BioCycle April 2009, Vol. 50, No. 4, p. 26
California Integrated Waste Management Board moves forward with development of renewable sources of energy and biofuels, including anaerobic digestion of MSW, an in-situ bioreactor and gasification of MRF residuals for fuel.
Ronald Lew

MILLIONS of metric tons CO2 equivalent (MTCO2E) have been reduced since 2006 when Californians met the first of several targeted greenhouse gas (GHG) reduction goals by disposing of less and reusing and recycling more than ever. But an estimated 42 million tons of waste is still sent to landfills each year. More than 25 percent of California’s waste stream consists of compostable organic materials. An additional 22 percent is construction and demolition debris that could be reduced through green building practices. Another 21 percent of the waste stream consists of paper, which could be recycled, composted or used to develop renewable sources of energy and biofuels. As a result, nearly 70 percent of California’s waste stream consists of carbon-based materials that could be diverted from the landfill, to help Californians further achieve targeted GHG reduction goals.
The energy equivalent of landfilled organic material is approximately 1,750 megawatts (MW) per year of electricity. According to the U.S. Department of Energy, the potential to produce ethanol and other liquid fuels from this landfilled organic material is estimated to be equivalent to about 300 million gallons/year, which equates to approximately one percent of annual gasoline consumption in the U.S.
An Executive Order (S-06-06) issued in April 2006, called for California to increase its share of biofuel production and electricity from biomass. The order stemmed from, among other factors, increased public concern over escalating fuel costs and reliance on petroleum, the desire for strong state advocacy on these issues and commitments for improving resource management and mitigating climate change. Materials in the waste stream can be used as resources to produce alternative renewable energy and biofuels, thereby increasing diversion, developing new markets and helping to mitigate climate change.
In response, California Integrated Waste Management Board (CIWMB) has striven to actively develop and fund numerous research projects in the emerging energy technology arena, and is currently engaged in various cross-media regulatory efforts to facilitate adoption of these technologies in California. This article details some of the research projects CIWMB is currently involved with and describes some of the regulatory efforts CIWMB is working on to bring these technologies to California.
ANAEROBIC DIGESTION OF MSW
Despite advances in organic waste diversion and a heightened interest in renewable energy production, anaerobic digestion (AD) of municipal solid waste (MSW) has not yet materialized in California. Handling and treatment of the organic fraction of MSW is more difficult than treating wastewater or manure and as such, AD of the organic fraction requires a larger amount of investment. The low tipping fees charged by landfills in California and relatively low energy prices compared to those in Europe make it difficult for AD and other conversion technologies to be cost competitive. However, recent volatility in energy prices and a predicted increase in prices for traditional fuels is changing the economics for AD.
Even though many landfills have installed landfill gas recovery systems, the waste management industry is still facing challenges such as limited land availability and ground water pollution from leachate. To reduce the amount of wastes destined for landfills, the organics from MSW can be separated and treated through emerging technologies for volume reduction and generation of valuable by-products, such as biogas energy and compost. Composting has been a more widely applied process for treating municipal organic solids compared to AD. However, in the U.S., the economical value of the MSW-derived compost is usually low, often less than $13/cy. Upward market pressures on energy prices makes AD an increasingly attractive process for achieving both waste reduction and energy recovery.
Because it is necessary to remove a certain amount of inorganic fractions (e.g., metal and glass) from raw MSW prior to AD, CIWMB has been interested in projects that could accomplish this task. These contaminants reduce digester efficiency, result in equipment degradation, and costly repairs and ultimately lead to processing failure.
CIWMB became interested in research being conducted by Dr. Ruihong Zhang at the University of California, Davis that could potentially solve the twin problems of removing inorganic materials from MSW streams while simultaneously improving output efficiency (i.e. reducing processing time while increasing biogas production) over conventional digester systems. Zhang has developed an anaerobic phased solids digester system (APS-Digester) that uses four hydrolysis reactors and a biogasification reactor with liquid circulation between both types of reactors to create optimized conditions for microorganisms. Such optimization expedites processing times and increases biogas production over traditional AD systems. This technology has been licensed to Onsite Power Systems, Inc. to develop and commercialize the technology. More information on Zhang’s research of rotary drum reactors (RDR) for pretreatment of MSW before AD is in an article on page 20 of this issue.
