Yinhua Wan

Enzyme adsorption and recycling during hydrolysis of wheat straw lignocellulose

The objective of this research was to investigate cellulase adsorption and recycling during enzymatic hydrolysis of two differently pretreated wheat straws (WS). Dilute acid treated WS showed lower hydrolysis yield of polysaccharides fraction and adsorbed more cellulase with hydrolyzed residue than dilute alkali treated sample. Four methods capable of recovering and recycling the enzyme bound to the residual substrate and the enzyme free in solution were used for three consecutive rounds of hydrolysis to compare their recycling efficiencies. Compared to the absorption recycling method, ultrafiltration recycling method possessed the capacity to retain β-glucosidase, thereby avoiding the supplementation of fresh β-glucosidase in subsequent rounds of hydrolysis. It was found that whatever recycling method was used, better recycling results were obtained for dilute alkali treated substrate than for dilute acid treated substrate. These results suggested that the great difference in the lignin content between acid treated WS and alkali treated WS would significantly affect enzymatic hydrolysis, cellulase adsorption and cellulase recycling efficiencies.

A two-stage ultrafiltration and nanofiltration process for recycling dairy wastewater.

A two-stage ultrafiltration and nanofiltration (UF/NF) process for the treatment of model dairy wastewater was investigated to recycle nutrients and water from the wastewater. Ultracel PLGC and NF270 membranes were found to be the most suitable for this purpose. In the first stage, protein and lipid were concentrated by the Ultracel PLGC UF membrane and could be used for algae cultivation to produce biodiesel and biofuel, and the permeate from UF was concentrated by the NF270 membrane in the second stage to obtain lactose in retentate and reusable water in permeate, while the NF retentate could be recycled for anaerobic digestion to produce biogas. With this approach, most of dairy wastewater could be recycled to produce reusable water and substrates for bioenergy production. Compared with the single NF process, this two-stage UF/NF process had a higher efficiency and less membrane fouling.

Separation of furfural from monosaccharides by nanofiltration.

Furfural, found in the lignocellulosic prehydrolyzates at high concentration, is a strong inhibitor of growth and ethanol fermentation of Saccharomyces cerevisiae. Removal of furfural and concentration of monosaccharides were investigated by using two commercial nanofiltraton (NF) membranes with synthetic glucose-xylose-furfural solution as model. The effects of main operating parameters such as feed pH, permeation flux, temperature and feed concentration on the rejections of the three solutes, were studied. Results showed that rejections of the three solutes decreased with increasing feed pH and temperature, and increased with increasing permeation flux for both membranes. The concentrations of the three solutes had interaction effect on the rejection of furfural by NF90 membrane and rejections of the three solutes by NF270 membrane. Furthermore, the effects of two filtration modes, concentration and diafiltration, on the separation of furfural from monosaccharides were also investigated. With the two commercial NF membranes, concentration and purification of monosaccharides in the model solution can be accomplished.

Pretreatment of wheat straw by nonionic surfactant-assisted dilute acid for enhancing enzymatic hydrolysis and ethanol production.

Pretreating wheat straw (WS) with combined use of varied sulfuric acid concentration (0-3%, w/v) and Tween 20 concentration (0-1%) was investigated in an attempt to enhance the hydrolysis and fermentability of pretreated WS. Enzymatic hydrolysis yield of glucan and xylan and ethanol production by simultaneous saccharification and fermentation (SSF) of water-insoluble solids (WIS) were significantly affected by the amount of Tween 20 added during acid pretreatment. Any further addition of Tween 20 in either hydrolysis stage or fermentation stage only led to small increase in glucan conversion and ethanol production. Determination of adsorption of cellulases during hydrolysis showed that Tween 20-assisted acid treated straw solution contained more free cellulases than individual acid treated straw solution, indicating that modification of lignin surface by Tween 20 added during pretreatment likely occurred. In addition, the effects of pretreatment conditions on overall recovery of glucose and xylose after pretreatment and enzymatic hydrolysis were also investigated.

Membrane fouling mechanism in ultrafiltration of succinic acid fermentation broth

The membrane fouling mechanism was studied in treating succinic acid fermentation broth during dead-end ultrafiltration. Different membranes were used and two models were applied to analyze the fouling mechanism. Resistance-in-series model was applied to determine the main factor that caused the operation resistance. Results indicated that most membranes tended to be fouled by cake layer or concentration polarization. Hermias model, which is composed of four individual sub-models, was used to analyze the predominant fouling mechanism. Results showed that the fouling of RC 10 kDa and PES 30 kDa was controlled by the complete blocking mechanism, while PES 100 kDa was controlled by the intermediate blocking and PES 10 kDa was controlled by cake layer. This conclusion was also proved by SEM photos. Membrane characteristics were monitored before and after ultrafiltration by AFM and goniometer. Both contact angle and roughness of most membranes increased after ultrafiltration.

An efficient process for lactic acid production from wheat straw by a newly isolated Bacillus coagulans strain IPE22.

