Structural and mineralogical variation upon reoxidation of reduced Fe-bearing clay minerals during thermal activation.

The hydroxyl radicals (OH) produced from Fe(II) oxidation upon reoxidation of reduced Fe-bearing clay minerals (RFC) have received increased attention and thermal activation was used to enhance Fe(II) oxidation to improve OH production. However, changes in mineral morphology and structure during thermally-activated RFC reoxidation are not yet clear. Herein, the Fe(II) oxidation extent was measured by chemical analysis during the reoxidation of model RFC (reduced nontronite (rNAu-2) at elevated temperatures. Mineralogical variation of rNAu-2 particles was observed by scanning electron microscopy (SEM), Mössbauer spectra, and X-ray photoelectron spectroscopy (XPS). The structural Fe(II) oxidation in rNAu-2 was accelerated with increasing temperature, accompanied by the transformation of structural entities and the dissolution of Fe and Si, while the overall structure of rNAu-2 minerals was relatively intact. The surface microstructure of particles showed the dissolved holes, net-shape flocs, and even large pore channels after Fe(II) oxidation by thermal activation. Moreover, the rearrangement of structural Fe(II) entities, the regeneration of edge Fe(II), and the electron transport from the interior to the edge were enhanced during rNAu-2 reoxidation by thermal activation. The increasing electron transfer at elevated temperatures could possibly be owing to the increasing number of reactive sites by increasing the internal disorder of rNAu-2. This work provides novel insights into the structural and mineralogical changes in promoting electron transfer upon RFC reoxidation.

Degradation mechanism of Ibuprofen via a forward osmosis membrane bioreactor.

Ibuprofen (IBU) is a non-steroidal drug that is classified as a trace organic compound (TrOC). A forward osmosis membrane bioreactor (FOMBR) has traditionally been a favored technology for wastewater treatment. In this study, the IBU degradation mechanism was clarified using an FOMBR. The results indicated that the average removal efficiencies of contaminants were greater than 96.32%. The ultra-performance liquid chromatography time-of-flight mass spectrometry (UPLC-TOF-MS) results demonstrated that there were 10 intermediates and 5 possible pathways during the IBU degradation. Decarboxylation and hydroxylation may be the primary pathways of IBU degradation. The microbial results illustrated that Proteobacteria was dominant and of utmost importance in the degradation process. Thauera and Azoarcus were the dominant genera that participated in contaminant degradation.

Carbamazepine removal from wastewater and the degradation mechanism in a submerged forward osmotic membrane bioreactor.

A submerged forward osmotic membrane bioreactor (FOMBR) was used to reveal the removal and degradation mechanism of carbamazepine (CBZ) from wastewater. The results showed that the removal mechanism consisted of the rejection of the forward osmotic (FO) membrane and biodegradation of the activated sludge. The removal efficiencies of COD, NH4+-N, and CBZ by the FOMBR were approximately 94.77%-97.45%, 93.56%-99.28%, and 88.20%-94.45%, respectively. Moreover, the COD and NH4+-N removal efficiencies were positively correlated with the increased CBZ concentrations. The results of the soluble microbial products (SMP) and extracellular polymeric substances (EPS) tests illustrated that the membrane fouling potential of EPS may be higher than that of SMP. According to the identified 14 degradation products, oxidation, hydroxylation, and decarboxylation were defined as the primary CBZ degradation mechanism. In addition, the RNA results showed that Delftia could be the characteristic bacteria in the CBZ degradation process.