CO-DIGESTION OF FOOD INDUSTRIAL RESIDUALS AND WASTE ACTIVATED SLUDGE: A PILOT STUDY

Potato chips and snacks industry generates wastewater with high solids content. Therefore, conventional wastewater treatment incorporates solids removal prior to an activated sludge process (Hadjivassilis et al., 1997). These steps both result in large quantities of waste solids which are collected and land applied or disposed in a landfill in common practice. Co-digestion is a residuals management alternative which has a potential to reduce the volume of the combined solids streams (Dinsdale et al., 2000). Furthermore, anaerobic biogas generated in the process may be used in the production facility's boilers for an added benefit.A pilot study was conducted with the following objectives:To evaluate volatile solids reduction and methane production in co-digestion of primary industrial solids and waste activated sludge;To recommend full scale design parameters of a co-digestion process; andTo identify operating and maintenance requirements.A 500-L loop digester with one draft tube and one shear nozzle was operated under mesophilic conditions for a period of four months. The digester feed consisted of primary clarifier underflow including potato and corn solids and waste activated sludge. The observed VS reduction of the mixtures improved from 45% to 67% as the industrial solids proportion of the mixture increased from 70% to 100% by volume, respectively. The pilot plant operated for an extended period of time at the hydraulic retention time (HRT) of 10 days under steady state conditions. The average observed methane yield was 0.8 m3/kg VS reduced and the average biogas methane content was 66% by volume. There will be hauling and disposal cost savings if co-digestion is adopted in the future.