Process Biochemistry 39 (2004) 869–875 Comparative evaluation of a laboratory and full-scale treatment alternatives for the vegetable oil refining industry wastewater (VORW) Nuri Azbar a,∗ , Taner Yonar b a Environmental Engineering Department, Balikesir University, Cagis, Balikesir 10145, Turkey b Environmental Engineering Department, Uludag University, Gorukle, Bursa 16059, Turkey Received 15 November 2002; received in revised form 26 February 2003; accepted 17 May 2003 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 2 O and FeCl 3 ·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. © 2003 Elsevier Ltd. All rights reserved. Keywords: Vegetable oil; Residual inert COD; Physicochemical treatment; Dissolved air floatation; Oil and grease 1. Introduction The discharge of poor quality effluents by the vegetable oil refining industry is posing a serious threat to water resources and publicly own wastewater treatment systems (POWS). Vegetable oil industry develops rapidly in Turkey with in- creasing cultivation of sunflower, cotton and maize. On av- erage, annually 1,000,000 tonnes of the pip of sunflower are produced in Turkey resulting in 300,000 tonnes of raw oil and 110,000 tonnes of edible oil per year [16]. Sunflower, corn, soybean and cotton seeds are the most commonly used raw materials for the production of edible oil. Oil processing consists of five main steps (Fig. 1) as fol- lows: Seed receiving and storage—seeds are received and transferred to a screening unit to remove impurities, fol- lowed by fine sieving to separate broken seeds and hulls. ∗ Corresponding author. Fax: +90-266-6121257. E-mail address: nuriazbar@yahoo.com (N. Azbar). Seed Preparation—clean seeds are weighed and passed to a destoner to remove stones and metals, then prepared for oil extraction and cooking. 50% of the crude oil content is extracted using expellers, while the seed cake (containing around 30% oil) is sent to the solvent extraction unit. Sol- vent extraction unit—the seed cake is fed into this unit and mixed with the hexane. This produces a solvent–oil mix- ture and an extracted meal (2% oil content), which is sent to DTDC (desolventising, toasting, drying and cooling). Crude oil is extracted from this mixture by a three-stage evapo- ration system. The evaporated hexane is recovered within the system and reused. Refining of crude oil—This includes degumming, which removes about 5–10% gums, neutraliza- tion (caustic soda) to remove fatty acids to generate soap- stock, washing and separation (by centrifuge), drying and bleaching to remove colour, deodorisation of the bleached oil by vacuum distillation. Generally, the first three stages of refining are carried out in the same reactor as a batch process that produces a soap stock from which fatty acids are recovered by means of “acid splitting”. Acid splitting is 0032-9592/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0032-9592(03)00193-6