Chromium Recovery from Tannery Wastewater Using Moleculary Imprinted Polymers

Tanning with chromium is a commonly used process to produce leather. A liquid waste stream of the process is tanning liquor, which can contain 4000-6500 ppm chromium. The chromium is a hazardous waste product which must be removed from the tanning liquor before the tanning liquor can be treated and discharged. The current method for chromium removal involves pH adjustment, precipitation and filtration before disposal of the solid chromium to hazardous waste land fill. In some countries, the waste tanning liquor is discharged directly into rivers and streams which can lead to pollution, disease and sickness. The disposed chromium represents a loss of valuable material and is also a non-sustainable practice. Thus, many previous studies have been completed which attempted to recover and reuse the chromium from tanning liquor. However, these studies had limited success due to other contaminants being present in the recovered chromium causing a reduction in tanned hide quality.

A molecularly imprinted polymer (MIP) has been developed which can selectively capture chromium from the tanning liquor. This study found the MIP could recover chromium from tanning liquor. A pilot plant capable of processing up to 100-250 L/hour of tanning liquor ran for three weeks at a local tannery and recovered enough chromium for multiple hide tanning trials. The chromium level in the treated tanning liquor was reduced by 85-90%. Hides tanned with the recovered chromium were analyzed and showed similar quality to hides tanned with virgin chromium. An industrial scale system capable of processing up to 5000 L/hour of tanning liquor with 5000 ppm chromium was designed and its capital cost to build using local fabrication and process control contractors was estimated to be NZ$600,000. The system operating full time at its maximum capacity had a payback period of 2.11 years.