Assessing the sustainability of small-scale anaerobic digestion systems with the introduction of the emergy efficiency index (EEI) and adjusted yield ratio (AYR).

Highlights: [•] Emergy analyses of digesters for human waste in Haiti and dairy manure in the US. [•] New emergy indices (EEI and AYR) were created for comparisons of analogous products. [•] Food and waste emergy analyses were conducted to determine waste emergy values. [•] Inputs from wastes accounted for more than 99% of the emergy in digesters. [•] When emergy waste values were zeroed, apparent sustainability improved. [ABSTRACT FROM AUTHOR]