## 4 Advanced Bioreactors for Hydrocarbon-Containing Wastewater Treatment  
### Aerobic bioreactors  
Bioreactor-based technologies allow more precise control and management of biodegradation parameters, such as temperature, pH, oxygen, nutrient and water contents, homogenous distribution of hydrophobic contaminants and biomass in the reactor volume, which leads to increased mass transfer and reaction rates. Aerobic bioreactors are intensively explored for the industrial effluent treatment due to their easy operation, high microorganism growth and organic carbon oxidation rates and resistance to toxic effects. Several laboratory and pilot studies were performed to treat oily wastewaters using aerobic bioreactors of various configurations and different microbial inocula. Selected examples of aerobic bioreactors used for hydrocarbon-containing wastewater treatment are shown in Table 2.  
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A continuously stirred tank bioreactor was applied to treat hydrocarbon-rich wastewater from a petroleum refinery site using an acclimatized indigenous microbial consortium [40]. The performance of the bioaugmented reactor was demonstrated by the reduction of chemical oxygen demand (COD) rates up to 95% and residual total petroleum hydrocarbon (TPH) concentration to 97.5% (from 320 mg/L to 8 mg/L). [PERSON] et al. [49] evaluated the performance of a sequencing batch reactor (SBR) with pre-grown activated sludge microorganisms to treat synthetic petrochemical wastewater containing mercury and cadmium. They found that COD removal and microbial population growth were inhibited by high metal concentrations, while metal removal rates were 76-90% for Hg and 96-98% for Cd. A two-stage SBR system was applied for treatment of refinery wastewater with high COD and O&G concentrations (up to 7.8 g/L and 13.4 g/L, respectively) using a gradual increase in wastewater load and methanol as the co-substrate [50]. This strategy enabled a short acclimation period of the sludge, resulting in 97.5% of COD removal and complete O&G removal. It should be noted that while the SBR technology is widely used for biotereatment of petroleum refinery wastewater, it cannot remove suspended solids (SS) completely, so the settleability of the activated sludge is adversely affected. The application of membrane separation instead of the settling phase of the SBR realized in a membrane sequencing batch reactor (MSBR) technology results in an effluent with negligible SS content. However, membrane fouling is a major problem in both membrane  
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bioreactors and MSBRs, thus increasing considerably the operational costs due to the periodical physical or chemical membrane cleaning. [PERSON] et al. [61] proposed a fouling mechanism for oily wastewater and they found that oil droplets were coalescing on the membrane surface, forming a continuous oil layer on the surface, different from a traditional cake layer made of separate particles. [PERSON] et al. [51] tested the effect of hydraulic retention time (HRT) on the performance and fouling characteristics of the MSBR used to treat synthetic petroleum wastewater with an average hydrocarbon concentration of 60 mg/L. They found that hydrocarbon removal efficiencies higher than 97% were possible with HRT values of 8, 16 and 24 h. Accordingly, the rate of membrane fouling increased with the decrease in HRT values. [PERSON] et al. [52] compared data from three stand-alone treatments of shipboard slop wastewater produced by the washing of oil tankers with seawater and characterized by high salinity (39 g/L of NaCl) and hydrocarbon contents (TPH of \(135\pm 38\) mg/L). The treatments were (1) a chemical treatment of coagulation-floculation with aluminum sulphate as coagulant and an anionic flocculant, (2) a physical treatment of adsorption on granular activated carbon (GAC), (3) two biological treatments represented by a membrane bioreactor (MBR) and a moving bed biofilm reactor (MBBR) with soft polyurethane sponges.