Qunhui Wang

Isolation, identification of sludge-lysing strain and its utilization in thermophilic aerobic digestion for waste activated sludge

A strain of sludge-lysing bacteria was isolated from waste activated sludge (WAS) in this study. The result of 16S rRNA gene analysis demonstrated that it was a species of new genus Brevibacillus (named Brevibacillus sp. KH3). The strain could release the protease with molecule weight of about 40 kDa which could enhance the efficiency of sludge thermophilic aerobic digestion. During the sterilized sludge digestion experiment inoculated with Brevibacillus sp. KH3, the maximum protease activity was 0.41 U/ml at pH 8 and 50 degrees C, and maximum TSS removal ratio achieved 32.8% after 120 h digestion at pH 8 and 50 degrees C. In the case of un-sterilized sludge digestion inoculated with Brevibacillus sp. KH3, TSS removal ratio in inoculated-group was 54.8%, increasing at 11.86% compared with un-inoculation (46.2%). The result demonstrated that inoculation of Brevibacillus sp. KH3 could help to degrade the EPS and promote the collapse of cells and inhibit the growth of certain kinds of microorganisms. It indicated that Brevibacillus sp. KH3 strain had a high potential to enhance WAS-degradation efficiency in thermophilic aerobic digestion.

Recent advances to improve fermentative butanol production: Genetic engineering and fermentation technology

Butanol has recently attracted attention as an alternative biofuel because of its various advantages over other biofuels. Many researchers have focused on butanol fermentation with renewable and sustainable resources, especially lignocellulosic materials, which has provided significant progress in butanol fermentation. However, there are still some drawbacks in butanol fermentation in terms of low butanol concentration and productivity, high cost of feedstock and product inhibition, which makes butanol fermentation less competitive than the production of other biofuels. These hurdles are being resolved in several ways. Genetic engineering is now available for improving butanol yield and butanol ratio through overexpression, knock out/down, and insertion of genes encoding key enzymes in the metabolic pathway of butanol fermentation. In addition, there are also many strategies to improve fermentation technology, such as multi-stage continuous fermentation, continuous fermentation integrated with immobilization and cell recycling, and the inclusion of additional organic acids or electron carriers to change metabolic flux. This review focuses on the most recent advances in butanol fermentation especially from the perspectives of genetic engineering and fermentation technology.

Continuous butanol fermentation from xylose with high cell density by cell recycling system

A continuous butanol production system with high-density Clostridium saccharoperbutylacetonicum N1-4 generated by cell recycling was established to examine the characteristics of butanol fermentation from xylose. In continuous culture without cell recycling, cell washout was avoided by maintaining pH>5.6 at a dilution rate of 0.26 h(-1), indicating pH control was critical to this experiment. Subsequently, continuous culture with cell recycling increased cell concentration to 17.4 g L(-1), which increased butanol productivity to 1.20 g L(-1) h(-1) at a dilution rate of 0.26 h(-1) from 0.529 g L(-1) h(-1) without cell recycling. The effect of dilution rates on butanol production was also investigated in continuous culture with cell recycling. Maximum butanol productivity (3.32 g L(-1) h(-1)) was observed at a dilution rate of 0.78 h(-1), approximately 6-fold higher than observed in continuous culture without cell recycling (0.529 g L(-1) h(-1)).

Effects of water-washing pretreatment on bioleaching of heavy metals from municipal solid waste incinerator fly ash

Previous studies demonstrated that the bioleaching of municipal solid waste incinerator fly ash by Aspergillus niger was an efficient green technology for heavy metals removal, however, it demanded a long operational period. In this study, water-washing was used as a fly ash pretreatment before the bioleaching process (one-step and two-step). This pretreatment extracted 50.6% of K, 41.1% of Na, 5.2% of Ca and 1% of Cr from the fly ash. Due to the dissolution of alkali chlorides which hold particles together, fly ash particles were smashed into smaller granules by the hydraulic flushing action caused by vibration. After the pretreatment, the lag phase and bioleaching period were reduced by 45 and 30%, respectively, in one-step bioleaching of 1% (w/v) fly ash. Meanwhile, the metals extraction yield both in one-step and two-step bioleaching was increased markedly, e.g. in two-step bioleaching, 96% Cd, 91% Mn, 73% Pb, 68% Zn, 35% Cr and 30% Fe was extracted from 1% water-washed fly ash, respectively. The reduction of the bioleaching period and improvement of metals extraction yield will likely allow the practical application of the bioleaching technology for heavy metals removal from fly ash.

