In the commercial manufacture of 3,3'-dichlorobenzidine hydrochloride, substantial quantities of acidic industrial effluents were generated. A combination of ultrafiltration and evaporation processes was investigated for the recovery of products and dilute hydrochloric acid. In a novel purification method, waste sulfuric acid is purified and reused four or five times in the hydrazobenzene-benzidine transformation step, resulting in a 75% reduction in the consumption of sulfuric acid, minimization of wastewater discharge and environmental hazards risk and significant economic, environmental and social benefits.