Demonstration-Scale of Primary Solids Harvesting for Energy Recovery at the UC Davis Wastewater Treatment Plant

The net energy consumption of wastewater treatment plants in the U.S. has been estimated to be in the order of 21 billion kilowatt hours per year (Werf, 2011). This level of energy use has been driving the interest for reducing energy costs and opportunities for converting by-product streams to energy. The concept of harvesting primary solids immediately downstream of the plant headworks (Fresh Solids) has been recently introduced (Tchobanoglous and Gikas, 2009; Noll, 2010) in consideration of their high value for energy recovery. Fresh solids comprise of tissue paper, fibrous material, fecal matter, food waste, small pieces of plastic, fats, oils and grease. Collection of these materials before they are degraded by biological processes maximizes their value as a source for energy. Furthermore, before their degradation, enhanced dewatering can be achieved by mechanical means.Microscreening is an emerging technology that can be used to address these needs. Solids separation through a MicroScreen is based on the filtration of particulate matter through a fine mesh wire cloth screen.This paper presents the results of demonstration-scale operation, over the course of 11 weeks, of a MicroScreen unit at the University of California, Davis wastewater treatment plant. The primary focus of the program was to demonstrate filtration performance, the machine's ability to clean the belt, and the efficiency of cake de-watering.