Inhibition of microbial activity of activated sludge by ammonia in leachate

Leachate samples were collected from the West New Territory Landfill (WENT), Hong Kong, and characterized in the laboratory. The analytical results confirmed that it has a typical nature of aged leachate with a low BOD₅/COD ratio of 0.22 and a high strength of ammonia-nitrogen around 5 g/L. A lab-scale study was conducted to investigate the inhibition of microbial activity of the activated sludge. In the first test, glucose-based synthetic wastewater was used in two parallel reactors. The experimental results demonstrated that COD removal declined from 95.1 to 79.1% and the dehydrogenase activity of the sludge decreased from 11.04 to 4.22 μg TF/mg mixed liquor suspended solids (MLSS), when the ammonia-nitrogen concentration increased from 50 mg/L to 800 mg/L progressively. The remaining NH₃⁺-N residue in the treated wastewater increased from 0.58 mg/L to 649 mg/L extensively. In the second test, mixed wastewater samples containing glucose and raw leachate were fed into six parallel biological reactors and operated on batch mode. The experimental results showed COD removal decreased from 97.7 to 78.1% and the dehydrogenase activity decreased from 9.29 to 4.93 μg triphenyl formazon (TF)/mg MLSS, respectively, when the ammonia-nitrogen concentration increased within the same range. Microbial inhibition could also be substantiated by a decrease of specific oxygen uptake rate (SOUR) from 68 to 45 mg O₂/g MLSS. These results suggested leachate containing high-strength ammonia-nitrogen should be pretreated to an acceptable NH₄⁺-N level before it is fed into biological reactors.     

Removal of copper from water using limestone filtration technique. Determination of mechanism of removal

This paper discusses heavy metal removal from wastewater by batch study and filtration technique through low-cost coarse media. Batch study has indicated that more than 90% copper (Cu) with concentration up to 50 mg/l could be removed from the solution with limestone quantity above 20 ml (equivalent to 56 g), which indicates the importance of limestone media in the removal process. This indicates that the removal of Cu is influenced by the media and not solely by the pH. Batch experiments using limestone and activated carbon indicate that both limestone and activated carbon had similar metal-removal efficiency (about 95%). Results of the laboratory-scale filtration technique using limestone particles indicated that above 90% removal of Cu was achieved at retention time of 2.31 h, surface-loading rate of 4.07 m3/m2 per day and Cu loading of 0.02 kg/m3 per day. Analyses of the limestone media after filtration indicated that adsorption and absorption processes were among the mechanisms involved in the removal processes. This study indicated that limestone can be used as an alternative to replace activated carbon.     

Oxygen demand, nitrogen and copper removal by free-water-surface and subsurface-flow constructed wetlands under tropical conditions

This study was conducted to: (1) assess the role of wetland vegetation in the removal of oxygen demand and nitrogen under tropical conditions, (2) estimate the uptake of nitrogen and copper by wetland plants and (3) investigate the speciation of Cu in wetland media among four operationally defined host fractions, namely exchangeable, carbonate, reducible and organically bound. Four laboratory-scale wetland units, two free-water-surface (FWS) and two subsurface-flow (SF) with one of each planted with cattails (Typha augustifolia), were fed with primary-treated sewage and operated at nominal retention times of 0.6-7 days. The influent and effluent BOD/COD and nitrogen concentrations were monitored to assess the performance of the wetland units for various mass loading rates. At the end of the study, all cattail plants were harvested and analyzed for total Kjeldahl nitrogen (TKN). Four other wetland units, which were identical to the first four, were fed with domestic wastewater spiked with copper in increasing concentrations. Copper speciation patterns in the sand layer were determined at the end of the study. The results showed that wetland vegetation did not play an important role in oxygen demand removal but were capable of removing about 22% and 26% of the nitrogen input in the FWS and SF wetland units, respectively. Mass balance analysis indicated that less than 1% of copper introduced was taken up by the cattails. Copper speciation patterns in the sand media showed that the exchangeable fraction contributed 30-57% and 63-80% of the nonresidual copper in the planted and unplanted FWS wetlands, respectively. For SF units, the percentages were 52-62% and 59-67%, respectively. This indicates that large amount of copper in the media were potentially remobilizable.     

