A Comparative Study of the Efficiency of Granular Activated Sludge and Common Activated Sludge in the Removal of Chromium (VI) from Synthetic Solutions

Introduction: Aerobic granules as a novel type of bio-sorbent have an excellent settling ability and high-porosity structure. This study investigated the feasibility of aerobic granules for chromium (VI) removal from synthetic aqueous solution and compare it with conventional activated sludge. Method: In this research the effect of some important parameters including pH (5, 7, and 9), initial chromium (VI) concentration (25, 50, and 100 mg/l), and equilibration time (30, 60, 120, 180, 240, and 360 minutes) in removal of chromium (VI) from synthetic aqueous solution in batch system have been studied. The amount of chromium (VI) was determined using Spectrophotometer at 540 nm. Results: The results indicated that at pH=5, initial chromium concentration of 25 mg/L  and equilibration time of 120 minutes, 97.65 % of chromium (VI) was found by aerobic granules. In the second stage, chromium (VI) removal was examined using conventional activated sludge which the efficiency of chromium (VI) were obtained 58% in the optimum conditions (pH=5, initial chromium (VI) concentration =25 mg/l, and retention time=120 minutes). Conclusion: Totally, it can be concluded that aerobic granules sludge as an effective and low-cost biodegradable adsorbent has a good performance for the removal of chromium (VI) from aqueous solutions.