TREATMENT OF WASTE-WATERS FROM EDIBLE OIL REFINERIES

The HOBUM edible oil refinery, Hamburg, is running a waste water treat ment plant serving as a reference plant for the whole german edible oi l industry. For that reason, its construction was financially supporte d 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 f or all german edible oil refineries. Main source of the waste water co ntamination is the wet chemical deacidification process. Before suppli ed to the waste water treatment system, a pretreatment (flotation. wit hout addition of chemicals) takes place to minimize the losses of usab le products. The waste water treatment system consists of a chemical-p hysical stage (neutralization, optional phosphorus precipitation, flot ation for discharge of chemical sludge), a 1st biological stage (aerob ic suspended sludge process with flotative discharge of excess sludge) and a 2nd biological stage (aerobic submerged fixed bed reactor). Inv estigations 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 showe d the ability of the treatment plant to meet a COD < 100 mg/L in the d ischarged waste water. However, for this it is necessary to avoid shoc k loadings, to ensure a BOD sludge load not higher than 0.08 kg/(kgxd) and a sufficient supplying with oxygen. Only when these conditions we re met, the fixed bed reactor was able to decompose not easily biodegr adable substances. This aim could not be reached in case of overloadin g the 1st biological stage. Due to the high COD load, the 1st biologic al 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 con centration may be a promissing element for buffering shock loads. Howe ver, in connection with nonsufficient oxygen supply, biological nondeg radable substances may occur which worsen the effluent quality.