Onshore oilfield produced water treatment by hybrid microfiltration-biological process using kaolin based ceramic membrane and oleaginous Rhodococcus opacus

Abstract

This study examined the treatment of onshore oilfield produced water by various strategies: microfiltration, biological treatment, microfiltration followed by biological treatment (MF-B), and biological treatment followed by microfiltration (B-MF). Microfiltration experiments were carried out at various applied pressures (69–345 kPa) using a tubular ceramic membrane prepared from inexpensive clays (kaolin and quartz). Maximum removal efficiency values of the parameters total suspended solids (TSS) (100 %), turbidity (100 %), total organic carbon (TOC) (84 %) and chemical oxygen demand (COD) (78 %) were obtained at a low pressure of 69 kPa. Complete removal of TSS and turbidity were observed at all the applied pressure values. However, the COD and TOC removal efficiency decreased with an increase in applied pressure from 69 to 345 kPa. In order to meet the discharge limits of the treated water parameters, other alternative techniques were investigated such as biological treatment, MF-B and B-MF. The oleaginous bacterium Rhodococcus opacus was used for the biological treatment of produced water. The results revealed that combined MF-B system was most effective, showing 99 % removal efficiency for TOC and COD compared to all other systems (microfiltration, biological treatment, and B-MF). Cleaning efficiency of membrane was investigated by using different chemical reagents and a mixture containing 0.10 wt% sodium dodecyl sulfate and 1 wt% NaOCl resulted in a maximum flux recovery of 92.60 %. Furthermore, toxicity assessment of the treated water obtained from MF-B system revealed maximum germination index of 74.30 % for Cicer arietinum and 71.10 % for Vigna mungo. Hence, it can be concluded that, hybrid MF-B system is highly efficient for complete removal of TOC, COD from produced water and reuse of the treated water.