(122b) The Feasibility of Material Recovery from Processing the Entire Municipal Waste Stream

A key challenge for environmental sustainability is management of solid waste streams, particularly Municipal Solid Waste (MSW). There is considerable effort to increase the collection and recycling of certain materials in MSW, but it has been only partially effective for a variety of reasons. Collecting and processing the entire MSW stream through Material Recovery Facilities (MRF) would maximize material recovery. Recent advances in MRF technology greatly increase the efficacy of sorting materials, and when employed with reliable and efficient processes for conversion of sorted streams into high value products, maximizes material recovery.

Depositing material in a landfill or combusting in a Waste to Energy (WTE) plant, as is a common practice for municipal solid waste (MSW), should be replaced with MRF. In some developing areas of the world, MSW is often dumped directly into the environment (land or water) and should be replaced with material recovery. In addition to wasting material resources, landfills and WTE have inherent environmental negatives, are difficult to site and permit, and face considerable public opposition.

MRF based waste processing facilities require a large initial capital investment which can be financed by collecting the highest market value for the recycled material in addition to a tipping fee. The value of the recycled material also aligns with environmental quality because, if a product has a high value, it is a scarce resource and/or it requires a lot of energy to produce.

The higher value recyclable materials include metals, paper, and plastic. As with metals and paper, no single process will optimally recover plastic wastes. The diversity of materials and applications for plastic is particularly challenging for recycling, and the technology is the least developed. Most polymers can be recycled mechanically, but that requires a clean stream of a single polymer which limits the application to about 20% of the total at best. Pyrolysis of hydrocarbon plastic waste extends the range of plastic that can be effectively recycled including mixed and contaminated streams. Other plastic waste can be recovered by chemolysis. For example, methanolysis is currently used to recover polyesters, and there is currently a lot of new process development for other plastics containing oxygen and other hetero molecules.

The remaining materials, which typically are more than half of the original waste stream, are mostly biomass derived or similar to biomass in composition: food waste, yard waste, wood, moisture, and uncaptured paper and plastic. Options for conversion of the unsorted materials include:

• An oxygen blown, high pressure gasification unit for conversion to syngas composed primarily of carbon monoxide and hydrogen to feed processes producing a variety organic oxygenates.
• Anaerobic digestion produces methane and carbon dioxide that can be reformed and converted to methanol.
• Fermentation into carboxylate salts will produce precursors for a variety of chemicals.

The latter two (bio) processes will produce a residue of primarily lignin that would require further processing. The products of each option can be converted into high value oxygenated chemical products.

The presentation will review the history and current state of the technology for processing plastic wastes and unsorted materials, and the relevance to material recovery and plastic recycling. Included in the presentation will be the fundamental process design, feedstock considerations, product output, energy consumption, and environmental impact. Preliminary economics of the processes will be reviewed including capital and operating costs and return on investment.

Single stream MRF represents a new paradigm for MSW disposal that requires the application of processes well understood by chemical engineers, but largely unknown within the incumbent waste disposal organizations. Key enabling processes that should be part of the MRF will be pyrolysis of mixed waste plastic and a process for conversion of otherwise non-recyclable material. Processing the full MSW stream in a MRF will maximize recycling rates and reduce plastic waste in the environment because gaining acceptance for anti-litter campaigns is easier than for more complicated recycling campaigns.