Energy regulators must improve their understanding of biogas and biomethane produced by a variety of feedstocks and anaerobic digesters in the state, according to a May 12 report by the California Energy Commission.
The development of biogas and biomethane is a high priority for the CEC and other state agencies, but more research is needed to better understand any unintended outcomes for public health and infrastructure, according to the report. Biogas can be used to generate electricity or can be upgraded to biomethane and injected into natural gas pipeline systems.
The state "has several issues related to biogas production" due to "the presence of compounds in biogas and biomethane that are not present in natural gas," the report says.
Biogas is produced by converting organic waste materials, such as those from landfills, wastewater-treatment plants and solid-waste facilities, into a mixture of carbon dioxide and methane. The report found that biogas has higher concentrations than natural gas of many organic sulfur types that can damage pipelines or form airborne particulate matter that affects human health. But the report also says facilities that upgraded their biogas to pipeline-quality biomethane were able to remove the majority of the sulfur compounds, meaning the compounds "do not rule out the future use of biogas in California," but rather indicate that more research is needed in order to minimize their potential negative effects.
Researchers measured 13 biogas or biomethane sample streams at various locations in California and compared those samples to the composition of a natural gas stream in a Pacific Gas & Electric pipeline that runs under the campus of the University of California, Davis. The study found cultivable aerobic and anaerobic bacteria at multiple biogas sites, but none were pathogens or likely to cause pipeline corrosion, the report says. Even so, upgrading biogas to biomethane did not completely remove the bacteria from the gas stream, suggesting that new technologies would need to be developed if bacteria control is desired in the future, according to the report.
Last month, the CEC in its 2019 Electric Program Investment Charge annual report highlighted a new biogas facility in San Luis Obispo that received EPIC funding. The facility can generate up to 6,200 MWh of electricity annually and has a power-purchase agreement with PG&E for about 13 cents/kWh (see CEM No. 1588).