An empirical model for primary sedimentation of sewage

Theoretical mathematical models of primary sedimentation and column settling tests have failed until now to predict the behaviour of sedimentation tanks under actual operating conditions due to the difficulties in simulating the effect of the density currents and the complex phenomenon of flocculation. Therefore, empirical models can be helpful in the design of sedimentation tanks. Using performance data from three different pilot-scale sedimentation tanks, empirical mathematical models were developed in this paper relating suspended solids (SS) removal efficiency to surface overflow rate, influent SS concentration, and sewage temperature. The model coefficients were derived from the combined analysis of three well correlated sets of data, thus giving a good indication for their possible general applicability. The analysis of experimental data also gave a relationship between SS and chemical oxygen demand (COD) removal efficiencies.     

Current status of urban wastewater treatment plants in China

The study reported and analyzed the current state of wastewater treatment plants (WWTPs) in urban China from the perspective of treatment technologies, pollutant removals, operating load and effluent discharge standards. By the end of 2013, 3508 WWTPs have been built in 31 provinces and cities in China with a total treatment capacity of 1.48 × 10⁸ m³/d. The uneven population distribution between China's east and west regions has resulted in notably different economic development outcomes. The technologies mostly used in WWTPs are AAO and oxidation ditch, which account for over 50% of the existing WWTPs. According to statistics, the efficiencies of COD and NH₃–N removal are good in 656 WWTPs in 70 cities. The overall average COD removal is over 88% with few regional differences. The average removal efficiency of NH₃–N is up to 80%. Large differences exist between the operating loads applied in different WWTPs. The average operating loading rate is approximately 83%, and 52% of WWTPs operate at loadings of < 80%, treating up to 40% of the wastewater generated. The implementation of discharge standards has been low. Approximately 28% of WWTPs that achieved the Grade I-A Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918–2002) were constructed after 2010. The sludge treatment and recycling rates are only 25%, and approximately 15% of wastewater is inefficiently treated. Approximately 60% of WWTPs have capacities of 1 × 10⁴ m³/d–5 × 10⁴ m³/d. Relatively high energy consumption is required for small-scale processing, and the utilization rate of recycled wastewater is low. The challenges of WWTPs are discussed with the aim of developing rational criteria and appropriate technologies for water recycling. Suggestions regarding potential technical and administrative measures are provided.     

Groundwater contamination by microbiological and chemical substances released from hospital wastewater: Health risk assessment for drinking water consumers

Contamination of natural aquatic ecosystems by hospital wastewater is a major environmental and human health issue. Disinfectants, pharmaceuticals, radionuclides and solvents are widely used in hospitals for medical purposes and research. After application, some of these substances combine with hospital effluents and, in industrialised countries, reach the municipal sewer network. In certain developing countries, hospitals usually discharge their wastewater into septic tanks equipped with diffusion wells. The discharge of chemical compounds from hospital activities into the natural environment can lead to the pollution of water resources and risks for human health. The aim of this article is to present: (i) the steps of a procedure intended to evaluate risks to human health linked to hospital effluents discharged into a septic tank equipped with a diffusion well; and (ii) the results of its application on the effluents of a hospital in Port-au-Prince. The procedure is based on a scenario that describes the discharge of hospital effluents, via septic tanks, into a karstic formation where water resources are used for human consumption. COD, Chloroform, dichlomethane, dibromochloromethane, dichlorobromomethane and bromoform contents were measured. Furthermore, the presence of heavy metals (chrome, nickel and lead) and faecal coliforms were studied. Maximum concentrations were 700 NPP/100 ml for faecal coliforms and 112 mg/L for COD. A risk of infection of 10^? 5 infection per year was calculated. Major chemical risks, particularly for children, relating to Pb(II), Cr(III), Cr(VI) and Ni(II) contained in the ground water were also characterised. Certain aspects of the scenario studied require improvement, especially those relating to the characterisation of drugs in groundwater and the detection of other microbiological indicators such as protozoa, enterococcus and viruses.     

