SCS Energy: Beneficial Use of Digester Gas to RNG in San Diego

Point Loma Wastewater Treatment Plant, San Diego, CA

digester gas projectThe Beneficial Use of Digester Gas (BUDG) Project is an RNG plant located at the Point Loma Wastewater Treatment Plant in San Diego, California. The Renewable Natural Gas (RNG), plant converts Digester Gas (DG) into RNG. DG is almost identical to LFG in that it has a high CO2 fraction, is saturated with moisture and contains H2S, siloxanes and other VOCs.

The RNG is delivered into San Diego Gas and Electric’s (SDG&E’s) pipeline and meets SDG&E’s stringent Rule 30 standards for pipeline quality gas for siloxane. The plant has not had a single violation of SDG&E’s stringent Rule 30 standard for siloxane.

It was the first and is in late 2018, one of two projects in California delivering RNG into a natural gas pipeline. The RNG plant has an inlet capacity of 1,100 scfm and a product gas capacity of 850 MMBtu/day. The RNG plant incorporates the following technologies:

  • Digester Gas refrigeration;
  • Digester Gas compression with flooded-screw compression;
  • SulfaTreat for H2S removal;
  • Membranes for CO2 removal;
  • TOX; and
  • 0.3-MW fuel cell to satisfy some of the plant’s power requirements.

SCS delivered the RNG plant on a design-construct basis, with full responsibility for the project, including the SDG&E RNG metering-monitoring station and the interconnecting pipeline. SCS also conducted pipeline pre-injection RNG sampling and analysis to confirm compliance with SDG&E Rule 30 pipeline quality gas standards. The plant began commercial operation in March 2012, with SCS operating the plant on a contract basis.