July 18, 2011 | General

Anaerobic Digest

BioCycle July 2011, Vol. 52, No. 7, p. 14

Columbus, Ohio
A new report, Waste to Wheels: Building for Success, summarizes the proceedings of a December 2010 workshop in Columbus cosponsored by the U.S. Department of Energy (DOE) Clean Cities initiative, Argonne National Laboratory and Clean Fuels Ohio. The workshop was organized by Energy Vision, a nonprofit whose mission is to analyze and promote ways for society to make a swift transition to pollution-free renewable energy sources including clean, petroleum-free transportation fuels. The workshop brought together 120 industry and government leaders to hear presentations on technologies, projects and financial incentives for waste-based fuel production.
The Waste to Wheels report discusses characteristics and production of waste-based fuel – aka renewable natural gas (RNG) or biomethane – and how it can be blended with, or used to replace, conventional natural gas. It culls major points, charts, graphs and other illustrations from workshop presentations. “Given the rising concerns nationally and globally about climate-changing greenhouse gases, RNG deserves ‘center ring’ attention as it is the lowest of low-carbon fuels in the world, and technologies for producing RNG are commercially available,” said Gail Richardson, Energy Vision Vice President for Programs and author of the report. “RNG is produced in Europe and used by multiple fleets in dozens of its cities. It is just emerging in the U.S.” View the full report and background materials, including workshop presentations, on the DOE website at
San Jose, California
On June 21, the San Jose City Council authorized City staff to negotiate and execute agreements with Zero Waste Energy Development Company (ZWED) and Allied Waste Services of North America to provide collection and processing of the City’s commercial waste through 15-year contracts. While both agreements’ negotiations are nearly final, the San Jose City Council’s scheduled break in July necessitated action in June. “For our agreement, three main things happened at the City Council meeting on June 21st,” says Emily Hanson of ZWED. “Our mitigated negative declaration was accepted, covering development of our anaerobic digestion and composting facility, authorization for the negotiation and execution of our lease with the city for the site was approved, and authorization for City staff to complete negotiations for our organics processing agreement was granted.” The mitigated negative declaration states that the facility will not cause any unmitigated significant impacts based on the findings of the comprehensive Initial Study conducted and provides the environmental clearance required to obtain permits.
The ZWED facility includes a dry fermentation anaerobic digestion process, followed by in-vessel composting. Phase I, scheduled to open on July 1, 2012, has been designed to process 90,000 tons/year of commercial organics. Part I of a two-part article series on San Jose’s new commercial waste management system appeared in the May 2011 issue of BioCycle (“New Frontier For Commercial Waste In San Jose”). Part II, which covers specific details about the collection and processing services, will run next month.
Reynolds, Indiana
BioTown Ag farm has completed construction of a large anaerobic digestion system that will begin supplying electricity to Northern Indiana Power Service Co. this summer. The system receives manure from 4,500 cattle and 800 hogs on-site. Owner/operator Brian Furrer will likely expand his livestock operation to provide more feedstock for the digesters.
The facility installed GHD, Inc. digester technology and three General Electric 1-MW Jenbacher JMS 320 generator sets. BioTown Ag plans to recover solids for bedding, convert post-digestion liquids into fertilizer and recycle water on-site. Reynolds, a town of about 500 people, was designated “BioTown” by Governor Mitch Daniels in 2005 because it’s the center of a region with adequate transportation infrastructure, a large livestock resource – some 150,000 hogs within a 15-mile radius – and abundant corn and soybeans crops. Cary Aubrey, bioenergy development manager for the Indiana Department of Agriculture, says the area is experiencing economic development due to state and federal grants as well as other interest. The city has built a wastewater treatment facility using algae, and a large wind farm has been developed. Tourism associated with the projects is on the uptick, and Aubrey sees BioTown Ag as a main tourist draw.
Woodland Park, Colorado
A new electro-hydraulic valvetrain – or “camless” engine – developed by Sturman Industries in Woodland Park has helped meet California’s ultra-low emission standards while enabling diesel engines to run reliably and efficiently on methane biogas. Working with the California Energy Commission’s PIER program, Sturman retrofitted a stock production 15L diesel engine – commonly used in both the transportation and power-generation markets – with the Sturman’s proprietary technology enabling the use of renewable natural gas (RNG). Reported results detail peak efficiencies exceeding 40 percent and fuel consumption reduction of up to 18 percent at part load.
