Aerobic Treatment of Waste Process Solutions from the Semiconductor Industry: From Lab to Pilot Scale

Tetramethylammonium hydroxide (TMAH) is widely used as a solvent in the semiconductor industry. After the photo-impression process, it is necessary to remove the photoresist (PR) layer from the surface of the circuits; for this purpose, a TMAH solution is usually used. This chemical compound is highly toxic and corrosive and cannot be discharged into the environment. This study was carried out in collaboration with LFoundry (SMIC group), in order to prove the feasibility of biodegradation under aerobic conditions, using microorganisms coming from the LFoundry's wastewater treatment plant (WWTP) at different operating conditions. The feed composition was modified in order to add a small but increasing amount of TMAH and PR. The aim was to verify if the increase of TMAH concentration was harmful to bacteria. The feed stream, containing TMAH and PR, was the only carbon source for the metabolism of the aerobic microorganisms. The results of this study demonstrated an effective biological degradation of TMAH and showed a total removal efficiency of more than 99.3%, with a final concentration of 7 mg/L. Moreover, the kinetic parameters of the Monod model were also calculated. The results obtained from the experimental campaign were used to design a pilot plant that will treat around 25 L/h of waste TMAH/PR solution.