BIO-GAS CONVERSION TO ELECTRICITY ALLOWS TWO MAJOR WASTEWATER UTILITIES IN TEXAS TO MEET STATE MANDATED ENERGY MEASURES USING D/B/O APPROACH

New legislation in Texas is driving utilities in the state to reassess their wastewater treatment plant operations in an effort to reduce energy consumption. This paper highlights the efforts of two Texas utilities – Dallas Water Utility (DWU) and San Antonio Water System (SAWS) – to meet energy reduction goals through the conversion of bio-gas to electricity. Facility Backgrounds The 4.82 m3/sec (110 MGD) Dallas Water Utility's Southside Wastewater Treatment Plant (WWTP) and the 5.48 m3/sec (125 MGD) San Antonio Water System's Dos Rios Water Recycling Center (WRC) consume approximately 60,000,000 kWh and 72,000,000 kWh, respectively, of grid-derived electricity per year to meet their operation needs.Both the Southside WWTP and Dos Rios WRC serve as centralized biosolids processing facilities for one or more other wastewater treatment facilities owned and operated by their respective utilities. Solids processing at both facilities consists of thickening followed by anaerobic digestion and mechanical belt-filter press dewatering. The bulk of the dewatered biosolids from the Southside WWTP is disposed via land application as a Class B product. Biosolids from Dos Rios WRC are either composted and marketed as a Class A product by an outside contractor or landfilled.At current solids production levels, the Southside WWTP has the near-term potential to produce over 56,000 m3 (2.0 million cubic feet) of bio-gas per day, while the Dos Rios WRC has the potential to produce over 43,500 m3 (1.5 million cubic feet) of bio-gas per day.This paper highlights bio-gas to electricity with heat recovery projects (i.e., cogeneration projects) developed by both DWU and SAWS to capitalize on bio-gas value, including an overview of project drivers, bio-gas generation estimates and alternative delivery approaches (addressing assessments of financial risks and benefits, required commercial terms, and basis of contract award).