Distribution and Mobilization of Pollutants in the Sediment of a Constructed Floating Wetland Used for Treatment of Combined Sewer Overflow Events

• Published in: Water environment research 2011-05, Vol.83 (5), p.427-439
• Main Authors: Van de Moortel, Annelies M. K., Du Laing, Gijs, De Pauw, Niels, Tack, Filip M. G.
• Format: Article
• Language: English
• Subjects: Aquatic plants; Belgium; Environmental Monitoring; Experiments; Flow velocity; Geologic Sediments - chemistry; metals; Metals, Heavy - analysis; mobility; nitrogen; phosphorus; Polycyclic aromatic hydrocarbons; Sewage - chemistry; stormwater; Surface water; Vegetation; Visual MINTEQ; wastewater treatment; Water Pollutants, Chemical - analysis; Water Purification - methods; Wetlands
• ISSN: 1061-4303; 1554-7531
• DOI: 10.2175/106143010X12851009156169

Sediments in combined sewer overflow treatment systems may exhibit elevated pollutant concentrations. Concentrations measured in the sediment of a floating treatment wetland ranged from 0.17 to 1.6 (cadmium), 28 to 142 (copper), 10 to 33 (chromium), 50 to 141 (manganese), 5 to 20 (nickel), 50 to 203 (lead), and 185 to 804 (zinc) mg/kg dry matter and 7.4 to 17 (iron), 2 to 8 (total nitrogen), and 1.3 to 4.4 (total phosphorus) g/kg dry matter. During overflow events, the entering water volumes can disturb the sediments. A greenhouse experiment was set up to evaluate the possible mobilization of pollutants through disturbation. The disturbation did not result in an increased mobilization of cadmium, copper, chromium, nickel, lead, zinc, nitrogen, phosphorus, and organic carbon towards the pore and surface water. Calcium concentrations in the surface water increased for all sediments, as a result of release from the exchangeable sediment pool and dissolution of carbonates. Geochemical speciation modeling indicated that, in the pore water, the free ion form was the most abundant for calcium, iron, manganese, cadmium, and nickel, with its fraction increasing with time.