City’s compost passes tests
By: John Upton
July 28, 2010
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Free dirt: In 2007, the San Francisco Public Utilities Commission began giving away biosolids compost to residents so they could use it in their gardens.
(getty images file photo)
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Sewage-based compost given out by San Francisco is laced with contaminants such as heavy metals, which exist in comparable levels in commercially available soil amendments, The City found.
Sewage is often treated and dried to create what’s called biosolids, then it’s heaped on agricultural land.
The San Francisco Public Utilities Commission in 2007 took the process further and began providing more-heavily treated biosolids compost to residents for gardens.
The program’s future was thrown into doubt this year after protests at City Hall by food-safety activists who characterized the compost as toxic sludge.
The organizers, some of whom advocate using personal composting toilets, have long opposed use of biosolids on farms because of contamination found in sewage.
In response, the SFPUC suspended the program and spent $25,000 analyzing its compost and seven commercial soil products.
Using sewage as compost returns nutrients to the soil, which replenishes land and minimizes landfill.
But sewage is not the only waste that ends up in sewers and treatment plants.
Plastic bottles, industrial solvents, agricultural runoff and oils flow into storm drains and mix with sewage or get flushed into
sewers.
Laboratory results published on the SFPUC’s website Tuesday show potentially dangerous materials exist in The City’s compost at levels considered safe by the federal Environmental Protection Agency and World Health Organization.
Many of the contaminants, however, are unregulated.
“This stuff doesn’t just magically appear,” SFPUC Manager Ed Harrington said. “We have control over this by what we eat and what we flush and what we put down sinks.”
Lab results showed that nonsewage derived composts sold at hardware stores contain similar contamination.
Anti-biosolids-compost campaigner John Mayer dismissed the comparison.
“Our position is that sewage sludge should not be used to grow food. Period,” Mayer said.
SFPUC staff plan to meet publicly with commissioners to seek guidance on the biosolids compost program, which could be canceled or continued depending on the public mood.
A new campaign could be launched to help reduce the flow of toxic materials into drains and sewers, according to Harrington.
Ken Cook, executive director of national nonprofit Environmental Working Group, analyzed the data and said it shows regulations are needed for all manner of soil amendments.
Cook doesn’t recommend using biosolids compost to grow food, but he said cities everywhere struggle to deal with sewage.
“San Francisco is probably in the best position politically to take some strong action to start cleaning up the stuff,” Cook said.
Compost contamination
Six of the 127 contaminants measured in testing for the SFPUC, and biosolids measurement from SFPUC versus highest tested commercial product and U.S. EPA limit stated in parts per million:
Arsenic
Biosolids compost: 5.32
Kellogg Nitrohumus: 7.48
EPA limit: 41
Chromium
Biosolids compost: 39.1
Kellogg Nitrohumus: 31.8
EPA limit: 1200
Copper
Biosolids compost: 242
Kellogg Nitrohumus: 203
EPA limit: 1500
Lead
Biosolids compost: 19.2
Kellogg Amend: 31.8
EPA limit: 300
Mercury
Biosolids compost: 0.69
Kellogg Nitrohumus: 0.8
EPA limit: 17
Nickel
Biosolids compost: 19.8
Kellogg Nitrohumus: 17.9
EPA limit: 420
Source: sfwater.org
