From Dirty Waste to Clean, Renewable Natural Gas

Since 1963, the Point Loma Wastewater Treatment Plant has been responsible for treating wastewater in San Diego. Currently, the plant treats wastewater for more than 2 million residents—removing organic and inorganic materials from approximately 175 million gallons of wastewater each day before discharging it back to the ocean. During this treatment process, methane gas is produced and then captured and converted into clean, renewable natural gas that helps power the facility, and integrated into SDG&E’s natural gas pipeline system.

Power from methane gas

The wastewater goes through several treatment processes to remove large particles like paper, plastic, and sand, as well as organic solids like grease and cooking oil.  It is then pumped into eight digesters where the organic material is reduced in volume through a heat and bacterial process similar to human digestion. Methane gas is a byproduct of the digestion process.

The methane gas is captured and cleaned or scrubbed, and used in two giant natural gas engines in the plant’s gas utilization facility that produce enough energy to power the plant, making it entirely self-sufficient. What is unique about the Point Loma Wastewater Treatment Plant is that some of the scrubbed methane gas—or renewable natural gas—is injected back into SDG&E’s pipeline system. That gas is being used to power a 2.8 megawatt (MW) fuel cell at the University of California, San Diego and another 1.4 MW fuel cell at San Diego’s South Bay Water Reclamation Plant.

Generating clean energy and reducing waste

In operation since 2011, this gas utilization facility at the Point Loma Wastewater Treatment Plant, which is owned by BioFuels Energy, was the first project in California to inject bio methane gas into a utility’s natural gas pipeline system. To ensure that the quality of the cleaned methane gas meets state pipeline quality standards, there is 24-hour monitoring of the production of that gas on site.

While this is a first of its kind project in the state and the only one in San Diego, our hope is that utilizing a natural gas transmission system to transport renewable natural gas becomes standard practice in the near future.

Click here to read more about how natural gas is fueling San Diego.