OPTIMIZING POLYMER ASSISTED DEWATERING IN RECUPERATIVE THICKENING VIA A LAB-SCALE SYSTEM FOR ENHANCED BIOGAS PRODUCTION IN ANAEROBIC DIGESTION PROCESSES

Abstract

There is growing interest in the use of high performance anaerobic digestion (AD) processes for the production of biogas at wastewater treatment facilities to offset the energy demands associated with wastewater treatment. Recuperative thickening (RT) is a promising technique which involves recycling a portion of the digested solids back to the incoming feed. In general there exists a significant number of knowledge gaps in the field of RT because the studies that have been conducted to date have almost exclusively occurred in pilot or full scale trials; this approach greatly limits the amount of process optimization that can be done in a given trial. In this work, a detailed and comprehensive study of RT processes was conducted at the lab scale; a demonstration of the optimization of polymer assisted dewatering is given and biogas production and quality monitored. Two custom designed digesters (capacity = 1.5 L) were operated in parallel with one acting as a ‘control’ digester and the other operating under a semi-batch RT mode; both digesters were also operated in parallel under RT with alternative polymer flocculants. There were no significant changes in the overall biogas methane composition; however the RT digester had an average biogas productivity over two times higher than the control one. It was found that the recycling of the polymer flocculant back into the RT digester resulted in a significant improvement in dewatering performance. At the highest polymer concentration tested, all polymer flocculants demonstrated equivalent dewatering performance achieving over 6 times lower CST’s than the control; at lower polymer concentrations the 4516 polymer flocculant had superior dewatering performance. Thus, there exists an opportunity to decrease the overall consumption of polymer flocculants through judicious selection of the flocculant and the dose that is used both for the thickening and end-stage dewatering processes in RT digesters.