Abstract
Small-scale anaerobic digestion (AD) can be an effective organic waste management system that also provides energy for small businesses and rural communities. This study measured fuel production from digestions of single and mixed feedstocks using an unheated, 2 m3 digester operated continuously in a temperate climate for over three years. Using local food waste, brewery waste, grease waste, and agricultural residues, this study determined that small-scale AD co-digestions were almost always higher yielding than single feedstocks during psychrophilic operation and seasonal temperature transitions. Agricultural residues from Miscanthus x giganteus had the greatest impact on biomethane production during co-digestion (4.7-fold greater average biogas %CH4), while mesophilic digestion of brewery waste alone produced the most biogas (0.76 gCH4 gVS−1 d−1). Biogas production during the transition from mesophilic to psychrophilic was temporarily maintained at levels similar to mesophilic digestions, particularly during co-digestions, but biogas quality declined during these temperature shifts. Full-time operation of small-scale, unheated AD systems could be feasible in temperate climates if feedstock is intentionally amended to stabilize carbon content.
Highlights
Anaerobic digestion (AD) is an accepted technology for organic waste management coupled with bioenergy production, but it is not clear that it is feasible at the scale of a rural family, small farm, or small business
This study examines the feasibility of using mono- and co-digestion mixtures of food waste (FW), brewery wastes (BW), grease waste (GW), and Miscanthus x giganteus (MC) feedstocks in a small-scale AD system with low energy inputs
When the N, P, and chemical oxygen demand (COD) measurements were standardized into units per g FW−1 L−1, there were no differences in the nutrient and COD contents of the FW used during the FWMC period relative to the FW feedstock use in all other digestion periods
Summary
Anaerobic digestion (AD) is an accepted technology for organic waste management coupled with bioenergy production, but it is not clear that it is feasible at the scale of a rural family, small farm, or small business. Smaller AD systems, and systems that use heterogeneous feedstocks as a substrate, represent a technology with great potential to provide distributed (i.e., decentralized) energy production and waste management in both urban and rural locales. To address the gaps in our understanding about these small-scale AD systems, this study evaluated the fuel quality produced from a non-mechanized 2 m3 digestion vessel that was operated continuously from 2015 to 2018. The results provide novel insight into the practical challenges of continuously operating a small-scale AD system through seasonal changes with different feedstocks
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