Pacific West biomass conference begins with AD tours

By Anna Austin | January 16, 2012

The third annual Pacific West Biomass Conference & Trade Show, held in San Francisco, Calif., Jan. 16-18, kicked off with a day-long tour, including one of the country’s most innovative wastewater treatment plants, as well as an on-farm dairy digester power system.

City intern and Aquatic Biomass Program lead researcher Cayden Hare said the city of Santa Rosa’s 21 million-gallon-per-day Laguna Wastewater Treatment Plant sends the water, which reaches the plant via an extensive, 500-mile underground piping system, through three phases. These include solids separation, clarification to settle out microbes, and a filtration process that utilizes anthracite coal. “Because we’re using UV (ultraviolet) disinfection, we need that filtration, or UV rays won’t be able to get what’s behind those particles that the coal would have filtered,” Hare told tour attendees. The UV system at LPT uses 1,080 UV bulbs.

LPT houses four 1 million-gallon anaerobic digesters that turn sludge separated from the water into Class B biosolids, which are sent across the street to a facility that transforms them into Class A biosolids. “The bulk of all of the treatment is done to the activated sludge,” Hare said.

Biogas emitted from the digesters is blended to a 50/50 mix with utility gas and is then combusted by three 0.8 MW engines to create a total of one-third of the plant’s electrical needs. “A combined-heat- and-power project to replace the existing facility began construction in spring 2011, and it’s expected to be finished in December of 2012,” Hare said.  When that’s complete, four 1 MW engine generators will burn the biogas, but also serve as standby power for the plant’s needs during utility outages.

Uniquely, some of the plant’s wastewaster is diverted to six channelized wetlands, where aquatic biomass cleanses the water, absorbs pollutants and is allowed to grow. The biomass is eventually transferred into two, 1,500-gallon vertical anaerobic digesters, Hare explained, along with waste glycerol and winery leaves. The digesters’ temperatures are kept stable by wire coils beneath their cemented surfaces.

More than half of the materials are digested into biogas and used to generate electricity to power small cars used on site, according to Hare, and the remaining half of the materials are used for composting. “As a society, we tend to look at all of these things as waste, but the truth is that there is energy in them,” he added.

At the Giacomini Dairy at Point Reyes, Calif., tour attendees were able to view an ambient temperature, covered lagoon anaerobic digester fuelled with manure from about 350 cows.

With financial aid from the USDA and other government grant programs, the digester has been operating 24/7 for the past two years, according to digester technician Douglas Williams. Biogas emitted from the digester is captured through a gas collection system modeled after those utilized by the German biogas industry, he explained, and then piped to a gas handling system.

Electricity produced from the biogas via an 80 KW generator powers the farm’s operations, and excess electricity is purchased by electric utility PG&E, according to Williams. “There’s also a CHP (combined-heat-and-power) aspect, as heat coming off the engine is used in the dairy and creamery,” he said.

Williams said that while the project development has been mostly smooth, there have been a few issues and challenges. One in particular has been difficulty finding appropriately sized equipment for a project of the dairy’s scale. And while the AD process sounds relatively simple, a project must be done very carefully, Williams added. “You really have to pull all of the right pieces together, especially in light of new air quality regulations.”