The effect of waste water treatment on river metal concentrations: removal or enrichment?

Abstract

Purpose Discharge of untreated domestic and industrial waste in many European rivers resulted in low oxygen concentrations and contamination with trace metals, often concentrated in sediments. Under these anoxic conditions, the formation of insoluble metal sulfides is known to reduce metal availability. Nowadays, implementation of waste water treatment plants results in increasing surface water oxygen concentrations. Under these conditions, sediments can be turned from a trace metal sink into a trace metal source. Materials and methodsIn an ex situ experiment with metal contaminated sediment, we investigated the effect of surface water aeration on sediment metal sulfide (acid volatile sulfides (AVS)) concentrations and sediment metal release to the surface water. These results were compared with long-term field data, where surface water oxygen and metal concentrations, before and after the implementation of a waste water treatment plant, were compared.Results and discussion Aeration of surface water in the experimental setup resulted in a decrease of sediment AVS concentrations due to sulfide oxidation. Metals, known to precipitate with these sulfides, became more mobile and increasing dissolved metal (arsenic (As), cadmium (Cd), copper (Cu)) concentrations in the surface water were observed. Contrary to As, Cd, or Cu, manganese (Mn) surface water concentrations decreased in the aerated treatment. Mn ions will precipitate and accumulate in the sediment as Mn oxides under the oxic conditions. Field data, however, demonstrated a decrease of all total metal surface water concentrations with increasing oxygen concentrations following the implementation of the waste water treatment plant. Conclusions The gradual decrease in surface water metal concentrations in the river before the treatment started and the removal of metals in the waste water treatment process could not be countered by an increase in metal flux from the sediment as observed in the experiment.

Metal bioleaching from anaerobic sediments from Reconquista River basin (Argentina) as a potential remediation strategy

“…This could be caused by exposure to oxygen, either by dredging operations or by drying effects (condition caused by a decrease in the water level). It could impact directly on the environment because of the sediment acidification and the heavy metal release into the water column while their bioavailability seems to be incremented (Förstner 2004;Seidel et al 2006a, b;Cappuyns et al 2006;Di Nanno et al 2007;Teuchies et al 2011;Porzionato et al 2014).…”

Development of sediment quality guidelines for freshwater ecosystems

“…Nowadays, surface water quality has improved due to enhanced sewage treatment, source control and other measures and it is expected that sediments will now act as a source of contamination for macroinvertebrates and organisms of higher trophic levels (Salomons and Brils 2004;Teuchies et al 2011). Consequently, achieving a "good ecological status" of surface waters, as required by the European Water Framework Directive (WFD, 2000/60/EC), may strongly depend on the management of sediments.…”

The Fate of Copper Added to Surface Water: Field, Laboratory, and Modeling Studies

“…Some studies in marine/estuarine systems have observed metal release, but the overall impact on water column dissolved copper concentrations was minor. Teuchies et al () observed a release of dissolved copper after aeration in laboratory systems, but the effect was not observable in the field. There has been evidence presented that once copper precipitates with sulfide in sediment, it is not readily released after exposure to oxic conditions (Simpson et al ; Sundelin and Eriksson ; De Jonge et al ; Costello et al ).…”