Disposal of San Francisco's Sewage Sludge
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Disposal of San Francisco's Sewage Sludge is a major threat to agricultural land in northern California. According to a public fact sheet, SFPUC disposed of its 82,000 tons of sewage sludge produced annually as follows in 2008:[1]
- 56% goes to the Hay Road Landfill in Vacaville, CA
- 28% is applied to land as fertilizer in Solano County, CA
- 14% is applied to land as fertilizer in Sonoma County, CA
- 1% is applied to land as fertilizer in Merced County, CA
- 1% went to the composting program to be given away to gardeners
San Francisco's disposal of sewage sludge should be seen in the greater context of the entire Bay Area's disposal of sewage sludge, as each municipality shares access to roughly the same nearby landfills, farmland, incineration facilities, etc. A 2009 document from the Bay Area Clean Water Agencies (BACWA)[2] estimated that the Bay Area produced 158,000 dry metric tons of sewage sludge annually, a number that would swell to 189,000 dry metric tons by 2010. This document breaks down the disposal of the Bay Area's 2007 sewage sludge as follows:
- 52% is used as Alternate Daily Cover in landfills
- 19% is applied to land as fertilizer
- 14% is incinerated
- 10% is disposed of in landfills
- 1% goes to "dedicated land disposal"
- 1% goes to long term storage
- 4% is disposed of via other means
Broken out by destination county, Bay Area 2007 sludge disposal is as follows:
- 35% Santa Clara
- 20% Solano
- 12% Alameda
- 8% Sonoma
- 7% Sacramento
- 7% Contra Costa
- 7% Merced
- 3% Marin
- 1% San Joaquin
- <1% San Mateo
The document notes that a survey of landfills within 200 miles finds insufficient capacity to dispose of all of the Bay Area's sludge as "Alternate Daily Cover." Also, as of the document's publication in 2009, 21 of California's 58 counties restrict land application of Class B Biosolids. The document identifies as a strategy mounting PR efforts to convince the public of the safety of sewage sludge:
"Overarching each of the challenges just listed are the public's perceptions about biosolids. These perceptions impact to some degree all of the biosolids management options the Bay Area currently relies upon. Increasing the public's awareness of and knowledge about biosolids management issues in the Bay Area is one of the most important tasks confronting biosolids management. Without informed public discussion, the region is unlikely to implement optimal management policies. Policies aimed at placating negative public perceptions about biosolids are a more likely outcome."
The document cites the "California Integrated Waste Management Act" (AB 939) of 1989, a bill passed by the state government requiring that 50% of sewage sludge is diverted from landfills by the year 2000. Of the possible options for sludge disposal outside of landfills, it claims that "Class B land application was the most environmentally sound option for biosolids management." In other words, applying sewage sludge to land where crops designated for animal feed are grown as fertilizer is their preferred method of disposing of sludge. Another option they cite is producing commercial fertilizer and compost products using sewage sludge:
"Other options for sustainable reuse of biosolids involve transforming biosolids into one or more marketable commodities. Examples include bulk and packaged compost, pelletized fertilizer, and inputs into the production of cement, bricks and glass. Bay Area wastewater agencies already convert some biosolids into Class A compost and several agencies are upgrading their treatment facilities to increase production of Class A biosolids."
The document goes on to mention how the state of California could assist them in disposing of sludge using their preferred methods. They recommend the following:
- Creation of private sector grants and tax credits "for the creation of new technologies supporting alternative applications of biosolids"
- Financial incentives provided to the composting industry for increasing use of sewage sludge in compost products. Such incentives include low interest loans and tax credits. They also recommend increasing tipping fees at landfills and earmarking the money raised for the expansion of composting.
- Eliminating barriers and creating incentives for wastewater facilities to "invest in B2E technologies." This refers to the use of sewage sludge for energy.
The use of sludge to create energy is a popular idea in the Bay Area, as it is the subject of the Bay Area Biosolids to Energy Project[3]
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