The Guelph wastewater treatment plant produces in excess of 4000 dry tonnes of biosolids per year. The City of Guelph (City) currently processes the biosolids discharged from the anaerobic digester system from the Guelph Wastewater Treatment Plant (WWTP). The anaerobic digester sludge is belt pressed to about 20-24% solids concentration and either composted in an enclosed vessel composting system or mixed with wood chips and transported to a municipal landfill. The City of Guelph is currently conducting a Biosolids Master Planning exercise to establish its biosolids handling and disposal opportunities and has established an objective to maximize the potential for beneficial reuse of biosolids. For beneficial recycling and agricultural utilization of municipal sludge, a high level of stabilization and sanitation of organic matter in the biosolids is required to maintain soil, water and air quality. More effective biosolids treatment and management technologies are being continually sought.

An innovative biosolids treatment and processing technology was successfully developed over a 3 year period at bench-scale, pilot tested and further scaled up with the collaborative efforts between the City of Guelph and Lystek International Inc. The technology involves a small foot of the Lystek system and the processing requires an optimum application of heat, chemical and mixing in a batch or semi-continuous system to achieve the desired microbiological, physical and chemical characteristics of the processed high-solids biosolids. The goal of the process was to produce a low-pathogen product that can be used as a soil conditioner without the health and environmental risks associated with the high-pathogen low solids biosolids currently being spread on the farm land.

The resultant processed product is a high solids concentration approximately 20%, pathogen-free liquid biosolids product which is fully compatible with standard handling equipment in use for land application of biosolids and liquid manure. The process achieves conversion of Class B biosolids to US EPA Class A biosolids. Processed material retains the pumpability needed to reduce the costs of biosolids handling, storage, transport and land application and is suitable for beneficial re-use and application as a fertilizer product even after prolonged seasonal storage at ambient temperature in Canadian weather conditions. Processed materials can be stored for long periods of time at ambient temperature without evidence of re-growth of harmful pathogens such as Escherichia coli, Salmonella and fecal coliforms.

The objectives of the study included optimization of various process conditions of biosolids treatment to establish a process which can be easily scaled-up and integrated into any existing wastewater treatment system, and evaluation of potential application of the processed biosolids product.