Anaerobic Digest

BioCycle  November 2017, Vol. 58, No. 10, p. 12

Sacramento, California: California Farm Digester Grants

The California Department of Food and Agriculture (CDFA) announced $35 million of grants to build 18 new dairy digesters, almost doubling the number of digesters in the state. CDFA received 36 applications. All the new facilities will process manure only, will utilize covered lagoon digester systems, and upgrade the biogas to renewable natural gas (RNG) for pipeline injection, according to the descriptions released by CDFA (link in online edition of Anerobic Digest). “Given local and regional air quality issues in the Central Valley, projects that get the gas out of the immediate region (and often incentivize the replacement of dirtier diesel engines with cleaner natural gas ones) won the public funding,” observes Peter Weisberg of The Climate Trust in Portland, OR. “Our read is that all but one of the award recipient projects will involve a cluster of digesters that pipe gas to a centralized cleaning and injection facility, for economies of scale. The RNG will either fuel trucks directly, or be used to replace natural gas in an ethanol refinery.” https://www.cdfa.ca.gov/oefi/ddrdp/

Washington, D.C.: Digestate Certification Available

The American Biogas Council (ABC) launched the Digestate Standard Testing and Certification Program (DSTCP) in October 2017. Patterned in part on the US Composting Council’s Seal of Testing Assurance program, ABC’s digestate certification creates a voluntary, industry-led, third party verified standard that quantifies, characterizes and communicates the physical and chemical qualities of digestate. The DSTCP prescribes standardized test methods, performed by laboratories certified under ABC’s Digestate Lab Certification Program, as well as provides a descriptive, quality hierarchy based on the feedstocks and analytical results for the digestate products. The documentation specific to the digestate produced can be used for both marketing materials to establish customer assurance for the purchase of a producer’s digestate, as well as regulatory submissions.

The DSTCP applies to digestate (either raw, whole, or separated into liquid and solids, but without further chemical modification) to be directly land applied or to be used as a feedstock in further processing or manufacturing. Digestate that is further processed via chemical, physical, or other modification into a fertilizer, compost, or other product — and marketed as such — is not currently addressed.

The program quantifies the beneficial physical and chemical changes resulting from the digestion process and delineates the physical and agronomic properties of the digestate products. This information includes input materials; physical characteristics of concern and importance; chemical characteristics of concern and importance; agronomic properties; and potential restrictions on use.

Testing to characterize digestates is administered by laboratories certified by the program. The characterization allows digestate producers to relay important information regarding composition and appropriate beneficial uses of digestate to regulators and end users. Currently, the University of Wisconsin Oshkosh-Environmental Research and Innovation Center (ERIC) is the only certified lab in the program.

All participants are required to comply with all applicable local, state, and federal legislation and/or regulations, irrespective of whether or not the raw or whole digestate, and any separated liquid and solids, is tested in accordance with the DSTCP. For the avoidance of doubt, the program does not provide any additional waivers or exemptions for digestate that derives from feedstocks that include waste activated sludge and other sewage products and are already subject to specific regulations per EPA 40 CFR Part 503. www.digestate.org.

London, England: Facility Achieves BSI PAS 100 Digestate Certification

Cattlegate Farm in Enfield, about 10 miles from London, installed a 1.5 MWe (Megawatts electric) anaerobic digestion plant in 2016 with capacity to process 27,000 tons/year of food waste produced by London’s households, restaurants and food industry. Willen Biogas, formed by Cattlegate Farm to manage its organics recycling and renewable energy operations, selected Xergi to build and operate its new digester. Digestate is used in Cattlegate Farm’s operations.

Willen Biogas has demonstrated that the plant can provide high quality digestate, having received the demanding BSI PAS 110 accreditation. The accreditation imposes strict requirements on the quality of the digestate. For example, restrictions apply to the amount of impurities, consisting of plastic, metal and the like, which should not end up on farmland. “Obtaining the accreditation involves a very stringent procedure,” explains Jørgen Fink, country manager for Xergi in the United Kingdom. “When the plant is in operation, you have to prove that the requirements are being fulfilled over a period of several months, during which the plant must be in stable operation.”

A key advantage of accreditation is that farmers can feel confident that they are receiving high quality digestate. Another advantage is that if the digestate were not BSI PAS 110 accredited, it would be considered waste and waste management controls would apply to its handling, transport and application.

Okanagan, British Columbia: Taking The “Stink” Out Of Treatment Plant Digesters

While anaerobic digestion (AD) is an effective way of recovering energy and nutrients from organic waste, several issues — including production of corrosive, highly odorous and toxic volatile sulfur compounds (VSCs) in digester biogas, and long digestion times to achieve sufficient pathogen reductions — can limit its wider adoption. Research conducted by the University of British Columbia’s Okanagan’s School of Engineering evaluated the addition of metal salts to a wastewater treatment plant’s digester feed to evaluate the effects on digester stability, organic removal, VSCs formation in digester headspace, pathogen removal and sludge dewaterability. The metal salts included Kemira™ PIX-311 (ferric chloride), PAX XL-6 (aluminum chloride hydroxide sulfate), and PAX XL-19 (polyaluminum chlorohydrate). After preliminary dose trials, two different doses of PIX-311, PAX XL-19, and a 1:1 mixture of PIX-311 and PAX XL-19 were selected. PAX XL-6 was removed from further study as dosing significantly increased VSC levels and the PAX XL-6 dosed digester exhibited signs of instability.

During the total operation period of 100 days, addition of PIX-311, PAX XL-19, a combination of PIX-311, PAX XL-19 at concentrations of 4,000 and 4,500mg/kg total solids (TS) to digester feed did not lead to process instability. Biogas yields of all digesters with metal added to the feed were similar to that of the control digester (no metal addition). PIX-311 achieved up to a 93 percent reduction in biogas VSCs, 82 percent better fecal coliform inactivation and exhibited improved dewaterability over the control digester. The PAX XL-19 dosed digester showed modest reductions in biogas VSC concentrations, pathogen levels and improved dewaterability versus the control. Metal addition can be an effective way to control odors from VSCs, pathogens and to improve dewaterability during AD.

Smithfield, Virginia: Pork Producer Launches Renewables Unit

Smithfield Foods, the world’s largest pork processor and hog producer, launched Smithfield Renewables to accelerate the $15 billlion company’s carbon reduction and renewable energy programs. The new renewables unit is expected to help Smithfield Foods reach its goal of becoming the first major protein company to reduce greenhouse gas emissions 25 percent by 2025, according to a Smithfield’s press release. Elements of the program include optimizing fertilizer usage and improve soil health on its feed grain farms, and to continue converting manure from hog farms into energy utilizing covered lagoon digesters.

The Smithfield Foods Hog Production Division in Missouri has been collaborating with Roeslein Alternative Energy (RAE) to install lagoon covers and related specialized equipment at a number of hog farms in exchange for the rights to sell the resulting energy. The project is ultimately expected to produce about 2.2 billion cubic feet of renewable natural gas (RNG) annually.

Smithfield Farms also has AD systems at a facility in Sioux Falls, South Dakota, that produces 305.3 million cubic feet/year of biogas, and a processing facility in Tar Heel, North Carolina, that operates two 5.75-acre anaerobic basins with an average production of 20.4 million cubic feet of biogas.

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