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Martin Brockmann, managing director of Aquantis, part of Veolia Water Solutions and Technologies, considers the reuse of industrial wastewater.

As global climate change reduces available water resources and the cost of mains-water supplies rises steadily, the manufacturing industry is beginning to focus on water management.

However, many factories are failing to make use of a potential low-cost and environmentally friendly source of water: effluent.

Treating and reusing effluent reduces the volume of water imported to a factory as well as lowering the volume of effluent discharge, effectively doubling the cost saving.

Cleaning up industrial wastewaters, especially those with high COD, used to be an expensive and messy procedure, but with current membrane technology it is possible to treat most effluents to at least process-water standard simply and economically.

Membrane bioreactors are a key process in treating effluent to a standard for recycling.

Aquantis, the membrane competence centre of Veolia Water Solutions and Technologies, has experience with the Biosep membrane bioreactor, treating both industrial and municipal wastewaters.

Membrane bioreactor technology is well proven.

In concept, it is simply an activated sludge plant with the final clarification stage replaced by a membrane filtration system.

Depending on the individual project, those membranes may be hollow-fibre, tubular or plate type.

The result is not only a smaller-footprint plant but one that produces a final effluent of such high clarity and low-bacteria count that it can be fed directly to a reverse-osmosis plant – the equally important second stage of treatment.

The solids-removal efficiency of the membrane means that the sludge can be contained in the system at mixed liquor suspended solids (MLSS) concentrations up to five times higher than is possible in conventional activated sludge plants.

This results in the more efficient removal of COD because a higher MLSS concentration results in a lower COD loading; this is particularly important in the case of high-strength effluents, which would otherwise need an aeration tank with three or four times the volume.

The membrane installation could be submerged in the aeration tank or a small separated filtration tank.

The treated effluent is extracted by pumping from the clean side of the membrane at a trans-membrane pressure of less than 0.5bar, so operating costs are relatively low.

Membrane fouling is minimised by directing the air scour flow across the membrane surface and by occasional back-flushing with filtrate.

Over the last five years, the increased use of membrane bioreactors has resulted in the price of membranes falling sharply and membrane bioreactors have now become economically competitive with traditional processes.

The Cooperl effluent treatment plant, whose pork slaughterhouse in Lamballe is one of the largest in France, processes around 60,000 pigs each week and produces about 16,500m3 per week of wastewater with a COD of 16,500mg per litre.

The wastewater is dosed with acid or caustic soda as required to adjust the pH to seven; then, a coagulant – ferric chloride – is added to coagulate colloidal material and precipitates some of the non-soluble COD.

This is followed by a flocculation stage with slow speed stirrers that generate consistent-sized floc particles, assisted by the addition of polyelectrolyte.

The flocculated wastewater is then clarified using dissolved air flotation, giving an overall reduction in COD of about 80 per cent.

Following clarification and flow buffering, the wastewater is fed to a Biosep membrane bioreactor with an upstream anoxic tank to provide the denitrification of nitrate.

The aerated section provides the biological degradation and oxidation of ammonia to nitrate.

The submerged ultra-filtration is followed by a reverse-osmosis plant to remove residual non-biodegradable COD and reduce the salinity of the effluent.

Permeate from the reverse-osmosis plant is chlorinated prior to reuse for washing pigs and trucks and for cooling water and boiler make-up.

The plant at Cooperl is just one example of the many industries, including food processing, pharmaceutical production, semiconductor manufacturing, textile dyeing and chemical production, that are benefiting from the use of Biosep technology to recycle effluent, reduce costs and help to preserve fast-diminishing water resources.

Veolia Water Solutions & Technologies

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