Environmental concerns of desalinating seawater using reverse osmosis

This Critical Review on environmental concerns of desalination plants suggests that planning and monitoring stages are critical aspects of successful management and operation of plants. The site for the desalination plants should be selected carefully and should be away from residential areas particularly for forward planning for possible future expansions. The concerning issues identified are noise pollution, visual pollution, reduction in recreational fishing and swimming areas, emission of materials into the atmosphere, the brine discharge and types of disposal methods used are the main cause of pollution. The reverse osmosis (RO) method is the preferred option in modern times especially when fossil fuels are becoming expensive. The RO has other positives such as better efficiency (30-50%) when compared with distillation type plants (10-30%). However, the RO membranes are susceptible to fouling and scaling and as such they need to be cleaned with chemicals regularly that may be toxic to receiving waters. The input and output water in desalination plants have to be pre and post treated, respectively. This involves treating for pH, coagulants, Cl, Cu, organics, CO(2), H(2)S and hypoxia. The by-product of the plant is mainly brine with concentration at times twice that of seawater. This discharge also includes traces of various chemicals used in cleaning including any anticorrosion products used in the plant and has to be treated to acceptable levels of each chemical before discharge but acceptable levels vary depending on receiving waters and state regulations. The discharge of the brine is usually done by a long pipe far into the sea or at the coastline. Either way the high density of the discharge reaches the bottom layers of receiving waters and may affect marine life particularly at the bottom layers or boundaries. The longer term effects of such discharge concentrate has not been documented but it is possible that small traces of toxic substances used in the cleaning of RO membranes may be harmful to marine life and ecosystem. The plants require saline water and thus the construction of input and discharge output piping is vital. The piping are often lengthy and underground as it is in Tugun (QLD, Australia), passing below the ground. Leakage of the concentrate via cracks in rocks to aquifers is a concern and therefore appropriate monitoring quality is needed. Leakage monitoring devices ought to be attached to such piping during installation. The initial environment impact assessment should identify key parameters for monitoring during discharge processes and should recommend ongoing monitoring with devices attached to structures installed during construction of plants.     

Chlorination Byproducts in Drinking Water Produced from Thermal Desalination in United Arab Emirates

Oil activities in the Arabian Gulf can potentially affect the quality of the intake water available for coastal desalination plants. This paper addresses such situation by investigating the quality of intake water and desalinated water produced by a desalination plant located near a coastal industrial complex in United Arab Emirates (UAE). Analyses of the organic compounds on the intake seawater reported non-detected levels in most samples for the three tested organic groups; namely Polyaromatic Hydrocarbons (PAHs), Phenols, and Polychlorinated Biphenyls (PCBs). Trihalomethanes (THMs) and Haloacetic Acids (HAAs) were also tracked in the intake sea water, throughout the desalination processes, and in the final produced drinking water, to evaluate the undertaken pre- and post chlorination practices. The levels of considered Chlorination Byproducts (CBPs) were mostly found below the permissible international limits with few exceptions showing tangible levels of bromoform in the intake seawater and in the final produced drinking water as well. Lab-controlled experiments on the final produced distillate showed little contribution of its blending with small percentage of seawater upon the formation of trihalomethane and in particular, bromoform. Such results indicate that the organic precursors originated in the seawater are responsible for bromoform formation in the final distillate.     

Performance Evaluation of Reverse Osmosis Desalination Plants for Rural Water Supply in a Developing Country – A Case Study

Performance evaluation of two reverse osmosis (RO) desalination plants (DSP) at villages: Melasirupodhu (30 m³ day^-1) and Sikkal (50 m³ day^-1) in Ramanathpuram district,Tamil Nadu (India) were studied so as to bring out the state-of-art of their operation and maintenance (O&M). Detailedinformation on plant design and engineering, water quality,plant personnel, and cost of O&M was collected for a period ofthree years after commissioning of the two plants. Feed waterwas brackish, the TDS varied in the range of 6500–8500 mg L^-1 at Melasirupodhu and 5300–7100 mg L^-1 atSikkal villages. The product water quality was observed to begradually deteriorating as the salt rejection by the membranesdecreased with time. The salt rejection was 97–99% atthe time of commissioning of the plants, and came down to89–90% at the end of 3 years of operation. Product water TDS soonafter installation of the plants was excellent and within desirable limits of BIS. After three years of operation, few parameters exceeded the desirable limits, however, they were found to be within permissible limits of BIS. The analyses of thedata showed that both plants were operated only at 30–36% of the design capacity. Plant shut-down due to inadequate and erratic power supply, and plant break-down and inherent delay in repairs due to lack of adequate infrastructure were found tobe the major causes for the low utilization of the plants. Consequently the recurring cost of product water production enhanced to Rs. 25.0/m³ at Melasirupodhu and Rs. 17.5 m^-3 at Sikkal, as against the estimated cost of Rs. 15.0/m³ and Rs. 11.0/m³, respectively, as per the design. Over the years, the energy consumption for the product water output increased reflecting higher operational pressures needed with the aging of the membranes.     

