Agenda - Council - 08/14/1984 - Laserfiche WebLink

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Page Seven I ' Research and clernam~ations of biological treat~t of solid waste have Increased in recent years. Anaerobic (oxygen-free) treatment produces methane gas and a humus like material. Aerobic (oxygen-rich) treatment produces a sterilized humus like material or compost. These biological treatment methods can reduce the weight of solid waste by approximately 50%. Aerobic treatment or composting can be applied to several kinds of solid waste including leaf waste and source separated organics such as food waste, and mixed municipal waste. Composting treatment of solid waste may be accomplished through windrow composting, aerobic chambers, or cloy digesters. Windrow composting is a biological process of composting~ similar to beckyard composting only on a larger scale using heavy equipment. Windrowing involves an aerobic decomposition through frequent turning of long rows of organic material. Windrow turning can be accomplished through a variety of methods utilizing machinery such as front end loaders or equipment designed specifically for turning compost windrows. Sewage sludge can be co-composted with mixed municipal waste in this method. A variety of aerobic chambers have bccn used in Europe to compost solid waste. While this compost technology is more capital intensive than windrowing, aerobic chambers speed up material processing because moisture, oxygen~ and temperature levels can be controlled. Sewage sludge can also be co- composted in aerobic chambers with mixed municipal wastes. I I I I I I I I I I I I I I I I Clay cllgester is an experimental technology that is in many respects a modified sanitary landfill operation to maximize biological activity, methane generation, and rapid stabilization of the waste. In many respects a clay digester is very similar to the type of second generation landfill design that was described in the County's abatement report as an "accelerated decomposition landfill." (See Appendix 1V.) Solid waste may also be processed to reduce volume through combustion of the solid waste materials. This combustion may take the form of incineration (simply the burning of the waste with no recovery of materials or energy) or energy recovery (burning of the waste with the recovery of energy for space heating and/or process energy). The only difference between the two concepts is the providing of equipment to recover the heat energy from the combustion chamber flue gases. Incineration and energy recovery may be done through the mass burning in a large scale waste to energy facility such as proposed by Hennepin County or through the use of a number of sinai let premanufacturecl modular combustion units. Large scale mass burn facilities and modular combustion units are basically similar in th~ they burn unprocessed waste and differ primarily only in terms of size. Modular combustion units normally are supplied in modules ranging in size from I$ - 150 tons per day and are available in approximately 25 - 50 tan increments. Primary combustion is usually followed by an after burner section to assure complete combustion, which may or may not be roi lowed by the recovery of heat. If heat recovery is provided the concept would be referred to as waste to energy. If heat recovery is not provided and all of the heat energy is vented up the stack, the process would be referred to as incineration. The combustion of solid waste as an abatement strategy could be expected to accomplish approximately 70 - :~0% reduction of the sanitary landfill needs of Anoka County. (See Appendix III for costs.)