Colour removal and biodegradability enhancement of biomethanated spent wash from distillery using wet oxidation treatment

In India, high strength spent wash (SW) produced from alcohol distilleries is preferably treated by biomethanation process. However, biomethanated SW (BMSW) still contains intensified dark brown colour, high chemical oxygen demand (COD) and poor biodegradability which requires further treatment before disposal. Wet oxidation (WO) is considered an effective treatment for high strength non-biodegradable wastewaters (COD > 10 g/L). Hence, the present study explored WO of BMSW (pH = 5.7, COD = 65.5 g/L, and total organic carbon (TOC) = 23.5 g/L) in a high pressure batch reactor (0.7 L capacity) at temperatures ranging from 160-220 degrees C and oxygen pressure of 1.1 MPa. At 220 degrees C temperature, TOC, COD and color removals of 39%, 59% and 90%, respectively, were observed after 3 h of reaction period. Meanwhile, biodegradability index (BI) was enhanced from 0.27 to 0.81. Carbon balance calculations showed that the oxidation reaction contribution in TOC removal was enhanced with increase in temperature (64 - 92% of total carbon removal). Fourier transform infrared (FTIR) analysis suggested the precipitation of carbonyl group and nitrogen containing compounds. During the reaction, volatile fatty acids (oxalic acid, malonic acid and acetic acid) formation was also confirmed in the treated wastewater.