Recent attention in the North American market has focused on managing food waste biologically using anaerobic digestion (AD) technology, which produces a biogas that can be used to generate electricity and a digestate or residue that can be used as a fertilizer, or composted and used as a soil amendment. The increased focus on AD is driven by the desire to increase waste diversion rates and a perception that AD is a “greener” approach to managing food waste than landfilling or conventional waste-to-energy (WTE) technology. Policy makers in some cases have already concluded that AD of source separated organics is preferable to landfilling and WTE. While the environmental benefits of AD over landfilling are obvious, especially for landfill sites without active gas collection systems, the benefits are less clear when compared to conventional WTE technology since relatively little analysis has been performed to date. Two environmental considerations often associated with being a “green technology” are energy recovery potential and greenhouse gas generation. This paper examines the amount of energy that can be produced by treating food waste biologically using AD compared to treating the same material thermally using mass burn WTE, which is the most commonly used WTE technology. The impact on net greenhouse gas emissions, namely carbon dioxide generation, from each technology is also compared taking into account a variety of factors including differences in the percentage of the feedstock carbon converted to carbon dioxide, the amount of fossil fuel avoided as a result of power generation, and the amount of vehicle emissions associated with collection and transportation of source separated food waste. This paper also compares other important considerations such as capital and operating costs, residuals management, and odor control.

Maine Energy Recovery Company is a waste-to-energy facility, firing refuse-derived fuel (RDF) in two B&W boilers to produce steam which is used to generate 22MW of electricity. As part of its on-going effort to study odor generation and enhance their odor control system, Maine Energy discovered that a greater quantity of volatile organic compounds (VOC) are generated by the waste itself than had previously been estimated. The VOCs that were found are primarily light alcohols, such as methanol, ethanol, and butanol, along with compounds such as acetone, methyl ethyl ketone (MEK), benzene, toluene, xylene, and others. These compounds are generated from the operation of diesel-fueled equipment in the facility’s tipping building, and from the decomposition of the waste itself. The VOC generation also has a strong seasonal component, where generation is highest in the warmer summer weather, and lowest in the depths of winter. In the summer of 2005, Maine Energy undertook a pilot scale study of VOC control using a proprietary concentrator technology from Munters Corporation, Zeol Division of Amesbury, Massachusetts. A scaled-down version of their rotary zeolite concentrator was employed at Maine Energy over a six week period from July to September 2005. Numerous samples were taken at the inlet and outlet of the device, and several extended tests were conducted using Fourier-Transform Infrared (FTIR) technology to search for specific organic compounds. The results showed that the device reduced VOC, as well as odors, by approximately 85%, without the benefit of extensive fine-tuning of the device or the process during this limited run. The testing also revealed the need for extensive particulate removal at the inlet to the device, which would have a significant effect on cost efficiency.