Browsing by Author "Zhang, Haifeng"
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Item Characterization of the fouling layer on the membrane surface in a membrane bioreactor: Evolution of the foulants’ composition and aggregation ability(2019) Yan, Linlin; Li, Ruixue; Song, Yu; Jia, Yanping; Li, Zheng; Song, Lianfa (TTU); Zhang, HaifengIn this study, the characteristics of membrane foulants were analyzed with regard to morphology, composition, and aggregation ability during the three stages of transmembrane pressure (TMP) development (fast–slow–fast rise in TMP) in a steady operational membrane bioreactor (MBR). The results obtained show that the fouling layer at the slow TMP-increase stage possessed a higher average roughness (71.27 nm) and increased fractal dimension (2.33), which resulted in a low membrane fouling rate (0.87 kPa/d). A higher extracellular DNA (eDNA) proportion (26.12%) in the extracellular polymeric substances (EPS) resulted in both higher zeta potential (-23.3 mV) and higher hydrophobicity (82.3%) for initial foulants, which induced and increased the protein proportion in the subsequent fouling layer (74.11%). Furthermore, the main composition of the EPS shifted from protein toward polysaccharide dominance in the final fouling layer. The aggregation test confirmed that eDNA was essential for foulant aggregation in the initial fouling layer, whereas ion interaction significantly affected foulant aggregation in the final fouling layer.Item Decolorization and Mineralization of Rhodamine B in Aqueous Solution with a Triple System of Cerium(IV)/H2O2/Hydroxylamine(2018) Wang, Shengli; Jia, Yanping; Zhang, Haifeng; Song, LianfaHydroxylamine (HA) can react with hydrogen peroxide (H2O2) to generate hydroxyl radical (HO•), but the reaction rate between them is very slow (2.2 × 10–4 M–1 s–1). We propose a new system to accelerate the formation of aminoxyl radical (NH2O•) by the addition of cerium [Ce(IV)] to induce the continuous production of HO• through reaction with H2O2. We also investigate the decolorization and mineralization of rhodamine B (RhB) and mechanism in the Ce(IV)/H2O2/HA system. The initial pH plays a significant role in decolorization of RhB. In this work, observation of the rapid decolorization process after 60 min revealed that approximately 80% of RhB was degraded at the initial pH of 4.0. The HO• radicals were considered as the primary reactive oxidant in the system, during its investigation through coumarin capturing, benzoic acid capturing, and radical quenching experiments. The results of the present study suggest that the addition of Ce(IV) can greatly enhance the production of HO•, and the rapid decolorization and mineralization of RhB can occur through the Ce(IV)/H2O2/HA system at acidic pH conditions.Item Metastable state of water and performance of osmotically driven membrane processes(2019) Zhang, Haifeng; Wang, Jie; Rainwater, Ken (TTU); Song, Lianfa (TTU)Semipermeable membranes play critical roles in many natural and engineering systems. The osmotic pressure is found experimentally much less effective than the hydraulic pressure to drive water through the membrane, which is commonly attributed to the internal concentration polarization (ICP) in the porous layer of the membrane. In this study, it has been shown that a necessary condition for the osmotic pressure to be effective is water continuity across the entire membrane thickness under negative pressure, i.e., the water inside the membrane remains in a metastable state. However, the metastable state of water cannot be maintained indefinitely, and cavitation will undoubtedly occur in the osmotically driven processes. Collapse of the water metastable state was suggested for the first time to be a more important and fundamental reason for the low water fluxes in the osmotically driven membrane processes.