Few people give a thought to what happens after water disappears down the drain. It’s messy stuff and we’d as soon believe it simply "goes away."

At Las Virgenes Municipal Water District, however, we pay a lot of attention to what happens to customers’ wastewater. It’s our responsibility to gather, treat, and dispose of the waste contributions of more than 80,000 local residents. Read on for the behind-the-scenes story of how we transform wastewater and solids from your home or business into a beneficial compost product.

Wastewater treatment begins at the Tapia Water Reclamation Facility, where the solids and liquid are separated. The 99 percent that is liquid goes on to be treated, filtered, and disinfected, to produce highly treated recycled water used for irrigation in our naturally arid region. (Click here to read part 1 of the Flush!)

What about the remaining 1 percent???

It’s a combination of human and food waste, called “biosolids”, and can be handled in different ways. In our area, it is composted.

Step 1:

Every day, 70,000 gallons of biosolids are pumped from Tapia, through underground pipelines, to holding tanks at Rancho Las Virgenes Composting Facility located 4 miles away.

Step 2:

Next, the solids are slowly fed into one of two immense digestion tanks that can each hold 1 million gallons. Working like huge slow-cooking crock-pots, the digesters contain beneficial anaerobic (without oxygen) microorganisms that break down the biosolids, neutralize them, and reduce their volume. During "digestion", methane gas is produced and harnessed on-site for use in two fuel cells. These cells produce enough supplemental electricity to help heat the digesters and support other electric needs throughout the facility. After about 25 days in the digester, the biosolids are ready to move on.

Step 3:

The digested biosolids next move into a centrifuge and polymers are added to help thicken the mix. Similar to a salad spinner or the spin cycle of a clothes washer, the spinning action (centrifugal force) separates the remaining liquids from the solids, to de-water them. The extracted liquid is sent back to Tapia for reprocessing (talk about recycling everything!). The remaining solids have a dense, moist, "cake" consistency.

Step 4:

The biosolids cake is now mixed with an amendment of wood chips or sawdust to give a lighter texture and make it easier for air to flow through the mixture. A small amount of completed compost is added to provide a "seed" or "starter" source of the beneficial aerobic (oxygen loving) microorganisms needed to perform the composting process. Rancho’s plant operators put together a precise "recipe" of all these elements, to ensure just the right mixture for current conditions.

Step 5:

The mixture next enters the in-vessel composting process. There, the biosolids/amendment mixture is heated by the natural process of composting. Using huge agitators that look like paddle wheels, the material is regularly mixed to keep the temperature even throughout and to introduce air, which is necessary for the beneficial microorganisms to do their work. It takes about 18 days for the mixture to gradually move from one end of the building to the other and finish this stage of composting.

Step 6:

The nearly finished material is next transferred to a huge building to cure. Here, the compost is stored in large piles where it continues processing for 15 to 30 days. Tests are conducted to ensure that standards set by the US Environmental Protection Agency have been met.

Step 7:

Finally, the compost is ready for use on landscapes and gardens as a top mulch or soil amendment. From beginning to end, the process takes approximately 90 days.

In this way, Rancho Las Virgenes provides a sustainable, self-sufficient, and environmentally sensitive way to dispose of biosolids collected from homes and businesses. The composting process at Rancho Las Virgenes transforms undesirable waste into a beneficial garden soil amendment. Rancho’s compost has been used at the Getty Museum, Palm Springs golf courses, and other locations throughout California.

Community Compost produced at Rancho is available free to the community, it's too good to waste. Open Saturdays 8am to 1pm at Rancho Las Virgenes Composting Facility, 3700 Las Virgenes Road, Calabasas, (about 1 1/2 miles south of the 101 freeway) Be sure to bring your own container. Need more than a few containers, call 818.251.2200 for more information. Tips on how to use Community Compost and nutrient analysis, are just a click away.

"Composting Facilities Apply Lessons Learned to Capital Improvements"
Article by Nora Goldstein
BioCycle, Journal of Composting & Organics Recycling; June 2004

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