The HOBUM edible oil refinery, Hamburg, is running a waste water treatment plant serving as a reference plant for the whole german edible oil industry. For that reason, its construction was financially supported by the german government. The values met by the discharged water of this treatment plant will influence a revision of the 4th Waste Water Administration Regulations, which lays down the minimum requirements for all german edible oil refineries. Main source of the waste water contamination is the wet chemical deacidification process. Before supplied to the waste water treatment system, a pretreatment (flotation. without addition of chemicals) takes place to minimize the losses of usable products. The waste water treatment system consists of a chemical-physical stage (neutralization, optional phosphorus precipitation, flotation for discharge of chemical sludge), a 1st biological stage (aerobic suspended sludge process with flotative discharge of excess sludge) and a 2nd biological stage (aerobic submerged fixed bed reactor). Investigations to obtain representative results were difficult because of a constantly higher COD space loading than assumed before start up of the treatment plant. Results obtained from several measurements showed the ability of the treatment plant to meet a COD < 100 mg/L in the discharged waste water. However, for this it is necessary to avoid shock loadings, to ensure a BOD sludge load not higher than 0.08 kg/(kgxd) and a sufficient supplying with oxygen. Only when these conditions were met, the fixed bed reactor was able to decompose not easily biodegradable substances. This aim could not be reached in case of overloading the 1st biological stage. Due to the high COD load, the 1st biological stage normally was run at a MLSS around 8 - 10 g/L. With respect to the high adsorption capacity of the suspended sludge, a high MLSS concentration may be a promissing element for buffering shock loads. However, in connection with nonsufficient oxygen supply, biological nondegradable substances may occur which worsen the effluent quality.
