacterial isolate.     

Modelling faecal <Emphasis Type="Italic">streptococci</Emphasis> mortality in constructed wetlands implanted with <Emphasis Type="Italic">Eichhornia crassipes</Emphasis>

Faecal streptococci mortality was investigated in a water hyacinth (Eichhornia crassipes) constructed wetland pond. The wetland was 7.5 m long, 1.5 m wide and 1.0 m deep, and was implanted with E. crassipes. In order to assess the performance of the system towards bacterial mortality, a mathematical model, based on plug flow philosophy was developed. The model incorporated the role of factors, namely solar intensity, pH, dissolved oxygen, temperature, sedimentation, and root attached growth. Model analysis strongly suggests that bacterial mortality rate constant was largely influenced by two factors, namely solar intensity and root biofilm attachment, with both contributing approximately 70.5% of removal. The contribution of other factors like temperature, dissolved oxygen, pH and sedimentation on bacterial mortality rate were less significant. For example, dissolved oxygen, pH and sedimentation contributed 5%, 8% and 0.82%, respectively. Thus, the sedimentation factor was omitted from the model because of its insignificant contribution. The same was done for temperature, due to low ambient temperature range (3.1°C) in the study area. The overall model bacterial removal efficiency was 83%.