A polished solution

Virotec provides tailored technology for the treatment of water and waste across a broad range of industries. General manager Simon Tillotson reports

Virotec provides solutions for the treatment of contaminated water, industrial and municipal wastewater and solids and other environmental remediation applications. The company's technologies include solutions for all manner of waste from the mining industry, wastewater and hazardous sludge treatment in industry and municipal applications, and contaminated soil remediation.

Central to Virotec's technology solutions is a range of 18 reagents with unique physical and chemical attributes, which, when brought into intimate contact with contaminated waters, solids or soils, result in the removal of dissolved phase metals (including arsenic) and phosphates, the neutralisation of acidity and odour control.

The reagents are fine grained (up to 80% of the grains are less than 10µm) and have a highly charged reactive surface resulting in high surface-area-to-mass and charge-to-mass ratios. Consequently, the reagents interact strongly with a wide range of chemical species including metals and oxy-anions such as phosphate.

Strong binding to the media surface results from a combination of physical (ionic) interactions, chemical precipitation, co-precipitation and recrystalisation reactions. The binding capacity (about 1500mEq/kg) and acid neutralisation (up to14 moles/kg) of Virotec's reagent are high.

Moreover, Virotec's reagents are highly insoluble (less than 2% of the constituent minerals are leachable by rainwater) and have strong settling and dispersive properties, and are thus well suited to applications in water and wastewater treatment where flocculation and formation of dense, easily de-waterable and stable sludges are desirable.

The initially high binding strength between metals and the media surface increases with time, demonstrably removing more than 99% dissolved metals, leaving treated water, wastewater, porewater or leachate with metal concentrations in the low ppb-range. Metals become permanently bound to the media, and are non-leachable and non bioavailable, even under acidic conditions (pH 2.9). By the simultaneous entrapment of fine organic particles, COD can also be reduced in contaminated water and wastewater.

Bound phosphates, while not permanently bound like metals, are also effectively retained but remain bioavailable and can be slowly leached from the media surface and re-released. As described later, Virotec's reagents are highly effective in removing phosphate from water and wastewater, but can alternatively be used in applications requiring later release of phosphate including fertilisation and soil improvement. Because of the permanent, non-leachable, removal of metals to the reagents, spent media will be classified as inert, or at worst non-hazardous for disposal.

However, because of its make-up, spent media is ideally reused or recycled into building construction materials, rather than disposed of to landfill. Additionally, media can be reused for water treatment before final disposal. An example of such reuse is its use in the treatment of phosphates from municipal wastewater having previously being used for minewater treatment, where it becomes up to 15% enriched in iron with enhanced performance for phosphate removal.

Virotec's reagents are toxicologically and ecologically safe. No adverse ecological impacts have been identified by toxicological tests. In fresh and marine waters and where ViroSoil Technology, for example, has been used to treat contaminated soils, enhanced plant growth is observed and even very ecologically sensitive fauna such as prawns thrive. Virotec's reagents can be added directly to contaminated water, either as a powder or as slurry, or the media can also be conveniently pelletised and used in passive flow through systems (ViroFilter treatment systems) for industrial treatment applications. In their pelletised form, the reagents have an open porous structure with good interconnectivity between the pores (see Figure 1), resulting in a permeable structure with a large internal surface area which is well suited to water and wastewater treatment applications.

The ViroFilter treatment system (Figure 2) is a containerised passive flow-through treatment system using any one of several pelletised Virotec reagents. In this form, ViroFlow Technology provides simple alternative treatment solutions for industrial wastewater problems, avoiding the need for conventional metal precipitation, settlement and filter press set-ups. Where the treatment of large flow volumes is required, such as a permeable reactive barrier, the reagents can be manufactured as large porous blocks.

Virotec's ViroFlow Technology offers solutions for a variety of industrial wastewater and solids problems, notably for metal and acidity control.

Direct addition applications use the reagent's very good flocculent properties, making ViroFlow Technology an attractive alternative to conventional lime treatment because of its better performance and the rapid formation of a dense, low-volume, sludge. For example, electroplating wastewater treated using ViroFlow Technology decreased sludge production by 50% from 16.8 (using conventional technology) to 8.4 tonnes per month. The resultant sludge also improved in quality, being classified as inert waste compared with hazardous waste under the lime treatment. The ViroFlow Technology treatment of this electroplating wastewater reduced chromium III, iron, tin and zinc from an influent concentration (in ppm) of 3000, 1550, 2800 and 2790 respectively to an effluent concentration of 0.03, 0.12, 0.74 and 0.23. This is substantially better than conventional treatment, which achieved effluent concentrations for these metals in the range of 5-50ppm.

Current developments in the UK mainly focus on the use of ViroFlow and ViroMine Technologies in ViroFilter treatment systems, using a range of pellet formulations (such as ElectroBind for zinc removal) for flow-through treatment of industrial and mining wastewater, leachate and contaminated waters.

