Treatment of TMAH solutions from the microelectronics industry: A combined process scheme

The microelectronics industry produces significant amounts of wastewaters containing inorganic substances such as fluorides, phosphates, and organic pollutants such as acetic acid (CH3COOH), and tetramethylammonium hydroxide (C4H13NO, TMAH). The objective of this manuscript is the description of the depuration process of three types of wastewaters, representative of real liquid wastes coming from a multinational company of semiconductor production. The first residual liquid flow (WW1) contained TMAH, the second one (WW2) contained fluorides and phosphates, while the last (WW3) was rich in nitrates, fluorides and acetic acid. Aerobic treatment of WW1 was investigated by using a lab scale reactor inoculated with an activated sludge coming from the company municipal wastewater treatment plant. Another residual industrial effluent (photoresist) was added, together with several micronutrients, to guarantee a good carbon/nitrogen ratio and a nutrient supply for bacterial growth. The results showed that after one day of acclimation, the microorganisms started to remove TMAH and 99% of degradation was reached in seven days. For WW2 and WW3, a pollutant removal of 99% was obtained by chemical precipitation with lime. An attempt was made to implement the research progress made on the laboratory-developed process at the pilot and industrial scale. To this end, a simulation of the combined process was performed by using a specific software, SuperPro Designer. The process analysis showed that the treated liquids, containing TMAH not degraded to trace levels and other residual substances, can be sent to the biological WWTP of the company for further treatment; after that, the treated water can be reused and/or discharged to surface waters.