In the refining of edible oil highly concentrated flows of various waste waters, particularly acidic water, are produced. The mixing of these waste waters with other flows that are only slightly contaminated will be prohibited in West Germany in future. Moreover, the legislation will demand biological treatment of the waste waters extending beyond the chemicophysical wastewater purification hitherto employed. A concept is presented for a process for purifying the waste waters produced in the refining of edible oil whose essential innovative element is a two-stage aerobic biological treatment with a discontinuous activated sludge process in the first stage, and a submerged fixed bed reactor in the second stage. The combination of processes was tested in pilot trials, which show that maximum elimination of the relevant waste water constituents can be achieved in this way. COD inlet concentrations of around 3000 mg/l have been reduced to residual contents of approx. 200 mg/l, and fats and easily degradable carbon compounds (BOD5) have been almost completely removed from the waste water. The biological treatment requires prior neutralisation and cooling of the wastewaters to 20 to 30°C, the controlled addition of nitrogen, and careful monitoring and control of the operation of the plant.

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