Single stage anaerobic bioconversion of food waste in mono and co-digestion with olive husks: Impact of thermal pretreatment on hydrogen and methane production

Single stage digestion tests were performed on food waste (FW) alone and mixed with olive husks (OH), to assess the influence of composition and pH on hydrogen and methane production. Process intensification with thermal pretreatment to further enhance the biological conversion of substrate constituents was investigated, too. Best performance in terms of H2 production (up to 87 NL/kg VSfed) was observed at initial pH 7 with the co-digestion of pretreated mix, because of the high amount of solubilized carbohydrates transformed rapidly during the first hours. Pretreatment of the sole FW enhanced hydrogen production only at initial pH 7, while successive methane production, ranging from 339 to 446 NL/kg VSfed, was not significantly affected. The strategy of co-digestion with untreated OH resulted encouraging to achieve contemporarily high methane and hydrogen conversion rates. The First Order/Modified Gompertz equation, the Logistic function and the Transference Function were used for experimental data fitting; the Modified Gompertz equation proved to be the best fit for this purpose.