Study On Electrocatalytic Properties Of PDAAQ/rGO Conductive Membrane Of Self-cleaning Sustainable MBR

Membrane bioreactors (MBR) are widely used in treating municipal and industrial wastewaters because of the advantages including compact structure, high volumetric load, low yield of surplus sludge, good effluent qualities and high automation degree, which uses membrane to replace the traditional gravitational settling tank. However, the serious membrane fouling in the process of operation is still the bottleneck and the main limitation of further development and commercial application of MBR. In this work, the antifouling and electro-conductive PDAAQ/rGO/PVDF blend modified membrane was prepared by the hydrophilic poly(1,5-diaminoanthraquinone)/reduced graphene oxide (PDAAQ/rGO) nanohybrid used as an additive and poly(vinylidene fluoride) (PVDF) powders as substrate.The effect of additives and external electric field on membrane fouling mitigation was researched, which based on integrated membrane-cathode membrane module to construct electrochemical membrane reactors with external electric field infliction. The research included:We facilely synthesized poly(1,5-diaminoanthraquuione)/reduced graphene oxide (PDAAQ/rGO) nanohybrid through a one-step potentiodynamic deposition method, in which RGO was generated by cathodic electro-reduction of GO and PDAAQ polymer was simultaneously produced by in situ anodic electro-oxidative polymerization of the 1,5-DAAQ monomer. The resultant nanohybrid was fully characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy (Raman), and X-ray photoelectron spectroscopy (XPS). Characterizations indicate that the PDAAQ polymer displays a barleycorn-like structure and is covalently grafted onto the rGO surface. Different mass retios of PDAAQ/rGO were researched by their electrochemical properties and electrochemical stabilities. The cyclic voltammetry (CV) of PDAAQ/rGO had both the properties of graphene and PDAAQ in sulfuric acid solution, becausethe CV exhibited large background of graphene and the oxygen reduction performance of PDAAQ. The CV test showed that the reduction of O2 began at ca.0.3 V. The overall number of electrons transferred in O2 reduction (n) for PDAAQ/rGO are dependent on the over-potential and vary between 1.5 and 3.0 in a wide potential range (-0.1 to -0.8 V) by RDE study. When the potential was-0.4V, O2 reduction on the PDAAQ/rGO proceeded through a 2e" reduction pathway to generate H2O2, but some of the produced H2O2can be further reduced to H2O at a more negative potential. A large number of PDAAQ/rGO nanohybrids were prepared by a two-step chemical oxidation polymerization-reduction process for further application on MBR. Comparition of the CVs of two composites, the electrochemical properties and electro-catalytic activity of the composite prepared by the chemical method were similar to the composite prepared by electrochemical process. In addition, the composites had good electrochemical stability by repeated cyclic scan test.A novel conductive and hydrophilic poly(1,5-diaminoanthraquinone)/reduced graphene oxide/polyvinylidene fluoride (PDAAQ/rGO/PVDF) blended membrane was prepared by the phase inversion method with the additive of PDAAQ/rGO nanocomposite. The hydrophilicity of PDAAQ/rGO accelerates the diffusionand exchange rate between the gelsand solvent during the phase separation processresulting in large pore formation, thus promoting the transportation of water.The contact angle of PDAAQ/rGO/PVDF blended membrane decreased 9.2% compared of the pristine PVDF membrane, which corresponds to a more hydrophilic membrane material. The change of the membrane morphology and structure was confirmed by SEM, AFM and FTIR, the results showed the modified membrane was successfully prepared. The effect of additive content on the membrane structure and antifouling performance wasevaluated. An obvious growth in pore size/porosity and surface roughness was observed for the 1.5 wt%PDAAQ/rGO nanohybrid blended membrane, which caused pure water flux 3.8 times than that of the pristine PVDF membrane.and the retention rate did not appear significant reduction. By applying an appropriate external electric field of 1.0 V/cm, the conductive PDAAQ/rGO/PVDF blended membrane exhibited an admirable electrocatalytic activity towards the oxygen reduction reaction, and 8.84 mg/L H2O2 was accumulated within 30 min electrolysis. Applying bovine serum albumin (BSA) as the model protein and 1.0 V/cm external electric field, the fouling rate of the conductive PDAAQ/rGO/PVDF blended membrane decreased by about 63.5% when compared with the control test during the long-term continuous-flow filtration process. The increased electrostatic repulsion forceinduced by the external electric field and the in situ electro-generated H2O2 contributed to the prominent filtration efficiency, fouling mitigation and fouling resistance.PDAAQ/rGO/PVDF conductive hybrid membrane working as filtration membrane andcathode, the stainless steel mesh as inert anode, to construct integrated electrochemical reinforced MBR sewage treatment system with external electric field. When the external 0.6V/cm electric field was applied, PDAAQ/rGO /PVDF membrane showed best anti-fouling property and lowest flux rate of decline in rapid filtration experiments, compared with the PVDF membrane and PDAAQ/rGO/PVDF membrane without electric field. In long-term filtration, PDAAQ/rGO/PVDF modified membrane with electric fieldwas cleaned on the 101st day of operation, while the PVDF membrane and PDAAQ/rGO/PVDF membrane without electric field were cleaned on the 39st and 65st day, respectively. The addition of PDAAQ/rGOnano conductive composite and the external electric field played an important role in the anti-fouling properties by the study of resistance of membrane and EPS, which contributed to the oxidation of H2O2 generated by ORR of PDAAQ/rGO catalytic action and the increased electrostatic repulsion force induced by the external electric field to the electronegative EPS. The internal blockage of membrane pores and membrane surface filter cake layer pollution was reduced by the combined effect, so that the cake layer was looser and thinner. Electric cleaning was an effective method by the high water flux recovery ratio and the result of scanning electron microscopy(SEM), which ensured the recovery rate, reduced cleaning time (from the chemical cleaning 25h to 2h), and avoided the use of chemical agents.