Preliminary Evaluation of Biological and Physical-Chemical Chromium Removal Mechanisms in Gravel Media Used in Constructed Wetlands

• Published in: Water, air, and soil pollution air, and soil pollution, 2011-02, Vol.215 (1-4), p.507-515
• Main Authors: Dotro, Gabriela, Larsen, Daniel, Palazolo, Paul
• Format: Article
• Language: English
• Subjects: Aerobic systems; Anaerobic microorganisms; Applied sciences; Artificial wetlands; Atmospheric Protection/Air Quality Control/Air Pollution; Bioremediation; Chemical oxygen demand; Chromium; Climate Change/Climate Change Impacts; Constructed wetlands; Construction; Dissolved oxygen; Earth and Environmental Science; Effluents; Environment; Environmental monitoring; Exact sciences and technology; Gravel; Hydrogeology; Iron; Iron oxides; Leather & leather products; Media; Microbiology; Microorganisms; Organic matter; Pollutants; Pollution; Reactors; Sediments; Soil Science & Conservation; Sorption; Steel production; Studies; Tanneries; Tannery wastes; Textile industry wastewaters; Waste water; Wastewater; Water Quality/Water Pollution; Wetlands
• ISSN: 0049-6979; 1573-2932
• DOI: 10.1007/s11270-010-0495-9

Constructed wetlands have been shown to achieve high chromium and organic matter removal efficiencies when treating tannery wastewaters. Further, findings suggested chromium was potentially binding to iron oxides and microbial surfaces on the wetland media. The purpose of the present study was to distinguish between physical-chemical and biologically mediated removal mechanisms operating on iron-containing media. A total of 12 small-scale reactors were used for testing three conditions: biotic, abiotic aerobic and abiotic anaerobic. All systems were operated in 3-day batches, with the biotic and abiotic aerobic systems operating for 11 batches and the abiotic anaerobic operating for five batches. The results show that biotic systems achieved significantly higher chromium removal efficiencies (83%) than both abiotic treatments (16%). Biotic reactors quickly lowered dissolved oxygen concentrations, removing an average of 53% of the influent organic matter in the process. Redox conditions were affected by microbial metabolism, favouring iron release from the media surface. Findings suggest that microbiological activity catalyses chromium removal from tannery wastewaters. Chromium removals achieved in sterile reactors illustrate that the media influences metal retention in constructed wetlands; however, microbial interactions with both the media and tannery effluent achieve overall greater chromium removal than achieved solely by physical-chemical mechanisms.