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

• Published in: Journal of environmental sciences (China) 2015-04, Vol.30 (4), p.252-258
• Main Authors: Zhang, Yu, Chen, Zhimin, An, Wei, Xiao, Shumin, Yuan, Hongying, Zhang, Dongqing, Yang, Min
• Format: Article
• Language: English
• Subjects: Agricultural Irrigation; Bioreactors; China; Genotype; Giardia; Giardia - genetics; Giardia - isolation & purification; Humans; MBR膜; Phylogeny; Polymerase Chain Reaction; Reclaimed water; Risk; Risk Assessment; Sequence Analysis, DNA; Waste Disposal, Fluid; Waste Water - microbiology; Water quality; 全尺寸; 整性; 污水处理厂; 细胞膜; 膜生物反应器; 贾第虫; 风险评估
• ISSN: 1001-0742; 1878-7320
• DOI: 10.1016/j.jes.2014.09.033

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 was9.83 × 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.