Project Development for Temperature Phased Anaerobic Digestion at the Western Lake Superior Sanitary District

The Western Lake Superior Sanitary District at Duluth, Minnesota is implementing major biosolids program changes involving the Temperature Phased Anaerobic Digestion (TPAD) process. The District's treatment plant has no digestion facilities currently, and, therefore, this project represents a major departure from the existing District sludge incineration system. This paper primarily describes the development of the digestion facilities design at the District's 162 megaliter/day (43 mgd) municipal wastewater plant. This development work involved a significant pilot testing program at Iowa State University to confirm performance of potential Class A sludge digestion processes. In particular, hydraulic retention times within the thermophilic and mesophilic stages of the TPAD system were varied to assess process performance. Additional evaluation and engineering work resulted in technical information used to develop the project design. Considerable input from and discussion with District staff occurred to develop the design and obtain concurrence on key issues. Facilities described are currently under construction.