(495d) Processes to Enable Full Material Recovery from Municipal Solid Waste

Recycling, or material recovery, is the key to sustainability. 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 material recovery facilities (MRF). In developing areas, 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.

Sustainable material recovery from waste streams requires deep sorting (the technology for which is continuing to develop rapidly) and reliable, efficient processes for conversion of sorted streams into high value products. MRF based waste processing facilities require a large initial capital investment financed by collecting a high 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; the latter for which the technology is least developed. No single process will optimally recover plastic wastes, but multiple processes, including mechanical, solvent, chemolysis, and pyrolysis can be combined to optimize recovery. Pyrolysis of plastic waste is important because it extends the range of plastic that can be effectively recycled including mixed and contaminated streams. Although not a new process, there is currently a lot of new development.

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 gasification, anaerobic digestion, and fermentation into carboxylate salts.

• An oxygen blown, high pressure gasification unit for conversion to syngas composed primarily of carbon monoxide and hydrogen can be used to feed a process to produce a variety organic oxygenates.
• Anaerobic digestion produces methane and carbon dioxide that can be reformed and converted to methanol.
• The carboxylate platform 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. These products have a higher inherent value because of the complexity of the synthesis and the lower volume.

The presentation will review the history and current state of the pyrolysis technology and the technologies for the 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.

Single stream MRF represents a new paradigm for MSW disposal that requires the application of processes well understood by chemical engineers, but 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.