Yu Zeng

Biosynthesis of xanthan gum by Xanthomonas campestris LRELP-1 using kitchen waste as the sole substrate

Herein, we report the production of xanthan gum by fermentation using kitchen waste as the sole substrate. The kitchen waste was firstly pretreated by a simple hydrolysis method, after which the obtained kitchen waste hydrolysate was diluted with an optimal ratio 1:2. In a 5-L fermentor, the maximum xanthan production, reducing sugar conversion and utilization rates reached 11.73g/L, 67.07% and 94.82%, respectively. The kinetics of batch fermentation was also investigated. FT-IR and XRD characterizations confirmed the fermentation product as xanthan gum. TGA analyses showed that the thermal stability of the xanthan gum obtained in this study was similar to commercial sample. The molecular weights of xanthan gum were measured to be 0.69-1.37×10(6)g/mol. The maximum pyruvate and acetyl contents in xanthan gum were 6.11% and 2.49%, respectively. This study provides a cost-effective solution for the reusing of kitchen waste and a possible low-cost approach for xanthan production.

Effect of pretreatment on the enzymatic hydrolysis of kitchen waste for xanthan production

The study was carried out to gain insight into the effect of pretreatment on enzymatic hydrolysis of kitchen waste (KW) for xanthan fermentation. Herein, various pretreatments were applied and it was found that chemical pretreatment had positive effect on the following enzymatic or overall hydrolysis process. The highest reducing sugar concentration was obtained as 51.87g/L from 2% HCl (90°C) pretreated sample, while the Kjeldahl nitrogen (KDN) concentration was 7.79g/L. Kinetic study showed that first order kinetic model was suitable to describe the enzymatic hydrolysis process. The obtained kitchen waste hydrolysate (KWH) was successfully applied for xanthan fermentation. Xanthan concentration reached 4.09-6.46g/L when KWH with 2% HCl (90°C) pretreatment was applied as medium. In comparison, a xanthan concentration of 3.25-5.57g/L was obtained from KWH without pretreatment. Therefore, pretreatment of KW using diluted acid is favorable for the overall hydrolysis process and effective for xanthan fermentation.

Bacteria-assisted preparation of nano α-Fe2O3 red pigment powders from waste ferrous sulfate.

Massive ferrous sulfate with excess sulfuric acid is produced in titanium dioxide industry each year, ending up stockpiled or in landfills as solid waste, which is hazardous to environment and in urgent demand to be recycled. In this study, waste ferrous sulfate was used as a second raw material to synthesize nano α-Fe2O3 red pigment powders with a bacteria-assisted oxidation process by Acidithiobacillus ferrooxidans. The synthesis route, mainly consisting of bio-oxidation, precipitation and calcination, was investigated by means of titration, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray fluorescence (XRF) to obtain optimum conditions. Under the optimum conditions, nano α-Fe2O3 red pigment powders contained 98.24wt.% of Fe2O3 were successfully prepared, with a morphology of spheroidal and particle size ranged from 22nm to 86nm and averaged at 45nm. Moreover, the resulting product fulfilled ISO 1248-2006, the standards of iron oxide pigments.

Effect of oxidation level on the inclusion capacity and solution stability of oxidized amylose in aqueous solution.

The oxidized amyloses with high oxidation level and carboxyl content were successfully prepared through a two-step oxidation method using hydrogen peroxide as the oxidant and copper sulfate as the catalyst. The results showed that oxidation would prevent the oxidized product to crystallize and induce depolymerization of amylose molecules. Accordingly, the helices and inclusion capacity of oxidized amylose molecules were reduced. However, the solubility of oxidized amyloses in water was highly improved due to the introduced carboxyl groups. The solution stability of oxidized amylose-guest inclusion complexes in aqueous solution was efficiently improved to a large extent. The result suggested that the two-step oxidation method was an efficient way to highly broaden the applications of amylose-guest inclusion complexes in water environment.

Ultrasonic-enhanced Fenton-like degradation of bisphenol A using a bio-synthesized schwertmannite catalyst

Schwertmannite (Sch) was synthesized by Acidithiobacillus ferrooxidans and used as Fenton-like catalyst for bisphenol A (BPA) degradation combining with ultrasonic technology (US). Physicochemical characterizations showed that the bio-synthesized Sch particles had a pompon-like morphology with high BET surface area of 92.92m2/g. The degradation reaction showed a two-stage pseudo-first-order kinetic process consisting of an induction period and a followed rapid degradation period. A synergistic effect existed between US and Sch on activating H2O2 and the synergy factor was calculated to be 2.32. The catalytic efficiency of the system was mainly affected by pH, Sch dosage and temperature, but less relevant to H2O2 concentration. Free OH radicals in the bulk solution were identified to be the dominant oxidant, which were produced by both heterogeneous and homogeneous processes. The promotional effect of US on Fenton-like degradation of BPA can be ascribed to the reasons of (1) increasing the radical generation by ultrasonic cavitation; (2) reducing the apparent activation energies of degradation reaction; (3) accelerating the dissolution of iron and (4) keeping the high surface area of catalyst by continuous surface cleaning. Ecotoxicity tests indicated lower toxicities of intermediates than BPA. In addition, Sch exhibited high reusability in the recycle study.

