Environmental implications and costs of municipal solid waste-derived ethylene

Carbon recycling, in which organic waste is recycled into chemical feedstock for material production, may provide benefits in resource efficiency and a more cyclical economy-but may also create "trade-offs" in increased impacts elsewhere. We investigate the system-wide environmental burdens and cost associated with carbon recycling routes capable of converting municipal solid waste (MSW) by gasification and Fischer-Tropsch synthesis into ethylene. Results are compared to business-as-usual (BAU) cases in which ethylene is derived from fossil resources and waste is either landfilled with methane and energy recovery (BAU#1) or incinerated (BAU#2) with energy recovery. Monte Carlo and sensitivity analysis is used to assess uncertainties of the results. Results indicate that carbon recycling may lead to a reduction in cumulative energy demand (CED), total material requirement (TMR), and acidification, when compared to BAU#1. Global warming potential is found to be similar or slightly lower than BAU#1 and BAU#2. In comparison to BAU#2, carbon recycling results in higher CED, TMR, acidification, and smog potential, mainly as a result of larger (fossil-based) energy offsets from energy recovery. However, if a renewable power mix (envisioned for the future) is assumed to be offset, BAU#2 impacts may be similar or higher than carbon recycling routes. Production cost per kilogram (kg) MSW-derived ethylene range between US$1.85 and US$2.06 (Jan 2011 US$). This compares to US$1.17 per kg for fossil-based ethylene. Waste-derived ethylene breaks even with its fossil-based counterpart at a tipping fee of roughly US$42 per metric ton of waste feedstock.