Article

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

Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands
Journal of Soils and Sediments (Impact Factor: 1.97). 11(2):364-372. DOI: 10.1007/s11368-010-0321-4

ABSTRACT PurposeDischarge 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 discussionAeration 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.

ConclusionsThe 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.

KeywordsAcid volatile sulfides (AVS)–Metal availability–Oxidation–Redox chemistry–Sediments–Simultaneously extracted metals (SEM)

0 Bookmarks
 · 
210 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The difference between the molar concentrations of simultaneously extracted metals (SEM) and acid volatile sulfides (AVS) is widely used to predict metal availability toward invertebrates in hypoxic sediments. However, this model is poorly investigated for macrophytes. The present study evaluates metal accumulation in roots and stems of the macrophyte Myriophyllum aquaticum during a 54 day lab experiment. The macrophytes, rooting in metal contaminated, hypoxic, and sulfide rich field sediments were exposed to surface water with 40% or 90% oxygen. High oxygen concentrations in the 90% treatment resulted in dissolution of the metal-sulfide complexes and a gradual increase in labile metal concentrations during the experiment. However, the general trend of increasing availability in the sediment with time was not translated in rising M. aquaticum metal concentrations. Processes at the root-sediment interface, e.g., radial oxygen loss (ROL) or the release of organic compounds by plant roots and their effect on metal availability in the rhizosphere may be of larger importance for metal accumulation than the bulk metal mobility predicted by the SEM-AVS model.
    Environmental Science & Technology 08/2012; 46(16):9129-37. · 5.26 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The combination of flood prevention and tidal marsh restoration will be implemented on a large scale in the Schelde estuary (Belgium). Densely populated and industrialized, this estuary was found to be severely contaminated with trace metals. In this study we evaluated the effect of tidal restoration on sediment trace metal concentrations. To asses historical contamination of embanked-, a restored- and natural tidal areas, deep sediment cores were sampled while the evolution of metal concentrations was determined by means of superficial samples taken during 10 sampling campaigns spread over the first 3 years of the restoration project. Metal concentrations in the natural tidal marsh reflected the estuaries' contamination history. Fertilization by irrigation caused high metal concentrations in superficial soil layers of some embanked areas. However, reintroduction of the tide resulted in deposition of a new sediment layer with lower metal concentrations, comparable to the natural tidal marsh. Despite diagenetic mobility of manganese no diagenetic movements of the trace metals were observed during these first three years. Removal of metals from the estuary and burial of contaminated sediments in the restored site emphasize the potential of these restoration projects to decrease metal contamination risks. However, more research under field conditions on the effects of changes in land use and inundation related changes in metal bioavailability is needed to draw clear conclusions on the environmental consequences.
    Science of The Total Environment 03/2012; 419:187-95. · 3.26 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Inundation of formerly embanked areas in order to combine flood control and tidal marsh restoration will be applied increasingly. However, areas suitable for the implementation are often found to be contaminated. Re-inundation of metal contaminated soils can have consequences on total metal concentrations as well as metal mobility. In this study, metal mobility in a tidal marsh restoration project was evaluated based on the modified BCR sequential extraction method, concentrations of acid volatile sulfides (AVS) and simultaneously extracted metals (SEM) and metal concentrations in plants. The results obtained from the sequential extraction suggest an increase in metal mobility following inundation due to the reduction of Fe and Mn oxides and the subsequent release of associated metals. However, the differences in results between sequential extraction and [SEM-AVS] may indicate that redistribution of the metals to the mobile fraction can be caused by sample processing. High AVS concentrations in newly deposited sediments in the restored marsh may indicate that the formation of insoluble metal-sulfide complexes will reduce metal mobility on the longer term. Processes following inundation of metal contaminated land are complex and different conditions prevailing in other sites or estuaries can result in different behavior of the trace metals. More in situ research is needed to get a better insight in the risks involved.
    Science of The Total Environment 02/2013; 449C:174-183. · 3.26 Impact Factor

Full-text (2 Sources)

View
56 Downloads
Available from
May 31, 2014