Enhancing Anaerobic Digestion of Waste Activated Sludge

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This proposal addresses a study of the integration of waste activated sludge (WAS) pretreatment technologies with anaerobic membrane bioreactors (AnMBR) for enhanced sludge digestion. AnMBRs decouple the hydraulic residence time from the solids residence time and have been found to achieve substantial solids destruction at high organic loading rates while producing a thickened product. It is hypothesized that pretreatment of the sludges would allow for even greater AnMBR throughput. The process would be more stable than the use of continuous flow stirred tank reactors for digestion and would achieve pathogen reduction that is similar to conventional anaerobic digestion due to the extended solids residence times. Hence, this integration has the potential to substantially reduce the capital and operating costs associated with sludge digestion while maintaining stable operation and production of a high quality digestion product. There are, however, issues associated with system integration, membrane fouling and simulation that need to be addressed before the integration of these technologies will be accepted in practice. Pretreatment (i.e. intensity) and digestion (i.e. hydraulic residence time and solids residence time) conditions need to be optimized for an integrated system. The potential for enhanced membrane fouling with pretreated sludges is of concern because of the increased colloidal matter that is often generated in pretreatment processes. Simulation of pretreatment and digestion has received little attention and hence it is currently challenging to analyze and design these systems without conducting costly pilot testing. The objectives of the proposed project are to: 1.) Optimize the combined use of hydrogen peroxide (H2O2) and ultrasound as an innovative pretreatment to maximize AnMBR throughput and minimize membrane fouling 2.) Optimize AnMBR parameters for integrating pre-treatment with AnMBR digestion 3.)Further develop models of sludge pre-treatment and AnMBR digestion