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 (COD s) (6500–7000 mg l −1), biochemical oxygen demand (BOD 5) (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(SO 4) 3·18H 2O and FeCl 3·6H 2O. 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.