Heavy metals extraction from municipal solid waste incineration fly ash using adapted metal tolerant Aspergillus niger.

This study focused on the adaptation of Aspergillus niger tolerating high concentration of heavy metals for bioleaching of fly ash. The Plackett-Burman design indicated that Al and Fe inhibited the growth of A. niger (AS 3.879 and AS 3.40) significantly. The single metal (Al and Fe) and multi-metals adapted AS 3.879 strain tolerated up to 3500 mg/L Al, 700 mg/L Fe, and 3208.1mg/L multi-metals, respectively. The order of metal extraction yield in two-step bioleaching of 60 and 70 g/L fly ash using Al adapted, multi-metals adapted and un-adapted AS 3.879 strains was as follows: multi-metals adapted>Al adapted>un-adapted. The multi-metals adapted strain grew with up to 70 g/L fly ash and secreted 256 mmol/L organic acids after 288 h, where 87.4% Cd, 64.8% Mn, 49.4% Zn and 45.9% Pb were dissolved. The extracted metals in TCLP test of the bioleached fly ash by multi-metals adapted strain were under the regulated levels in China.

Optimization of the medium and process parameters for ethanol production from kitchen garbage by Zymomonas mobilis.

Plackett-Burman design was employed to screen 13 parameters for ethanol production from kitchen garbage by Zymomonas mobilis in simultaneous saccharification and fermentation. The parameters were seven enzymes for the fermentation, four kinds of nutrition salts, and two physical-chemical parameters. Only the protease and glucoamylase were determined to be significantly affecting factors for ethanol production. As a follow-up, a single factor experiment was carried out to determine the optimum usage of these two enzymes. They both showed the optimum effect at the usage of 100 U/g. Then the optimization for physical-chemical parameters during the fermentation were determined as follows: the solid to liquid ratio was 1:0.5, the initial pH 5, the incubation temperature 35°C, the inoculum size 10%, the culture time 40 h, and the corresponding ethanol yield was 53.40 g/L.

A comprehensive study on activated carbon prepared from spent shiitake substrate via pyrolysis with ZnCl2

Activated carbon was produced from spent shiitake substrate (SSS) via ZnCl2 activation. The product was studied by scanning electron microscopy (SEM), N2-adsorption, Fourier transform infrared spectroscopy and X-ray diffraction (XRD), and its adsorptive behavior was quantified using methylene blue. The pyrolysis of SSS with ZnCl2 was investigated by thermogravimetric analysis, XRD, SEM and energy dispersive X-ray spectrometry. Pyrolysis kinetic was analyzed via Coats–Redfern method. Experimental results demonstrated that the product had surface area of 1,743xa0m2xa0g−1 and total pore volume of 0.930xa0cm3xa0g−1. The adsorption equilibrium data followed Langmuir isotherm model with a monolayer adsorption capacity of 408.16xa0mgxa0g−1, and pseudo-second-order kinetic model better described the adsorption kinetic. The adsorption mechanism was well described by the intraparticle diffusion model. SSS can transform into a plastic phase during activation, and zinc oxide chloride hydrate (Zn2OCl2·2H2O) was formed above 260xa0°C. The diffusion of the ZnCl2 gas generated from the decomposition of Zn2OCl2·2H2O around 500xa0°C was responsible for the porosity development. ZnO was the main zinc-containing matter in the carbon at high pyrolysis temperatures. With the addition of ZnCl2, the activation energy of the pyrolysis of the lignocellulose structure in SSS was reduced to 12.27xa0kJxa0mol−1.

