August 10, 2017 | General

Anaerobic Digest

BioCycle August 2017

Videbaek, Denmark: Milk Powder Producer Commissions Large-Scale Digester
Danish milk powder company Arla Foods is installing an anaerobic digester with capacity to process 660,000 tons/year of feedstocks — of which 44,000 tons is its own 14 percent solids residual milk product. The remaining 620,000 tons of biomass will come primarily from agricultural sources of manure and poultry litter, as well as residual products from other food industries. Digestate will be used as fertilizer by local farmers. Arla Foods selected Xergi to install the five digester reactors that will produce 16.5 million cubic meters (582 million cubic feet) of biomethane annually. The biomethane will be fed into a shared biogas grid that serves three milk processing plants within a 3.1 mile radius. Feedstocks will be pretreated using Xergi’s FLEXFEED technology, a combined feeding, heating and mixing module.  Start-up is expected in the fall of 2018.

London, England: Biogas Powering Over 1 Million U.K. Homes

According to a new report from the Anaerobic Digestion and Biogas Association (ADBA) in the United Kingdom, biogas from AD facilities in the U.K. provides enough electricity to meet the demand of over 1 million homes.  During 2016, 554 AD plants in the U.K. had a total generating capacity of 730 megawatts (MW) of electricity, with total energy generation (electricity, biomethane and thermal energy) of 10.7 terawatt-hours (TWh) — a 20 percent growth over 2015.  Load factors increased from 69 to 73 percent. Total employment in the U.K.’s AD industry is over 3,500 people.
Of the 10.7 TWh, 3.5 TWh were used to make biomethane for injection into the natural gas grid; 2.8 TWh of electricity were produced, and the remainder (4.4 TWh) was thermal energy. More U.K. AD operators are finding productive uses for this thermal energy. ADBA members have provided data from a variety of operational plants with generation capacities in the 500 to 5,000 kW range on actual heat used. Examples include:
• May Farm Anaerobic Digester/Barway Farms Ltd (Shropshire Energy) operate a 2.4 MWe food waste plant in Shropshire that uses 34 percent of available heat: 3 percent for digester heating, 32 percent for pasteurization and 65 percent employed in adjacent mushroom farms.
• Greenshoots Energy uses 60 percent of its 1,200 kW capacity supplying steam for a feed mill and for district heating.
• An unnamed food waste AD facility uses 30 percent of the heat output from its 1.5 MW combined heat and power engine for parasitic heating of digester tanks.

Montreal, Canada: Low Temperature Anaerobic Digestion

Researchers from Concordia University’s Department of Building, Civil and Environmental Engineering in Montreal, in collaboration with Bio-Terre Systems Inc., have demonstrated the viability of using anaerobic digestion (AD) in a low-temperature environment (20°C (68°F)) to convert solid food waste into renewable energy and organic fertilizer. The findings were reported in the January 2017 issue of the Institute of Chemical Engineering journal, Process Safety and Environmental Protection. The aim of the research was to improve AD of food waste (FW) with or without animal manure in a low-cost psychrophilic anaerobic digester in sequencing batch reactor (PADSBR) at 20°C. Feed solid content was varied from 37 percent to 13 percent, mainly to validate the stability of a digestion process suitable for different scenarios; the organic loading rate (OLR) was increased from 0.8 to a maximum of 4.2 kg VS/m3 d (volatile solids/m3/day).
Results showed that methane (CH4) production from the FW mixture was feasible at low temperature and a specific methane yield of 0.401 ± 0.01 m3 CH4/kg VSfed was observed even at high OLR. When the loading rates applied to the bioreactors were increased by 225 percent, methane conversion rates decreased only by 10 percent, while maintaining the operational stability (e.g. no foaming, no acidification). Methane content was constantly in the range of 64 to 69 percent, indicating the quality of biogas was excellent and remained almost steady. The results suggest that PADSBR at 20°C is comparatively efficient in saving the heat energy and at the same time obtains the CH4 values close to mesophilic/thermophilic conditions. This concept is particularly applicable in cold countries facing energy constraints.

Tulare, California: City Signs Digester Gas Purchase Agreement

Tulare, a city of 60,000 in the Central Valley of California, has signed a biogas purchase agreement with FuelCell Energy.  The City is leasing a site at its wastewater treatment facility to FuelCell Energy, which will install, operate and maintain a 2.8 MW fuel cell power plant. The City’s facility primarily treats effluent from a number of large milk processing plants. The digester gas agreement enables FuelCell Energy to proceed under the State of California Bioenergy Market Adjustment Tariff (BioMAT) program with a 20-year power purchase agreement (PPA) with Southern California Edison. The company will also install its SureSource Treatment™ biogas conditioning system. “This project perfectly highlights how sustainability pays,” notes Joe Carlini, Tulare’s City Manager. “We are selling our biogas, generating a new source of revenue for the City, and supporting emission-free power generation so our citizens have clean air to breathe.”

Leatherhead, Surrey, U.K.: Unilever Executes Biomethane Purchase Agreement

Unilever UK & Ireland has signed a deal with GENeco, a renewable energy company, to use 10,000 MWh of biomethane to power its offices in England, and its food and drink factories in Norwich and Trafford Park (England) and in Cork, Ireland. The biomethane is generated by GENeco’s anaerobic digester in Avonmouth, England, which converts inedible food waste and biosolids into biogas to produce renewable energy. With electricity already coming from certified renewable sources, the purchase of a certified supply of biomethane means that Unilever has become carbon neutral (from energy sources) at these five sites, according to the company. Unilever has cut its manufacturing greenhouse gas footprint by 39 percent per metric ton of production since 2008 — the equivalent of 1 million metric tons of CO2 per year.
In late November 2015, Unilever outlined its plan to become carbon positive, eliminating fossil fuels from its operations and directly supporting the generation of more renewable energy than it consumes. Under the Sustainable Living Plan, Unilever will:
• Source 100 percent of its total energy across its operations from renewable sources by 2030
• Source all electricity purchased from the grid from renewable sources by 2020
• Eliminate coal from its energy mix by 2020
• Directly support the generation of more renewable energy than the company consumes and make the surplus available to the markets and communities in which it operates.

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