Biological Treatment of Leather-Tanning Industrial Wastewater Using Free Living Bacteria

Abstract

The present study aimed to investigate decontamination of tannery wastewater in terms of removal capacity and efficiency using indigenous and/or exogenous bacteria. Wastewater samples were collected from leather tanning factory. Three out of 17 indigenous tannery wastewater plus 3 exogenous bacterial isolates were identified and used in a batch mode remediation process as individual or mixed free living cultures. The tested tannery effluents had extremely high levels of all the tested parameters indicating high pollution potential, dangerous effects on the receiving environments and creating many treatment difficulties. Treatment of the tannery effluent was a function of time and bacterial species. Pseudomonas stutzeri (PS) considered the most while Bacillus sp. (RE12) considered the least efficient in removing all the tested parameters. Removal efficiencies (REs) were significantly and proportionally correlated with time regardless of bacterial species or parameters. However, bulk changes in all parameters were achieved within the first 24 h. The highest removals recorded were 86.7, 94.14%, 79.16, 95.64, 36.33, 93.66 and 44.91% for total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), fat, oil and grease (FOG), ammonia (NH₃), chromium (Cr) and hydrogen sulphide (H₂S), respectively after only 24 h. On the other hand, total dissolved solids (TDS) and nitrates (NO₃) recorded the highest increase (97.68 and 45.87%) after one and 7 days, respectively. Despite the highly efficient removals achieved for the tested parameters, their residual levels were slightly higher than the maximum permissible limits (MPL) for the safe discharge. Therefore, it is highly recommended to use the most promising bacteria in a fixed form to bring the effluent to the safe limits for the environment.

Keywords: Bacteria, Chromium, Leather, Nitrogen, Organic Matter, Pollution Control, Tanning Industry, Wastewater