World production and trade of fruits generate losses in the harvest, post-harvest,
handling, distribution and consumption phases, corresponding to 6.8% of total production.
These residues present high potential as a substrate for the anaerobic digestion process and
biogas generation. Thus, the energy valuation of the agro-industrial residues of kiwi production
was evaluated by anaerobic digestion, aiming at optimizing the biogas production and its
quality. Ten assays were carried out in a batch reactor (500 mL) under mesophilic conditions
and varying a number of operational factors: different substrate/inoculum ratios; four distinct
values for C: N ratio; inoculum from different digesters; and inoculum collected at different
times of the year. The following parameters were used to control and monitor the process: pH,
alkalinity, volatile fatty acids (VFA), volatile solids (VS) and chemical oxygen demand
(COD). Among the tests performed, the best result obtained for the biogas production
corresponded to the use of 2 g of substrate and 98 mL of inoculum of the anaerobic digester of
the Wastewater Treatment Plant (WWTP) of Bragança, with addition of 150 mg of bicarbonate
leading to a production of 1628 L biogas.kg-1 VS (57% methane). In relation to the biogas
quality, the best result was obtained with 20 g of substrate and 380 mL of inoculum from the
anaerobic digester sludge of WWTP of Ave (with addition 600 mg of sodium bicarbonate),
presenting a value of 85% of CH4, with a production of 464 L biogas.kg-1 VS.
World production and trade of fruits generate losses in the harvest, post-harvest, handling, distribution and consumption phases, corresponding to 6.8% of total production. These residues present high potential as a substrate for the anaerobic digestion process and biogas generation. Thus, the energy valuation of the agro-industrial residues of kiwifruit production was evaluated by anaerobic digestion, aiming at optimizing the biogas production and its quality. Ten assays were carried out in a batch reactor (500 mL) under mesophilic conditions and varying a number of operational factors: different substrate/inoculum ratios; four distinct values for C: N ratio; inoculum from different digesters; and inoculum collected at different times of the year. The following parameters were used to control and monitor the process: pH, alkalinity, volatile fatty acids (VFA), volatile solids (VS) and chemical oxygen demand (COD). Among the tests performed, the best result obtained for the biogas production corresponded to the use of 2 g of substrate and 98 mL of inoculum of the anaerobic digester of the Wastewater Treatment Plant (WWTP) of Bragança, with addition of 150 mg of bicarbonate leading to a production of 1628 L biogas.kg-1 VS (57% methane). In relation to the biogas quality, the best result was obtained with 20 g of substrate and 380 mL of inoculum from the anaerobic digester sludge of Ave WWTP (plus 600 mg of sodium bicarbonate), presenting a value of 85% of CH4, with a production of 464 L biogas.kg-1 VS.
