Purification of tannery effluents by ultrafiltration in view of permeate reuse

Tanneries wastewaters are characterized by high organic matter and salt concentrations. Beamhouse operations, in particular unhairing, are the processes that provide the most concentrated effluents concerning the organic matter. Besides, the unhairing wastewater includes a high sulphides concentration. Thus, the separated management of the unhairing effluents has been considered in the last 20 years with the aim of their recycling and reuse. Ultrafiltration was a promising technique to separate the organic matter from the chemicals (lime and sulphides) that could be reused in the unhairing process. However, the membrane fouling has avoided its application at an industrial scale. The main aims of this paper are to study the influence of the reuse of the ultrafiltration permeate on the quality of the final leather and the comparison among different types of membrane cleaning. Ultrafiltration experiments, including cleaning procedures, were carried out in a module for plane membranes with 30 cm2 of active surface. Sodium dodecyl sulphate, two different enzymes and sodium hypochlorite were used as cleaning chemicals. In addition, the module configuration with only a plane membrane let the study of the effect of providing air from the permeate side. Laboratory drums with a 5 L maximum capacity were used for the permeate reuse and further hide samples processing in order to study the final quality of the leathers. Results showed that the final quality of the leather was not modified by using ultrafiltration permeate for the unhairing process. Concerning the membrane cleaning, the best results in terms of flux recovery were achieved with 1000 mg L−1 of sodium hypochlorite (92% of flux recovery) and with the air dosing from the permeate side. Flux recovery with enzymatic cleaning hardly reached an efficiency of 35%.