Effect of reactor operating conditions on carboxylate production and chain elongation from co-fermented sludge and food waste

摘要

Nowadays, fermentation of organic wastes for the production of carboxylic acids as precursors of higher value products has attracted significant attention. In this paper, sewage sludge and food waste were co fermented to produce carboxylic acids and study the subsequent chain elongation process. The Copenhagen waste stream scenario was taken as a case study. Firstly, design of experiments was used to investigate the overall carboxylic acids and hexanoic acid production in batch, as a function of the co fermentation ratio, substrate to co-culture ratio and initial pH. Optimal operating conditions for hexanoic acid were obtained with SS/FW 6.61, S/Xo 6.73 and initial pH 6.83. Statistical optimization increased the overall carboxylic acid titer by 41%, while co-fermentation allowed to increase hexanoate annual production up to 77%. Furthermore, a continuous fermentation experiment was performed to study the effect of reactor operating conditions. The overall carboxylates titer was 2 times higher, which also favored chain elongation compared to batch mode. An increasing loading rate did not affect the overall carboxylate titer, however the hexanoic acid titer increased by 44%. A maximum titer of 4.9 g/l of hexanoic acid was produced, achieving a productivity of 2.46 g/l/d of hexanoic acid with a retention time of 2 d and no external electron donor addition. This would correspond to 610 t/y of hexanoic acid and 350 t/y of other carboxylic acids that could be produced, based on the waste availability in Copenhagen. (c) 2021 Elsevier Ltd. All rights reserved.