Assessment of geochemical processes occurring in groundwaters in the coastal alluvial aquifer

Groundwater samples are collected from 30 observation wells in the study area to analyze the hydrochemical quality for determining the seawater encroachment in the part of Central Godavari Delta, Bay of Bengal, India. In order to establish the baseline hydrochemical conditions and processes determining the groundwater quality, an integrated investigation coupled with multivariate statistical analysis and hydrochemical methods are used to identify and interpret the groundwater chemistry of the aquifer system. The major land use is irrigated agriculture and aquaculture in the study area. The ground waters affected by the seawater intrusion featured high levels of sodium (Na⁺), chloride (Ca⁺), and TDS, which are the simplest common indicators for seawater influence. The elevated levels of NO₃–N at some monitoring wells indicate nitrate pollution of groundwater due to anthropogenic origin such as septic effluents or chemical fertilizers. Besides the major chemical compositions, it was also demonstrated that ionic ratios would be useful to delineate seawater intrusion and they include Na⁺/Ca²⁺, Mg²⁺/Ca²⁺, SO₄ ^2?/Ca²⁺, Na⁺/(Na⁺?+?Cl^?), and Ca^?/sum of anions. This paper demonstrates the variations in hydrochemical quality of groundwater and its evolution processes in two different seasons in the coastal aquifer alluvial settings     

Water chemistry influences the toxicity of silver to the green-lipped mussel Perna viridis

The study determined the influence and relative importance of water chemistry parameters (pH, alkalinity, hardness) on the acute toxicity of silver to the green mussel Perna viridis. A preliminary bioassay revealed that 4 mg L^???1 of silver caused 50% mortality (LC₅₀) in 96 h for mussels placed in seawater with pH 8.5, hardness 1,872 mg L^???1, and alkalinity 172 mg L^???1. Mortality of mussels increased with decreasing pH and increasing hardness and alkalinity variables. In contrast the mortality decreased with increasing pH and decreasing hardness and alkalinity values. The water chemistry also affected the concentration of sliver in experimental seawater and bioaccumulation of silver in mussels. The results revealed that the chemical properties of seawater must be considered while conducting toxicity tests with metals like silver. The possible explanations for the influence of water chemistry on silver toxicity to P. viridis are discussed.     

Assessment of seawater impact using major hydrochemical ions: a case study from Sadras, Tamilnadu, India

The impact of seawater intrusion was investigated using major hydrogeochemical ions to evaluate the origin of salinity in Sadras watershed located between Buckingham Canal and Bay of Bengal in the southeastern coast of India. From empirical data collected twice during pre- and post-monsoon seasons, it was found that groundwater was slightly acidic to mildly alkaline, and more than 44% of groundwater samples had EC > 3,000 ??S/cm in both the seasons. Results of principle component analysis (PCA) showed that Na^?+?, Cl^???, Mg^2?+?, and SO $_{4}^{\,\, 2-}$ concentrations had the highest loading factor and the samples affected by saline/seawater were separated from the cluster. Hydrochemical processes that accompany the saline/seawater were identified using ionic changes. It was observed during sampling periods that the mixing due to saline/seawater intrusion varied from 4.82?C7.86%. Negative values of ionic change (e _change) for Na^?+? and K^?+? decreased with the increasing fraction of seawater. Furthermore, salinity, sodium adsorption ratio, percentage of sodium Na (%), and exchangeable sodium percentage in well samples showed that groundwater was unsuitable for irrigation purposes.     

