Comprehensive Enhanced Digestion Evaluations at Blue Plains Advanced Wastewater Treatment Plant

The District of Columbia Water and Sewer Authority (DCWASA) has undertaken a long-term study to evaluate the performance and operational aspects of various sludge digestion alternatives. While the initial goal of this study was to determine an appropriate digestion technology for Blue Plains Advanced Wastewater Treatment Plant, the outcome has been an increased awareness of the fundamental digestion parameters that impact solids degradation. These studies have been performed since 2003 at Virginia Polytechnic Institute and State University (VT) with a consistent reactor design and operational protocol so as to allow direct comparison between digestion technologies. In addition, conventional mesophilic anaerobic digestion has been maintained nearly continuously at VT over the course of the project in order to observe any potential shifts in the biodegradability of the source sludge from Blue Plains.To date, detailed investigations have been performed on the following technologies (each with significant operational variation, e.g. solids retention time, temperature, etc.):Single Stage Digestion:Mesophilic anaerobic digestion (MAD)*Thermophilic anaerobic digestion (49–58°C)*Multiple Stage Digestion:Acid Gas Anaerobic Digestion (AGAD)Temperature Phased Anaerobic Digestion (TPAD)Cambi Thermal Hydrolysis followed by MAD**Post aerobic digestion following these technologies has also been investigated.This paper summarizes these digestion process evaluations by investigating the effect of global system variables (e.g. digester temperature, anaerobic staging, anaerobic/aerobic staging) on solids removal efficiency and when applicable, nutrient and odor reduction potential.