(cest2017_00401) Chromium recovery by membranes for process reuse in the tannery industry

摘要

Leather tanning is a wide common industry all over theworld. In leather processing, water is one of the mostimportant medium, almost 40-45 L water kg-1 raw-hide orskin is used by tanneries for processing finished leathers.The composition of tannery wastewater presentsconsiderable dissimilarities in the concentration range ofpollutants both of inorganic (chlorides, with concentrationranging from several hundred to over 10,000 mg L-1 Cl-;sulphate (VI), ammonium ions and sulphide ions,exhibiting concentration that ranges from tens to severalhundred mg L-1) and organic (the COD value is usuallyseveral thousand mg L-1 O2). Throughout the years, manyconventional processes have been carried out to treatwastewater from tannery industry: unfortunately, in thiscase, biological treatment methods give rise to anexcessive production of sludge, whereas physical andchemical methods are too expensive in terms of energy andreagent costs. In this work, a membrane process based onNF membrane modules was adopted to treat the tanneryfeedstock after primary conventional treatment. In a firststep, the determination of all boundary flux parameters, inorder to inhibit severe fouling formation during operation,were performed. After this, experimental work was carriedout to validate the approach. The target of waterpurification was reached, that is the legal discharge tomunicipal sewer system in Italy of 90% of the initialwastewater stream volume. This allows having animmediate cost saving of 21%. Moreover, the developedprocess leads to a second benefit, that is the production of5% of the initial volume as a highly chromium-richconcentrate at no cost suitable to tannery process recycleand reuse. In this case, cost saving rates exceeds 40%. Atthe end, scale-up of the investigated process will bediscussed from technical and economic point of view.