Alternate: Biogas to RNG - A Case Study

Throughout the United States, over 1,500 wastewater treatment plants (WWTP) are equipped with anaerobic digestion to stabilize sewage sludge into biosolids. In those facilities, the byproduct of digestion is biogas, a methane rich gas that has the potential to be used as a renewable energy source. Only a fraction of the WWTPs however utilize their biogas for renewable energy, outside of being used in boilers for process heating. If biogas is upgraded to biomethane, the gas is equivalent in quality to natural gas, only from a renewable source, then it is termed Renewable Natural Gas (RNG). Due to the environmental benefit of RNG, through GHG emission reductions and offsetting of fossil fuel natural gas, the value of RNG exceeds its energy value. With this in mind, Bartlett & West teamed up with the Oakland WWTP in Topeka, KS to develop a project for upgrading their biogas to RNG. The project was funded in 2018 and fully commissioned in 2022. This presentation will outline the process details along with design considerations and performance of the design. The treatment train consists of bulk desulfurization, biogas drying and boosting, activated carbon system, compressor and 3 stage membrane carbon dioxide removal. Construction, balance of plant requirements, and the injection station interface are important factors to consider and design around. The presentation will also focus on the economics, not only on a monetary but also the environmental benefit. The capital and operating expenses are apart of the overall proforma. And the final section will cover the lessons learned throughout the 4 year journey to completion.