Biotechnology shows its liquid assets

Three recently completed demonstrator projects, part of the DTI's BIO-WISE programme, have successfully proven that biotechnology processes can remove pollutants from waste streams across a variety of industries.

BIO-WISE is a government programme, funded by the Department of Trade and Industry, that aims to improve the competitiveness of UK manufacturing industry through the use of biotechnology and to support the development of the UK biotechnology supplier industry.

Two BIO-WISE projects demonstrated the removal of dye from textile company wastewater and the other demonstrated the treatment of liquid waste from chemical manufacture. All three treatments have application potential for other companies in a range of sectors.

The DTI will be disseminating the results of its 21 successful BIO-WISE demonstrator projects over the next two years.

Natural adsorbents

Carafiltration, a spin-off from the University of York, has developed natural adsorbents, called Carasols, which have the capacity to bind a range of contaminating molecules from both aqueous and gaseous effluents generated by industrial and agricultural processes. The result is clean water and air, which can be safely released into the environment or recycled.

Carasols are derived from a waste material of the food processing industry (carapace – the shells of marine crustaceans), which at the moment attracts a cost for disposal. Being a natural product, it is low-cost, completely safe to handle and biodegradable in landfill.

Carasols are able to remove contaminating molecules including a range of heavy metals in solution, pigments and colour from dyes and inks, and acid and odorous gases. Their versatility stems from dual mechanisms of adsorption – physical and chemical – used to trap contaminants. They have a physical microstructure not dissimilar to some types of activated carbon, but in addition they have a natural biochemistry, which provides a number of active chemical binding groups.

Two years ago Herbert Roberts, a textile dye house, won one of the first DTI BIO-WISE demonstrator project awards with Carafiltration, and GSPK Engineering, to investigate the efficiency of colour removal from dye-contaminated wastewater.

A pilot unit with the capacity to deal with relatively small volumes (3m3) of real effluent was installed at the dye house and a series of trials performed. In total, the binding efficiency of 19 different types of commonly used dyestuffs was determined and all were better than 87 per cent removed by the Carasols. Many such as direct dyes were removed by more than 96 per cent. Carasols also have a high affinity for reactive dyes, which are problematic as they react with water and are difficult to separate. Many dye wastes contain highly toxic organometallic residues, which are also readily removed by Carasols.

A further benefit to dyers and textile processes is the ability of Carasols to remove residues in wastewater from ‘finishes’ such as flame proofing and moth repellents, and their ability to neutralise acidic waste.

Colour issues dyeing out

Another new process for removing dyes from dye house effluents has been successfully demonstrated by the Applied Technology Unit (ATU) at Queen’s University’s QUESTOR Centre in Belfast.

The BIOCOL process, developed in co-operation with British Textile Technology Group, and funded by the BIO-WISE demonstrator project competition, removes reactive dyes.

BIOCOL uses filter cartridges packed with a special carbon-based material, which are coated with patented microbes that degrade the dyes into non-toxic colourless breakdown products.

The process has been specifically designed to treat concentrated, spent and reactive dye liquors that are released at the end of the cold pad batch dyeing process.

The size of the BIOCOL unit is a fraction of those used for conventional technologies as the dyes are treated at source before being diluted with non-colour effluent streams. The compact size of the unit means that it can be easily moved by forklift and sited almost anywhere with a minimum of installation work. It also means that the costs of removing colour using the process are significantly lower than alternative, conventional techniques.

A pilot BIOCOL plant was installed at John Hanna, a textile dyer in Kells, County Antrim.

The results from the pilot scale trials show reductions in the optical density of the effluent by more than 95 per cent, typically from 3.5 to 0.2 units. Effluent at the site is currently collected in a balancing tank before discharge to sewer, but the company is under increasing pressure from the Department of Agriculture and Rural Development (Northern Ireland) to meet colour consents prior to discharge to sewer. Consequently, a full-scale BIOCOL unit is currently being designed for the site.

The BIOCOL unit is now being used to demonstrate the process to a number of other interested companies.

Liquid waste

Selden Research is a medium-sized chemical manufacturing company in Derbyshire. In May 2000, the company received a BIO-WISE demonstrator project grant to demonstrate a low-cost process to render liquid waste from chemical manufacture virtually harmless. The project has now reached completion and the results are encouraging, particularly in light of the Landfill Directive banning the disposal of liquid waste to landfill in July 2002.

Many chemical manufacturing companies produce effluent that is difficult to treat on-site and has to be taken away by road tanker for expensive treatment at specialist facilities. This process offers an improved method of breaking down chemical effluent containing a mixture of waste substances.

The process involves a novel technique where different, naturally occurring microbes are harnessed to break down different toxins in a sequenced reaction. This explains the technical description of the process as a ‘sequencing batch reactor’.

Sequencing batch reactor

The Staffordshire-based company Zylo Technology, designed and engineered the system, with technical support (including laboratory testing and sample analysis) from Aqua Enviro, a small company associated with the University of Leeds.

The reactors were initially set up with activated sludge from a local wastewater treatment works. Initial acclimatisation of the biomass was performed using dilute washings, which were gradually added to the reactors. The COD of the waste was approximately 40,000mg/litre or 60kg/day.

The addition of the effluent caused some organisms in the sludge to die (eg nematodes and metazoans) but close inspection revealed that the microorganisms responsible for COD removal (eg flagellates) were still viable. After an acclimatisation phase of three months, the effluent showed an 80 per cent reduction in COD levels. After 15 months, the system is reducing COD in the effluent by as much as 95 per cent. This is because the biomass has continued to develop as a result of ongoing biological selection.

The result of the demonstrator project is a cleaner effluent that can be discharged to sewer at a much lower cost, eliminating the need for off-site disposal. Selden Research expects to save approximately £25,000 per year, which includes water cost savings, reduction in sewerage charges, elimination of tanker disposal costs, and accounts for the small cost of disposal of solids from the reactor.

The real impact of this type of small, operationally flexible, biological reactor is its potential for wide application at relatively low cost. There are opportunities for uptake across the chemicals industry and beyond, particularly in the food-processing sector.

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