On-field study of anaerobic digestion full-scale plants (Part I): An on-field methodology to determine mass, carbon and nutrients balance

► We looked for the mass balances of full-scale anaerobic digestion plants. ► We looked for a simple/reliable method for routine applications. ► We verified a linear equation as a tool for easily calculating input–output flows. ► This tool allowed determining carbon and nutrients balances in three full-scale plants. ► C, N, P, and K balances are necessary for digestate land applications as fertilizer. The mass balance (input/output mass flows) of full-scale anaerobic digestion (AD) processes should be known for a series of purposes, e.g. to understand carbon and nutrients balances, to evaluate the contribution of AD processes to elemental cycles, especially when digestates are applied to agricultural land and to measure the biodegradation yields and the process efficiency. In this paper, three alternative methods were studied, to determine the mass balance in full-scale processes, discussing their reliability and applicability. Through a 1-year survey on three full-scale AD plants and through 38 laboratory-scale batch digesters, the congruency of the considered methods was demonstrated and a linear equation was provided that allows calculating the wet weight losses (WL) from the methane produced (MP) by the plant (WL=41.949*MP+20.853, R2=0.950, p