Effect of propionic acid on citric acid fermentation in an integrated citric acid–methane fermentation process

In this study, an integrated citric acid-methane fermentation process was established to solve the problem of wastewater treatment in citric acid production. Citric acid wastewater was treated through anaerobic digestion and then the anaerobic digestion effluent (ADE) was further treated and recycled for the next batch citric acid fermentation. This process could eliminate wastewater discharge and reduce water resource consumption. Propionic acid was found in the ADE and its concentration continually increased in recycling. Effect of propionic acid on citric acid fermentation was investigated, and results indicated that influence of propionic acid on citric acid fermentation was contributed to the undissociated form. Citric acid fermentation was inhibited when the concentration of propionic acid was above 2, 4, and 6 mM in initial pH 4.0, 4.5 and, 5.0, respectively. However, low concentration of propionic acid could promote isomaltase activity which converted more isomaltose to available sugar, thereby increasing citric acid production. High concentration of propionic acid could influence the vitality of cell and prolong the lag phase, causing large amount of glucose still remaining in medium at the end of fermentation and decreasing citric acid production.     

White-rot fungus <Emphasis Type="Italic">Ganoderma</Emphasis> sp.En3 had a strong ability to decolorize and tolerate the anthraquinone,indigo and triphenylmethane dye with high concentrations

The ability of the white-rot fungus Ganoderma sp.En3 to decolorize different kinds of dyes widely applied in the textile and dyeing industry, including the anthraquinone dye Remazol Brilliant Blue R (RBBR), indigo dye indigo carmine and triphenylmethane dye methyl green, was evaluated in this study. Ganoderma sp.En3 had a strong capability of decolorizing high concentrations of RBBR, indigo carmine and methyl green. Obvious reduction of Chemical Oxygen Demand was observed after decolorization of different dyes. Ganoderma sp.En3 had a strong ability to tolerate RBBR, indigo carmine and methyl green with high concentrations. High concentrations of RBBR, indigo carmine and methyl green could also be efficiently decolorized by the crude enzyme of Ganoderma sp.En3. Different redox mediators such as syringaldehyde, acetosyringone and acetovanillone could enhance the decolorization capability for higher concentration of indigo carmine and methyl green. Different metal ions had little effect on the ability of the crude enzyme to decolorize indigo carmine and methyl green. Our study suggested that Ganoderma sp.En3 had a strong capability for decolorizing and tolerating high concentrations of different types of dyes such as RBBR, indigo carmine and methyl green.     

Enzymatic formation of carbohydrate rings catalyzed by single-walled carbon nanotubes

Macrocyclic carbohydrate rings were formed via enzymatic reactions around single-walled carbon nanotubes (SWNTs) as a catalyst. Cyclodextrin glucanotransferase, starch substrate and SWNTs were reacted in buffer solution to yield cyclodextrin (CD) rings wrapped around individual SWNTs. Atomic force microscopy showed the resulting complexes to be rings of 12–50 nm in diameter, which were highly soluble and dispersed in aqueous solution. They were further characterized by Raman and Fourier transform infrared spectroscopy and molecular simulation using density functional theory calculation. In the absence of SWNT, hydrogen bonding between glucose units determines the structure of maltose (the precursor of CD) and produces the curvature along the glucose chain. Wrapping SWNT along the short axis was preferred with curvature in the presence of SWNTs and with the hydrophobic interactions between the SWNTs and CD molecules. This synthetic approach may be useful for the functionalization of carbon nanotubes for development of nanostructures.     

