Comparative evaluation of a laboratory and full-scale treatment alternatives for the vegetable oil refining industry wastewater (VORW)

Abstract

The efficiency of alternative treatment processes in producing a final effluent conforming to regulatory standards with regards to chemical oxygen demand (COD) and oil and grease (O&G) loads was assessed. The study was conducted in three principal stages: waste characterization, lab-scale treatability studies and full-scale applications. The effluent were characterized in terms of pH (6.3-7.2), total COD (13,750-15,000 mg l(-1)), soluble COD (CODs) (6500-7000 mg l(-1)), biochemical oxygen demand (BOD5) (4300-4700 mg l(-1)), O&G (3600-3900 mg l(-1)), total suspended solids (TSS) (3800-4130 mg l(-1)), total Kjeldahl nitrogen (TKN) (636-738 mg l(-1)) and total phosphorus (TP) (61-63 mg l(-1)). After analyzing various raw effluent parameters, lab-scale chemical treatability studies were conducted using Al-2(SO4)(3).18H(2)O and FeCl3.6H(2)O. The results showed 88 and 84% influent COD reduction, while O&G removal was 81 and 93%, respectively. The removal of total suspended solids (TSS) varied from 78 to 86%. Lab-scale aerobic biological treatment reactors with a HRT of 24 h and food to microorganism ratio of 0.3-0.5 were also run to assess the process efficiency and determine the residual soluble COD in the effluent. Residual soluble COD was 59-70 mg l(-1). Based on the results from waste characterization and treatability studies, a continuous full-scale treatment system was constructed and operated in two vegetable oil refining plants with a different pretreatment flow scheme. The overall percentage removal of COD, TSS, and O&G was 92-96, 83-98 and 93-95%, respectively.