Evaluation of Industrial Effluent Treatment Systems and NESREA Compliance at Tanneries in Kano State

The tanning industry in Kano State, North West Nigeria, one of the oldest in sub-Saharan Africa, generates highly toxic effluents laden with chromium, sulphide, ammonia, and high biochemical oxygen demand that are discharged into the Challawa River and its tributaries. This study evaluates the performance of effluent treatment systems at six operational tanneries in the Challawa and Sharada Industrial Estates against NESREA effluent discharge standards. Tannery effluent samples were collected before and after treatment systems at biweekly intervals over six months and analysed for pH, chromium, sulphide, biochemical oxygen demand, chemical oxygen demand, total suspended solids, and ammoniacal nitrogen. Chromium concentrations in raw effluent ranged from 780 to 2,340 mg/L, consistently above the NESREA limit of 1.0 mg/L. Post-treatment chromium concentrations at two facilities met the regulatory limit, while four facilities remained non-compliant. Sulphide removal in all existing treatment systems was below 60%, resulting in persistent violations. The most common treatment deficiency was under-capacity alkaline precipitation systems and inadequate sludge dewatering infrastructure. Two facilities operated with defunct effluent treatment plants. The study recommends a sector-wide clean production programme for Kano tanneries, incorporating chromium recovery and recycling, closed-loop sulphide management, and mandatory effluent pre-treatment certification before expansion licensing. Keywords: tannery effluent, chromium, NESREA compliance, Kano State, Challawa River