Pre-Treatment of Separately Collected Biowaste as a Way to Increase Methane Production and Digestate Stability.

To produce a valuable final product from anaerobic digestion (AD), one of the preferred methods of organic recycling, high quality feedstock must be ensured. In this study, separately collected real biowaste (B) was used, consisting of 90% food waste and 10% green waste. The priority issues of AD are both high methane production (MP) and high organics removal efficiency (as organic matter, OM and dissolved organics, and D_COD), which may be improved after pre-treatment. In this study, the effect of hydrothermal pre-treatment (B_HT) and enzymatic additives (B_E) on MP and organics removal from biowaste in mesophilic (37 °C) conditions was analyzed. To assess the adequacy of pre-treatment application, biowaste without treatment (B_WT) was used. Pre-treatment of biowaste prior to AD affected the maximal MP, the removal effectiveness of both OM and D_COD, and the kinetic parameters of these processes. For B_WT, the maximal cumulative MP reached 239.40 ± 1.27 NL/kg OM; the kinetic coefficient of MP (k_CH4) and the initial MP rate (r_CH4) were 0.32 ± 0.02 d⁻¹ and 76.80 ± 1.10 NL/(kg OM·d), respectively. After hydrothermal pre-treatment, the MP of B_HT (253.60 ± 1.83 NL/kg OM) was 6.3% higher than B_WT. However, the highest MP was found for B_E, 268.20 ± 1.37 NL/kg OM; to compare, it increased by 12.1% and 5.5% with B_WT and B_HT, respectively. However, the kinetic parameters of MP were highest with B_HT:k_CH4 0.56 ± 0.02 d⁻¹ vs. 0.32 ± 0.02 d⁻¹ (B_WT) and 0.34 ± 0.02 d⁻¹ (B_E); r_CH4 141.80 ± 0.02 NL/(kg OM·d) (B_HT) vs. 76.80 ± 1.10 NL/(kg OM·d) (B_WT) and 89.80 ± 0.50 NL/(kg OM·d) (B_E). The effectiveness of OM removal was highest with B_E, similarly to the MP with the use of an enzymatic additive. The kinetics of OM removal (r_OM, k_OM) were highest with B_HT, similarly to the kinetics of MP (r_CH4, k_CH4). The highest effectiveness of OM and, consequently, its lowest final content obtained with BE means that the organics were used most efficiently, which, in turn, may result in obtaining a more stable digestive system. [ABSTRACT FROM AUTHOR]