Biosolids Beneficial Reuse Program
Committed to responsible, economical reuse

Before the Biosolids Beneficial Reuse Program was introduced at the Laguna Treatment Plant in 1985, all the solids that passed through the plant went to the Sonoma County landfill. By 1997, only a third of the biosolid material was sent to landfill; the remaining two-thirds were used in land application as fertilizer or turned into marketable compost. Currently, with stepped up land application and composting programs, only twenty percent of the biosolids reach the landfill.

In land application (or land spread), a total of 11,000 wet tons of highly treated biosolids are trucked to local farms each year where it is used as fertilizer or soil amendment on fodder crops (i.e., animal feed and fiber crops). Land application is the most economical use of biosolids. It increases crop yields for the farmers, reduces disposal costs for the City, and conserves landfill space. However, public perception and changing government regulations could prevent land spread in the future, or make it prohibitively expensive.

Turning biosolids into compost is a more involved and expensive process than land application, but the end product is marketable and its use is approved by the EPA for gardening as well as landscape application in places such as parks, schools, and golf courses. As part of the composting process, yard or green waste collected curbside by area refuse companies is used as a bulking agent. About one part biosolids is blended with four parts green waste. Treatment and processing takes about two weeks and then the product is cured for at least another 30 days. The Laguna Composting Facility produces 20,000 cubic yards of compost each year, most of which is sold on the bulk market.

A byproduct of treating and processing biosolids is methane gas. At the Laguna Treatment Plant, this gas is used to generate about thirty percent of the energy needed to run the plant.

In 2005, a new storage facility was added, which allows what is produced in winter to be stored until spring and summer, when there is greater demand for land application and compost materials. Also, this year, a new type of belt press was approved for the processing facility. By the end of the year, two of the new belt presses were online; installation of two more will be completed in early 2006. A belt press removes water from the solid waste while also transporting the biosolids from one step in the process to another. The new equipment is more efficient in that it allows the sludge to be pumped rather than conveyed.

Watch the Biosolids Reuse Video