## 4 Advanced Bioreactors for Hydrocarbon-Containing Wastewater Treatment
### Anaerobic and Hybrid (An anaerobic-Aerobic) Bioreactors  
An anaerobic digestion has been recognized as the sustainable wastewater treatment because it requires less space, generates low sludge amount compared to aerobic treatment and produces methane as a renewable energy. Currently, anaerobic baffled reactors (ABR), sequencing batch and up-flow anaerobic sludge blanket (UASB) reactors are applied to treat oily wastewater. Selected examples of  
Figure 2: SEM images of _Rhodococcus_ cells immobilized (**a**) on hydrophboized sawdust [41] and (**b**) in granulated poly(vinyl alcohol) cryogel [63]. anaerobic bioreactors used for hydrocarbon-containing wastewater treatment are shown in Table 3. [PERSON] et al. [43] studied an ABR start-up and operational performance (total 212 days) in treating oilfield produced water using mixed acclimated oilfield and urban sewage sludges. Such long ABR treatment under the COD load of 0.2-0.5 kg/m3-day resulted in COD and oil removals of 65% and 88% for heavy oil produced water with poor nutrient (COD: N: P, 1200:15:1) and high salt concentration (1.15-1.46%). An UASB bioreactor inoculated with digested sludge from a dairy industry was used to treat petroleum refinery effluent under mesophilic conditions (38 \(\pm\) 1 \({}^{\circ}\)C) for over120 days [44]. The authors used response surface methodology to optimize the efficient factors (influent COD of 630 mg/L, upflow velocity of 0.27 m/h and HRT of 21.4 h). Under these optimum conditions, the COD removal efficiency was 76.3% and the biogas production rate was 0.25 L biogas/L feed day. More recently, artificial neural networks were used to model the UASB reactor behavior during 180 d treating petroleum refinery wastewater under six different organic loads (from 0.58 to 4.14 kg COD/m3-day) [64]. The highest COD removal of 82% shown in the laboratory bioreactor was confirmed by using the best selected model with the Tansig-Purelin transfer function and 12 neurons. However, anaerobic treatment alone does not always meet the requirements of water discharge and requires subsequent treatment using, for example, an aerobic process [15]. A laboratory treatment  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Wastewater Type** & \ \begin{tabular}{c} **B bioreactor** \\ **Configuration** \\ \end{tabular}  & **Operational Conditions** & \begin{tabular}{c} **Treatment** \\ **Efficiency** \\ \end{tabular}  & **Reference** \\ \hline \multirow{3}{*}{Oilfield produced water} & \multirow{3}{*}{ABR} & Start-up and operational performance (total 212 days) with mixed acclimated oilfield and urban sewage sludges. & COD and oil & \multirow{3}{*}{COD and oil} & \multirow{3}{*}{COD and oil} & \multirow{3}{*}{COD and oil} & \multirow{3}{*}{[43]} \\  & & & & & 88\% \\ \hline \multirow{3}{*}{Petroleum refinery effluent} & \multirow{3}{*}{UASB} & Mesophilic conditions (38 \(\pm\) 1 \({}^{\circ}\)C) for over120 days. Digested sludge from a dairy industry. & 76.3\% COD removal, 0.25 L biogas/L feed d & & \multirow{3}{*}{[44]} \\  & & & & & 0.25 \\ \hline \multirow{3}{*}{Petroleum refinery wastewater} & \multirow{3}{*}{UASB} & Treating under six different organic loads (from 0.58 to 4.14 kg COD/m3-day) during 180 days. & \multirow{3}{*}{COD removal of 82\%} & \multirow{3}{*}{[64]} \\  & & & & 8 \% \\ \hline \multirow{3}{*}{Heavy oil wastewater} & \multirow{3}{*}{HA-MBBR} & Sludge from anaerobic and aerobic tanks of petroleum refinery AS plant. Effluent concentrations of COD, oil and ammonia were 48, 1.3 and 3.5 mg/L.