Treatment of wastewater from an oil and soap factory via dissolved air flotation

Highly polluted wastewater from oil and soap factories has been treated via coagulation followed by dissolved air flotation. Ferric chloride and alum were used as coagulants at their optimal pH value and dosages. Factors affecting the efficiency of the dissolved air flotation process, such as detention time and air-solids ratio, have been investigated. The results obtained showed that this process proved to be very efficient in removing the organic contaminants. The oil removal value reached 99.1%. The COD, BOD, and turbidity removal achieved 94.5%, 96% and 99.3%, respectively.     

Parameters affecting biological phosphate removal from wastewaters

This paper reviews some of the key wastewater composition parameters, which influence the biological removal of phosphate from wastewaters, such as COD content, volatile fatty acid (VFA) content, cation concentration, phosphorus load, pH and food to microorganism ratio. The discussion also focuses on operational parameters affecting successful nutrient removal in wastewater treatment plants, such as temperature, sludge quality, sludge settlement, dissolved oxygen (DO) concentration, anaerobic P-release and secondary P-release. The aim of this review is to compile an updated document for researchers and operators of biological nutrient removal (BNR) systems. In addition, the article will provide a good foundation for readers with no prior knowledge of the process.     

Removal of nutrients and heavy metals from anaerobic waste by aerobiological treatment

This study was conducted to investigate the effectiveness of aerobic biological treatment in removal of nitrogen, phosphorous, and heavy metals from a unique anaerobic liquid waste, produced at a solid waste-to-methane anaerobic digestion facility. Laboratory scale continuous flow activated sludge reactors were employed in this study. The liquid waste has moderate BOD/COD ratio with BOD concentration of 1300 mg/L and high concentration of essential nutrients, making the liquid waste biologically treatable. Results showed that aerobic biological treatment can remove nitrogen and phosphorous on the order of 85%. Metal removal efficiencies vary widely for 11 metals studied in this investigation.     

Potential use of solar energy for waste activated sludge treatment

The use of solar energy as a disintegration unit operation for waste activated sludge was tested in a pilot plant. The effect of the treatment process on chemical oxygen demand (COD), total suspended solids (TSS), settling time and filtration index was investigated in single (solar) and sequential processes (solar & biological). Solar oxidation was found to be a good sludge disintegration technology. Available solar photons were utilised to degrade the soluble organic matter and release the cell liquids. The highest COD and TSS removal efficiencies were obtained by the month of June. Sequential process efficiencies were related to accumulate solar photons, aerobic treatment time and operational condition. Sequential process resulted in COD and TSS removal efficiency of 16% and 13%, respectively. Increasing aerobic treatment time and/or mixing the oxidised sludge with fresh sludge improved COD and TSS removal efficiencies to 23% and 27%, respectively. The use of sequential processes improves the settling tendency of sludge by bio-oxidation of the released portions and eliminates protein charge effect on sludge settling.     

Simultaneous biological removal of endosulfan (alpha+beta) and nitrates from drinking waters using wheat straw as substrate

Nitrate and endosulfan (alpha+beta) removal was studied in an upflow biological denitrification reactor packed with wheat straw as carbon source and support particles for microorganisms. While almost complete nitrate elimination and between 65% and 70% endosulfan (alpha+beta) elimination occurred when the temperature was higher than 20 degrees C; below that value, nitrate removal efficiency decreased to about 10%. Nitrate, dissolved organic carbon (DOC), and endosulfan (alpha+beta) removal efficiencies decreased considerably at 1500 microg/l endosulfan concentration in the batch experiments. Although a high removal efficiency was observed for endosulfan (alpha+beta) and nitrate in the biological denitrification continuous reactor, the effluent water could not be used for drinking purpose because of the unacceptable levels of endosulfan (alpha+beta), colour and dissolved organic content. During the continuous study, 23.4% of the initial weight of wheat straw was lost and 24 g was consumed per gram of nitrogen removed. The results of the continuous study showed that 21.3% of the endosulfan removal was achieved by adsorption onto the wheat straw and 68.2% of the endosulfan removal occurred by biological activity and the remaining portion was detected in the effluent water.     

