Enhanced energy recovery in Australian industry through anaerobic co-digestion

03 July 2018
Focus area: Waste
Program stream: Sustainability
Project number: 2014-1073
This project was a collaboration between AMPC, Queensland Urban Utilities, Pork CRC, Melbourne Water Corporation and The University of Queensland. It investigated how to improve the economics of biogas projects by maximizing renewable energy recovery from anaerobic digestion infrastructure. 

The project was structured into two sub-projects. Sub-project 1 conducted laboratory studies via two PhD projects (1A and 1B), and sub-project 2 validated the laboratory results by testing industrial wastes and monitoring co-digestion trials.

Sub-project 1A investigated the effect of waste mixture composition on co-digestion performance. It discovered that co-digestion performance would likely be reasonable if adequate amounts of essential nutrients were available and inhibition thresholds for ammonia were not exceeded and loading limits were not exceeded. 

Sub-project 1B investigated the effect of lower temperatures (15-25°C) on co-digestion capacity for ambient temperature covered ponds. This project discovered microbial community structure in a covered pond depends on the waste feed type. These different communities have different digestion capacities and a decrease in temperature decreased the rates of biological processes, meaning that digestion will be slower at colder temperatures. 

The applied research in sub-project 2 tested 30 wastes as possible co-substrates and discovered that glycerol and fat oil and grease ranked highest due to very high concentration and good biological performance. 

Sub-project 2 also tracked two full-scale co-digestion trials and these outcomes were translated into a co-digestion simulation tool that estimates anticipated methane production, residual solids, digestate/sludge properties, and risk of exceeding digestion capacity.

This project determined that co-digestion needs to balance improvements in biogas revenue with increased residue disposal costs and increased nutrient management costs. The loading capacity for co-substrates depend on carbon types (carbohydrates/lipids/proteins), operating temperature and digester configuration (covered pond vs. mixed heated digester).
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