Forward osmosis (FO) is becoming a versatile platform membrane-based technology, which has received increasing attention recently. Despite several studies have proved that membrane fouling is less detrimental to FO performance than other membrane processes, membrane fouling is also one of the major drawbacks for FO and has raised extensive concern over the recent years. Moreover, fouling layer formation mechanisms and fouling control ways often significantly different resulted from diverse types of foulants. This paper provides an up-to-date review of the FO membrane fouling behaviors and pays special attention to various foulants during the FO operation. For the sake of investigating fouling behaviors in FO processes, a clear cognition of membrane fouling monitoring methods is a prerequisite and foundation for researchers. Therefore, we briefly summarize the advanced membrane fouling research techniques based on the indicators for membrane fouling. Besides, we demonstrate the differences between FO and reverse osmosis in the various types of membrane fouling since they help guide future investigations in FO membrane fouling. Furthermore, the challenges still faced and perspectives for the future of investigations on FO membrane fouling have been discussed.

Cd(II) adsorption onto Fe(II) modified Layered double hydroxide–graphene oxide (LDH–GO@Fe(II)) was investigated using batch experiments. With the modification of Fe(II), LDH–GO maintained its structure, while Fe(II) species formed non-crystalline iron oxide clusters on the surface of the LDH/GO. A kinetics study indicated that adsorption obeyed a pseudo-second-order rate law. The equilibrium data were fitted well with the Langmuir isotherm model. The maximum adsorption capacity of LDH–GO@Fe(II)₁₀ was 28.98 mg g⁻¹, higher those that of pure LDH–GO and LDH–GO@Fe(II)₅₀. The increased sorption capacities could be explained by the increased specific surface area. Modification with Fe(II) would lead to the generation of amorphous Fe oxides and Fe could occupy the binding sites for Cd(II), thus excess Fe in the structure will restrain the adsorption of Cd(II). The XRD and XPS patterns revealed the formation of Cd(OH)₂ after adsorption. Batch experiments indicated that precipitation and surface complexation were the main pathways for Cd(II) removal.

Two novel adsorbents (LDH@GO-NH₂ and LDH@GO-SH) were successfully synthesized by grafting thiol- or amino-functionalized GO onto LDH and their adsorption capacities for heavy metal ions (Cu(II) and Cd(II)) were significantly enhanced. Characterization experiments illustrated that the thiol group (–SH) or amino group (–NH₂) was grafted onto LDH@GO-NH₂ or LDH@GO-SH. Adsorption isotherms were satisfactorily fitted by both Langmuir and Freundlich models. The maximum adsorption capacity of Cd(II) on LDH@GO-SH at 308 K was 102.77 mg/g, which was about triple that of LDH@GO-NH₂. The enhancement in adsorption capacity of LDH@GO-SH was due to the cooperative effect of LDH and GO-SH. The kinetic experimental data for LDH@GO-NH₂ and LDH@GO-SH were found to be in good agreement with the pseudo-second-order model. The thermodynamic parameters calculated from the temperature-dependent adsorption isotherms indicated that the adsorption was spontaneous and an endothermic process. The possible adsorption mechanisms comprising formation of precipitation, isomorphic substitution of Mg(II), and formation of complexation with amino groups or thiol groups were proposed. Desorption experiments put into evidence that LDH@GO-NH₂ and LDH@GO-SH may be promising suitable candidates for the remediation of metal ions from aqueous solutions in real work in the near future.

The electro-Fenton (EF) process was applied to treat mother liquor of gas field wastewater (ML-GFW). The Fe-Fe electrodes were used and H ₂ O ₂ was added to the EF system. Effect of initial pH on chemical oxygen demand (COD) removal efficiency, specific electrical energy consumption (SEEC), specific electrode plate consumption (SEPC) and organic matter removal mechanism was investigated. The results showed that COD removal efficiency reached the maximum (71.9%) at initial pH of 3 after reaction for 3 h. Besides, considering with the SEEC and SEPC, pH of 3 was also the best choice, at which SEEC was 4.7 kW h kg _COD ⁻¹ , SEPC was 0.82 kgFe kg _COD ⁻¹ . Organic matter removal was achieved by two ways: oxidation and flocculation, and oxidation played a major role. With the analysis of GC-MS, the possible degradation pathways of the representative contaminants in the ML-GFW were given.

Cobalt nanowires and cobalt particles are introduced into CoAl-LDHs@Fe ₃ O ₄ , and the effect of the former is better in the application of electro-Fenton process.

Different metal cation (Co²⁺, Fe²⁺, La³⁺, and Zn²⁺)-doped layered double hydroxides (LDHs), yielded CoMgAl-LDH, FeMgAl-LDH, MgAlLa-LDH, and ZnMgAl-LDH, respectively. The four LDHs synthesized from same molar ratio of M^II:M^III had different adsorption capacities toward Cr(VI) and fluoride (F⁻). Single and competitive adsorption kinetic and isotherms of Cr (VI) and F⁻ were studied. For each LDH, the adsorption capacity of Cr(VI) was higher compared with F⁻ in single adsorption, which confirmed that the LDHs were more selective for Cr(VI) adsorption. In single adsorption, CoMgAl-LDH achieved the best sorption capacity for F⁻ and Cr(VI) removal, reaching 38.01 and 59.27 mg/g, respectively. The maximum adsorption capacity of CoMgAl-LDH to Cr(VI) and F⁻ was 39.33 and 13.46 mg/g in competitive adsorption. Various experimental parameters, such as pH, contact time, concentration of coexisting anions, and anion (F⁻ and Cr(VI)) addition order were investigated in competitive adsorption system. Cr(VI) and F⁻ competed for active sites during adsorption and the affinity of Cr(VI) to LDHs was stronger compared with F⁻. Co-doped method is a valid method to improve adsorption performance of the LDHs.