Application of multivariate statistical techniques in the assessment of groundwater quality in seawater intrusion area in Bafra Plain, Turkey

Multivariate statistical techniques such as cluster analysis and principal component analysis were performed on 28 groundwater wells in Bafra Plain. Cluster analysis results show that the groundwater in the study area is classified into three groups (A, B, and C), and factor analysis indicates that groundwater is composed of 89.64 % of total variance of 12 variables and is mainly affected by three factors. Factor 1 (seawater salinization) includes concentrations of electrical conductivity, TDS, Cl^?, Na⁺, and sodium adsorption ratio, factor 2 (mixing water) includes δ¹⁸O, δD, and T, and factor 3 (fresh) includes Ca²⁺. For determination of the source of water, Ca/Cl, Cl/HCO₃, Mg/Cl, and Ca/Na as initials and Mg/Ca and SO₄/Cl as molar rates which were identified, the rates had been found to be very useful. Cluster analysis was made by using these rates and the waters were classified in two groups (group 1 and group 2). First group waters were affected by seawater, and the second group were very less affected by freshwater or seawater. According to the comparison of two different parameters, group 1 comprised group A and group B-2, -3, and -4 from the same wells, and group 2 comprised group B-1 and group C from the same well. As a result of this study, it could be said that multivariate statistical methods gave very useful results for the determination of the source.     

Water quality decline in coastal aquifers under anthropic pressure: the case of a suburban area of Dakar (Senegal)

In recent years, the unregulated increase of the population in coastal areas of developing countries has become source of concern for both water supply and quality control. In the region of Dakar (Senegal), approximately 80% of water resources come from groundwater reservoirs, which are increasingly affected by anthropogenic pressures. The identification of the main sources of pollution, and thus the aquifer vulnerability, is essential to provide a sound basis for the implementation of long-term geochemically based water management plans in this sub-Saharan area. With this aim, a hydrochemical and isotopic survey on 26 wells was performed in the so-called Peninsula of Cap-Vert. Results show that seawater intrusion represents the main process affecting groundwater chemical characteristics. Nitrates often exceed the World Health Organization drinking water limits: stable isotopes of dissolved nitrate ( $\updelta ^{15}$ N and $\updelta ^{18}$ O) indicate urban sewage and fertilizers as a major source of contamination. Results depict a complex situation in which groundwater is affected by direct and indirect infiltration of effluents, mixing with seawater and freshening processes from below. Besides the relevance of the investigation at a regional level, it represents a basis for decision-making processes in an integrated water resources management and in the planning of similar monitoring strategies for other urban coastal regions.     

Characteristics of Iron Ore Tailing Slime in India and Its Test for Required Pond Size

The physical and chemical nature of the tailingslime depends on milling operations and water contentin the effluent. The characteristics of the tailingsdictate the type of disposal facility required.Characteristics of the tailings, transportation frombeneficiation plants and disposal system are described.Studies on tailing slime have been carried out at ironore mines in Orissa and the results are discussed. Thetailings contain toxic elements and find their wayinto the water environment. Sedimentation test was carriedout on tailings and the area required for tailing pondwas found to be 3155 m² in comparison to10 000 m² obtained from the use of an empiricalequation. Provision of tailing pond for the disposalof tailings is a conservation of resources in additionto pollution control, and sedimentation test is essentialfor required pond size calculation.     

Comparative study of the microstructural and magnetic properties of fly ashes obtained from different thermal power plants in West Bengal, India

This paper deals with the physical nature of the fly ashes obtained from two thermal power plants, situated in West Bengal, India. The fly ash samples are characterized by using comprehensive techniques with an emphasis on their ultrafine nature. The particle sizes of the samples are estimated using scanning electron microcopy (SEM) and found to lie within 0.18–5.90 μm. For morphology and compositional analysis, we also use SEM coupled with energy dispersive X-ray spectrometry. From X-ray study of the fly ashes the nature of conglomeration is seen to be crystalline, and the major components are mullite (Al₆Si₂O₁₃) and quartz (SiO₂). The magnetic measurement of the fly ash samples was carried out by SQUID magnetometer. ⁵⁷Fe Mössbauer spectra are obtained using a conventional constant-acceleration spectrometer with a ⁵⁷Co/Rh Mössbauer source. The hyperfine parameters obtained, in general, support the findings as made from XRD analysis and provide a quantitative measure of different iron ions present in the samples. The paper presents experimental data on the physical aspects of the fly ash samples of the thermal power plants which comprise coarse, fine, and ultrafine magnetic particulate materials and attempts to provide an exhaustive analysis.     

