This study investigated the effect of pH buffer and solids retention time (SRT) on the anaerobic fermentation of vegetable and salad waste (VSW). Experiments were carried out in batch and semi-continuous reactors at 35 °C. In the batch experiments, the effect of pH buffer on the production of volatile fatty acids (VFAs) and ethanol was investigated. Acetate and butyrate were the main fermentation products. The maximum total product concentration was 43.3 and 18.5 g COD l-1 in the buffered and unbuffered batch reactors resulting in a yield of 62 and 27% (CODtotal product/CODfeed) respectively. Volatile suspended solids (VSS) removal was higher in the buffered semi-continuous reactor (57%) compared to the unbuffered-acidic reactor (39%), but similar yields (15%, CODtotal product/CODfeed) were observed because biogas production was stimulated in the buffered reactor. The effect of SRT on the VSS removal and product distribution in unbuffered systems was investigated at 10, 20 and 30 days SRT. The VSS removal increased as the SRT increased, ranging between 18.2-49.1%, likewise the total product concentration, 9.1-19.4 g COD l-1 , and product yield, 7-24% (CODtotal product/CODfeed). Acetate and butyrate were the prevalent fermentation products at all conditions followed by caproate although caproate was only detected at 20 and 30 days SRT. Total COD removal ranged between 15.2 and 35.1% with the highest removal observed at 30 days SRT.
In the context of the anaerobic digestion of slowly biodegradable substrates for energy and chemicals production, this study investigated the anaerobic digestion of cellulose without any chemical pre-treatments using open (undefined) mixed microbial cultures. The anaerobic conversion of cellulose was investigated in extended-length (run length in the range 518–734 days) batch and semi-continuous runs (residence time 20–80 days), at high cellulose concentration (20–40 g L−1), at temperatures of 25 and 35 °C. The maximum cellulose removal was 77% in batch (after 412 days) and 60% (at 80 days residence time) in semi-continuous experiments. In semi-continuous experiments, cellulose removal increased as the residence time increased however the cellulose removal rate showed a maximum (0.17 g L−1 day−1) at residence time 40–60 days. Both cellulose removal and removal rate decreased when cellulose concentration in the feed was increased from 20 to 40 g L−1. Liquid-phase products (ethanol and short chain organic acids) were only observed under transient conditions but not at the steady state of semi-continuous runs. Most of the observed results were well described by a mathematical model which included cellulose hydrolysis and growth on the produced glucose. The model provided insight into the physical phenomena behind the observed results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.