Perspectives on variabilities in biomethane potential test parameters and outcomes: A review of studies published between 2007 and 2018.

Biomethane Potential (BMP) test continues to be a useful and inexpensive assay to estimate the digestibility and maximum methane production of various organic substrates in anaerobic digestion or co-digestion processes. Despite its usefulness and several published efforts toward standardizing it, the BMP test still do not follow a universally accepted standard protocol. This makes the comparison of results among studies quite challenging. In this context, this paper analyzes 78 peer-reviewed BMP studies published between 2007 and 2018 that used the BMP test primarily to assess methane potential of commonly digested substrates, such as food waste, wastewater sludge and manure. We focused on the similarities and differences in the methodologies used and, where possible, the results obtained from these studies were compared and discussed. It was observed that many studies do not provide adequate information on salient aspects of the BMP methodology, and results are sometimes reported in different units of measurements. The inoculum to substrate ratio (ISR), substrate concentration and/or load should be clearly indicated in future studies, and positive controls should be included to validate BMP results. It is recommended that more studies assess the impact of nutrient addition, potential effects of continuous and intermittent mixing and mixing intensities and the influence of reactor size and headspace volume on BMP results.