Fouling characterisation in PVDF membrane contactors for dissolved methane recovery from anaerobic effluents: effect of surface organofluorosilanisation

Abstract

Characterisation of the fouling attached to PVDF membranes treating an anaerobic effluent for dissolved CH4 recovery was carried out. A commercial flat-sheet PVDF membrane and a PVDF functionalised by grafting of organofluorosilanes (mPVDF) that increased its hydrophobicity were subjected to a continuous flux of an anaerobic reactor effluent in long-term operation tests (> 800 h). The fouling cakes were studied by the membrane autopsy after these tests, combining a staining technique, FTIR, and FESEM-EDX, and the fouling extraction with water and NaOH solutions. Both organic and inorganic fouling were observed, and the main foulants were proteins, polysaccharides, and different calcium and phosphate salts. Also, a significant amount of live cells was detected on the fouling cake (especially on the non-modified PVDF). Although the fouling cake composition was quite heterogeneous, a stratification was observed, with the inorganic fouling mainly in the bulk centre of the cake and the organic fouling mainly located in the lower and upper surfaces of the cake. The mPVDF suffered a more severe fouling, likely owing to a stronger hydrophobic-hydrophobic interaction with the foulants. Irreversible fouling remained on both membranes after the extraction, although a higher irreversible fouling was detected in the mPVDF; however, a complete polysaccharide removal was observed. Regarding the operation performance, PVDF showed a lower stability and suffered a severe degradation, resulting in a lower thickness and perforations. Finally, the decrease in the methane recovery performance of both membranes was associated with the fouling depositions. Graphical Abstract

Stability of Superhydrophobicity and Structure of PVDF Membranes Treated by Vacuum Oxygen Plasma and Organofluorosilanisation

“…In this regard, recent efforts have especially focused on the development of membrane distillation for the water desalination of seawater, brackish water and brines [ 3 , 4 , 5 ], gas separation for carbon dioxide (CO 2 ) removal from flue gases and biogas [ 6 , 7 ], and pervaporation systems for the biobutanol and dissolved methane (CH 4 ) recovery from biological effluents and wastewaters [ 8 , 9 ]. However, membranes tend to suffer from wetting and fouling, especially in those applications that involve highly contaminated or quite complex liquid feeds, such as industrial brines or anaerobic effluents [ 10 , 11 , 12 , 13 ]. Wetting and fouling phenomena lead to an additional mass transfer resistance located inside and on the surface of the membrane, respectively, reducing the separation efficiency and involving additional cleaning processes [ 14 ].…”