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).