Pavlo Bohutskyi1, Duc Phan2, Anatoliy M Kopachevsky3, Steven Chow4, Edward J Bouwer4, Michael J Betenbaugh5. 1. Biological Sciences Division, Pacific Northwest National Laboratory, 3300 Stevens Dr., Richland, WA 99354, United States. Electronic address: pavlo.bohutskyi@pnnl.gov. 2. Department of Environmental Health and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686, United States; Department of Civil and Environmental Engineering, The University of Texas at San Antonio, 1 UTSA Cir, San Antonio, TX 78249, United States. 3. Department of Water Supply and Sanitary Engineering, Academy of Construction and Architecture of V.I. Vernadsky Crimean Federal University, 4 Prospekt Vernadskogo, Simferopol 295007, Republic of Crimea; Water Technologies Research and Production Company, 7 Petropavlovskaya Street, Simferopol, 295000, Republic of Crimea; Water of the Crimea State Unitary Enterprise, 1а Kievskaya Street. Simferopol, 295053, Republic of Crimea. 4. Department of Environmental Health and Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686, United States. 5. Department of Chemical & Biomolecular Engineering, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218-2686, United States.
Abstract
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.
This study investigated enhancing methane production from algal-bacteria biomass by adjusting the C/n class="Chemical">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.
Keywords:
Biogas and methane production kinetic models; Carbon to nitrogen ratio; Digester energy balance; Net energy ratio; Synergistic co-digestion of algae with cellulose