Recovery of Chromium from the Tannery Wastewater by Use of Bacillus Subtilis in Gujranwala, Pakistan

Abstract

Tanneries discharge wastes without any treatments on the vast areas of vacant land around them. Untreated effluents contain toxic materials like hexavalent chromium and sulphides which accumulate in soils and cause many health hazards. Hexavalent chromium is toxic and carcinogenic and is being extensively used in the tanning industry of Pakistan. The tannery wastewater samples were collected from two tanneries in Gujranwala, Pakistan. Chromium in these samples was determined using fractionation technique, spectrophotometry and MIBK extraction procedure. These samples were analyzed to recover chromium and chrome cake was purified using chemical treatment which can be used in recycling process. Enzyme was used to recover chromium from the samples. Two strains S1 and S2 of the Bacillus subtilis (isolated and identified from soil and tannery wastewater respectively) were used for enzymatic processing. Isolates were screened for extracellular protease activity. The strain S2 of the Bacillus subtilis showed maximum zones of hydrolysis (2.3cm) and proteolytic activity of 107 PU/ml at 65 0 C temperature, 150 rpm agitation speed and7.5 pH on Shake Flask Fermentation. The One-step and the Two-step methods were employed for chromium recovery using the S2 strain of the Bacillus subtilis. From the One-step method 96% chromium was recovered from sample-A and 92% from the sample-B. From the Two-step method of chromium recovery 98% of chromium was recovered from the sample-A and 97% from the sample-B. This paper evaluates the alternative treatment options used to treat, recover or recycle chromium from the waste water in order to minimize the environmental pollution.