Groundwater stress and vulnerability in rural coastal aquifers under competing demands: a case study from Sri Lanka

Rural coastal aquifers are undergoing rapid changes due to increasing population, high water demand with expanding agricultural and domestic uses, and seawater intrusion due to unmanaged water pumping. The combined impact of these activities is the deterioration of groundwater quality, public health concerns, and unsustainable water demands. The Kalpitiya peninsula located northwest of Sri Lanka is one area undergoing such changes. This land area is limited and surrounded almost completely by sea and lagoon. This study consists of groundwater sampling and analysis, and vulnerability assessment using the DRASTIC method. The results reveal that the peninsula is experiencing multiple threats due to population growth, seawater intrusion, land use exploitation for intensive agriculture, groundwater vulnerability from agricultural and domestic uses, and potential public health impacts. Results show that nitrate is a prevalent and serious contaminant occurring in large concentrations (up to 128 mg/l NO₃?CN), while salinity from seawater intrusion produces high chloride content (up to 471 mg/l), affecting freshwater sources. High nitrate levels may have already affected public health based on limited sampling for methemoglobin. The two main sources of nitrogen loadings in the area are fertilizer and human excreta. The major source of nitrogen results from the use of fertilizers and poor management of intense agricultural systems where a maximum application rate of up to 11.21 metric tons N/km² per season is typical. These findings suggest that management of coastal aquifers requires an integrated approach to address both the prevalence of agriculture as an economic livelihood, and increasing population growth.     

Different hydrodynamic processes regulated on water quality (nutrients,dissolved oxygen,and phytoplankton biomass) in three contrasting waters of Hong Kong

The subtropical Hong Kong (HK) waters are located at the eastern side of the Pearl River Estuary. Monthly changes of water quality, including nutrients, dissolved oxygen (DO), and phytoplankton biomass (Chl-a) were routinely investigated in 2003 by the Hong Kong Environmental Protection Department in three contrasting waters of HK with different prevailing hydrodynamic processes. The western, eastern, and southern waters were mainly dominated by nutrient-replete Pearl River discharge, the nutrient-poor coastal/shelf oceanic waters, and mixtures of estuarine and coastal seawater and sewage effluent of Hong Kong, respectively. Acting in response, the water quality in these three contrasting areas showed apparently spatial–temporal variation pattern. Nutrients usually decreased along western waters to eastern waters. In the dry season, the water column was strongly mixed by monsoon winds and tidal currents, which resulted in relatively low Chl-a (<5 μg l^?1) and high bottom DO (>4 mg l^?1), suggesting that mixing enhanced the buffering capacity of eutrophication in HK waters. However, in the wet season, surface Chl-a was generally >10 μg l^?1 in southern waters in summer due to halocline and thermohaline stratification, adequate nutrients, and light availability. Although summer hypoxia (DO <2 mg l^?1) was episodically observed near sewage effluent site and in southern waters induced by vertical stratification, the eutrophication impacts in HK waters were not as severe as expected owing to P limitation and short water residence time in the wet season.     

Quantitative detection of nitrate in water and wastewater by surface-enhanced Raman spectroscopy

The presence of inorganic nitrogen species in water can be unsuitable for drinking and detrimental to the environment. In this study, a surface-enhanced Raman spectroscopy (SERS) method coupled with a commercially available gold nanosubstrate (a gold-coated silicon material) was evaluated for the detection of nitrate and nitrite in water and wastewater. Applications of SERS coupled with gold nanosubstrates resulted in an enhancement of Raman signals by a factor of ～10⁴ compared to that from Raman spectroscopy. The new method was able to detect nitrate with linear ranges of 1–10,000 mg NO₃ ^?/L (R ²?=?0.978) and 1–100 mg NO₃ ^?/L (R ²?=?0.919) for water and wastewater samples, respectively. Among the common anions, phosphate appeared to be the major interfering anion affecting nitrate measurement. Nevertheless, the percentage error of nitrate measurement in wastewater by the proposed SERS method was comparable to that by ion chromatography. The nitrate detection limits in water and wastewater samples were about 0.5 mg/L. The SERS method could simultaneously detect sulfate, which may serve as a reference standard in water. These results suggested that the SERS coupled with nanosubstrates is a promising method to determine nitrate concentrations in water and wastewater.     

