Low-strength electronic wastewater treatment using immobilized cells of TMAH-degrading bacterium followed by activated carbon adsorption

An immobilized-cell process followed by activated carbon adsorption was developed to treat the tetra-methyl ammonium hydroxide (TMAH) containing low-strength electronic wastewater. The isolated TMAH-degrading bacterium (Mycobacterium sp. TMAH-W0418) and activated sludge were entrapped in polyethylene glycol cubes. The packing rate of 60% (v/v), biomass ratio between Mycobacterium and activated sludge of 2:3 (w/w), and total biomass of 7,000mg/L were found to be optimal for removing dissolved organic carbon (DOC) and TMAH with the concentrations around 1 and 0.2mg/L, respectively. Granular activated carbon was used to further decrease the DOC and TMAH in the effluent, and the concentrations of DOC and TMAH in the effluent of the combined system were below 1mg/L and almost 0mg/L, respectively. Scanning electron microscope results confirmed that cells were effectively immobilized in the polymer matrix. Thick biofilm on the surface of both polymer carriers and activated carbon granules was observed. The microorganism concentration estimated by protein assay increased and the immobilized-cell activity maintained constant during the operation period. From these observations, it was concluded that immobilized-cell process combined with activated carbon system could successfully treat low-strength electric wastewater to yield effluent with DOC level below 1mg/L.