In the interim, Dr. Zhang’s team at UC Davis has produced an excellent overview of the current state of AD technology in processing MSW in the U.S., Europe and elsewhere. It can be accessed on our website at: www.ciwmb.ca.gov/Publications/default.asp?pubid=1275.
IN-SITU ANAEROBIC DIGESTION
Although AD and biogas capture at landfills are viable options, both have shortcomings. Anaerobic digesters have large capital costs and require a reliable and consistent source of feedstock to be secured before the system is operational. These unique requirements could be an obstacle to widespread implementation. Landfills with biogas capture are not as efficient (see “Stop Trashing The Climate,” BioCycle August 2008), and moreover, potentially valuable organic residuals remain in the landfill, and are not recovered for beneficial reuse such as a soil amendment. This is mainly due to the added cost and difficulty of mining and sorting of the impurities from mixed MSW.
CIWMB hence became interested in a project in Yolo County that avoids some of these shortcomings of AD and landfill biogas capture. It involves the development of a lined digester cell at an existing landfill that was designed both as a way to manage source separated green waste (grass, yard clippings and leaves), generate biogas, control air emissions and leachate, and produce a quality compost product. This hybrid approach, drawing from all three waste management techniques (landfilling, composting and anaerobic digestion) has the potential to provide a low cost, less technologically intensive way to produce renewable power from organic wastes.
The Yolo County Landfill-Based Anaerobic Digestion Compost Pilot Project was funded by CIWMB in 2007; the project is ongoing. The digester was constructed as a two-phase batch anaerobic digester, using a single lined cell at the landfill to demonstrate the effectiveness of converting source separated organics to methane and finished compost. The cell was constructed in the summer of 2007, filled with 1,890 tons of source separated green waste, 18 tons of woodchips, 130 tons of horse manure and 25 tons of limestone, and covered with an impermeable liner to control emissions and maximize capture of biogas.
In order to fully assess the system, the project will quantify the economic and material inputs/outputs of the process (including emissions); calculate a mass balance for the materials after excavation; quantify permitting, construction and operating costs; analyze quality and economic value of decomposition products (gas and compost); and compare estimated construction and operating costs to the cost of other forms of organics processing systems.
As of September 2008, 2 million cubic feet (cf) of methane gas has been generated and collected from the cell. Estimates are that an additional 2.5 million cf of methane will be collected by the end of the project. In late September 2008, the project moved to the aerobic phase, with sampling of green waste and emissions following. The aerobic phase is scheduled to be completed in early summer (late May), with excavation scheduled for June (depending on weather). Once the material has been composted, it will be excavated and tested according to U.S. Composting Council standards.
The project is expected to be completed November 2009. The final report, which will detail findings and methodology, will be available at www.ciwmb. ca.gov/Organics/Conversion.
GASIFICATION OF MRF RESIDUALS
CIWMB is also exploring gasification as a technology to process post-MRF residuals into biofuels, and is currently funding a thermochemical gasification project being developed by the University of California (San Diego, Davis and Berkeley) and co-funded by the UC Discovery Program and West Biofuels LLC. Located on a 16-acre property in Yolo County near Woodland, this two-year research/demonstration project uses a 5 ton/day research reactor to convert carbon in biomass to a mixed alcohol liquid fuel. The reactor is currently under construction, but when complete will be comprised of a dual-fluidized bed gasifier to generate producer gas, a regenerative reformer to produce synthetic gas, and a reactor to produce a mixed alcohol.
Fabrication of the gasifier stage of the biomass research reactor was completed and test fired in December 2007 in Idaho Falls, Idaho. The gasifier was then disassembled and shipped to the Woodland facility for reinstallation. Subsequent assembly of the reformer and synthesis stages of the research reactor will be completed over the next several months. Along with the mixed alcohol (mostly ethanol) end product, the project intends to use excess producer gas available from the gasification system to generate 100 kW for the grid with a spark ignition (SI) engine/generator set. A combination of emissions control technologies including a biofilter, baghouse and catalytic converter will be used for emissions control to comply with the conditions of an air permit issued by the Yolo/Solano Air Quality Management District.