UV/H2O2 oxidation of arsenic and terbuthylazine in drinking water

Arsenic is a widespread contaminant in the environment. The intake of water containing high concentrations of arsenic could have serious impact on human health, such as skin and lung cancer. In the European Union, thus, also in Italy, the arsenic limit in drinking water is 10 μg L^?1. Several water remediation treatment technologies are available for arsenic removal. For some processes, the removal efficiencies can be improved after an oxidation step. Most full-scale applications are based on conventional oxidation processes for chemical micropollutant removal. However, if water contains arsenic and refractory organic contaminants, the advanced oxidation processes could be considered. The aim of this work was to investigate the effectiveness of ultraviolet (UV) radiation alone and in combination with hydrogen peroxide for the oxidation of arsenic and terbuthylazine (TBA). The experimental tests were performed in groundwater at the laboratory scale (0.1 mg L^?1 As(III) and 10 μg L^?1 TBA). Hydrogen peroxide alone (15 mg L^?1) was ineffective on both arsenic and TBA oxidation; the 253.7-nm radiation alone did not oxidize arsenic(III), but photolyzed efficiently TBA (52 % removal yield at a UV dose of 1,200 mJ cm^?2). The UV/H₂O₂ advanced oxidation (UV dose 600–2,000 mJ cm^?2, 5–15 mg L^?1 H₂O₂) was the most effective process for the oxidation of both arsenic and TBA, with observed oxidation efficiencies of 85 and 94 %, respectively, with 5 mg L^?1 H₂O₂ and a UV dose of 2,000 mJ cm^?2.     

Impact of Coal Power Plant Emission on the Foliar Elemental Concentrations in Plants in a Low Rainfall Tropical Region

A field study was conducted around two thermal power plants of India to quantify the changes in foliar elemental concentrations due to emission in a low rainfall tropical area. Sulphur dioxide and particulates were at high levels which may cause serious ecological effects. Emission from the power plants has altered the elemental concentrations in the leaves of evergreen and deciduous plants. The foliar total-S and SO₄ ^2–-S levels were significantly higher in all the plants growing at polluted sites. However, the organic-S content was more or less unaltered. In evergreen plants, the SO₄ ^2–-S content increased gradually from summer through winter, whereas in the deciduous plants there was a higher magnitude of increase after onset of new leaves during summer. With the increasing pollution load, foliar Ca²⁺ and K⁺ contents increased, whereas N content decreased. The reduction in N content was greater during summer in evergreen plants and during winter in deciduous plants. The plants growing closer to the power plants accumulated more trace elements (Mn, Fe, Cd, Pb and Ni) as compared to those growing at distant sites. In deciduous plants the leaf fall during winter lowered down the trace element     

Some issues of environmental concern in Kampala,the capital city of Uganda

Kampala, the capital city of Uganda is the administrative, political, commercial, industrial, educational and cultural centre of Uganda. The city has an area of 190 km² and is located 8 km north of Lake Victoria (the second largest fresh water lake in the world) and approximately 42 km north of the equator. The population varies from about 1.2 million during the day to perhaps 0.9 million at night. The anthropogenic activityof this population far exceeds the infrastructure capacity of the city, leading to the deterioration of the urban environment. This article highlights the major sources of environmental degradation and pollution in the city, which include solid waste,abattoir waste, sewage, sanitation, drainage, industrial pollution, traffic pollution, atmospheric pollution, urban agriculture, rapid urbanisation and water hyacinth.     

Influence of coal-based thermal power plants on the spatial–temporal variability of tropospheric NO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript> column over India

The oxides of nitrogen—NO _x (NO and NO₂)—are an important constituent of the troposphere. The availability of relatively higher spatial (0.25° grid) and temporal (daily) resolution data from ozone monitoring instrument (OMI) onboard Aura helps us to better differentiate between the point sources such as thermal power plants from large cities and rural areas compared to previous sensors. The annual and seasonal (summer and winter) distributions shows very high mean tropospheric NO₂ in specific pockets over India especially over the Indo-Gangetic plains (up to 14.2 × 10¹⁵ molecules/cm²). These pockets correspond with the known locations of major thermal power plants. The tropospheric NO₂ over India show a large seasonal variability that is also observed in the ground NO₂ data. The multiple regression analysis show that the influence of a unit of power plant (in gigawatts) over tropospheric NO₂ (×10¹⁵ molecules/cm²) is around ten times compared to a unit of population (in millions) over India. The OMI data show that the NO₂ increases by 0.794 ± 0.12 (×10¹⁵ molecules/cm²; annual) per GW compared to a previous estimate of 0.014 (×10¹⁵ molecules/cm²) over India. The increase of tropospheric NO₂ per gigawatt is found to be 1.088 ± 0.18, 0.898 ± 0.14, and 0.395 ± 0.13 (×10¹⁵ molecules/cm²) during winter, summer, and monsoon seasons, respectively. The strong seasonal variation is attributed to the enhancement or suppression of NO₂ due to various controlling factors which is discussed here. The recent increasing trend (2005–2007) over rural thermal power plants pockets like Agori and Korba is due to recent large capacity additions in these regions.     

