Zisheng Zhang

Applications of Photocatalytic Disinfection

Due to the superior ability of photocatalysis to inactivate a wide range of harmful microorganisms, it is being examined as a viable alternative to traditional disinfection methods such as chlorination, which can produce harmful byproducts. Photocatalysis is a versatile and effective process that can be adapted for use in many applications for disinfection in both air and water matrices. Additionally, photocatalytic surfaces are being developed and tested for use in the context of “self-disinfecting” materials. Studies on the photocatalytic technique for disinfection demonstrate this process to have potential for widespread applications in indoor air and environmental health, biological, and medical applications, laboratory and hospital applications, pharmaceutical and food industry, plant protection applications, wastewater and effluents treatment, and drinking water disinfection. Studies on photocatalytic disinfection using a variety of techniques and test organisms are reviewed, with an emphasis on the end-use application of developed technologies and methods.

Advancements and future directions in enzyme technology for biomass conversion.

Enzymatic hydrolysis of pre-treated lignocellulosic biomass is an ideal alternative to acid hydrolysis for bio-ethanol production, limited primarily by pre-treatment requirements and economic considerations arising from enzyme production costs and specific activities. The quest for cheaper and better enzymes has prompted years of bio-prospecting, strain optimization through genetic engineering, enzyme characterization for simple and complex lignocellulosic feedstock, and the development of pre-treatment strategies to mitigate inhibitory effects. The recent shift to systematic characterizations of de novo mixtures of purified proteins is a promising indicator of maturation within this field of study, facilitating progression towards feedstock assay-based rapid enzyme mixture optimization. It is imperative that international standards be developed to enable meaningful comparisons between these studies and the construction of a database of enzymatic activities and kinetics, aspects of which are explored here-in. Complementary efforts to improve the economic viability of enzymatic hydrolysis through process integration and reactor design are also considered, where membrane-confinement shows significant promise despite the associated technological challenges. Significant advancements in enzyme technology towards the economic conversion of lignocellulosic biomass should be expected within the next few years as systematic research in enzyme activities conforms to that of traditional reaction engineering.

Lipase immobilized by modification-coupled and adsorption-cross-linking methods: A comparative study.

Candida antarctica lipase was immobilized by an adsorption and cross-linking method with NW-ZT2 and by modification-coupled method with a silica-PEG gel. The final product silica-PEG-lipase was confirmed by IR spectra. The optimum pH value, the optimum temperature, the thermo-stabilities and operational stabilities for two kinds of immobilized lipase were also determined. Results show that the silica-PEG-lipase gel was superior to the lipase immobilized by adsorption and cross-linking, however both are viable for use in transesterification reactions.

Control of protozoa contamination and lipid accumulation in Neochloris oleoabundans culture: Effects of pH and dissolved inorganic carbon

Combined effects of pH (i.e., 7.5, 8.5, and 9.5) and bicarbonate (i.e., 0, 80 and 160mM NaHCO3) on lipid accumulation and on biological contaminant viability in a protozoa-contaminated culture of the freshwater microalga Neochloris oleoabundans were studied. Cultures grown in the media containing 160mM NaHCO3 at pH 9.5 obtained the highest biomass concentration (DCWmax=1.32g/L), lipid content (LC=327mg/g), which corresponded to a lipid productivity of 56mg/(L·d), and the culture was protozoa free one day after inoculation. Other cultures, 160mM NaHCO3 at pH 8.5 (DCWmax=1.32g/L, LC=223mg/g), and 80mM NaHCO3 at pH 9.5 (DCWmax=1.25g/L, LC=264mg/g) could delay protozoan growth, but not inhibit it completely. These results suggest 160mM NaHCO3 or slightly above at pH levels of 8.5-9.5 may be used in outdoor cultivation processes of freshwater N. oleoabundans to control protozoa contamination while maintain a high lipid content.

Synthesis and characterization of a core–shell BiVO4@g-C3N4 photo-catalyst with enhanced photocatalytic activity under visible light irradiation

Novel core–shell structured ellipsoid-like BiVO4@g-C3N4 composites, with different amounts of g-C3N4, have been successfully prepared by a simple hydrothermal-chemisorption method. Their performance as photocatalysts was systematically evaluated during RhB degradation under visible light irradiation. The composite with 7 wt% g-C3N4 was found to be 7 times more efficient as a photocatalyst than pristine BiVO4. Its core–shell structure and activity were also found to be highly stable after it was used for 5 times in RhB degradation. The new composites were examined by various characterization techniques. The core–shell structure enhanced the contact area between the BiVO4 core and g-C3N4 nano-sheet shell, which provided more active sites and strengthened the chemical band interaction. The thin g-C3N4 nano-sheets reduced the charge carrier transfer distance, which further suppressed the recombination of the photo-induced electron–hole pairs and therefore enhanced the photocatalytic activity of the composites. A reaction mechanism of the photocatalytic RhB degradation was proposed and discussed in detail.

