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 degrees 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 center dot 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 center dot d) (B-HT) vs. 76.80 +/- 1.10 NL/(kg OM center dot d) (B-WT) and 89.80 +/- 0.50 NL/(kg OM center dot 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.

Automated summary

This study analyzed the effects of hydrothermal pre-treatment and enzymatic additives on anaerobic digestion of organic waste. It was found that hydrothermal pre-treatment improved methane production and organic matter removal efficiency, while enzymatic additives further enhanced methane production. Hydrothermal pre-treatment showed better performance in organic matter removal, while enzymatic additives had a more significant impact on methane production.