Dairy wastewater treatment using water treatment sludge as coagulant: a novel treatment approach

The dairy industry is among the most polluting industries as it produces large volume of wastewater that may adversely affect the environment if discharged untreated. Dairy wastewater is characterized by high COD, BOD and nutrient levels. In this study, water treatment sludge was used as a coagulant for the treatment of synthetic dairy wastewater in the pH range of 4–10. Turbidity, COD, BOD, TSS and TDS removals from the synthetic dairy wastewater were found to be around 93, 65, 67, 84 and 85%, respectively, at the optimum conditions. Water treatment sludge was found to perform even better than other conventional coagulants used for the same. Results showed that it has the potential to substitute the conventional coagulants partially or fully in the primary treatment of dairy wastewater. The utilization of water treatment sludge at dairy wastewater treatment plants would provide sustainable sludge management and cost-effective dairy wastewater treatment.     

中国经济发展与水环境压力脱钩态势评价与展望

在对经济发展的水环境压力概念进行合理界定基础上,建立经济发展与水环境压力的脱钩指标体系。通过国内外相关文献研究与数据收集,构建了中国经济发展与水环境压力的脱钩潜力评价与时态分析模型,评价1986~2010年水利发展不同阶段中国经济总量增长与废水排放的脱钩潜力与脱钩时态、以及经济总量增长与工业废水化学需氧量的脱钩时态。在此基础上,根据水环境库茨涅茨曲线变化趋势,对我国废水排放总量的自然发展趋势进行预测,并根据国家发展规划对废水排放总量预测结果进行修正。同时,结合国家发展规划和环境保护规划,对水环境压力脱钩进行展望。结果表明,我国经济发展与废水排放总量总体处于弱脱钩发展态势、与工业废水化学需氧量排放总量总体处于强脱钩发展态势。预计2020年左右,我国经济发展与水环境压力有望保持绝对脱钩的发展态势,水环境得到彻底改善与净化     

上海城市河岸带对降雨径流氮垂直去除研究

在上海市城市河岸带人工绿地建设了微区径流场,进行了5次模拟降雨径流实验,研究了人工绿地岸带下渗流中氮浓度和去除率的时空变化。结果表明：人工绿地岸带对垂直下渗流中氮有显著的净化作用,且主要集中于土壤的0~30 cm以内,TN和NH4+去除率在399%和398%以上,NO3-+NO2-去除率除11月为负值外,其余月份均在100%以上;在30~60 cm深度,由于土壤氮的析出导致径流中氮浓度增加,去除率降低;而60~90 cm深度的去除率增加。径流场内下渗流中氮浓度具有明显的水平空间变化,随距入水端距离的增加,30 cm深度下渗流中氮浓度先上升后下降;人工绿地岸带对下渗流中氮的净化作用均随淹水时间的延长呈降低趋势,且季节变化明显,在10月和4月具有较高的去除率,0~30 cm内TN、NH4+和NO3-+NO2-的去除率可分别达635%、891%和416%以上     

基于环境基尼系数的控制单元水污染负荷分配优化研究

将基尼系数这一福利经济学概念引入松花江流域水污染物负荷分配过程,综合考虑水循环的社会-经济-资源-环境因素,从社会经济发展、科技进步水平、水污染治理水平和资源禀赋差异角度出发,遴选出人均GDP、重污染行业总产值比重、人均水污染物产生强度、工业水污染物去除率、生活水污染物去除率、单位国土面积水资源量、国控劣Ⅴ类断面占比7项指标,以COD及NH_3-N负荷为控制因子,辅以贡献系数这一表征外部不公平性参数,构建了以基尼系数为度量标准的流域水污染负荷优化分配模型,并据此制订了松花江流域33个控制单元基于公平性的水污染负荷分配方案。研究表明,2012年松花江流域基于7项指标的基尼系数值均大于0.4,超过了基尼系数合理警戒线,说明流域控制单元间COD及NH_3-N排放在社会经济和资源环境方面存在不公平现象,其中松花江干流和第二松花江流域是不公平性特征最为突出的两个流域。在Lingo模型优化分配得到的2020年流域各单元COD削减方案中,单元21的年削减量最大,为1.82万t/a,单元10的年均削减率最高,达8%;在相应NH_3-N削减方案中,单元21的年削减量及削减率均为最大,分别达到0.08万t/a及8%。     

