Comparative evaluation of treatment alternatives for wastewaters from an edible oil refining industry

The aim of this study was to investigate the treatment alternatives for high-strength acid waters from an edible oil refinery and to determine an appropriate treatment system. The study was conducted in three stages: waste characterization, treatability studies and wastewater treatment system design. Based on preliminary lab-scale flotation experiments a full-scale Dissolved Air Flotation (DAF) plant was constructed. The removal of fatty materials (FM) was more than 80% without using any chemical reagent in the DAF unit. Physicochemical treatability studies were conducted by using FeCl₃, Al₂(SO₄)₃ and Ca(OH)₂ as coagulants. Aerobic treatability experiments were carried out by means of an in situ pilot-scale activated sludge (AS) unit with a volume of 240 l. A BOD₅ removal of 85% and FM removal of 95% were achieved for the organic loading rate (OLR) of 0.45 kg BOD₅kg VSS.d. The biological sludge had an excellent settling property with a sludge volume index (SVI) of 55 to 74 ml/g. Anaerobic sulphate removal kinetics was also investigated as a comparable alternative to physico-chemical treatment both in a pilot upflow anaerobic sludge blanket reactor (UASBR) and anaerobic filter (AF). Anaerobic treatability experiments showed that the linearized second-order substrate removal kinetics could be used to explain the anaerobic sulphate removal from acid waters of edible oil refineries. The maximum sulphate removal efficiency of the AF was about 60% for a hydraulic retention time of two days.