An Advanced Biosolids Treatment Process and Potential Beneficial Applications of the Processed Biosolids

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ABSTRACT
An innovative and cost-effective biosolids treatment and processing technology was developed and demonstrated at a pilot and full-scale at the Guelph Wastewater Treatment Plant in Ontario. The Lystek process involves a low but optimized application of heat, alkali, and mixing in a batch or semi-continuous system to achieve the desired physical, chemical and microbiological characteristics of the processed biosolids. The resultant processed product is a high solids concentration (12 - 14%), pathogen-free liquid biosolids product which is fully compatible with standard equipment in use for land application of biosolids and liquid manure. The process achieves conversion of Ontario’s Nutrient Management Act 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 room temperature (17-22oC) without evidence of re-growth of harmful pathogens such as Escherichia coli, Salmonella and fecal coliforms. Application of Lystek process on raw sewage sludge and other intermediate wastewater solids indicated the versatility of the process that may have a potential to minimize the burden on the existing intermediate biosolids/sludge handling processes within the wastewater treatment facility, increase energy recovery, reduce the total biosolids generated and reduced storage capacity in the plant.

INTRODUCTION
Biosolids waste generators continue to face new technical and financial challenges in processing, safe disposal or utilization due to a growing public interest and involvement. Currently, threequarters of all biosolids processed through wastewater treatment operations in the United States and Canada (>8 million dry tonnes a year) are disposed of by beneficial application to agricultural land in a liquid state (2-3% solids), incinerated or by direct burial at approved
landfill sites.

For beneficial recycling and agriculture 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. In Ontario, material applied to agricultural land must meet the prescribed requirements made in the Nutrient Management Act (NMA) 2003. Such materials are classified as “Class B” biosolids. Similarly in the United States, the Environmental Protection Agency (US EPA) establishes standards for beneficial reuse under Part 503 Biosolids Rule (US EPA, 1992). The overall intent of both the NMA and US EPA Part 503 Biosolids Rule is to provide the regulatory framework for the protection of the public and environment associated with beneficial reuse of biosolids. Conventional stabilization methods include drying, chemical treatment, aerobic or anaerobic digestion and composting. Although composting is an effective method for stabilizing biosolids and producing a useful product (Witter and Lopez-Real 1987; Lynch 1993; Epstein 1997), it is difficult to reach and maintain the sanitizing temperature throughout the composting mass for the appropriate time, which often results in only partially stabilized product (Burge et al. 1987; Dumontet et al. 1999). Since application of improperly stabilized biosolids as a soil amendment and source of nutrients for plants poses a serious threat to human and animal health (Straub et al., 1993; US EPA, 1999; Brown et al., 2002), more effective biosolids treatment and management technologies are being continually sought.

An innovative biosolids treatment and processing technology was successfully developed over a 2 year period at bench-scale, pilot tested and further scaled up with the collaborative efforts of Lystek and the City of Guelph, Ontario at the Guelph wastewater treatment plant. 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 biosolids. The goal of the Lystek Process is 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 biosolids currently being spread on the farm land.

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. This paper presents some of the results of pilot- and full-scale feasibility studies conducted by Lystek at the Guelph Wastewater Treatment Plant and describes the benefits of the process and the beneficial recycling potential of the Lystek processed high solids pathogen-free liquid biosolid product.

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