Feasibility of feedlot manure pre-treatment systems for optimal biogas production

Summary

Anaerobic digestion has the potential to reduce greenhouse gas (GHG) emissions while also providing biogas as an energy source. With rising energy costs and the introduction of the Emissions Reduction Fund (ERF), there has been an increasing interest in extracting energy from feedlot manure in the form of biogas. While biogas capture has been cost effective in the Australian pig industry, the successful conversion of beef feedlot manure into biogas has not been proven on a similar scale. This is largely because feedlot pen manure in its current form is an unsuitable substrate for biogas production.
There is currently a lack of knowledge within the Australian feedlot industry regarding the biomethane potential (BMP) of beef feedlot manure of differing ages and how harvest techniques impact on BMP values. Consequently there is a need for further analysis and understanding of 1) feedlot manure as a substrate for methane production and 2) the techno-economic feasibility of using this feedstock to produce biogas. Specific project objectives of this study include:A comprehensive review on the application of anaerobic digestion technologies treating agricultural waste for energy recovery including the identification of technically-feasible technologies for beef feedlot manure.
An understanding of feedlot feedstock and current manure handling practices at feedlots throughout Australia.
A technical and economic assessment of the different anaerobic treatment systems.
The results of biomethane potential (BMP) using different aged manures at lab scale.
Development of a pre-treatment system(s) to produce optimal influent material from feedlot manure as managed in existing systems.
Recommendations for systems worth trialling in a future farm-scale pilot trial.
A preliminary economic assessment of the system at a 10,000 head feedlot.

A comprehensive review of the literature has revealed that the economic value of feedlot manure for anaerobic digestion is largely determined by the composition (quality) of the manure. Pen cleaning timing, frequency and method affects the quality of the manure removed. The wide range of organic (volatile solid (VS)) content in material harvested from feedlot pens obtained from literature demonstrates the influence of pen design and management on the quality of manure removed from the pens. Data from these feedlots suggest that the material harvested contains material other than manure. This additional material (e.g. rocks and/or soil) influences the biomethane potential results by increasing the quantity of material harvested and lowering the organic content. The data from the literature highlights the need to be fully aware of the circumstances behind pen manure samples when assessing the substrate as a biogas feedstock. Low VS contents can either be due to prolonged manure breakdown or due to mixing of manure with soil.