Risk assessment of Giardia from a full scale MBR sewage treatment plant caused by membrane integrity failure

Membrane bioreactors (MBR) are highly efficient at intercepting particles and microbes and have become an important technology for wastewater reclamation. However, many pathogens can accumulate in activated sludge due to the long residence time usually adopted in MBR, and thus may pose health risks when membrane integrity problems occur. This study presents data from a survey on the occurrence of water-borne Giardia pathogens in reclaimed water from a full-scale wastewater treatment plant with MBR experiencing membrane integrity failure, and assessed the associated risk for green space irrigation. Due to membrane integrity failure, the MBR effluent turbidity varied between 0.23 and 1.90 NTU over a period of eight months. Though this turbidity level still met reclaimed water quality standards (≤5 NTU), Giardia were detected at concentrations of 0.3 to 95 cysts/10 L, with a close correlation between effluent turbidity and Giardia concentration. All β-giardin gene sequences of Giardia in the WWTP influents were genotyped as Assemblages A and B, both of which are known to infect humans. An exponential dose-response model was applied to assess the risk of infection by Giardia. The risk in the MBR effluent with chlorination was 9.83 × 10^-3, higher than the acceptable annual risk of 1.0 × 10^-4. This study suggested that membrane integrity is very important for keeping a low pathogen level, and multiple barriers are needed to ensure the biological safety of MBR effluent.     

INACTIVATION OF GIARDIA MURIS CYSTS BY CHLORAMINES1

ABSTRACT: In a study to measure the efficacy of chioramines at inactivating Giardia cysts, the ability of cysts to excyst was measured after exposure to different concentrations of chloramines, for different times, and at different temperatures and pH. The chloramines were generated by mixing ammonium sulfate and sodium hypochlorate in water to approximate a 7:1 chlorine:ammonia ratio by weight. Times of 40, 80, 180, and 270 minutes; temperatures of 3, 10, and 18°C; target chioramine concentrations of 0.4, 1.4, 2.0, and 2.6 mg/L; and pH of 7.0 and 8.5 were the actual values tested. The combinations of these variables that were able to inactivate >99.8 percent of the cysts were a minimum chloramine concentration of 2.26 mg/L applied for 270 minutes at a water temperature of 10°C; and at 18°C, averaged minimum chloramine concentrations of 2.14 and 1.55 mg/L applied for 180 and 270 minutes, respectively. The minimum CT values corresponding to these combinations capable of >99.8 percent cyst inactivation, are 610 at 10°C and 385 at 18°C. Temperature was noted to exert a major effect on the ability of chloramines to inactivate cysts. Modifications of the methods used to generate chloramines may have an effect on the capacity of this disinfectant to inactivate cysts.     

污水再生处理絮凝工艺去除病原性原虫的机制分析

通过考察在不同的絮凝剂种类、投加量、pH和温度等操作条件下隐孢子虫和贾第鞭毛虫(以下简称"两虫")的去除特性,探讨了污水深度处理絮凝工艺去除病原性原虫的作用机制.研究发现,污水经絮凝处理后,水样中胶体的平均ζ电位与2种荧光微球(两虫替代物)去除率和剩余浊度的线性相关度不高(R:0.49、0.48、0.65);而2种荧光微球之间的去除率线性相关性较高(R=0.99),并且与水样剩余浊度的变化趋势呈一定的指数相关关系(R=0.92、0.95).因此,在本研究的各种絮凝工况下.卷扫网捕是去除病原性原虫和浊度的重要作用机制.在相同操作条件下,贾第鞭毛虫的去除率大于隐孢子虫.     

水环境中隐孢子虫和贾第鞭毛虫检测方法研究

我国最新《城市供水水质标准》(2005年6月)提出了关于隐孢子虫和贾第鞭毛虫的控制指标,但其推荐检测方法还没有产生.本文针对美国EPA1623检测方法中的3个关键步骤,在浓缩、分离和染色等过程中进行了相应的改进或替代,并对各种备选的方案进行了探讨和比较分析.结果表明,微孔滤膜过滤→乙酸乙酯福尔马林分离→改良抗酸 铁苏木联合染色具有较好的敏感性,操作简单且成本较低,适宜作为国内普通自来水厂的初级检测方法.图2表4参20     

ISOLATION AND DETECTION OF GIARDIA CYSTS FROM WATER USING DIRECT IMMUNOFLUORESCENCE1

ABSTRACT: A water-sampling apparatus used for the isolation and detection of Giardia cysts in water has been designed and tested. The sampling apparatus uses one of a variety of pumps or waterline pressure to move water through a filter. Two of the optional pumps are lightweight enough to make the apparatus portable and thus suitable for sampling in remote areas. This technique of sample processing produces good cyst recovery in much less time than is required with previously established methods. Giardia cysts are identified using direct immunofluorescence.     

水质对污水再生絮凝工艺中病原性原虫去除的影响

采用荧光微球模拟隐孢子虫和贾第鞭毛虫(简称两虫),考察了有机物和颗粒物的浓度、组成等水质特性对污水再生处理絮凝工艺中两虫去除特性的影响.结果表明,腐殖酸浓度增加可提高水样中胶体浓度,从而提高对两虫的去除率;而酪氨酸虽然能改变胶体表面性质,但不参与絮凝过程,故对两虫的去除率无明显影响.水样初始浊度对两虫去除率影响较小;但水样中颗粒物的粒径分布,特别是1nm～100μm粒子的比例与对两虫去除效果间存在较好的相关关系.     

THE OPPORTUNITY COST OF TIME AND AVERTING EXPENDITURES FOR SAFE DRINKING WATER1

ABSTRACT: A survey of individuals during a Giardia contamination incident provided data to calculate the cost of boiling, hauling, or purchasing water to avoid infection. Three different approaches to the valuation of time were used to assess the implications of the opportunity cost of time for the measurement of averting costs. Mean monthly household averting costs were $33.47 using family income to value time, $13.07 using the minimum wage to value time, and $5.60 using zero opportunity cost of time. Comparisons of the mean costs for different sources and household characteristics indicated the value of time from family income was too high and that the other methods of valuing time were superior.     

隐孢子虫和贾第鞭毛虫的危害及其控制技术

病原微生物对水体的污染以及在饮用水中的存在是一个重要的公共卫生问题.微小隐孢子虫和蓝氏贾第鞭毛虫(简称两虫)被认为是世界上最主要的导致人体腹泻的水源性原生动物寄生虫,隐孢子虫卵囊和贾第鞭毛虫孢囊具有个体微小,致病量低、抵抗环境选择性压力强、易于造成两虫病暴发流行等特点,对公共健康及公共安全具有潜在的风险.饮用水处理中,...     

Wash water in waterworks: contaminants and process options for reclamation

Reclamation of clean water from filter backwash water was studied through pilot-scale experiments.The pilot plant consisted of clarification,sand-filtration,and ultrafiltration modules in sequence,with a provision to bypass the sand filter.Clean water that conformed to World Health Organization (WHO) guidelines on Potable Quality was reclaimed.Turbidity,aluminum and iron were found to be critical contaminants in process selection and design.Clarification,followed by sand filtration,was found to be the minim...