Lipid inhibition and foaming in anaerobic digestion of food processing wastewater

High-strength wastewater is a suitable substrate for the anaerobic digestion (AD) to generate a higher yield, as it is a high organic matter source. However, several backlashes, such as foaming and scum formation incidents, lead to unstable operation and reduced digester working volume, decreasing microbial activity and biogas yield. This research was carried out to identify the effect of protein and lipids on scum formation and foam in one-stage and two-stage AD. Besides that, the scum reduction efficiency using natural oils and biosurfactants was also assessed. The one-stage process was carried out through a batch test in 1L and 10 L bottles. Meanwhile, the two-stage AD was through a continuous process at a hydraulic retention time (HRT) of 0.5 days, a temperature of 35-38°C, and a pH of 7 in 30 L fermenters. The inoculum was anaerobic sludge (AS) and cow manure (CM) for one-stage AD, while for the two-stage only AS was used. The substrate was synthetic wastewater (SW) and food processing wastewater (FPW). Antifoams such as natural oils (rapeseed oil (RO), palm oil (PO)) and biosurfactants (Rhamnolipid (RL) and tea saponin (TS)) were employed in the two-stage reactor to combat the scum formation. Performance of the AD process was analyzed by COD, protein and lipid removal efficiencies, total volatile fatty acid (VFA), ammoniacal nitrogen (AN) concentration, pH, and biogas accumulation. The foam was analyzed using an aeration-based foaming assay and the scum reduction efficiency through volume. This research shows that protein-induced foaming in one-stage AD was not present in two-stage AD. Foaming was also not observed in one-stage and two-stage digesters fed with FPW. On the other hand, scum was only present in two-stage AD treating FPW. The fatty acid analysis revealed that scum consists mainly of saturated and α-linoleic fatty acids. This shows that the scum in the digester is indeed from lipid inhibition. The best performance was at 6g/L lipid at COD removal of 93.8%, AN of 52.9 mg/L, total VFA of 4.44 g/L and biogas of 0.364 L/L/D in Tank 2, day 4. The 0.5% v/v RO could suppress scum in two-stage AD by 32%, while 0.5% v/v PO only suppressed by 7% with a biogas accumulation of 0.201 L/L/D and 0.220 L/L/D significantly lower than blank (0.364 L/L/D). The biosurfactants, RL and TS, increased the hydrolysis and acidogenesis; however, scum was not successfully suppressed. A reduction of biogas in Tank 2 of two-stage AD (methanogenesis phase) was observed in both applications of natural oil and biosurfactants, indicating a detrimental effect.

Text FK 2023 17 - Full Text.pdf Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (3MB) Text FK 2023 17 - Declaration Form.pdf Restricted to Repository staff only Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (458kB) Text FK 2023 17.pdf Restricted to Repository staff only Available under License Creative Commons Attribution Non-commercial No Derivatives. Download (3MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18933

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