CIWMB became interested in this project due to the potential to use post-MRF organic residuals as feedstock for the gasifier that would otherwise be destined for disposal. The project, as initially envisioned, planned to use wood waste as its main feedstock, but with CIWMB’s input it was modified to include MRF residuals ranging from food waste, green waste, wood waste and other organic materials. These preprocessed residuals, which have had recyclable material removed, will be sourced from a local waste management facility.
Of particular interest to CIWMB is how different combinations of organic residuals effect process inputs and outputs. Some of the performance benchmarks and metrics being explored include: Evaluating and calculating mass balance metrics including amounts and composition of feedstock to produce electric and/or thermal energy, liquid and/or gaseous fuels; Analyzing characteristics of products and demonstrating a viable end-use for waste products; Quantifying amount of material diverted, and landfill diversion potential for the project during operating life of the facility; and, Analyzing and quantifying environmental externalities (including air criteria pollutants, dioxins, furans, greenhouse gases, etc.), water and solid waste pollutants (including heavy metals) and methods and costs for remediation where control technologies are available. The facility will be coming online in the next several months and testing is scheduled to begin in the summer of 2009. Results should be available in early 2010.
REGULATIONS
CIWMB is involved in various regulatory and program activities designed to facilitate renewable fuel and energy production deployment in California. Most important and overarching is its participation in the California Air Resources Board’s development of the AB 32 Scoping Plan, the framework in which California will combat climate change in the coming decades.
CIWMB has developed an AD action measure as part of the Scoping Plan that maps out a strategy for widespread deployment of digesters as a method to achieve green housegas (GHG) reduction goals. Anaerobic digestion was chosen as the preferred technology because of the high probability of adoption and deployment in the next decade. Although it is capital intensive, the ability to reduce GHGs, capture energy and produce material to compost makes AD a relatively low cost option vis a vis other technologies. As part of the analysis required for the action measure, CIWMB estimated that a ramping up of facilities over a 10-year period could effectively save 2.2 million MTCO2E of GHGs by 2020.
The AD Scoping Plan complements other regulatory efforts CIWMB is engaged in, and may serve as a vehicle for satisfying multiple policy goals. Some of these other policies and regulations that could use AD to fulfill programmatic goals include: Renewable Portfolio Standard (RPS), which requires electricity companies to increase procurement from eligible renewable energy resources by at least one percent of their retail sales annually, until they reach 20 percent by 2010 and 30 percent by 2020, respectively; Low Carbon Fuel Standard (LCFS), which establishes protocols for measuring the life cycle carbon intensity of transportation fuels and implementing those standards by 2010; and, AB 118, which establishes a low emissions vehicle fuels program that seeks to develop alternative low carbon fuels that can be used in California fleet vehicles.
CIWMB is currently reviewing its regulations to ensure that they are up to date and reflect changes in the state of scientific knowledge, market conditions and technology to allow achievement of broader environmental goals. One of the priority areas identified as needing further work is in the production of renewable fuel and energy from MSW feedstocks, where there has been the lack of clear guidance in existing regulations pertaining to permitting of these facilities. CIWMB is evaluating how best to achieve clear and effective regulations for these types of facilities. The process being used to develop new, or modify existing regulations in the emerging technologies arena include: gather information/data collection, literature search, and site visits; identify issues relative to current regulations; actively solicit input from other agencies and stakeholders (1st Quarter 2009); draft white paper (2nd Quarter 2009); hold workshops (2nd Quarter 2009); and present to the Board results of the regulatory review and any recommendations on regulatory changes (3rd Quarter 2009). Dates of public workshops and presentation of findings to the Board will be announced as they become available on CIWMB’s website.
Ronald Lew is an Integrated Waste Management Specialist at CIWMB.