Life cycle assessment of portable two-stage anaerobic digestion of mixed food waste and cardboard

Abstract

Biogas produced from organic waste can reduce waste and produce renewable energy and is a viable waste treatment alternative for remote encampments. Portable, small-scale anaerobic digestion (AD) units can be used to sustainably produce biogas in remote areas and reduce landfilled waste. This project investigated the life cycle impacts of a portable AD unit and the effects of organic loading rate (8–32 g chemical oxygen demand (COD) L−1 d−1) and waste composition (food versus cardboard waste ratios of 35:65 and 65:35) on biogas production efficiency. Optimal biogas production was obtained using a 65% food to 35% cardboard waste mixture and a mid-range organic loading rate (16 g COD L−1 d−1); this scenario also yielded the lowest climate change impact [37.4 ± 0.7 g CO2 eq per kg COD waste] due to greater biogas conversion efficiency. However, the overall life cycle impacts of biogas production were not significantly affected by waste mixtures or feed rates in the AD portable system and experiments evaluated. Life cycle impacts due to portable AD processing were overall agnostic to feedstock variability. Thus, waste type and volume variations generated by encampments with fluctuating populations can likely be accommodated by the portable AD system without substantially affecting short term process sustainability. Portable AD system biogas generation rates were comparable to conventional, full-scale waste to energy facilities, while combustion impacts were more sustainable than those associated with conventional fossil fuels. Portable AD units represent a sustainable energy resource, waste reduction, and landfill alternative for remote areas.