Arsenic uptake and loss in the American oyster,Crassostrea virginica

In addition to a control Crassostrea virginica was treated with 3 and 5 g As kg^p-1 for 16 wks at ambient seawater salinity and temperature to determine the potential of C. virginica as an indicator of arsenic pollution. Prior to spawning, as much as 10.3±1.5, 12.7±2.7, and 14.1±3.7 g As g^p-1 dry weight were accumulated in the total soft parts of oysters after treatment with ambient (control), 3 and 5 g As kg^-1, respectively. Immediately after spawning, an increase in tissue arsenic concentration was observed in all treatments up to week 12, after which a decrease in tissue arsenic concentrations occurred despite continuous addition of arsenic to the seawater. During the uptake period, a significant inverse relationship existed between dry weight and tissue arsenic concentration, whereas a significant direct relationship was apparent between dry weight and tissue content. Arsenic concentration in the total soft parts is not significantly related to seawater arsenic concentration over the range of concentrations used in this study. In all three treatments, arsenic uptake as concentration (g g^p-1) is not a significant linear function of time. Weight loss was significant but gradual during the first 16 wks of treatment and did not change significantly during the depuration period (wks 17–25). Tissue arsenic concentrations increased significantly in oysters from all three treatments during the depuration period. Generally, arsenic body burdens increased with increases in phytoplankton concentration and it appears that food contributes more to arsenic uptake than seawater arsenic concentrations. Since a relationship between tissue arsenic concentration and seawater arsenic concentration does not appear to exist, C. virginica would not be a good biological indicator of arsenic concentration in its environment.     

Distribution and bioaccumulation of organochlorine pesticides (OCPs) in food web of Nansi Lake,China

The concentration of 12 organochlorine pesticides (OCPs) were measured in water, sediment, aquatic plant, and animal (shrimp and fish) of Nansi Lake by gas chromatography equipped with an electron capture detector. The total OCPs concentrations were 65.31–100.31 ng L^?1 in water, 2.9–6.91 ng g^?1 dry weight (dw) in sediments, 1.29–6.42 ng g^?1 dw in aquatic plants and 7.57–17.22 ng g^?1 dw in animals. The OCPs composition profiles showed that heptachlor compounds was also the predominant OCPs contaminants in addition to hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in Nansi Lake. According to the source of HCHs and DDTs in sediment samples, there was no new input and the HCHs pollution mainly came from the use of Lindane in Nansi Lake. Bioaccumulation of OCPs in aquatic biota indicated that DDTs and heptachlor compounds had a strong accumulation, followed by HCHs and drins. The accumulation abilities of fish for OCPs were higher than those of plants and shrimps. The OCPs biota-sediment accumulation factor values of Channa argus was the highest in fish samples, followed by Carassius auratus, and Cyprinus caspio. Risk assessment of sediment showed that heptachlor epoxide had a higher occurrence possibility of adverse ecological effects to benthic species. Based on the calculation of acceptable daily intake and hazard ratio, HCHs in fish and shrimps from Nansi Lake had a lifetime cancer risk of greater than one per million. The risk assessment of water, sediment, and fish indicated the water environment of Nansi Lake is at a safe level at present.     

厌氧-缺氧-好氧处理工艺的污水处理厂进出水的毒性评价

为了准确评估厌氧-缺氧-好氧（A²/O）处理工艺对废水毒性的削减效率，采用斑马鱼胚胎急性毒性实验、发光细菌急性毒性实验和小鼠L929细胞毒性实验进行测试，结合理化指标，通过毒性当量（TU）法、平均毒性（AvTx）法、毒性指数（TxPr）法、最敏感测试（MST）法和潜在生态毒性效应（PEEP）法对常州市6家污水处理厂（生活污水、综合废水、化工废水、制药废水）进水和出水的生物毒性进行了评价。结果表明，斑马鱼胚胎的毒性敏感程度最高，3种受试生物的毒性评价结果具有较好的一致性。理化达标的污水处理厂出水仍存在一定的生物毒性效应，出水毒性较大的是综合污水处理厂，排入受纳水体后可能会对周围的生态环境产生潜在的生态风险。A²/O处理工艺对各污水处理厂进水的毒性削减较好，其中对制药废水的毒性削减最高，AvTx、TxPr、MST和PEEP的毒性削减率分别为99.45%、99.64%、99.48%和69.66%。与AvTx、TxPr、MST法相比，PEEP法能够更综合地评价废水毒性。