Biogas production from the liquid waste of distilled gin production: Optimization of UASB reactor performance with increasing organic loading rate for co-digestion with swine wastewater

This study is the first test that proves high rate anaerobic digestion as an efficient technological process for the treatment of gin spent wash. The gin spent wash was co-digested in UASB reactors with swine wastewater, which provided nutrients and alkalinity. The process was optimized by increasing the proportion of gin spent wash in the feed, and thus the organic loading rate (OLR) up to reactor failure. Stable high- efficiency operation was reached at an OLR as high as 28.5 kg COD m^-3 d^-1, yielding 8.4 m³ CH₄ m^-3 d^-1 and attaining a COD removal of 97.0%. At an organic loading rate of 32.0 kg COD m^-3 d^-1, the process became unstable and the reactor underwent over-acidification that drastically lowered the pH and suppressed methanogenesis. The failure of the reactor was caused by a combination of an organic overloading and alkalinity deficit that uncoupled acidogenesis and methanogenesis.