Stillage reflux in food waste ethanol fermentation and its by-product accumulation

Raw materials and pollution control are key issues for the ethanol fermentation industry. To address these concerns, food waste was selected as fermentation substrate, and stillage reflux was carried out in this study. Reflux was used seven times during fermentation. Corresponding ethanol and reducing sugar were detected. Accumulation of by-products, such as organic acid, sodium chloride, and glycerol, was investigated. Lactic acid was observed to accumulate up to 120g/L, and sodium chloride reached 0.14mol/L. Other by-products did not accumulate. The first five cycles of reflux increased ethanol concentration, which prolonged fermentation time. Further increases in reflux time negatively influenced ethanol fermentation. Single-factor analysis with lactic acid and sodium chloride demonstrated that both factors affected ethanol fermentation, but lactic acid induced more effects.

Metabolic analysis of butanol production from acetate in Clostridium saccharoperbutylacetonicum N1-4 using 13C tracer experiments

During acetone–butanol–ethanol (ABE) fermentation by clostridia, acetate is reutilised for butanol production. In this study, we investigated the characteristics of ABE production from acetate and analysed the metabolism of exogenously added acetate by Clostridium saccharoperbutylacetonicum N1-4. Supplementation of 4 g L−1 exogenous acetate, to media containing glucose, increased not only concentrations of butanol (48.3%) and acetone (90.5%), but also the ratio of acetone to butanol (27.1%), which suggested that acetate addition altered the metabolic flux. Acetate could not be metabolised in the absence of glucose, thus glycolysis appeared to be necessary for acetate utilisation. In order to clarify the metabolism of exogenous acetate, 13C tracer experiments were performed by supplementing [1,2-13C2] acetate in a culture broth. Based on the results of gas chromatography-mass spectroscopy analysis, we first confirmed both butanol and acetone formation from acetate. Further, the acetate-to-butanol efficiency will significantly decrease when more acetate than 2–4 g L−1 is added to the fermentation, while acetate-to-acetone efficiency may remain high (up to a ratio of 2 mol acetate per 1 mol glucose fed). Moreover, the culture supplemented with acetate exhibited an increase in conversion efficiency of glucose to butanol and acetone, from 0.196% to 19.5% and from 0 to 7.64%, respectively, even during acidogenesis. Thus, we first revealed quantitatively that acetate addition induced solvent production during the early growth phase, and increased metabolic flux to acetone and butanol production from both acetate and glucose.

High acetone–butanol–ethanol production in pH-stat co-feeding of acetate and glucose

We previously reported the metabolic analysis of butanol and acetone production from exogenous acetate by (13)C tracer experiments (Gao etxa0al., RSC Adv., 5, 8486-8495, 2015). To clarify the influence of acetate on acetone-butanol-ethanol (ABE) production, we first performed an enzyme assay in Clostridium saccharoperbutylacetonicum N1-4. Acetate addition was found to drastically increase the activities of key enzymes involved in the acetate uptake (phosphate acetyltransferase and CoA transferase), acetone formation (acetoacetate decarboxylase), and butanol formation (butanol dehydrogenase) pathways. Subsequently, supplementation of acetate during acidogenesis and early solventogenesis resulted in a significant increase in ABE production. To establish an efficient ABE production system using acetate as a co-substrate, several shot strategies were investigated in batch culture. Batch cultures with two substrate shots without pH control produced 14.20xa0g/L butanol and 23.27xa0g/L ABE with a maximum specific butanol production rate of 0.26xa0g/(gxa0h). Furthermore, pH-controlled (at pH 5.5) batch cultures with two substrate shots resulted in not only improved acetate consumption but also a further increase in ABE production. Finally, we obtained 15.13xa0g/L butanol and 24.37xa0g/L ABE at the high specific butanol production rate of 0.34xa0g/(gxa0h) using pH-stat co-feeding method. Thus, in this study, we established a high ABE production system using glucose and acetate as co-substrates in a pH-stat co-feeding system with C.xa0saccharoperbutylacetonicum N1-4.