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: 2.11). 02/2010; 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)

  • 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. DOI:10.1016/j.scitotenv.2013.01.053 · 3.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Sediments from polluted urban streams act as a sink of contaminants. The high content of organic matter and sulphides makes the system appropriate for binding heavy metals. However, changes in the redox potential leads to processes in which sediments acts like a low sulphidic ore in an oxidizing environment, and could generate acid drainages. Human and not human disturbances of the sediments could derive in its oxidation catalyzed by sulphur oxidizing bacteria (SOB). This process leads to acidification and metal release. In this study we analyze the acidification potential of anaerobic sediments of polluted streams near Buenos Aires with static and kinetic methods. The results remark the necessity to consider this process before any sediment management action.
    10/2013; 825:496-499. DOI:10.4028/
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This study aimed at evidencing contaminant inputs from a rapidly growing population and the accompanying anthropogenic activities to river sediments. The Fez metropolitan area and its impacts on the Sebou's sediments (the main Moroccan river) were chosen as a case study. The Fez agglomeration is surrounded by the river Fez, receiving the wastewaters of this developing city and then flowing into the Sebou. The sediment cores from the Fez and Sebou Rivers were extracted and analysed for major elements, butyltins and toxic metals. Normalised enrichment factors and geoaccumulation index were calculated. Toxicity risk was assessed by two sets of sediment quality guideline (SQG) indices. A moderate level of contamination by butyltins was observed, with monobutyltin being the dominant species across all sites and depths. The lowest level of metal pollution was identified in the Sebou's sediments in upstream of Fez city, whilst the Fez' sediments were heavily polluted and exhibited bottom-up accumulation trends, which is a clear signature of recent inputs from the untreated wastewaters of Fez city. Consequently, the sediments of Fez and Sebou at the downstream of the confluence were found to be potentially toxic, according to the SQG levels. This finding is concerned with aquatic organisms, as well as to the riverside population, which is certainly exposed to these pollutants through the daily use of water. This study suggests that although Morocco has adopted environmental regulations aiming at restricting pollutant discharges into the natural ecosystems, such regulations are neither well respected by the main polluters nor efficiently enforced by the authorities.
    Environmental Monitoring and Assessment 01/2014; 186:2851-2865. DOI:10.1007/s10661-013-3585-5 · 1.68 Impact Factor

Full-text (2 Sources)

Available from
May 31, 2014