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Synergistic co-digestion of wastewater grown algae-bacteria polyculture biomass and cellulose to optimize carbon-to-nitrogen ratio and application of kinetic models to predict anaerobic digestion energy balance

Bohutskyi, Pavlo, Phan, Duc, Kopachevsky, Anatoliy M., Chow, Steven, Bouwer, Edward J., Betenbaugh, Michael J.
Bioresource technology 2018 v.269 pp. 210-220
algae, anaerobic digestion, biogas, biomass, carbon nitrogen ratio, cellulose, energy balance, energy efficiency, feedstocks, kinetics, methane, methane production, models, prediction, synergism, wastewater
This study investigated enhancing methane production from algal-bacteria biomass by adjusting the C/N ratio through co-digestion with a nitrogen-poor co-substrate – cellulose. A biomethane potential test was used to determine cumulative biogas and methane production for pure and co-digested substrates. Four kinetic models were evaluated for their accuracy describing experimental data. These models were used to estimate the total energy output and net energy ratio (NER) for a scaled AD system. Increasing the algal C/N ratio from 5.7 to 20–30 (optimal algae:cellulose feedstock ratios of 35%:65% and 20%:80%) improved the ultimate methane yield by >10% and the first ten days production by >100%. The modified Gompertz kinetic model demonstrated highest accuracy, predicting that co-digestion improved methane production by reducing the time-lag by ∼50% and increasing rate by ∼35%. The synergistic effects increase the AD system energy efficiency and NER by 30–45%, suggesting potential for substantial enhancements from co-digestion at scale.