Efficiency assessment in co-production systems based on modified emergy accounting approach

•Methodological aspects of emergy assessment in co-production systems assessed.•A modified physical quantity method (MPQM) has been proposed.•MPQM provided accurate results as compared to other emergy methods.•Findings to strengthen emergy accounting based on the physical quantity criterion. Emergy accounting in a system with co-production branch is of great scientific interest since each branch corresponds to a different transformity value. In previous studies, limitations associated with emergy accounting in co-production systems have been highlighted where some “inputs” have to be added to obtain a “useful” product from a “co-product” – giving rise to inaccuracies in the emergy accounting process. To address these methodological aspects of emergy assessment in co-production systems, a modified physical quantity method (MPQM) – that goes in line with the standard emergy algebra – has been proposed in order to provide a different perspective for accounting co-products efficiency. The robustness of MPQM has been verified by taking the case study of Eucalyptus pulp production and a comparison is made against conventional and energy/exergy weighting methods. As per the results, MPQM was able to provide accurate results for co-production systems as compared with other emergy accounting methods. However, the case of Eucalyptus pulp production was found to be “inefficient” following the MPQM approach. These findings are expected to strengthen the methodological aspects of emergy accounting based on the physical quantity criterion.