Characterization of tannery effluents by analyzing the recalcitrant organic pollutants and phytotoxicity assay

The tannery industries have greatly improved their treatment system; treated effluents still need to be properly delineated for contaminants and toxicity. In this study, the analysis of both raw and treated tannery effluents (TEs) revealed the maximum reduction of chromium (91%), followed by chemical oxygen demand (COD) (76.7%), total dissolved solids (TDSs) (43.3%), oil and grease (37.2%), and biological oxygen demand (BOD) (33.3%) after common effluent treatment plant (CETP) treatment. Further, the concentration of TDS (13,317 ± 2.7 mg/l), BOD (280 ± 4.47 mg/l), COD (409 ± 2.4 mg/l), sulfate (3773 ± 7.3 mg/l), nitrate (734.86 ± 0.4 mg/l), chloride (8053.59 ± 18.7 mg/l), and chromium (7.153 ± 0.02 mg/l) in treated TE was 6.3-, 9.3-, 1.6-, 3.8-, 73.4-, 13.4-, and 3.6-fold higher than the permissible limit fixed by Central Pollution Control Board. Gas chromatography–mass spectrometry analysis revealed the presence of recalcitrant organic pollutants such as furan, phthalate, and fatty acid in CETP-treated TE. Phytotoxicity investigation of TE on fenugreek ( Trigonella foenum-graecum L.) and mung bean ( Vigna radiata L.) seeds germination shows that both raw and CETP-treated TEs were inhibitory for seed germination and plant growth. Further, treated TE inhibited seed germination (30%), root length (97.3%), and shoot length (88.7%) in T. foenum-graecum and at 50% concentration, respectively. However, CETP-treated TE was less toxic than the raw TE. Further, fenugreek seeds were more sensitive to TE, as they could not be germinated in both undiluted raw and treated TEs. The finding of the present study reveals that CETP-treated effluents contain a complex mixture of toxic contaminants, indicating that it is not safe to discharge these effluents into the environment.