Nitrate concentration-shift cultivation to enhance protein content of heterotrophic microalga Chlorella vulgaris: Over-compensation strategy

Protein production from microalgae requires both high cell density during cultivation and high protein content in cells. Heterotrophic microalgae can achieve high cell density, and yet are confronted with the problem of low protein content. Based on over-compensation strategy, a new concentration-shift method was proposed to cultivate heterotrophic Chlorella vulgaris, aiming to increase protein content. With a prior starvation period, microalgae utilized more nitrate and accumulated more proteins compared to one-stage cultivation. Considering the convenience of operation, nitrate-added culture was adopted for producing heterotrophic microalgae, rather than sterile centrifugal culture. Operating parameters including nitrate concentration in N-deficient medium, N-starved time and nitrate concentration in N-rich medium were optimized, which were 0.18gl-1, 38h and 2.45gl-1, respectively. Under the optimized conditions, protein content in heterotrophic Chlorella reached 44.3%. Furthermore, the heterotrophic microalga was suggested to be a potential single-cell protein source according to the amino acid composition.

Bioconversion of Welan Gum from Kitchen Waste by a Two-Step Enzymatic Hydrolysis Pretreatment

Kitchen waste (KW) is a worldwide issue, which can lead to environment pollution. Nevertheless, it is also a low-cost and sustainable resource for bio-production. Meanwhile, welan gum (WG) is one kind of the most important exopolysaccharide but with high material cost. The aim of this study was to adopt two-step enzymatic hydrolysis to improve the release and recovery of both sugar and protein in KW for subsequent WG production. As the results, the recovery rates of sugar and protein reached 81.07 and 77.38%, which were both satisfactory. After the conditions optimized in flasks, the welan fermentation was conducted in a 5-L fermentor, and the WG yield, utilization rates of reducing sugar and KDN, respectively, reached 5.57xa0gxa0L−1, 94.25% and 61.96%. Moreover, the kinetic analyses demonstrated that the WG fermentation in KWH was a partly growth-associated process. The KW was successfully treated by fermentation for the bioconversion to WG.

One-pot hydrothermal synthesis of micaceous iron oxide pigment from jarosite waste

In this study, jarosite waste was adopted as feed material for micaceous iron oxide (MIO) pigment preparation by a one-pot hydrothermal reaction. The formation of MIO started from jarosite decomposition into akaganeite (β-FeOOH) nanoparticles in alkali solution, which then recrystallized and transformed into MIO crystals under high temperature and OH− concentration. The influences of NaOH concentration and reaction temperature on MIO formation were investigated. It was found that MIO formed when NaOH concentration and reaction temperature were equal to or higher than 2xa0M and 180°C, respectively. With an increase of NaOH concentration or reaction temperature, the particle size of MIO increased, leading to darkened color of the product. Moreover, quality evaluation indicated that the synthesized MIO fulfilled the required characteristics of micaceous iron oxide pigments for paints and the international standard of ISO 10601-2007 MIO-A1.

A new approach for excess sludge reduction by manganese dioxide oxidation: performance, kinetics, and mechanism studies

A considerable amount of excess sludge, a kind of hazardous waste, is produced from the conventional wastewater treatment systems such as activated sludge process, and efficient sludge reduction processes are needed. A new chemical method for sludge reduction was proposed by using manganese dioxide as oxidant in this study. A favorable condition for sludge reduction is determined as manganese dioxide dosage of 0.165xa0gxa0g−1 wet sludge, sulfuric acid concentration of 3xa0molxa0L−1, and reduction temperature of 90xa0°C for 90xa0min, where the sludge reduction efficiency can reach 73.30%. Reaction kinetic study revealed that the sludge reduction rate was controlled by the surface chemical reaction and the reaction followed a shrinking core kinetic model with apparent activation energy of 37.76xa0kJxa0mol−1. Furthermore, reaction process analysis indicated that the sludge hydrolysis included two steps, i.e., floc destruction and microbial cell disruption. Considering the high efficiency and short treatment time, manganese dioxide oxidation is suggested to be a feasible method for disintegration of excess activated sludge.

Utilization of Waste Biomass (Kitchen Waste) Hydrolysis Residue as Adsorbent for Dye Removal: Kinetic, Equilibrium, and Thermodynamic Studies

Kitchen waste hydrolysis residue (KWHR), which is produced in the bioproduction process from kitchen waste (KW), is usually wasted with potential threats to the environment. Herein, experiments were carried out to evaluate the potential of KWHR as adsorbent for dye (methylene blue, MB) removal from aqueous solution. The adsorbent was characterized using FT-IR and SEM. Adsorption results showed that the operating variables had great effects on the removal efficiency of MB. Kinetic study indicated pseudo-second-order model was suitable to describe the adsorption process. Afterwards, the equilibrium data were well fitted by using Langmuir isotherm model, suggesting a monolayer adsorption. The Langmuir monolayer adsorption capacity was calculated to be 110.13xa0mg/g, a level comparable to some other low-cost adsorbents. It was found that the adsorption process of MB onto KWHR was spontaneous and exothermic through the estimation of thermodynamic parameters. Thus, KWHR was of great potential to be an alternative adsorbent material to improve the utilization efficiency of bioresource (KW) and lower the cost of adsorbent for color treatment.