This two-year innovative technology project is led by Dr. Steven Liss, Vice-Principal Research, Queen’s University.

Problem

Disinfection of wastewater by exposing it to high levels of ultraviolet (UV) light is a common and widely used treatment in the wastewater industry. Disinfection is essential because it reduces the risk of outbreaks of waterborne diseases such as cholera, typhoid and hepatitis.

Unlike chemical disinfectants, UV disinfection systems produce few if any harmful by-products. However, biological aggregates in wastewater can protect waterborne pathogens from exposure to sufficient quantities of UV light. In extreme cases, large aggregates may completely shield waterborne pathogens from UV, which prevents UV disinfection from occurring at all and may threaten both environment and human health.

Many types of wastewater, including combined sewer overflows, primary effluent and stormwater, contain large numbers of suspended aggregates, making their disinfection with UV light uneconomical. Further complicating disinfection are the differing properties of the particles or aggregates from these wastewaters.

Suspended aggregates in wastewater can be removed by filtration or membrane separation, but these technologies require significant capital investments. An alternate approach is to disrupt the suspended aggregates to improve UV disinfection. Preliminary research in the laboratories of Dr. Liss and his collaborators has indicated that suspended aggregates can be disrupted if they are hydrodynamically stressed.

Hydrodynamic particle disruption (HD) has the potential to provide a simple, low cost, compact and robust technology to make suspended aggregates more amenable to UV disinfection. HD could be an effective alternative to particle removal by filtration or membranes, with the additional benefit of having significantly lower capital and operating costs, a smaller footprint, no sludge generation and easier retrofitting.

Innovative research

For HD technology to be successfully implemented, it is necessary first to identify the optimum hydrodynamic flow conditions that would maximally enhance UV disinfection. As well, researchers need to take into account that the physical, chemical and biological structure of suspended aggregates in wastewater effluents is highly variable. To meet wastewater discharge standards a more fundamental understanding of particle structural characteristics and their impact on HD-assisted disinfection are required.

Innovative HD-UV disinfection process
A major outcome of this project is the development of a novel wastewater treatment system by integrating hydrodynamic particle disruption with existing UV technology. The research will involve pumping effluent through a flow restrictor before UV exposure to disrupt particles and augment UV disinfection. Early results by Dr. Liss’s team indicate that the cost and capital requirements of HD technology are low.

Systematic studies will be conducted to optimize particle-disruption performance. Design optimization will include modelling studies using computational fluid dynamics to achieve maximum disinfection at minimum capital and operating costs. A key outcome of this research is the development of a design tool to scale-up the HD-UV technology.

Regulatory implications
Because high concentrations of suspended aggregates are a barrier to conventional UV disinfection, the successful development of a low cost particle-disruption technology has the potential to increase the effective operating range of current UV disinfection systems. This, in turn, will increase the number and types of wastewater effluents that can be treated where before no economical technology existed.

Potential applications for the proposed research include the chemical-free disinfection of combined sewer overflows and primary effluent. Furthermore, this compact, robust and low-cost technology has potential use as a portable technology in remote environmentally sensitive arctic locations, military bases and mining camps.

Particle characterization and microbial interactions
A critical outcome of this research is to better understand how floc structure and the relationship between floc and pathogens influences particle break-up and disinfection. The modelling studies will permit better understanding of particle break-up and disinfection.

Research team

Steven Liss is a well-recognized environmental biotechnology researcher, with a particular interest in microbial processes in engineered and natural systems. He is the project’s leader and manager.

Ian Droppo is a Research Scientist at Environment Canada. He provides expertise in sediment dynamics and the source, fate and effect of pathogens within natural and engineered systems, as well as co-ordinates the study of particle-pathogen interactions.

Ramin Farnood is an Associate Professor in the Department of Chemical Engineering and Applied Chemistry and the Associate Director of the Pulp & Paper Centre at the University of Toronto. He is an expert on UV disinfection and the study of wastewater floc disruption using hydrodynamic shear and ultrasound cavitation. He co-ordinates the study of disinfection modelling and optimization.

Cheng He is a Research Scientist with Environment Canada. He provides expertise in hydraulics and modelling of hydraulic conditions and particle transport in both environmental and industrial flows.

Bill Cairns is a Chief Scientist at Trojan Technologies who has more than 30 years of academic, institutional and industrial research experience in fundamentals and applications of microbial systems, photochemistry and biological photoresponses. He will help develop and find markets for the HD technology.

Azita Soleymani is a researcher at Trojan Technologies, with considerable experience in analyzing fluid behaviour in Trojan’s UV reactors. She works primarily with Dr. Farnood and others on the research team to model hydraulics and fluid dynamics.

Peter Seto is the Principal Advisor of Environment Canada’s Wastewater Program. He is a senior engineer and researcher with considerable expertise in all aspects of wastewater and water treatment. He co-ordinates and oversees operations primarily at the National Water Research Institute.

André Schnell is a Pollution Control Engineering Advisor with the Standards Development Branch at the Ontario Ministry of the Environment. He will assist with the application and legislative aspects of this new technology.

Four students will help the team conduct the research — two MASc students (one to study particle-pathogen characterization and another to model particle breakage using computational fluid dynamics), as well as one summer student and co-op student per year.

Partners

Ontario Ministry of Environment
This project is a part of a larger collaborative research project on particle-disruption methods for improved disinfection, supported by the Ontario Ministry of Environment Best in Science Program. MOE will advise on policy, guidelines and legislative aspects of the HD technology being advanced in this project.

Trojan Technologies
Trojan will provide industrial expertise on wastewater issues and markets. In addition to core expertise in UV disinfection, Trojan will be contributing more specifically to the computational fluid dynamic work being conducted at the University of Toronto.

Environment Canada
Environment Canada’s technical assistance and instrumentation will be made available to characterize flocs and particles.