Biofiltration Process
The District’s treatment plan uses a two stage biofiltration process followed by ammonia removal and filtration. Before discharge the treated sewage is chlorinated to kill bacteria and then dechlorinated to remove the chlorine toxicity. The solids removed by the process are put through an anaerobic (oxygen-free) digestion process where bacteria breaks down the organic matter and turns it into what we call biosolids.
Biosolids as a Resource
Biosolids are a nutrient- and energy-rich resource that innovative wastewater utilities like the District capture and utilize. After biosolids are produced they are temporarily stored before they are spread onto a dedicated nine-acre area on District property, where they become part of the soil. This is a permitted, approved method of disposing of biosolids — but our goal is to treat them as a resource, not as a disposal issue. In keeping with District’s philosophy of environmental sustainability we are exploring ways to beneficially use the nutrient value of biosolids
After biosolids are produced they are temporarily stored before they are spread onto a dedicated nine-acre area on District property, where they become part of the soil. This is a permitted, approved method of disposing of biosolids — but our goal is to treat them as a resource, not as a disposal issue. In keeping with District’s philosophy of environmental sustainability we are exploring ways to beneficially use the nutrient value of biosolids.
There are potential alternatives to disposal — for example on certain crops biosolids can be applied to reduce the use of chemical fertilizer. Another option is to compost biosolids with locally-generated green waste to produce a high-quality compost product. The District’s Board and senior staff keep a focus on implementing innovative operational improvements that will give us the ability to take full advantage of all the nutrient and energy value that biosolids have to offer.
For a great overview of biosolids, please see this fact sheet – Biosolids: A Renewable Resource (pdf), provided by the California Association of Sanitation Agencies.
Methane Gas as a Resource
Another byproduct of the process is methane gas which is produced by the digesters. The District uses that to operate microturbines which generate on-site electricity, while the heat they produce goes back to the digester to support that process. The methane can also be used to fuel one of the District’s vehicles.
For a detailed diagram of how it all works, see the Detailed Plant Diagram