## 4 Advanced Bioreactors for Hydrocarbon-Containing Wastewater Treatment
### Aerobic bioreactors
Both reactors were equipped with ultrafiltration hollow fiber membrane modules. To limit the fouling, each membrane was periodically backwashed (every 4 min for a period of 1 min) by pumping a fraction of permeate back through the membrane. The bioreactors operated continuously with HRT in the range of 12-15 h. As a result, the GAC treatment registered the highest removal efficiency of TPHs up to 85%, while the coagulation-floculation treatment reported the lowest (57%) removal of TPHs. The 70% TPH removal was obtained with the MBBR fed with 100% volume of slop, thus suggesting a biomass acclimation to salinity and hydrocarbons. Alternatively, [PERSON] et al. [53] used suspended ceramic foam carriers with a high mechanical strength, optimum density (close to water) and high porosity to treat oilfield produced water (COD of 343-365 mg/L; TPH of 24-28 mg/L) in MBBRs operating at HRT values ranging from 36 to 10 h. The highest COD, PAH and ammonia N removal rates were recorded at HRT of 10 h in the MBBR filled with sepiolite-modified carriers characterized by a larger specific surface area for the biofilm growth, followed by the MBBR with unmodified carriers, with the lowest removal efficiency in the MBBR with the activated sludge only. A full-scale application of continuous flow intermittent cleaning (CFIC) biofilm technology based on the MBBR concept was performed recently in the Biowater Technology AS in Norway to treat petrochemical wastewater of fluctuating concentrations with the COD ranging from 7 to 35 g/L [7]. The CFIC reactor contained highly packed polymer biofilm carriers (over 90% filling ratio) was operated continuously at the flow rate of 240 m\({}^{3}\)/day, resulting in over 90% COD removal. Excess biofilm/sludge was washed off during periodic washings, thus maintaining a thin and effective biofilm in the reactor. [PERSON] et al. [39] investigated the use of biological aerated filter (BAF) reactors inoculated with the commercial oil-degrading inocula immobilized on a patented poly-ammoniacum carrier to pre-treat the oilfield wastewater before desalination. By operating the bioreactors for 142 days under low COD load (1.07 kg COD/m\({}^{3}\).day) and high salinity conditions, the mean degradation efficiencies of 64-78% for total organic carbon (TOC), 86-94% for oil and 84-90% for PAHs were achieved. More recently, a bench-scale BAF reactor with GAC was examined for effective removal of organic matter and solids from produced water using three GAC carriers (one spent and two new) and two nutrient supplements [54]. The spent GAC with an existing biofilm from the previous treatment of surface water demonstrated up to 81% COD removal in 24 h (from initial COD values of \(1368\pm 312\) mg/L), indicating that appropriate GAC selection and pre-developed biofilm is critical for efficient BAF performance. Interestingly, recent evaluation of different inocula for treating high salinity produced water in a batch stirred tank bioreactor [55] revealed a higher efficiency of the acclimated indigenous halophilic microorganisms compared to that of the commercial inocula used in Reference [39]. Selected bacterial strains with broad hydrocarbon-oxidizing activities and resistance to toxic petroleum constituents were used as bioreactor inocula. For example, [PERSON] et al. [56] used an internal loop airlift bioreactor inoculated with a chitosan-immobilized bacterium _Sphingobium_ sp. P2 for the removal of automotive lubricants from emulsified wastewater. The reactor operated continuously at the HRT of 2.0 h for over 70 days, resulting in the removal of \(85\pm 5\%\) TPH and \(73\pm 11\%\) COD from the carwash wastewater with 25-200 mg/L amended lubricant. [PERSON] et al. [57] demonstrated a simultaneous \(n\)-alkane biodegradation and production of neutral lipids in a concentrated produced water stream by _Alcanivorax borkumensis_ SK2 as the sole reactor inoculum. \(n\)-Alkane removal efficiency up to 99.6%, with influent alkane COD of 7.4 g/L, was achieved in a continuously operated stirred tank reactor.