## 5 Sequentially Coupled Physico-Chemical and Biological Treatments  
In recent years, great efforts and progress has been made in the combination of biological treatment with cutting-edge physico-chemical technologies, including advanced oxidation, electrocoagulation and electroflotation, UV irradiation, sonication, bioelectrochemical processes, innovative membrane and sorption materials. Most of these technologies are used as pre-treatment methods aimed at reducing a toxic shock from concentrated wastewater to microorganisms operating in bioreactors [71]. [PERSON] et al. [72] reviewed four advanced oxidation processes (AOPs)--photocatalytic oxidation, Fenton/photo-Fenton oxidation, wet air oxidation and catalytic wet air oxidation, which can be used as pre-treatment methods to increase the performance capability of the biological treatment. Depending on wastewater characteristics and operational conditions, the AOP converts recalcitrant organic components into lower molecular weight compounds, which are more amenable to biological degradation and hence an easier decomposition in a biological treatment plant can be achieved. [PERSON] et al. [73] applied a vacuum ultraviolet (VUV, 185 nm) and TiO\({}_{2}\) oxidation system for the pre-treatment of oily wastewater. The results indicated that the VUV/TiO\({}_{2}\) process reduced significantly COD, BOD and oil content and improved the biodegradability of oily wastewater, thus paving the way for subsequent biological treatment. [PERSON] et al. [74] studied a sequentially coupled electrocoagulation (EC) and a fixed film aerobic bioreactor to treat highly concentrated (COD of 19.4 g/L; TPH of 10.2 g/L) petroleum refinery wastewater. Under the optimized EC conditions (6.5 V, 0.1 M NaCl, 4 electrodes without initial pH adjustment), over 88% of COD and >80% of TPH were removed and the effluent biodegradability increased from the BOD/COD value of 0.015 up to 0.5. Further bioreactor treatment using bacteria isolated from the wastewater and immobilized on _tezontle_, a red basaltic scoria, resulted in the overall removal of 95 and 98% for COD and TPH respectively after 30 days. A combination of surfactant-modified zeolite (SMZ) adsorbent beds and an MBR was used to reduce the organic carbon content of produced water prior to reverse osmosis (RO) [75]. In the pilot plant, pre-treated produced water from gas and oil fields was cycled through the SMZ adsorbent column to remove volatile organic compounds (BTEX, acetone) and semi-volatile organics (e.g., napthalene). The effluent from the SMZ column was fed to the submerged MBR for the removal of organic acid components of TOC. Continuous operation of the SMZ/MBR system at 9.6-h HRT resulted in the overall 92% removal efficiency of the influent TOC. BTEX concentrations were reduced from the initial input level of 70 mg/L to 5 mg/L by the SMZ units and to an average of 2 mg/L after the MBR. [PERSON] et al. [76] compared the MSBR and MSBR/RO efficiencies in treating oilfield produced water (COD of 1240 \(\pm\) 119 mg/L; O&G of 15 \(\pm\) 1.8 mg/L). Different HRT values of 8, 20 and 44 h were investigated in the MSBR operations and the results demonstrated that for the HRT of 20 h, the combined COD, TOC and O&G removal efficiencies were 90.9%, 92% and 91.5%, respectively. The MSBR effluent concentration levels met the requirements for oil well reinjection. The RO treatment decreased the salt and organic contents to acceptable levels for irrigation and industrial re-use. Fouling of the membrane surface consisted mainly of inorganic (salts) and organic (microorganisms and their products, hydrocarbon components) substances. A full-scale application of the integrated treatment process, including a pre-treatment (microaerobic hydrolysis and acidification, MOHA), biological treatment (A/O process) and advanced treatment (micro-flocculation dynasand filtration and catalytic ozonation, MFDF-CO) was demonstrated in the Chinese biggest petrochemical wastewater treatment plant [77].