Miguel Raimao, who is responsible for business development at Sturman, said the company asked itself what RNG customers really wanted and came up with the answer in “clean, efficient and reliable engines.” Then they designed and built one. “Stoichiometric engines have very low emissions by way of a three-way catalyst, but suffer from lower efficiencies in particular at part load,” explained Raimao. “Lean-burn engines deliver good fuel economy by running unthrottled, but they require very expensive aftertreatment to meet emission requirements. It was clear we had to combine the best attributes of each approach, so we chose to apply our Hydraulic Valve Actuation (HVA) system to eliminate the throttling losses with a simple three-way catalyst to clean up remaining emissions.”
The diesel engine was fitted with a commercial natural gas fuel system and Sturman’s HVA system, which provides independent control of valve timing, duration and cylinder deactivation capacity. A Sturman Total Engine Controller (STEC) was used to control the stock turbocharging and exhaust gas recirculation (EGR) systems. The technology allowed for a compression ratio increase from 10:1 to 14:1. The project team was able to run the engine unthrottled and intermittently on only three cylinders in order to improve part load efficiency. Combustion was optimized over various operating conditions without the risk of knock, thus eliminating the need for costly lean NOx aftertreatment. “The application of variable valve actuation combined with Sturman’s closed-loop combustion control allowed this 15L engine to meet its performance requirements even with low quality natural gas,” said Dan Giordano, Program Lead for the California Energy Commission Program.
Nantwich, Cheshire, UK
Reaseheath College has been working to demonstrate the viability of small-scale, anaerobic digestion (AD) technology for on-farm energy production. At the commissioning of the college’s demonstration AD plant, Charlotte Morton, chief executive of the UK’s Anaerobic Digestion and Biogas Association, said the plant would contribute significantly to understanding the technology and its potential, the Crewe Chronicle reports. The college’s plant is based on two small-scale, low capital systems that can be replicated on farms or elsewhere where organic feedstocks are available. The continuous stirred tank reactor (CSTR) digester system and a smaller “plug-and-play” digester take slurry from the college’s dairy herd and straw-based manure from a commercial pig unit.
The project is run in partnership with local farmers and is meant to assess both financial viability and efficient use of available resources. The college also plans to measure the effect of other regionally available organics feedstocks as cost-effective biogas production enhancers. “The government has made a commitment to deliver a huge increase in energy from waste through AD,” said Morton. “To achieve this, we will need to attract a large number of producers and the industry will need to gear up fast, which includes receiving training.”
Saginaw, Michigan
Two engineering students at Saginaw Valley State University in University Center, Michigan, recently conducted a study of the potential for densification of anaerobic digestate in small-scale anaerobic operations. Although valuable as a soil amendment, digestate in a loose form is difficult to load and ship. L. White and J. Parsons took digestate from Phase 3 Renewables, LLC, which operates an anaerobic digester on Scenic View Farms near Fennville, Michigan, and created pellets that were compressed at 110°C and 130°C for four minutes using a HB43 Halogen Moisture Analyzer. They tested dimension, mass, density and tensile strength and found that the pellets were dimensionally stable over a one-week period and broke up within 30 minutes when submerged in water.
Putting digestate into pellets allows a farmer to “tie up the nutrients and apply them on farm fields as needed,” says Christopher Schilling, professor of engineering at Saginaw Valley. He adds that in the study completed by the students, the digestate emerges from a screw press and needs to be cured for a few days in a composting operation to assure pathogens are killed before the pelletization process. “The digestate is high in binders (protein and lignin), so it forms durable pellets without any costly additive. The savings in use of pellets versus digestate is all about energy density. The problem with biomass in general is that there’s too much air. If you don’t densify it, you’re moving too much air.”

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