For several US communities municipal waste combustor (MWC) ash recycling has been a commercial reality for almost a decade with over 1 million tons processed and beneficially used to date. Yet, despite the successes to date a recent report by the Integrated Waste Services Association shows less than 5% of the 7.5 million tons of ash generated in the US is recycled and beneficially used [1]. The technological, scientific and myriad of commercial successes categorically demonstrate the feasibility of ash recycling. The next step is for communities, regulatory agencies, transportation departments, and customers to partner with businesses to recycle their ash stream in an economically and environmentally sound manner. An example of this “ partnering for progress ” is the focus of this paper. The ash recycling partnership described in this paper was presented the Pennsylvania Governor’s Award for Environmental Excellence in 1999. Proving that Partnering is a win-win situation for businesses, communities and the environment.

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.

Chemical rate and heat transfer theory indicates that the combustion performance and productivity of a moving grate waste-to-energy boiler should be enhanced by means of pre-shredding of the MSW, thus reducing the average particle size, homogenizing the feed, and increasing its bulk density by an estimated 30%. However, the capital, operating and maintenance costs of the shredding equipment should be low enough so that existing or new WTE facilities consider pre-shredding of the MSW. In cases where MSW is transported to a central WTE from a number of Waste Transfer Stations (WTS), pre-shredding may take place at the WTS, thus increasing density and decreasing transportation costs. This is a mechanical engineering study that examined the evolution and present state of shredding equipment since 1994 when the last WTE shredder in the U.S. was installed at the SEMASS facility. The quantitative benefits realized through the pre-processing of MSW by means of modern shredding equipment are evaluated both for the traditional high speed hammermills and the new generation of low-rpm, high-torque shredders. The combustion characteristics of shredded MSW were analyzed and compared to those of the “as-received” material that is presently combusted in mass burn WTEs. The emphasis of the project has been on equipment that can be integrated in the traditional flowsheet of a WTE and serviced readily. The most important criterion in the final design will be that the economic and energy benefits of pre-shredding be clearly greater than the conventional operation of combusting as received MSW.

The management of municipal solid wastes (MSW) in Puerto Rico is becoming increasingly challenging. In recent years, several of the older landfills have closed due to lack of compliance with federal landfill requirements. Puerto Rico is an island community and there is limited space for construction of new landfills. Furthermore, Puerto Rico residents generate more waste per capita than people living on the continental US. Thermal treatment, or waste to energy (WTE) technologies are therefore a promising option for MSW management. It is critical to consider environmental impacts when making decisions related to MSW management. In this paper we quantify and compare the environmental implications of thermal treatment of MSW with modern landfilling for Puerto Rico from a life cycle perspective. The Caguas municipality is currently considering developing a thermal treatment plant. We compare this to an expansion of a landfill site in the Humacao municipality, which currently receives waste from Caguas. The scope of our analysis includes a broad suite of activities associated with management of MSW. We include: (i) the transportation of MSW; (ii) the impacts of managing waste (e.g., landfill gas emissions and potential aqueous run-off with landfills; air emissions of metals, dioxins and greenhouse gases) and (iii) the implications of energy and materials offsets from the waste management process (e.g., conversion of landfill gas to electricity, electricity produced in thermal treatment, and materials recovered from thermal treatment ash). We developed life cycle inventory models for different waste management processes, incorporating information from a wide range of sources — including peer reviewed life cycle inventory databases, the body of literature on environmental impact of waste management, and site-specific factors for Puerto Rico (e.g. waste composition, rainfall patterns, electricity mix). We managed uncertainty in data and models by constructing different scenarios for both technologies based on realistic ranges of emission factors. The results show that thermal treatment of the unrecyclable part of the waste stream is the preferred option for waste management when compared to modern landfilling. Furthermore, Eco-indicator 99 method is used to investigate the human health, ecosystem quality and resource use impact categories.

Most every one of the approximate 90 operating waste-to-energy facilities in North American have a ferrous metals recovery system to extract these metals from the ash stream before the ash is disposed as a waste. Recovery of this ferrous metal obviously reduces the significant landfill disposal cost and associated ash hauling cost for the facility by reducing the volume of materials being disposed. The volume of the ferrous metals stream typically ranges between 1.0 to 4.0 percent of the incoming waste volume. But for facilities which manage hundreds of thousands of materials per year, this relatively small stream of material in many facilities present such a nuisance that the operators at some plants have a penchant not to bother with it for the tenuous value they have received. The value received has been exposed to extreme variations and uncertainty due from the fragmented scrap metal markets, transportation costs, quality of the recovered product (or lack thereof), cost of recovery, and a number of other constraints and issues, some in the control of the facility operator and some not in the control of the operator. As a result, the attention given to this area is also very variable across facilities, even within the same parent company.

The potential for global climate change due to the release of greenhouse gas (GHG) emissions is being debated both nationally and internationally. While many options for reducing GHG emissions are being evaluated, MSW management presents potential options for reductions and has links to other sectors (e.g., energy, industrial processes, forestry, transportation) with further GHG reduction opportunities.

This technology could change the logistics of solid waste management in the Army. Successful completion of the Mobile Integrated Sustainable Energy Recovery (MISER) project will lead to dramatic logistics changes. Where petroleum is now used to fuel generators, waste may be used in the future, substantially reducing solid waste disposal and transportation requirements.