Treatment of Industrial Wastewater in a Floating Treatment Wetland: A Case Study of Sialkot Tannery

Abstract

The city of Sialkot in Pakistan is a hub of leather tanneries, with approximately 260 tanneries in operation and, while producing millions of leather products per day, the city discharges millions of gallons of untreated effluent into drains each day. In order to devise a cost-effective system for the treatment of tannery wastewater, a floating treatment wetland (FTW) was established to treat the effluent using local plant species through phytoremediation. The efficiency of the FTW was tested with three different plant species, each grown separately and operating for three months in the FTW tank. Two of the plant species introduced, water hyacinth and water lettuce, were floating and vascular; the third plant species Typha latifolia was vegetated on a floating mat of styrofoam while the roots extended down to the contaminated water. Wastewater from a tannery drain was pumped into the FTW tank with a flow of 0.5 L per minute and was given a retention time of six days. The influent and effluent from the FTW were periodically tested to determine the percentage removal of contaminants, primarily the total suspended solids, biochemical oxygen demand, chemical oxygen demand, and chromium. After two months with each species, a significant change in the quality of wastewater was measured: chromium was removed by up to 95 percent by the water hyacinth and water lettuce and 33 percent by the Typha latifolia. The pilot model indicates that FTWs are an effective system to treat effluent from tanneries in a cost-effective way as an alternative to establishing an expensive treatment system with high associated operational costs. It can help in achieving the circular economy concept of conventional wastewater schemes towards more sustainable ones. Moreover, to achieve the principles of circular economy and environmentally friendly development, it is crucial that the substances used for a wetland foundation have the capacity to be recycled, are available at a cheap price, and are locally available.