Physico-chemical, microbial and toxicity assessment of industrial effluents from the southern Tunisian tannery

The management of tanning effluents is a real problem for leather-producing countries. Therefore, the treatment solution search for this potentially toxic industrial wastewater constitutes a priority. In this study, the physicochemical, microbiological, and spectral characterizations as well as micro-toxicity study, of these effluents, were carried out. The physico-chemical analyses showed the complex nature of such untreated effluent. In fact, its composition revealed a high biochemical oxygen demand (BOD5 = 3100 +/- 100 mg/L), chemical oxygen demand (COD = 14,065.2 +/- 155 mg/L), total suspended solids (TSS = 12.30 +/- 2.64 mg/L), total dissolved solution (TDS = 44.2 +/- 3.46 mg/L), sulphate (2076.068 +/- 50.27 mg/L), chromium (4.525 +/- 0.23 mg/L), sodium (22,800 +/- 80.16 mg/L), and lead (0.739 +/- 0.04 mg/L) content with alkaline pH (12.93) and greenish-blue color. Moreover, the spectral analyses (UV-vis and FT-IR) of the basin 1, 2 and 3 effluents show its complexity, before treatment, which justifies the physico-chemical characterization. The final effluent (basin 5), after biological treatment, was characterized and a decrease was noticed in all cited parameters. In addition, the ratio COD/BOD5 was decreased 3.3 folds. The microbiological characterization revealed the presence of revivable aerobic bacteria as; total coliforms, fecal coliforms, Pseudomonas, Enterococcus (streptococci D), sulphite-reducing bacteria, and fungi. In contrast, a complete absence of Salmonella, Yersinia enterocolitica, Vibrio cholerae, and Helminth egg was noted. To confirm the efficiency of the biological treatment via an adapted consortium, micro-toxicity tests using Escherichia coli and Bacillus subtilis were carried out. Results of this monitoring showed an important decrease in the toxicity levels for the final effluent.