Clogging mechanisms of biological aerobic filter in a petro-chemical wastewater treatment plant: A field study

Clogging reduces the treatment capacity of the Biological Aerobic Filter(BAF). Revealing the cause of clogging is the key to maintaining normal treatment of BAF. In a petrochemical wastewater treatment plant, two identical structure BAF exhibit different clogging situations. Pre-BAF was clogged with slurry while Posterior-BAF was clogged with medium hardening. SEM showed the medium granular of Posterior-BAF were glued by crystal scale. The crystal scale was detected as calcite by XRD. Water quality analysis illustrated that the raw water contained high concentrations of Ca2+ and HCO3−, the calcium carbonate solubility products of the Pre-BAF and Posterior-BAF water were 6.5 × 10−8 and 3 × 10−8, both are over deposition value. The concentration of TOC in the Pre-BAF influent water was 67.8 mg/L, 7 times higher than that in the Posterior-BAF. The calcium content in the Posterior-BAF scaling along the flow direction shows the proportions were 8.2 %, 19.1 % and 30.7 % in the front, middle and back sections respectively. Thermal gravimetric analysis of the crystalline scale illustrated there were organic weight loss peaks in the front section while only calcite peaks in the back section. It is concluded the organic content is the main reason for the clogging difference in the two BAFs. The organic substance exerts an effect on the scale composition and the calcite crystal perfect in the Posterior-BAF.