March 27, 2006 | General

Diverting Food Residuals Into Power In Sacramento

BioCycle March 2006, Vol. 47, No. 3, p. 26
The Municipal Utility District’s “Leftovers to Lights” program advances to achieve its Renewable Portfolio Standard of 23 percent by 2011.
Ruth MacDougall

AS IT MOVES forward to achieving its Renewable Portfolio Standard (RPS) goals, the Sacramento Municipal Utility District (SMUD) will have reached 15 percent by the end of 2006. Renewable energy from biomass is contributing about a quarter of that amount. Making it the rest of the way to 23 percent by 2011 will be challenging because California’s RPS mandate has helped to create a seller’s market for renewable energy.
So SMUD is looking to its own customers to help provide local sources of renewable energy. A check of inventory revealed that municipal solid wastes (MSW) are the largest untapped biomass resource in Sacramento. In addition to construction waste, yard trimmings and MSW, over 200,000 tons of food residuals are disposed each year in Sacramento County jurisdictions. Because they have high moisture and organic content, food residuals contribute significantly to the cost and environmental impacts of transportation, and once in the landfill they contribute to air and water pollution problems.
Determining how to turn this resource into energy was one of the reasons SMUD launched the Leftovers to Lights program. Dr. Ruihong Zhang of the University of California at Davis (UC Davis), Biological and Agricultural Engineering Department, is heading the research. UC Davis just completed an in-depth survey of 45 different businesses within the Sacramento region. The survey targeted large generators of food waste, such as food processors, hotels, hospitals and prisons.
Researchers asked what food waste was being generated, how it was being disposed of, and whether the business was interested in alternatives to disposal. All the businesses interviewed were very happy to participate in the Leftovers to Lights program and eager to see their waste turned into energy. What we found was the potential for almost 5 megawatts of renewable electricity from the 45 businesses surveyed.
The survey found that a couple of Sacramento businesses have enough waste and enough space to house an on-site digester. Pre-feasibility studies have determined that these businesses can also utilize the waste heat recovered from the generator. This method, sometimes called Combined Heat and Power (CHP), improves the system-wide energy efficiency and provides a better return on investment.
This spring, SMUD plans to host a forum on Anaerobic Digestion to provide participants in the Leftovers to Lights Program and others with information about available technologies and options for converting food waste to energy.
To further encourage self-generation of renewable energy, SMUD added biomass to its Solar Net Metering Rate in 2005. This allows the utility to net meter biomass projects in the same way it net meters its customers with solar panels. As SMUD continues working to develop local biomass for renewable energy, it is considering all options, including yesterday’s leftovers.
Ruth MacDougall is Biomass Program Manager with the Sacramento Municipal Utility District’s Advanced Renewables and Distributed Generation program. She can be contacted via e-mail at
IN order to meet its Renewable Portfolio Standard (RPS), which requires 23 percent retail electricity from renewable sources by 2011, the Sacramento (CA) Municipal Utility District (SMUD) is exploring local renewable resources to help achieve this goal. One of the targeted resources is urban food residuals. Last year, Sacramento’s City Council asked its waste management agency to look into the feasibility of a food residuals collection program. SMUD is helping the City of Sacramento by conducting a study of existing collection programs in several jurisdictions in the United States.
The objective of the study is to understand how these programs were implemented and how they perform in order to identify a model that could work in Sacramento. To achieve this understanding, a SMUD contractor contacted 42 targeted jurisdictions and identified 26 that currently have food residuals collection programs in place. Most of these programs are on the West Coast, particularly in California. While 17 jurisdictions have implemented residential food residuals collection programs, 15 have commenced programs for commercial organics.
Jurisdictions have targeted food residuals as a notable component of the disposed solid waste stream that can be diverted. They have estimated that approximately 18 to 20 percent of the generated waste stream is food residuals. Most jurisdictions have integrated collection with yard trimmings composting. However, the study has indicated that a number of jurisdictions are also viewing food residuals as an energy source for capturing the biogas produced via anaerobic digestion technologies.
The City of Los Angeles has started a program with characteristics that most closely match the criteria preferred by Sacramento. These include an open, competitive collection and disposal market, comparable disposal facility gate fees, similar climate conditions, and a multiyear phased implementation program. A goal of the Los Angeles program is to become self-supporting within three years of its implementation. Like the City of Sacramento, Los Angeles has an open market configuration for solid waste collection with several franchised haulers.
Several jurisdictions have identified the implementation of anaerobic digestion in their programs; among them are the cities of Los Angeles, Seattle, and Toronto. Turning food residuals into energy may help provide a revenue stream that would make the collection and diversion of source separated food residuals a cost-effective and desirable diversion program option.

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