Mosquito larvae density and pollutant removal in tropical wetland treatment systems in Honduras

Constructed wetlands offer a low-cost wastewater treatment option for tropical developing countries. The vast majority of published treatment wetland research has been conducted in temperate regions. Because the function of treatment wetlands is related to the environmental conditions, more research specific to the tropics should be completed. A six-cell free water surface (FWS) wetland mesocosm was constructed in Santa Rosa de Copán, Honduras that received input from an open-sewer/wastewater-impacted stream. Three cells were planted with Typha domingensis Pers., and three cells were left unplanted. Both planted and unplanted wetlands were constructed with three different surface areas to concurrently study different hydraulic retention times (HRTs) and hydraulic loading rates (HLRs). Results from 6 months of operation showed improved water quality and mosquito larvae populations affected by their specific environment. Five-day biochemical oxygen demand (BOD) removal appeared to be proportional to HRT and HLR, and BOD concentration in the effluent was higher in unplanted cells than in planted cells (P<0.05). BOD removal approached 60% for greater than 3.5 days HRT. Total phosphorus (P) removal and coliform bacteria removal were found to be correlated with pollutant load, and P removal was found to be correlated with HRT but not HLR. A second municipal wastewater FWS treatment wetland in Copán Ruinas, Honduras that had been established for 15 years, was also evaluated. BOD removal in the Copán Ruinas system was determined to be 93% with 2.6 day HRT. These pollutant removal rates are higher than would be expected in temperate regions. Mosquito larvae density was correlated with depth of the wetland. Mosquito larvae densities were higher in cells that were operating below design depth of 0.2 m (P<0.005). Results indicate that it is possible to design FWS wetlands in the tropics for effective BOD removal and reduced mosquito larvae development.     

Toxicological effects of disinfections using sodium hypochlorite on aquatic organisms and its contribution to AOX formation in hospital wastewater

Sodium hypochlorite (NaOCl) is often used for disinfecting hospital wastewater in order to prevent the spread of pathogenic microorganisms, causal agents of nosocomial infectious diseases. Chlorine disinfectants in wastewater react with organic matters, giving rise to organic chlorine compounds such as AOX (halogenated organic compounds adsorbable on activated carbon), which are toxic for aquatic organisms and are persistent environmental contaminants. The aim of this study was to evaluate the toxicity on aquatic organisms of hospital wastewater from services using NaOCl in pre-chlorination. Wastewater samples from the infectious and tropical diseases department of a hospital of a large city in southeast of France were collected. Three samples per day were collected in the connecting well department at 9 a.m., 1 p.m. and 5 p.m. during 8 days from 13 March to 22 March 2001, and a mixture was made at 6 p.m. with the three samples in order to obtain a representative sample for the day. The toxicity test comprised the 24-h EC50 on Daphnia magna and a bioluminescence assay using Vibrio fischeri photobacteria. Fecal coliforms and physicochemical analyses such as total organic carbon (TOC), chloride, AOX, total suspended solids (TSS) and chemical oxygen demand (COD) were carried out. Wastewater samples highlighted considerable acute toxicity on D. magna and V. fischeri photobacteria. However, low most probable numbers (MPN), ranging from <3 to 2400 for 100 ml, were detected for fecal coliforms. Statistical analysis, with a confidence interval of 95%, gave a strong linear regression assessed with r=0.98 between AOX concentrations and EC50 (TU) on daphnia. The identification of an ideal concentration of NaOCl in disinfecting hospital wastewater, i.e. its non-observed effect concentration (NOEC) on algae and D. magna, seems to be a research issue that could facilitate the control of AOX toxicity effects on aquatic organisms. Therefore, it would be necessary to monitor the biocide properties of NaOCl on fecal coliforms at various doses and its toxicity effects on aquatic organisms.     

