UC Irvine

The primary concern associated with water reuse practices is the public health risk caused by the potential exposure to microbial contaminants, such as pathogenic protozoa, bacteria and viruses. The detection and removal of microbial pathogens is therefore of great importance to ensure the reclaimed water is “safe” for the intended end uses. This research studied the microbial pathogen removal in three different water reuse schemes. In the first study, a rapid direct virus detection method based on Accuri C6 flow cytometry (FCM) was developed to quantify the virus removal rate in a water reclamation plant using microfiltration-reverse osmosis (MF-RO) process for indirect potable reuse water production. This new method, in combination with online total organic carbon and nanoparticle analysis, has shown to be a viable way for online monitoring of high-pressure RO membrane integrity and the potential breakthrough of viral particles. In the second study, the effectiveness of microbial pathogen removal by constructed stormwater wetlands (CSW) in the U.S. and Australia was investigated using digital droplet PCR (ddPCR) and 454-pyrosequcing techniques. The results showed that the two US CSW and one of the three Australian CSW had good performance in terms of indicator bacteria removal during dry weather flow. The treated stormwater can meet the recreational water quality criteria/guidelines. No Cryptosporidium was detected in any of the CSW, while Adenovirus were present at all sites. Human specific HF183 Bacteroides were only found in Australian sites indicating the potential contamination from sewage ingression. The microbial community analysis showed a clear increase of Cyanobacteria in the outflow of CSW with better performance. The water residence time was determined as a critical factor affecting the efficacy of microbial pathogen removal or inactivation. In the last study, pathogen removal efficiency was investigated in a solar-powered mobile toilet system for decentralized wastewater treatment. The wastewater electrolysis cell (WEC) uses solar energy to generate oxidants via electrochemical (EC) reaction for of microbial pathogen disinfection. The results showed 5 log10 reductions of bacteria (E. coli and Enterococcus) and viruses (coliphage MS2 and adenovirus) were achieved within 1 h reaction at applied cell voltage of +4V. The dominating role of free reactive chlorine generated in situ during EC disinfection process was verified using laboratory model waters. The formation of organic disinfection byproducts trihalomethanes (THMs) and haloacetic acids (HAA5) during EC treatment were found to increase with the rise of applied cell voltage. The EC treated toilet wastewater is suitable for many non-potable reuse applications (e.g., toilet flushing and irrigation) with significantly reduced microbial infection risk. As there is no need for supporting chemicals, the WEC system can be developed into commercial viable, self-sufficient, solar-powered mobile toilets for decentralized wastewater treatment.