Comprehensive comparison of water quality risk and microbial ecology between new and old cast iron pipe distribution systems

The effects of cast iron pipe corrosion onwater quality risk and microbial ecology in drinking water distribution systems(DWDSs)were investigated.It was found that trihalomethane(THMs)concentration and antibiotic resistance genes(ARGs)increased sharply in the old DWDSs.Under the same residual chlorine concentration conditions,the adenosine triphos-phate concentration in the effluent of old DWDSs(Eff-old)was significantly higher than that in the effluent of newDWDSs.Moreover,stronger bioflocculation ability andweaker hy-drophobicity coexisted in the extracellular polymeric substances of Eff-old,meanwhile,iron particles could be well inserted into the structure of the biofilms to enhance the mechanical strength and stability of the biofilms,hence enhancing the formation of THMs.Old DWDSs significantly influenced the microbial community of bulk water and triggered stronger mi-crobial antioxidant systems response,resulting in higher ARGs abundance.Corroded cast iron pipes induced a unique interaction system of biofilms,chlorine,and corrosion prod-ucts.Therefore,as the age of cast iron pipes increases,the fluctuation of water quality and microbial ecology should be paid more attention to maintain the safety of tap water.

Risk-based water quality decision-making under small data using Bayesian network

A knowledge-based network for Section Yidong Bridge,Dongyang River,one tributary of Qiantang River,Zhejiang Province,China,is established in order to model water quality in areas under small data.Then,based on normal transformation of variables with routine monitoring data and normal assumption of variables without routine monitoring data,a conditional linear Gaussian Bayesian network is constructed.A "two-constraint selection" procedure is proposed to estimate potential parameter values under small data.Among all potential parameter values,the ones that are most probable are selected as the "representatives".Finally,the risks of pollutant concentration exceeding national water quality standards are calculated and pollution reduction decisions for decision-making reference are proposed.The final results show that conditional linear Gaussian Bayesian network and "two-constraint selection" procedure are very useful in evaluating risks when there is limited data and can help managers to make sound decisions under small data.

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 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.