Jing Guan

Effect of temperature variation on membrane fouling and microbial community structure in membrane bioreactor

This study aimed to investigate the effect of temperature variation on membrane fouling and microbial community in a membrane bioreactor (MBRs). The results indicated that extracellular polymer substances (EPS) and soluble microbial products (SMPs) increased due to decreasing temperature, which triggered membrane fouling as evidenced by the trans-membrane pressure (TMP) increase rate. Moreover, fluorescent intensity variations in the excitation-emission matrix (EEM) fluorescence spectroscopy of SMPs were closely related to rapid increase in TMP, suggesting that they might be used to monitor SMPs variations and indicate membrane performance. In addition, 16S rRNA clone library and sequence analyses results demonstrated the predominant phyla were always Proteobacteria, Nitrospira and Bacteroidetes. However, at lower temperature, α-proteobacteria and some filamentous bacteria such as Actinobacteria, Haliscomenobacteria and Thiothrix were relatively rich. At higher temperature, Zoogloea showed its presence. Detrended correspondence analysis (DCA) and Mantel test results also demonstrated that temperature had strongly influence on microbial community.

Photo-Fenton degradation of dichloromethane for gas phase treatment

A continuous photo-Fenton process has been used for the degradation of gaseous dichloromethane (DCM). By absorbing gaseous DCM into a reactive Fenton mixture, the scrubbing and degradation processes could be completed in the one reactor. Operating with a Dark Fenton solution did not result in removal of DCM any better than simply using MilliQ water. This was because the Fe(II) quickly converted to Fe(III) but was unable to regenerate. After a short time, the Fenton process was no longer operating and the DCM quickly accumulated in the reaction solution, preventing further accumulation due to a decreasing concentration gradient in the reactive solution. However, by using UV light and increasing the retention time from 20 to 50 s, there was sufficient time for the reactive solution to regenerate and continuous operation could achieve at least 65% removal of DCM from the gaseous phase at ambient temperature.

COMPARISON OF THE REACTIVITY OF NANOSIZED ZERO-VALENT IRON (nZVI) PARTICLES PRODUCED BY BOROHYDRIDE AND DITHIONITE REDUCTION OF IRON SALTS

Dithionite can be used to reduce Fe(II) and produce nanoscale zero-valent iron (nZVI) under conditions of high pH and in the absence of oxygen. The nZVI is coprecipitated with a sulfite hydrate in a thin platelet. The nanoparticles formed are not pure iron but this feature does not appear to affect their degradation performance under air or N2 gas conditions. The efficiency of trichloroethylene (TCE) degradation, when one is employing nanoparticles manufactured using dithionite (nZVIS2O4), is similar to if not slightly better than that of the more conventional borohydride procedure (nZVIBH4). The other advantages of the dithionite method are that (i) it uses a less expensive and widely available reducing agent, and (ii) there is no production of potentially explosive hydrogen gas. Oxidation of benzoic acid using the nZVIS2O4 particles results in different byproducts than those produced when nZVIBH4 particles are used. The low oxidant yield based on hydroxybenzoic acid generation is offset by the production of higher concentrations of phenol. The high concentration of phenol compared to hydroxybenzoic acids suggests that OH• addition is not the primary oxidation pathway when one is using the nZVIS2O4 particles. It is proposed that sulfate radicals () are produced as a result of hydroxyl radical attack on the sulfite matrix surrounding the nZVIS2O4 particles, with these radicals oxidizing benzoic acid via electron transfer reactions rather than addition reactions.

Optimization of membrane unit location in a full-scale membrane bioreactor using computational fluid dynamics

The location of membrane units in the membrane tank is a key factor in the construction of a full-scale membrane bioreactor (MBR), as it would greatly affect the hydrodynamics in the tank, which could in turn affect the membrane fouling rate while running. Yet, in most cases, these units were empirically installed in tanks, no theory guides were currently available for the design of a proper location. In this study, the hydrodynamics in the membrane tank of a full-scale MBR was simulated using computational fluid dynamics (CFD). Five indexes (iLu, iLa, iLb, iLint, iLw) were used to indicate the unit location, and each of them was discussed for their individual impact on the risk water velocity (v0.05) in the membrane unit region. An optimal design with all the indexes equaling 0.6 was proposed, and was found to have a promotion of 146.9% for v0.05.

Role of adsorption in combined membrane fouling by biopolymers coexisting with inorganic particles

This study was conducted in order to obtain a better understanding of the combined fouling by biopolymers coexisting with inorganic particles from the aspects of fouling index, fouling layer structure and biopolymer-particle interactions. Calcium alginate was used as the model biopolymer and Fe2O3, Al2O3, kaolin, and SiO2 were used as model inorganic particles. Results showed that the combined fouling differed greatly among the four types of inorganic particles. The differences were attributed particularly to the different adsorption capacities for calcium alginate by the particles with this capacity decreasing in the order of Fe2O3, Al2O3, kaolin and SiO2. Particle size measurement and electron microscopic observation indicated the formation of agglomerates between calcium alginate and those inorganic particles exhibiting strong adsorption capacity. A structure was proposed for the combined fouling layer comprised of a backbone cake layer of alginate-inorganic particle agglomerates with the pores partially filled with discontinuous calcium alginate gels. The filterability of the fouling layer was primarily determined by the abundance of the gels. The strength of physical interaction between calcium alginate and each type of inorganic particle was calculated from the respective surface energies and zeta potentials. Calculation results showed that the extent of physical interaction increased in the order of Al2O3, Fe2O3, kaolin and SiO2, with this order differing from that of adsorption capacity. Chemical interactions may also play an important role in the adsorption of alginate and the consequent combined fouling. High-resolution XPS scans revealed a slight shift of electron binding energies when alginate was adsorbed.