Engineering strategies for enhanced production of protein and bio-products in Pichia pastoris: A review

Pichia pastoris has been recognized as one of the most industrially important hosts for heterologous protein production. Despite its high protein productivity, the optimization of P. pastoris cultivation is still imperative due to strain- and product-specific challenges such as promoter strength, methanol utilization type and oxygen demand. To address the issues, strategies involving genetic and process engineering have been employed. Optimization of codon usage and gene dosage, as well as engineering of promoters, protein secretion pathways and methanol metabolic pathways have proved beneficial to innate protein expression levels. Large-scale production of proteins via high cell density fermentation additionally relies on the optimization of process parameters including methanol feed rate, induction temperature and specific growth rate. Recent progress related to the enhanced production of proteins in P. pastoris via various genetic engineering and cultivation strategies are reviewed. Insight into the regulation of the P. pastoris alcohol oxidase 1 (AOX1) promoter and the development of methanol-free systems are highlighted. Novel cultivation strategies such as mixed substrate feeding are discussed. Recent advances regarding substrate and product monitoring techniques are also summarized. Application of P. pastoris to the production of biodiesel and other value-added products via metabolic engineering are also reviewed. P. pastoris is becoming an indispensable platform through the use of these combined engineering strategies.

Cultivation of Neochloris oleoabundans in bubble column photobioreactor with or without localized deoxygenation

This study evaluated long-term non-sterile cultivation of freshwater green alga Neochloris oleoabundans in a 15-liter bubble column photobioreactor (BCPBR) and the effects of a membrane-based localized oxygen remover (LOR) on deoxygenation, cell growth, and lipid production of N. oleoabundans. Batch and continuous cultivations were carried out under non-sterile conditions for 53 days with no detectable protozoa or other biological contaminants, indicating successful long-term contamination-free cultivation. The results show that the BCPBR equipped with LOR (BCPBR-LOR) has enhanced deoxygenation efficiency and were able to maintain dissolved oxygen at a level of around 120% air saturation, which was 32% lower than that of the conventional BCPBR, which had no LOR. While similar biomass concentration and productivity were obtained in both systems, significantly higher lipid cell content and lipid productivity of microalgae were obtained in the latter, which was attributed to the low dO2 in culture due to enhanced deoxygenation efficiency of BCPBR-LOR.

Effects of glucose and nitrogen source concentration on batch fermentation kinetics of Lactococcus lactis under hemin-stimulated respirative condition

Analytical solutions to the ordinary differential equations governing the kinetics of cell growth, substrate utilization, and product formation of batch fermentation processes were derived and used to study the kinetics of the hemin‐stimulated respiratory cultivation of Lactococcus lactis at varied initial glucose concentrations and nitrogen source concentrations. Studies revealed that initial glucose concentration varying in the range of 60 to 90 g/L had no significant substrate inhibitive effect. Furthermore, elevating the concentration of complex nitrogen sources while maintaining glucose concentration at 60% led to a high final biomass concentration of 6.6 g/L, substantially higher than that obtained with the basic medium, which was 4.1 g/L.

Preparation of Hierarchical BiOBr Microspheres for Visible Light-Induced Photocatalytic Detoxification and Disinfection

Photocatalytic degradation is a promising alternative to traditional wastewater treatment methods. Recently developed visible light-responsive photocatalyst, BiOBr, has attracted extensive attentions. Hereby, a detailed investigation of application of BiOBr to bacterial inactivation and organic pollutants degradation is reported. Hydrothermal catalyst was prepared using template-free method. While, for solvothermal synthesis, CTAB was used as a template. Results indicate a higher photocatalytic activity by the solvothermally prepared catalyst. Solvothermally prepared BiOBr exhibited high photocatalytic activities in both water detoxification and disinfection.

Palladium nanoparticles and rGO co-modified BiVO 4 with greatly improved visible light-induced photocatalytic activity

A ternary composite, Pd-rGO-BiVO4, was fabricated with reduced graphene oxide (rGO) and palladium nanoparticles decorated on the surface of BiVO4. As-prepared samples were tested for the photocatalytic degradation of phenol under visible light irradiation. Enhancement was observed for the ternary structure, merits of which may be as follows: 1) rGO wrapped BiVO4 facilitated the photogenerated electrons transfer, 2) palladium nanoparticles served as electron acceptors, 3) palladium nanoparticles on the surface were capable of absorbing visible light photons. The uptake of photogenerated charge carriers would improve their separation and more oxidative species may be produced that can participate in the degradation of organics. Due to the SPR effect of palladium nanoparticles on the surface, the harvesting capacity of the photocatalyst to absorb visible light photons was increased, and thus its photocatalytic activity was improved. It should be noted that phenol was more easily adsorbed by rGO due to the π-π interaction between rGO and phenol, which also contributed to the enhancement in the photocatalytic activity. This work provides new evidence to confirm the advances of ternary structures applied in the photocatalytic removal of phenolic compounds in water under visible light irradiation.