FOG can be a big problem in San Francisco — not the misty kind that famously blankets the City by the Bay, but sewer-clogging fats, oils, and grease. FOG is a sticky problem for the San Francisco Public Utilities Commission (SFPUC), largely because of the many restaurants for which the city is known.
The men and women of SFPUC fight to keep FOG out of the city’s 1,000 miles of combined sewers, which carry 80 mgd of wastewater. They clean out gooey plaque that causes blockages. They clean up FOG-caused sewage backups and overflows. They fix sections of sewer broken as a result of clogs and backups. And they try to convince residents and business owners to take steps to avoid dumping FOG into the system.
And now, the commission uses a new technology to convert grease collected from commercial grease traps into high-quality fuels. The technology produces ASTM-certified biodiesel fuel, a renewable, nontoxic fuel that can be used in any diesel application, from vehicles to household furnaces, without modifying the machinery.
It’s all part of a new, comprehensive FOG-control program that the commission expects to help reduce sewer blockages, save on emergency responses and cleanups, and keep costs down for ratepayers.
Good food, bad clogs
Collection System Division manager Lew Harrison says his department handles about 9,000 work orders each year, about 6,000 of them related to sewer blockages, of which 44 percent are caused by grease. All told, the city spends about $3.5 million per year on grease-related blockages, and that doesn’t include the cost to private businesses and homes.
One reason FOG has been such a challenge is the city’s appreciation of good food. “San Francisco has more than 2,600 restaurants packed into a relatively small geographic area bounded by water on three sides,” says Harrison. “I’ve been told the city is home to more restaurants per capita than anywhere else in the country.”
In any city, restaurant food preparation, cooking, and cleanup generate the vast majority of the FOG. A restaurant that doesn’t follow the best anti-FOG practices and that isn’t equipped with a well-maintained grease trap can send an enormous amount of FOG down the drain every day.
Multiply that by hundreds of restaurants, and the volume of FOG flushed into the sewers adds up in no time. Harrison estimates that 9 million gallons of FOG enters the San Francisco sewer system daily. Once there, it cools, solidifies, clings to the sewer walls, and slows the flow of wastewater.
When wastewater moves slowly, or stops, odors build up. Eventually a heavy blockage causes sewage to back up into streets, commercial buildings, and houses, causing health hazards and costly cleanups and repairs.
