How Microsludge Can Lower Greenhouse Gases at Wastewater Treatment Plants

Municipal biological wastewater treatment plants (WWTPs) generate greenhouse gases (GHGs) in three main ways: (1) by consuming large amounts of energy from electrical and natural gas utilities to operate the plant, (2) by inherently generating CO₂ that is lost to the atmosphere, and (3) by generating excess microorganisms that must be disposed of. Effective conversion of these microorganisms or "waste activated sludge" (WAS) to biogas in an anaerobic digester and converting this biogas to energy are the two most important steps that a WWTP can take to minimize its direct and indirect generation of GHGs. Maximizing biogas production can decrease a WWTP\´s reliance on non-renewable energy sources that generate GHGs as well as decrease the costs of purchased energy. Sludge that is not converted to biogas will lead to GHG emissions to the atmosphere. Therefore, minimizing the amount of residual sludge that must be hauled off site to be either landfilled, applied to agricultural land, or incinerated also minimizes GHG emissions. Conventional mesophilic (37degC) anaerobic digesters (CMADs) at municipal WWTPs are not efficient at converting WAS to biogas, achieving 15 to 30% volatile solids reduction of WAS in typical 15 day treatment times. They capture only a small fraction (15 to 30%) of their biogas potential, resulting in a large portion (70 to 85%) of biosolids that still require disposal. Pre-treatment of WAS is needed to improve the performance of anaerobic digestion. MicroSludge is a sludge pre-treatment technology that greatly improves the efficiency of anaerobic digestion of WAS. MicroSludge results in: (1) more recoverable energy from biogas being available and therefore less non-renewable energy required to operate a WWTP; (2) less residual solids requiring transport either to a landfill, land application site, or incinerator; and (3) fewer GHGs being generated from the fugitive emissions of less residuals.