For mining applications, acid mine drainage (AMD) has been successfully treated in the UK using ViroMine Technology. Dissolved iron has been efficiently removed (more than 99.8%), together with acid neutralisation and other metal contaminant reduction (arsenic, zinc and copper removed 90-99% to final concentrations of less than 10ppb), upon passage of the mine waters through ViroFilter treatment systems.

Virotec's reagents have good sorption properties not only for metals, but also for phosphates; the removal of fine suspended solids, including organic solids, by precipitation and entrapment is also achieved. The ViroFilter passive flow-through treatment system is, therefore, also well suited to municipal wastewater treatment, effectively removing phosphate and simultaneously polishing metals, suspended solids and COD/BOD, while reduced effluent colour and odour is also achieved.

The ViroFilter treatment system can be fitted in-line with existing secondary treatment systems at WwTWs in the most suitable configuration, either for horizontal-flow, vertical-flow or trickling-filter dependent upon the location and space available. Secondary effluent is passed through the ViroFilter beds to improve effluent quality, reducing phosphate concentrations to less than 1mg/l.

The effectiveness of ViroFilter Technology for phosphate removal and ancillary secondary effluent polishing has been shown both in long-term lab-scale trials conducted by Virotec and in independent trials conducted by the UK Water Research Council (WRc). In these independent trials, influent (secondary effluent containing 6-9mg/l phosphorus) was passed through ViroFilter beds. The study's aims were to examine the phosphorus removal capacity of ViroFilter Technology, the treatment efficiency at different hydraulic residence times (between 4 and 12 hours), and the effect of pH adjustment on treatment efficiency.

The phosphorus removal efficiency throughout the 27-week WRc trials was 80-85%, and the removal capacity of the medium (5kg/tonne) measured did not approach the maximum capacity in this time-span. This is consistent with Virotec's own trials that demonstrate a phosphorus removal capacity of the media in excess of 20kg/tonne without reaching exhaustion. WRc concluded bed lifetime to be at least 20 times that of conventional gravel media in a reed bed (see Figure 3).

The effect of influent pH adjustment was shown to be minimal, and effective wastewater treatment was achieved with hydraulic retention times of just 6-12 hours. The WRc trials also demonstrated improvements in effluent solids (about 60% reduction to 4±3mg/l), COD (about 35% reduction to 32mg/l) and removal of colour and odour.

The WRc trials concluded that ViroFilter Technology was suitable as a tertiary bed at small WwTWs without chemical dosing, and at larger plants to provide tertiary polishing for phosphorus removal.

ViroFilter Technology is especially suited to deployment at smaller or unmanned WwTWs, particularly where strict discharge consents are set by regulators and existing treatment systems require upgrading or effluent quality must be improved. The passive flow-through units have a minimal power requirement, and the longevity and phosphorus removal capacity of the pellets without the need for pH adjustment or chemical dosing ensures effective treatment without the need for operator intervention. Treatment is achieved in short hydraulic residence times, so variable effluent flows are not problematic for the system.

Flexible installation and a small footprint allow ViroFilter Technology to be deployed in-line with existing treatment plant. The system is a robust, reliable and cost-effective approach to municipal secondary effluent polishing, and offers many advantages over conventional chemical treatment technologies.

Virotec provides a broad range of sustainable and ecologically safe technology solutions for the treatment of contaminated water, industrial and municipal wastewater and solids, leachate, and also soils and sediments, for the reduction of acidity, dissolved metals and phosphate. Measures such as reduced BOD, COD, odour, suspended solids, and other parameters have also been achieved.

The reagents developed by Virotec act by permanently removing metals by a combination of physical and chemical adsorption mechanisms to the media surface, becoming non-leachable and non-bioavailable. Metal removal efficiencies of more than 99% have been routinely achieved. The 18 reagents can be used either by direct addition to contaminated waters or formulated as a porous and permeable pellet that can be used for passive flow through water treatment systems.

The direct addition formulation has been shown to successfully treat acidic, metal-rich aqueous wastes more effectively than conventional alternatives such as lime treatment, while producing significantly reduced quantities of sludge which itself is classified as inert, or at worst non-hazardous for the purposes of disposal. Spent reagents can also be reused or recycled, providing sustainability credentials to Virotec's treatment solutions.

ViroFilter Technology is suitable for the phosphorus reduction and polishing of municipal secondary effluent. The phosphorus removal efficiency (80-85%) and capacity (more than 20kg/tonne) of the reagents, confirmed by independent tests conducted by WRc, significantly improve upon conventional alternatives.
ViroFilter Technology can be retro-fitted to existing treatment systems, and ensures high-quality polished effluent even at remote or unmanned locations. The technology therefore offers an attractive solution where improved secondary effluent treatment is required.

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