Overaa Constructors and Water Works Engineers developed a design-build proposal for the City of Richmond to install a new cogeneration facility to convert digester gas from their WWTP into electricity. The City of Richmondís WWTP has a dry-weather capacity of 16 mgd and operates a 2.0 MG digester. Currently, all of the bio-gas produced by the digester is either burned in a boiler for sludge heating or flared. The intent of this project is to recover the energy in the flared digester gas to reduce the carbon footprint of the City.
The Overaa/WWE team produced preliminary designs and firm design-build prices for the purchase and installation of two alternative equipment packages:
300 kW Fuel Cell unit
335 kW Internal Combustion Engine
The Overaa team was selected by the City of Richmond as providing the best value to the City and the IC engine option was selected. The design-phase of the work started with further analysis of digester gas production at the facility and truth-checking that production against wastewater treatment model given actual loadings and process performance. That detailed analysis led to developing a new option for a 280 kW IC engine and comparing its cost to a 335 kW IC engine. The City then selected moving forward with the 280 kW IC engine option and awarded the design-build contract to the Overaa team. Shortly after the award, the City determined that they didnít have the funding for the project, and cancelled it.