Estimation of septic tank setback distances based on transport of E. coli and F-RNA phages

Setback distances between septic tank systems and the shorelines of Lake Okareka, New Zealand were determined from model simulations for a worst-case scenario, using the highest hydraulic conductivity and gradient measured in the field, removal rates of the microbial indicators (Escherichia coli and F-RNA phages) determined from a column experiment, and maximum values of the design criteria for the disposal system, and assuming an absence of an unsaturated zone, a continuous discharge of the raw effluent from a failed or non-complying treatment system (both indicators at concentrations of 1x10(7) counts/100 ml) into the groundwater and no sorption of pathogens in the aquifer. Modelling results suggest that the minimal setback distances were 16 m to satisfy the New Zealand Recreational Water Quality Guidelines for E. coli <126 per 100 ml (Ministry for the Environment, 1999) and 48 m to meet the Drinking-Water Standards for New Zealand 2000 for enteric virus <1 per 100 l (Ministry of Health, 2000). These distances may be applicable for other lakeshores in pumice sand aquifers with groundwater velocities <7 m/day. Findings of laboratory column and batch experiments provided an insight into the microbial attenuation and transport processes in pumice sand aquifers. Bacterial removal was predominately through filtration (87-88%) and partially by die-off (12-13%), while viral removal was by both die-off (45%) and filtration (55%). In addition, microbial die-off in groundwater without aquifer material (i.e., free microbes) was much lower than die-off in groundwater with aquifer material (i.e., sorbed microbes) and contributed only 2-6% to the total removal. This implies that the setback distances estimated from die-off rates for the free microbes, determined in the laboratory without considering aquifer media and other removal processes, which are often reported in the literature, could be larger than necessary.     

水生高等植物对悬浮泥沙的去除研究

根据自然水体湿生植物（挺水植物）、浮叶植物以及沉水植物的空间分布规律，利用风车草（Cyperus alternifolius）、石菖蒲（Acorus tatarinowii）、菱（Trapa japonica）、金鱼藻（Ceratophyllum demersum）、轮叶黑藻（Hydrilla verticillata）和苦草（Vallisneria spiralis）等水生植物构建由挺水植物、浮叶植物到沉水植物的串联系统，含沙水依次流经挺水植物、浮叶植物和沉水植物，测定各级植物对泥沙的去除效果。结果显示，输入悬浮泥沙浓度依次为21.76、37.04、45.09、71.18 mg/L，水力停留时间（HRT）分别为12、16、24、24 h，水生高等植物串联系统对悬浮泥沙的去除率分别为68.1%、71.7%、77.5%、74.0%，表明水生高等植物可有效去除水体中的悬浮泥沙，改善了透明度。水力滞留时间对植物去除悬浮泥沙的效果有较大的影响，水力滞留时间长，即使输入悬浮泥沙浓度很高，去除率和单位时间的净去除量也较高;浅水区的挺水植物对进水高浓度悬浮泥沙的有效过滤作用减缓了悬浮泥沙对深水区沉水植物的胁迫压力;沉水植物能进一步去除悬浮泥沙，抑制再悬浮作用，对水生生态系统的稳定有十分重要的作用。     

复合垂直流人工湿地氧化还原特征及不同功能区净化作用研究

研究了复合垂直流人工湿地系统氧化还原电位（Eh）的时空变化规律及不同功能区中污染物的净化效果。结果表明：湿地系统下行流池表层、两池底层、上行流池表层Eh的变化范围分别为402～585、-87～-130、308～432 mV，沿水流方向依次形成了好氧A区/缺氧、厌氧区/好氧B区3个功能区。好氧A区是污染物去除的主要区域，BOD₅、COD_Cr、NH⁺_4- N的去除率分别为430%、484%、541%，特别是NH+4 N去除率占总去除率的79%；缺氧、厌氧区主要是进行反硝化反应和有机物的厌氧分解；好氧B区则主要是去除厌氧分解后的有机物以及进一步脱氮。另外，NH+4 N的去除率与系统各功能区Eh呈显著相关关系（〖WTBX〗p〖WTBZ〗＜001），而BOD₅、COD_Cr、NO^-_3-N的去除率与系统各功能区Eh相关性不显著。