Improved Biosolids Stabilization Utilizing Temperature Phased Anaerobic Digestion

In 2012, the Fox Metro Water Reclamation District (District) completed a construction project that upgraded their existing conventional mesophilic anaerobic digestion facility to a batched temperature phased anaerobic digestion (TPAD) facility. Through the TPAD project, the District was able to increase their digestion capacity without constructing additional digesters. The District’s volatile solids reduction (VSR) increased from approximately 59% to 72%, and their gas production increased by approximately 37%. The District centrifuge cake solids also increased as a result of the project. The combined impact of the greater VSR and drier biosolids is an approximately 38% reduction in biosolids volume to beneficial reuse on farm fields. The design approach, additional operating results, and a few operational and maintenance issues are reviewed.