Enhancement of methanogenic biodegradation of tetramethylammonium hydroxide wastewater by co-digestion with ethyl lactate wastewater

Abstract Large and increasing volumes of wastewater are produced from the electrical and electronics manufacturing industries, and therefore, wastewater treatment has become a challenging task for manufacturers. This study investigated the anaerobic treatment of tetramethylammonium hydroxide (TMAH) wastewater by co-digestion with ethyl lactate (EL) wastewater; both of these are major organic wastewaters generated from the manufacture of semiconductors and thin-film transistor liquid crystal displays (TFT-LCDs). Biochemical potential tests showed that both the methane production rate and yield were enhanced significantly when TMAH and EL wastewaters were digested in a mixture than when they were digested alone. Correspondingly, the synergy index calculated based on the methane yield was significantly higher than 1 (i.e., synergistic effect) throughout the 60-day incubation period in all co-digestion runs, with the optimal mixing ratio of TMAH and EL wastewaters for methanogenic treatment ranging between 50:50 and 25:75 (total carbon basis). The overall results suggest that anaerobic co-digestion can offer a cost-effective option for the treatment and valorization of TMAH and EL wastewaters, thereby potentially helping to reduce wastewater treatment costs in the semiconductor and TFT-LCD industries.