Improving Microbial UV Disinfection for Wastewater Systems

Ian G. Droppo, Peter Seto, Cheng He, and John Gibson of Environment Canada (EC), with Prof. Steven Liss (University of Guelph), Prof. Ramin Farnood (University of Toronto), Dr. Bill Cairns (Trojan Technologies) and Andre Schnell (Ontario Ministry of the Environment) were successful in obtaining a 2-year grant from the Canadian Water Network for investigating applying hydrodynamic particle breakage to improve microbial UV disinfection for wastewater systems. Much of the work will take place in the Wastewater Technology Centre of the Water S&T Directorate and will include graduate students from the universities of Guelph and Toronto working on-site and co-supervised by EC staff. The Wastewater Technology Centre is one the few places in North America equipped for the large-scale evaluation of new wastewater technologies. This research is expected to lead to development of an innovative, more cost-effective technology for wastewater disinfection. The technology may also enhance the opportunity for wastewater reuse initiatives.

Wastewater disinfection is vital for reducing the risk of waterborne diseases such as cholera, hepatitis, E. coli infection, cryptosporidiosis and giardiasis. Ultraviolet light (UV) disinfection is widely used, with several thousand installations around the world. Unlike chemical disinfectants, UV does not produce harmful by-products. However, biological aggregates found in wastewater protect pathogens from UV photons increasing the required UV dose. This increases both the size of the UV system, its electrical energy usage, and greenhouse gas emissions. Inadequate or incomplete disinfection of pathogens associated with suspended aggregates in wastewater poses a threat to the environment and human health.

Biological aggregates can be removed by filtration or membrane separation. However, these technologies require significant capital investments. Continuous disruption of biological aggregates represents a low-cost alternative. The disrupted aggregates are known to be less resistant to UV disinfection. Recent research in the Enivornment Canada laboratory indicates that suspended aggregates could be effectively disrupted under hydrodynamic stress. Hydrodynamic particle disruption (HD) is potentially a cost-effective alternative to full-flow particle removal by filtration or membrane treatment, with lower capital costs, smaller footprint, no sludge generation, and easier retrofitting. A key outcome of this project is the development of a novel treatment system by integrating hydrodynamic particle disruption with existing UV technology that will be of keen interest to the wastewater sector in Canada and abroad.