A thermophilic lactic acid (LA) producer was isolated and identified as Bacillus coagulans strain IPE22. The strain showed remarkable capability to ferment pentose, hexose and cellobiose, and was also resistant to inhibitors from lignocellulosic hydrolysates. Based on the strains promising features, an efficient process was developed to produce LA from wheat straw. The process consisted of biomass pretreatment by dilute sulfuric acid and subsequent SSCF (simultaneous saccharification and co-fermentation), while the operations of solid-liquid separation and detoxification were avoided. Using this process, 46.12 g LA could be produced from 100g dry wheat straw with a supplement of 10 g/L corn steep liquid powder at the cellulase loading of 20 FPU (filter paper activity units)/g cellulose. The process by B. coagulans IPE22 provides an economical route to produce LA from lignocellulose.

Application of ultrafiltration and nanofiltration for recycling cellulase and concentrating glucose from enzymatic hydrolyzate of steam exploded wheat straw

Application of combined ultrafiltration (UF) and nanofiltration (NF) was examined to recycle cellulase and concentrate glucose present in lignocellulosic hydrolyzate. With PES10 membrane operated at 25.6 l/m(2) h, 73.9% of cellulase protein present in the hydrolyzate suspension could be recovered while allowing free transmission of glucose. The permeate obtained from UF was then concentrated by NF. With NF270 membrane operated at 13.3 l/m(2) h, the glucose concentration in the ultrafiltered hydrolyzate increased from 30.2 to 110.2 g/l. Recycling cellulase by UF could reduce the hydrolysis cost of lignocellulosic feedstock, while concentrating glucose by NF could improve the fermentation efficiency of lignocellulosic hydrolyzate and lower the separation and purification cost of fermentative product. Therefore, the use of UF and NF for treating lignocellulosic hydrolyzate could be a promising approach in fermentative production of bioproducts and biofuels using lignocellulosic feedstock as substrate.

Improving lactic acid productivity from wheat straw hydrolysates by membrane integrated repeated batch fermentation under non-sterilized conditions

Bacillus coagulans IPE22 was used to produce lactic acid (LA) from mixed sugar and wheat straw hydrolysates, respectively. All fermentations were conducted under non-sterilized conditions and sodium hydroxide was used as neutralizing agent to avoid the production of insoluble CaSO4. In order to eliminate the sequential utilization of mixed sugar and feedback inhibition during batch fermentation, membrane integrated repeated batch fermentation (MIRB) was used to improve LA productivity. With MIRB, a high cell density was obtained and the simultaneous fermentation of glucose, xylose and arabinose was successfully realized. The separation of LA from broth by membrane in batch fermentation also decreased feedback inhibition. MIRB was carried out using wheat straw hydrolysates (29.72 g/L glucose, 24.69 g/L xylose and 5.14 g/L arabinose) as carbon source, LA productivity was increased significantly from 1.01 g/L/h (batch 1) to 2.35 g/L/h (batch 6) by the repeated batch fermentation.

Efficient production of acetone-butanol-ethanol (ABE) from cassava by a fermentation-pervaporation coupled process

Production of acetone-butanol-ethanol (ABE) from cassava was investigated with a fermentation-pervaporation (PV) coupled process. ABE products were in situ removed from fermentation broth to alleviate the toxicity of solvent to the Clostridium acetobutylicum DP217. Compared to the batch fermentation without PV, glucose consumption rate and solvent productivity increased by 15% and 21%, respectively, in batch fermentation-PV coupled process, while in continuous fermentation-PV coupled process running for 304 h, the substrate consumption rate, solvent productivity and yield increased by 58%, 81% and 15%, reaching 2.02 g/Lh, 0.76 g/Lh and 0.38 g/g, respectively. Silicalite-1 filled polydimethylsiloxane (PDMS)/polyacrylonitrile (PAN) membrane modules ensured media recycle without significant fouling, steadily generating a highly concentrated ABE solution containing 201.8 g/L ABE with 122.4 g/L butanol. After phase separation, a final product containing 574.3g/L ABE with 501.1g/L butanol was obtained. Therefore, the fermentation-PV coupled process has the potential to decrease the cost in ABE production.

Novel membrane-based biotechnological alternative process for succinic acid production and chemical synthesis of bio-based poly (butylene succinate)

Succinic acid was produced in a novel membrane-based fermentation and separation integrated system. With this integrated system, product inhibition was alleviated by removing acids and replenishing fresh broth. High cell density maintain for a longer time from 75 to 130h and succinic acid concentration increased from 53 to 73g/L. In the developed separation process, succinic acid was crystallized at a recovery of 85-90%. The purity of the obtained succinic acid crystals reached 99.4% as found by HPLC and (1)H NMR analysis. A crystallization experiment indicated that among by-products glucose had a negative effect on succinic acid crystallization. Poly (butylene succinate) (PBS) was synthesized using the purified succinic acid and (1)H NMR analysis confirmed that the composition of the synthesized PBS is in agreement with that from petro-based succinic acid.