Debottlenecking Anaerobic Digester Capacity – Sometimes WAS Thickening Isn't Enough

Abstract

The objective of this paper is to summarize the solids handling evaluation conducted by the Gwinnett County Department of Water Resources (GCDWR) and Hazen and Sawyer (H&S). The solids handling evaluation was initiated by GCDWR's decision to process the residuals from the 22-mgd Yellow River Water Reclamation Facility (YRWRF) at the 60-mgd F. Wayne Hill Water Resources Center (FWHWRC) located in Buford Georgia. The evaluation also reviewed the capacity impacts from receiving fats, oils and grease and high strength waste (FOG/HSW) into the anaerobic digesters at the FWHWRC to boost digester gas production from codigestion. The solids processing evaluation concluded that several unit processes in the solids treatment train did not have adequate capacity with the increased loading from the YRWRF and the new FOG/HSW receiving station in conjunction with residuals generated by treatment at the FWHWRC. The evaluation recommended co-thickening of primary sludge (PS) and waste activated sludge (WAS) to free up anaerobic digester capacity for these increased loads which both reduced total digestion volume required for accommodating the increased loadings and deferred construction of the additional anaerobic digester tanks further into the future. An additional benefit to the increased anaerobic digestion capacity was realized through increased digester gas production to feed the new 2.1 mega watt (MW) combined heat and power (CHP) system operating at the FWHWRC site. Therefore this evaluation helped to unlock the potential benefits of increased anaerobic digester loading on green energy production and achieve maximum month treatment capacity at the FWHWRC.