Cloning and characterization of two distinct water-forming NADH oxidases from <Emphasis Type="Italic">Lactobacillus pentosus</Emphasis> for the regeneration of NAD

Two uncharacterized nicotinamide adenine dinucleotide (NADH) oxidases (named as LpNox1, LpNox2) from Lactobacillus pentosus ATCC 8041 were cloned and overexpressed in Escherichia coli BL21 (DE3). The sequence analysis revealed that the two enzymes are water-forming Noxs with 64 % and 52 % identity to LbNox from Lactobacillus brevis DSM 20054. The optimal pH and temperature of the purified LpNox1 and LpNox2 were 7.0 and 8.0 and 35 and 40 °C, respectively, with K _M of 99.0 μM (LpNox1) and 27.6 μM (LpNox2), and yielding catalytic efficiency k _cat/K _M of 1.0 and 0.2 μM^?1 s^?1, respectively. Heat inactivation studies revealed that the two enzymes are relatively instable. The application of LpNox1 for the regeneration of NAD⁺ was demonstrated by coupling with a glycerol dehydrogenase-catalyzed oxidation of glycerol to 1,3-dihydroxyacetone. The characteristics of the LpNox1 could prove to be of interest in industrial application such as NAD⁺ regeneration in dehydrogenase-catalyzed oxidations.     

Production of butanol and isopropanol with an immobilized <Emphasis Type="Italic">Clostridium</Emphasis>

Clostridium beijerinckii optinoii is a Clostridium species that produces butanol, isopropanol and small amounts of ethanol. This study compared the performances of batch and continuous immobilized cell fermentations, investigating how media flow rates and nutritional modification affected solvent yields and productivity. In 96-h batch cultures, with 80 % of the 30 g L^?1 glucose consumed in synthetic media, solvent concentration was 9.45 g L^?1 with 66.0 % as butanol. In a continuous fermentation using immobilized C. beijerinckii optinoii cells, also with 80 % of 30 g L^?1 glucose utilization, solvent productivity increased to 1.03 g L^?1 h^?1. Solvent concentration reached 12.14 g L^?1 with 63.0 % as butanol. Adjusting the dilution rate from 0.085 to 0.050 h^?1 to allow extended residence time in column was required when glucose concentration in fresh media was increased from 30 to 50 g L^?1. When acetate was used to improve the buffer capacity in media, the solvent concentration reached 12.70 on 50 g L^?1 glucose. This continuous fermentation using immobilized cells showed technical feasibility for solvent production.     

Enhanced dewatering of waste-activated sludge by composite hydrolysis enzymes

The feasibility of composite hydrolysis enzymes in enhanced dewatering of waste-activated sludge (WAS) was verified in this study. A Pearson correlation analysis was conducted to explore the roles of different extracellular polymeric substance (EPS) fractions on WAS dewaterability. The results indicated that tightly bound EPS (TB-EPS) was released into the liquid phase consistently during enzymatic hydrolysis to form soluble EPS (S-EPS) and loosely bound EPS and that the TB-EPS content was positively correlated with the capillary suction time of WAS. A kinetic analysis was carried out to gain further insights into the kinetic variation in TB-EPS removal. It was found that TB-EPS reduction fit a first-order kinetic model and that mild temperature (25–30 °C) and a slightly acidic condition were favorable for the improvement of enzyme activity. Solid phase extraction combined with UV–Vis spectroscopy analysis was used to characterize the processes of migration and transformation of the hydrophobic (HPO), transphilic and hydrophilic (HPI) fractions in EPS during the enzymatic process. The results revealed that HPO and HPI were mainly composed of PN and PS, respectively, and that the enzymatic hydrolysis could enhance the transformation of HPI from TB-EPS to S-EPS, which was the dominant mechanism of improving WAS dewaterability.     

Predictive functional profiling using marker gene sequences and community diversity analyses of microbes in full-scale anaerobic sludge digesters

