Performance of pilot-scale constructed wetlands for secondary treatment of chromium-bearing tannery wastewaters

• Published in: Journal of hazardous materials Vol. 239-240; pp. 142 - 151
• Main Authors: Dotro, Gabriela, Castro, Silvana, Tujchneider, Ofelia, Piovano, Nancy, Paris, Marta, Faggi, Ana, Palazolo, Paul, Larsen, Daniel, Fitch, Mark
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.11.2012
• Subjects: Adsorption; Anaerobic; biological treatment; Chromium; constructed wetlands; effluents; Horizontal flow constructed wetlands; Industrial Waste; leather; Pilot Projects; Sizing; Solids; subsurface flow; tanneries; Tanning; Waste Disposal, Fluid - methods; wastewater; Water Pollutants, Chemical; Wetlands; Chromium; Solids; Horizontal flow constructed wetlands; Sizing; Anaerobic
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2012.08.050

► Wetlands can enhance the reliability of primary treatment of industrial effluents. ► High removal rates for Cr, COD and TSS can be achieved. ► Chromium can be retained in wetlands with non-specialized media. ► Pilot testing resulted in improved design criteria than literature values. Tannery operations consist of converting raw animal skins into leather through a series of complex water- and chemically-intensive batch processes. Even when conventional primary treatment is supplemented with chemicals, the wastewater requires some form of biological treatment to enable the safe disposal to the natural environment. Thus, there is a need for the adoption of low cost, reliable, and easy-to-operate alternative secondary treatment processes. This paper reports the findings of two pilot-scale wetlands for the secondary treatment of primary effluents from a full tannery operation in terms of resilience (i.e., ability to produce consistent effluent quality in spite of variable influent loads) and reliability (i.e., ability to cope with sporadic shock loads) when treating this hazardous effluent. Areal mass removal rates of 77.1g COD/m2/d, 11g TSS/m2/d, and 53mg Cr/m2/d were achieved with a simple gravity-flow horizontal subsurface flow unit operating at hydraulic loading rates of as much as 10cm/d. Based on the findings, a full-scale wetland was sized to treat all the effluent from the tannery requiring 68% more land than would have been assumed based on literature values. Constructed wetlands can offer treatment plant resilience for minimum operational input and reliable effluent quality when biologically treating primary effluents from tannery operations.