Beneficial effects of micro-electrolysis process in the treatment of TDI wastewater: experimental study and engineering analysis

ABSTRACT Wastewater generated during toluene diisocyanate (TDI) production contains significant levels of nitrobenzenes (NBs), necessitating preliminary treatment to mitigate biotoxicity and improve biodegradability. Micro-electrolysis has been demonstrated to be an effective method for the degradation of NBs. Combined with Fenton oxidation and biochemical treatment, it has the potential to achieve stable compliance with wastewater standards during TDI production. This study evaluates micro-electrolysis and its synergistic effects with other treatment methods, based on both experimental and engineering practices. Experimental results revealed that micro-electrolysis degraded 48.57% of NBs at a pH of 3 and 0.1% of cast iron powder. Coupling micro-electrolysis with Fenton oxidation boosted degradation to 82.86%. The B/C ratio (B/C, defined as biological oxygen demand/chemical oxygen demand) improved from 0.047 to 0.252. In actual practice, micro-electrolysis reduced the effluent CODcr (chemical oxygen demand with dichromate) of the subsequent Fenton oxidation unit by approximately 24.07%. Furthermore, under the synergistic effect of micro-electrolysis and Fenton oxidation, the effluent CODcr from the hydrolysis–acidification process and the two-stage AO (anoxic–oxic) units were reduced by 28.41 and 15.27%, respectively. These results demonstrate its positive impact on subsequent treatment stages.