Dairy Manure Digester to RNG Upgrade

A private utility developed a renewable energy project, turning dairy manure into renewable natural gas (RNG). Symbiont, now a Mead & Hunt company, was selected for engineering, procurement, and construction at two dairy farms located in South Dakota. We designed and built two miles of piping to move manure from two dairy farms—with ~12,000 cows combined—to a central location for anaerobic digestion. Adaptability to accept manure trucked in from a third farm was built into the design, which also included the ability to return digestate to the third farm as needed. Four anaerobic digesters, 2 million gallons each, convert the manure waste stream into raw biogas. Biogas treatment consisted of two feed compressors with aftercoolers, four-membrane purification system, gas dryer, final compressor and flare, and thermal oxidizer. We successfully constructed eight miles of pipe to transport upgraded RNG to its pipeline injection point. The upgraded system converts ~1,200 SCFM of biogas into pipeline-ready RNG.