South Africa piggery powered by biogas from anaerobic digestion

May 12, 2014 | AD & Biogas

Anaerobic Digest

BioCycle May 2014

Costa Mesa, California: Curbside Organics To Digester Feedstock

Beginning in January 2015, residents of Costa Mesa, parts of Newport Beach and unincorporated Orange County, serviced by the Costa Mesa Sanitary District (CMSD), will no longer dispose of their household waste in a single cart. Residents will still have the luxury of commingling trash and recyclables, but organics — including food scraps and green waste — will be placed in a designated cart for processing at a new anaerobic digester to be owned and operated by CR&R in Perris, California. All food scraps, including meat, breads, produce and compostable bags, will be accepted. In a county where composting facilities are limited and landfill space is quickly disappearing, alternative means of managing waste are welcome. “We want to be in the frontline before everyone else is scrambling to figure out what to do with their organics and composting companies are being maxed out,” says Scott Carroll, CMSD General Manager, of the CMSD Directors’ unanimous decision to begin source separated organics recycling. “Plus the result is a marketable product.”
Hauling services for commingled trash/recyclables and organics will be provided by CR&R (using a separate truck for organics). CMSD estimates approximately 250 tons of organics will be collected for digestion weekly. In the current one cart system, residential waste and recyclables (including green waste) are separated at a transfer station. CMSD achieves a diversion rate of 57 percent, with most of the green waste used as alternative daily cover at landfills. According to Carroll, the diversion rate is expected to increase to 75 percent with the new collection service.
Changes in rates for residents will be minimal, he adds. CR&R has agreed to reduce rates for CMSD from $125/ton to $71.50/ton using public funds they received, including a $4.52 million grant from the California Energy Commission. As a result, residential fees will only increase by $1.91/month. A survey of 1,000 customers indicated that 41.4 percent of customers would be willing to pay more for collection services if it meant diverting more waste from the landfills. CMSD also held four town hall meetings and plans to involve the public in three more to communicate the changes and answer any questions before the new program starts. CMSD will also run public service announcements on TV and radio stations and update customers in its quarterly newsletter.

Mills River, North Carolina: LEED Gold Digester For Sierra Nevada

In January 2014, on 190 acres along the French Broad River about 20 minutes from Asheville, Sierra Nevada Brewing inaugurated a LEED Gold two-stage anaerobic digester, an integral part of its brand new East Coast brewery. (See “Anaerobic Treatment, Fuel Cell At Brewery,” January 2009 for a description of the digester installed at the company’s first brewery in Chico, CA.) Constructed by Milwaukee-based Symbiont Science Engineering & Construction, the Anaerobic Contact Sequencing Batch Reactor (ACSBR) treats over 220,000 gallons/day of wastewater and yeast (based on production of 700,000 barrels of beer per year). Wastewater and yeast enter a two-stage anaerobic equalization/hydrolysis tank to maximize biogas production in the ASCBR (second phase). Digested effluent flows to a post aeration tank prior to being discharged to the municipal sewer. The gas is fed into a biogas compression skid (with an emergency flare). A portion of the biogas is delivered at 90 psi to 200-kW Capstone microturbines; power is fed into the grid. Conditioned biogas also goes to the brewery boilers to heat the brewery, and to the brewery’s wastewater treatment plant boiler to provide heat to the digester. “It is supplying nearly all of the power needed to run the wastewater treatment plant,” says Tom Bachman, Symbiont’s vice-president of sales and marketing.
The ACSBR technology is proving exceptionally efficient, he adds. Incoming BOD and COD are 6,900 mg/L and 14,600 mg/L respectively, and total suspended solids is 14,600 mg/L. The treated wastewater meets the municipal sewer surcharge limits of 210 mg/L on BOD and 210 mg/L TSS. In addition, typical brewery treatment systems have a micro-screen prior to anaerobic treatment to further remove solids after grain has been separated out, explains Bachman. “We designed the system so that we could put in a [micro-]screen, but in 6 months of operating we have not noticed any need. In addition, after six months, we have only 4 feet of active bacteria and the tank can go up to 16 feet, so we don’t expect to have to clean out any bacteria. It is just digesting those solids.”

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