Bioenergy and bioproducts from municipal organic waste as alternative to landfilling: a comparative life cycle assessment with prospective application to Mexico.

Abstract

A life cycle assessment (LCA) of a four-stage biorefinery concept, coined H-M-Z-S, that converts 1t of organic fraction of municipal solid waste (OFMSW) into bioenergy and bioproducts was performed in order to determine whether it could be an alternative to common disposal of OFMSW in landfills in the Mexican reality. The OFMSW is first fermented for hydrogen production, then the fermentates are distributed 40% to the methane production, 40% to enzyme production, and 20% to the saccharification stage. From hydrogen and methane, up to 267MJ and 204kWh of gross heat and electricity were produced. The biorefinery proved to be self-sustainable in terms of power (95kWh net power), but it presented a deficit of energy for heating services (-155MJ), which was partially alleviated by digesting the wastes from the bioproducts stages (-84MJ). Compared to landfill, biorefinery showed lower environmental impacts in global warming (down to -128kg CO2-eq), ozone layer depletion (2.96 × 10-6kg CFC11-eq), and photochemical oxidation potentials (0.011kg C2H4-eq). The landfarming of the digestates increased significantly the eutrophication impacts, up to 20% below the eutrophication from landfilling (1.425kg PO4-eq). These results suggest that H-M-Z-S biorefinery could be an attractive alternative compared to conventional landfilling for the management of municipal solid wastes, although new alternatives and uses of co-products and wastes should be explored and tested. Moreover, the biorefinery system would benefit from the integration into the market chain of the bioproducts, i.e., enzymes and hydrolysates among others.