Anaerobic digestion (AD) is widely used in treating the sewage sludge, as it can reduce the amount of sludge, eliminate pathogens and produce biofuel. To enhance the operational performance and stability of anaerobic bioreactors, operational and conventional chemical data from full-scale sludge anaerobic digesters were collected over a 2-year period and summarized, and the microbial community diversity of the sludge sample was investigated at various stages of the AD process. For the purpose of distinguishing between the functional and community diversity of the microbes, Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) software was used to impute the prevalence of 16S rDNA marker gene sequences in the difference in various sludge samples. Meanwhile, a taxa analysis was also carried out to investigate the different sludge samples. The microbial community diversity analysis of one AD sludge sample showed that the most dominant bacterial genera were Saccharicrinis, Syntrophus, Anaerotruncus and Thermanaerothrix. Among archaea, acetoclastic Methanosaeta represented 56.0 %, and hydrogenotrophic Methanospirillum, Methanoculleus, Methanothermus and Methanolinea accounted for 41.3 % of all methanogens. The taxa, genetic and functional prediction analyses of the feedstock and AD sludge samples suggested great community diversity differences between them. The taxa of bacteria in two AD sludge samples were considerably different, but the abundances of the functional KEGG pathways took on similar levels. The numbers of identified pathogens were significantly lower in the digested sludge than in the feedstock, but the PICRUSt results showed the difference in “human diseases” abundances in the level-1 pathway between the two sludge samples was small.     

The influence of polymeric membrane gas spargers on hydrodynamics and mass transfer in bubble column bioreactors

Gas sparging performances of a flat sheet and tubular polymeric membranes were investigated in 3.1 m bubble column bioreactor operated in a semi batch mode. Air–water and air–CMC (Carboxymethyl cellulose) solutions of 0.5, 0.75 and 1.0 % w/w were used as interacting gas–liquid mediums. CMC solutions were employed in the study to simulate rheological properties of bioreactor broth. Gas holdup, bubble size distribution, interfacial area and gas–liquid mass transfer were studied in the homogeneous bubbly flow hydrodynamic regime with superficial gas velocity (U _G) range of 0.0004–0.0025 m/s. The study indicated that the tubular membrane sparger produced the highest gas holdup and densely populated fine bubbles with narrow size distribution. An increase in liquid viscosity promoted a shift in bubble size distribution to large stable bubbles and smaller specific interfacial area. The tubular membrane sparger achieved greater interfacial area and an enhanced overall mass transfer coefficient (K _La) by a factor of 1.2–1.9 compared to the flat sheet membrane.     

Optimization of aeration for biodiesel production by <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis> grown in municipal wastewater

Despite the significant breakthroughs in research on microalgae as a feedstock for biodiesel, its production cost is still much higher than that of fossil diesel. One possible solution to overcome this problem is to optimize algal growth and lipid production in wastewater. The present study examines the optimization of pretreatment of municipal wastewater and aeration conditions in order to enhance the lipid productivity of Scenedesmus obliquus. Results showed that no significant differences were recorded in lipid productivity of S. obliquus grown in primary settled or sterilized municipal wastewater; however, ultrasound pretreatment of wastewater significantly decreased the lipid production. Whereas, aeration rates of 0.2 vvm significantly increased lipid content by 51 %, with respect to the non-aerated culture, which resulted in maximum lipid productivity (32.5 mg L^?1 day^?1). Furthermore, aeration enrichment by 2 % CO₂ resulted in increase of lipid productivity by 46 % over the CO₂ non-enriched aerated culture. Fatty acid profile showed that optimized aeration significantly enhanced monounsaturated fatty acid production, composed mainly of C18:1, by 1.8 times over the non-aerated S. obliquus culture with insignificant changes in polyunsaturated fatty acid proportion; suggesting better biodiesel characteristics for the optimized culture.     

Releasing intracellular product to prepare whole cell biocatalyst for biosynthesis of <Emphasis Type="Italic">Monascus</Emphasis> pigments in water–edible oil two-phase system

Selective releasing intracellular product in Triton X-100 micelle aqueous solution to prepare whole cell biocatalyst is a novel strategy for biosynthesis of Monascus pigments, in which cell suspension culture exhibits some advantages comparing with the corresponding growing cell submerged culture. In the present work, the nonionic surfactant Triton X-100 was successfully replaced by edible plant oils for releasing intracellular Monascus pigments. High concentration of Monascus pigments (with absorbance nearly 710 AU at 470 nm in the oil phase, normalized to the aqueous phase volume approximately 142 AU) was achieved by cell suspension culture in peanut oil–water two-phase system. Furthermore, the utilization of edible oil as extractant also fulfills the demand for application of Monascus pigments as natural food colorant.