Dairygold's European first

Irish food and drink processor Dairygold has installed a unique Wehrle Membrane Bioreactor (MBR) effluent treatment plant on its Mitchelstown site. In fact, the cross-flow MBR is the first of it's kind in Europe, if not the world.

In 1999, Dairygold were faced with two unresolved matters - the need to comply with the stringent Irish EPA requirements for effluent discharge to river, and a predicted increase in wastewater due to an increase in whey processing capacity.

The Mitchelstown site has four distinct food operations - a Cheddar cheese plant, pig/bacon process factory, milk powder plant, and a whey processing and protein recovery plant; the latter is the largest and most modern facility in Europe. All site operations discharge their wastewater effluent to the Dairygold effluent treatment plant (ETP).

Extending the activated sludge ETP was not an option as the process plant addition, necessary to comply with the EPA regulations, would simply demand too much space. The most cost-effective solution was to separate the whey processing plant effluent and treat this separately in a MBR plant. Not only would the latter fit into the small space available, but with approximately 25% of the total site volume/COD load being diverted to the MBR, the existing ETP would become more efficient.

The MBR plant, supplied by Wehrle Environmental, is designed to treat 2,000m3/day of whey effluent, which first undergoes a phosphate precipitation phase. The subsequent influent to the MBR has to cope with 2,000mg/l of total solids, the latter resulting from the precipitation process. The plant consists of a 2,000m3 bioreactor for BOD reduction and nitrification, coupled with a 400m3 anoxic tank for de-nitrification. The biological sludge is then re-circulated via a high flux/low energy ultrafiltration plant and the permeate (effluent) is discharged direct to the local river without any further treatment, as the quality is well within the strict EPA consents.



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