These estimates were developed by contacting some of the largest agencies in the state, plus one medium sized plant, which collectively represent 35% of wastewater flow in the state. Using data on volume of digester capacity and current Mean Cell Residence Time (MCRT) in anaerobic digestion, flow was calculated based on current conditions. Using the same digester capacity, flow was then also calculated based on an MCRT of 15 days (minimum required in state and federal regulations). e difference in flow represents the estimate of excess capacity.
CASA then applied a multiplier of 37% to estimate the capacity of the remaining 136 existing treatment plants that have anaerobic digestion and manage more than 1 million gallons per day (MGD) of wastewater. Note that the remaining 136 plants represent 65% of the in influent flow in the state, which indicates the 37% multiplier is a conservative assumption.