Study of the SBAR performance in COD removal of Petroleum and MTBE

The petroleum refineries, water are used for different purposes, such as extraction of contaminants. Some of these pollutants such as petroleum and Methyl Tertiary Butyl ether (MTBE) can be noted that have less biodegradability than other organic compounds. Discharge of these pollutants into water, and the presence of them in drinking water make huge environmental concerns.
A sequencing airlift reactor (SBR) along with an internal riser is called sequencing batch airlift reactor (SBAR); it has a similar structure to SBR and purifies wastewater with a certain temporal cycle in a single reactor. The SBAR system, which is used along with granules to treat wastewater, is known as granule sequencing batch airlift reactor (GSBAR). Using this system for biodegrading requires a high concentration of biomass (aerobic granules.
In recent years, several studies have been conducted on the use of aerobic biogranules. Mousavi et al., examined the removal of phenol with an initial concentration of 1000 mg/L from saline wastewater using GSBAR with aerobic granules 2 mm in size. The results indicated that 99% of phenol was removed. Bao et al., studied the effect of temperature on the formation of aerobic granules and on the removal of nutrients by SBAR system. The granules had an average diameter of 3–4 mm, density of 1.036 g/mL, sludge volume index of 37 mL/g, and sedimentation rate of 18.6–65.1 cm/min. The input load rate of COD, NH4–N, and PO4–P was 1.2–2.4, 0.122, and 0.012–0.024 kg/m3/day, respectively and the removal efficiency at low temperatures was 90.6–95.4, 72.8–82.1, and 95.8–97.9%, respectively. Taheri et al., examined the formation of aerobic granules in SBR for treating saline wastewater. In this study, the granules were 3–7 mm in size, had a fall speed of 0.9–1.35 cm/s, and density of 32-60 g/L. Using aerobic granules with a diameter of 1–2 mm to biologically restore 2, 4-di-chlorophenol with an initial concentration of 4.8 mg/L, Wang et al., achieved the removal efficiency of 95% and 94% for COD and di-chlorophenol, respectively. Siroos Rezaei et al. reported that COD removal efficiency of synthetic wastewater was 95% with the glucose carbon source in six 4-h cycles with a loading rate of 1500 mg/L in SBAR system using aerobic granules. The new granules had different diameters in the range of 0.5–5 mm, high sedimentation ability, and SVI of 100 mL/g. Ghaderi et al., investigated the performance of the biofilm reactor and SBR in removing formaldehyde from wastewater. The results revealed that removal efficiency of CODs less than 200 mg/L was 100% and removal efficiency of CODs between 200–450 mg/L was 90% after 48 h.
The aim of this study was evaluating the ability of SBAR system in quick produce of granules and achieving high removal of petroleum and MTBE in a short time. For this purpose, 2 similar SBAR systems with Circular cross-section were used. Outer Cylinder's diameter and length was respectively 8cm and 110 and the internal riser's diameter and length was respectively 4 cm and 90 cm. In the first system (R1) petroleum was treated in 6 hours and in the second system (R2) MTBE wastewater was treated in 4 hours. In COD equivalent to 600 mg/L, the removal efficiency of R1 and R2 were equal to 81.1 and 84.2%. These values were respectively 82.8 and 90% in COD equivalent 500 mg/L. Consider to granules changes, optimal COD was respectively equivalent to 600 and 500 mg/L in R1 and R2. By reducing retention time to 5 and 3 hours in R1 and R2, removal efficiency of pollutants in optimal COD of each system was respectively 77.8 and 90 %. The first granules were observed in the seventh day of operating system. During this period, the size of the granules increased to 1.3 and 0.6 mm in R1 and R2. Density and velocity of the granules were in the range of 0.0252-1.1998 gr/mL and 3.02-3.32 cm/s in R1 and 0.05-0.06502 gr/mL and 0.4-0.9 cm/s in R2. SVI was in the range of 42-65 mL/g, pH and DO was in the range of 6.8-7.2 and 2-6 mg/L and ORP was always above 100 mV.