Appendices to Integrated Resources & Solid Waste Management Plan - Dec 2009

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HAWAII COUNTY MECHANICAL - BIOLOGICAL TREATMENT FACILITY CONCEPTUAL DESIGN Using composting as the biological treatment component is the most common approach at MBT plants currently operating in North America. Composting is a controlled aerobic biological process in which a succession of bacteria and other microbial populations decompose organic material, converting it into a biologically stable product. If implemented in its entirety, the composting process results in the production of "compost" which is stabilized enough to use as a soil supplement. However, at some facilities the composting process is cut short, and instead of being used to create compost, is used only to stabilize organic wastes prior to disposal. Mixed municipal solid waste (MMSW) composting is a type of MBT facility that has been implemented in nearly a dozen jurisdictions in the United States and Canada. The first generation of these MMSW composting facilities were developed in the 1980s and early 1990s, and involved short -term (i.e., 1 to 3 days) biological treatment in a large rotating drum similar to a cement kiln, following by composting. Data from operating MMSW facilities indicates that, relative to facilities that compost source - separated organic wastes, they are subject to higher costs, more frequent equipment breakdowns, and require a steady market for the compost end - products. For example, the latest MMSW composting plant built in North America (Edmonton, Alberta) has faced a number of challenges related to equipment failures and maintenance since it opened in 20001. Over the past five years, the City of Edmonton, which owns the facility, has implemented several modifications and is considering additional changes to improve the economics of the plant. The quality of the compost produced from an MBT or MMSW composting facility depends on the specific processes used, the quality of the feedstock, and the ability to separate metals, plastics, glass fragments, and toxic materials from the organic fraction. In general, the quality of the compost produced at an MBT facility is lower than that produced at a composting facility that processes source - separated organic material such as green waste or food waste. In some cases the product is not saleable. On the other hand, soil conditions, and the lack of soil cover in some areas on the island of Hawaii could create many potential uses for composts of varying quality. Issues associated with compost marketing are discussed below. A final important concern at MBT facilities is the management of odors both from waste handling and from the biological treatment process. Experience within the organic waste industry during the past 20 years has more than adequately demonstrated the need to monitor and manage potentially offensive odors. Management and control of nuisance odors can significantly effect construction and operating costs for a facility. For example, bio filters are effected methods of mitigating odors, but add significantly to operational costs. MBT Management Issues Odor Management Odor is perhaps the most common problem associated with both anaerobic digestion and composting facilities. Failure to sufficiently address odor issues has led to unpleasant relationships with neighbors and, in several instances, litigation or closure of anaerobic digestion and composting facilities. For example, a manure and organic waste composting facility (former Unisyn Biowaste Technologies facility) located on Oahu was closed after 1 Gamble, S, "Five Years of Composting in Edmonton" Biocycle Vol 46, No 10