Belgian technology targets UK
OVAM, the Flemish equivalent of the UK's Environment Agency, was first given powers to enforce clean-up of contaminated sites by a Parliamentary Waste Decree of 1981. In the UK, by contrast, similar powers will only come into force with the implementation of Part IIA of the 1990 Environmental Protection Act - due this Summer. In short? The Belgians are coming.
OEC boasts a full multi-disciplinary capability for major soil and groundwater remediation projects, specialising in turnkey, integrated solutions. Its core activities include ex-situ and in-situ treatments of water, soil and silt, site remediation and recycling, and landfill construction and capping.
The company's technological armoury includes award-winning mobile and semi-mobile soil and groundwater treatment and recycling facilities; in-situ and ex-situ bioremediation and physico-chemical techniques; and advanced technologies for removal of heavy metals such as bi-polar electrolysis and Metasorb, a new granular adsorbent for large-scale water decontamination projects.
Soils NV, an OEC sister company operating in Belgium, has demonstrated that bipolar electrolysis is a cost-effective option for the removal of arsenic and other heavy metal contaminants from groundwater. A pilot project at a heavily contaminated zinc refinery site, for a large Belgian non-ferrous metals group, centred on an area which served as an industrial landfill for over 100 years. Leachate has contaminated the groundwater with high levels of arsenic, zinc and cadmium, to depths of up to 80m.
The new research was undertaken in close association with IWT, the Flemish Institute for Scientific and Technological Research. This extensive body of work has confirmed the relative insensitivity of bipolar electrolysis to the complex composition of contaminated groundwaters - a factor that has underpinned its successful use.
The system is based on the separation of anode and cathode in the electrolysis cell by means of a bipolar electrode, creating a cathode and anode cell. Both cells are divided by membranes, forming four distinct compartments. By applying an appropriate electric current and varying the make-up of the membranes and electrodes, the electro-chemical conditions in each compartment may be finely adjusted. Metals such as copper, cadmium, zinc and lead may be precipitated as hydroxides. Mercury can be removed as a carbonate, while arsenic can be precipitated in the form of arsenates.
The prototype bipolar electrolysis unit, with a capacity of 20m3/hr, has been in operation for the past twelve months, demonstrating that it would be possible to build and successfully operate - over an extended period of years, if necessary - a large-scale, high efficiency bipolar electrolysis decontamination system. Success at the pilot site will encourage the large-scale application of bipolar electrolysis at other contaminated sites in Western Europe.
Project manager Stany Pensaert says: "Removal of arsenic to levels specified in new groundwater quality standards is a major challenge. Arsenic behaves very differently from other metal pollutants, as it is dissolved in anionic form (arsenite or arsenate) and cannot be precipitated as a hydroxide. Most traditional techniques rely on an insoluble arsenate, such as ferric or calcium arsenate. Our technology is based on oxidizing arsenite into arsenate, which reacts with ferric ions brought into solution by electrolytical dissolution of an iron anode."
The pilot unit exceeded expectations, reducing arsenic levels in groundwater from 0.6mg/l to below 0.02mg/l, seven per cent above the baseline requirement of 90%. The best that could be hoped for from traditional approaches would be 0.1mg/l. Zinc and cadmium levels were also reduced to dramatically low levels. The demand for power ran at below 1.2kWhr/m3 of groundwater - at a cost of around 12p/m3. Cost-efficiency would be even better for a larger system, with a capacity of perhaps 200m3/hr.
Further innovations developed in-house by DEME specialists, and now offered by OEC on the UK market, include a highly efficient pumping system for extraction of pure product from water tables, pump and heat techniques, sparging, horizontal drainage installation techniques for sludge consolidation, and hydrobotanic facilities for cost-effective small-scale wastewater treatment. Several of these "alternative" facilities, using floating reed beds to extract impurities, are operating successfully on commercial contracts in Belgium.
OEC Technical and Commercial Executive Ivo Pallemans says: "We are actively seeking project partnerships with private or public organisations in the UK to implement our know-how on contaminated soil, sludge and groundwater treatment, remediation and restoration of industrial sites, waste management, construction of confined disposal sites, and engineering, installation and operation of soil and sludge treatment/recycling centres."