Carbon Credits Required to Make Manure Biogas Plants Economic

Abstract

Anaerobic digestion (AD) of manure in mixed farming areas can produce biogas from which electrical power or pipeline grade natural gas can be produced. In this study, the cost of power and gas and the carbon emission reduction from AD plants receiving manure from multiple sources is calculated for plants of varying scale. The study area is Red Deer County, Alberta, a typical mixed farming area. Costs are based on a detailed analysis of manure and digestate transport and processing costs at an AD plant; carbon emission reductions from power generation are calculated for displacement of coal and natural gas sourced power. The required value of carbon credit in dollars per tonne of CO2 to cover the cost of AD power or gas is calculated for two cases: gas and power sale, and gas and power sale plus a subsidy plus, for the power generation cases, the sale of waste heat. The cost of power and gas shows a significant economy of scale, with the lowest cost coming from a single AD plant processing manure from the entire county. The required carbon credit to cover the cost of AD processing of manure is greater than $125 per tonne of CO2. These results show that AD treatment of manure from mixed farming areas is not economic given current values of carbon credits. Other factors that might motivate AD processing of manure from mixed farming areas are issues of water quality, odor control, and excess phosphate levels in soils.