Design, Synthesis and Second-Order Nonlinear Optical Properties of Azobenzene-Based Polysiloxanes.

To study the effect of polymeric structures on second-order nonlinear optical properties, polysiloxanes materials based on azobenzene as chromophore have been designed and synthesized successfully. Herein, the siloxane monomer is directly bonded to azobenzene units by palladium catalysis, which avoids the influence of flexible chains on the photoelectric properties of azobenzene. According to the different positions of azobenzene units in the polymers, it is divided into side-chain, main-chain, and alternative-type polymers. The chemical structures of obtained polysiloxanes are confirmed by nuclear magnetic resonance spectra and mass spectra. Three polymers present high thermal decomposition temperatures and the medium glass transition temperatures. The effects of polymeric structures on the second-order nonlinear properties are compared. The main-chain polysiloxane possesses the highest thermal stability because of its rigid architecture. The side-chain polysiloxane shows the fastest isomerization transformation rate due to the large free volume. Besides, the alternative polysiloxane displays the best second-order nonlinear performance with second harmonic generation coefficient (d33 ) value of 47.6 pm V-1 , which is 3 times higher than the side-chain one.

Optimization of Cellulase Immobilization with Sodium Alginate-Polyethylene for Enhancement of Enzymatic Hydrolysis of Microcrystalline Cellulose Using Response Surface Methodology.

A novel method of immobilizing cellulase on sodium alginate (SA)-polyethylene glycol (PEG) enabled the cellulase to be used repeatedly. The matrix of the immobilized cellulase was detected and characterized using Fourier transform infrared spectroscopy and scanning electron microscopy. In comparison with SA-immobilized cellulase, the relative enzyme activity and immobilization rate increased by 25% and 18%, respectively. The application range of the immobilized enzyme in terms of temperature and pH was larger than that of the free enzyme, and its thermal stability increased. The immobilized enzyme was used in enzymatic hydrolysis, in which MCC was used as the substrate. The optimal conditions for enzymatic hydrolysis were as follows: the dosage of SA-PEG-immobilized cellulase was 3.55 g/g total solids of the substrate, the concentration of the substrate was 13.16%, and the pH was 5.11. In comparison with the yield of reducing sugars in the first round of hydrolysis of MCC by SA-immobilized cellulase, the yield in the hydrolysis of MCC by SA-PEG-immobilized cellulase increased by 133%. After five cycles of repeated use, the total yield of reducing sugars when MCC was hydrolyzed by SA-PEG-immobilized cellulase was similar to that achieved with free cellulase. In comparison with the free enzyme, the highest yield when the immobilized enzyme was used was 22.68%. Therefore, the immobilized cellulase exhibited high performance in enzymatic hydrolysis.

Enhancing anaerobic digestion performance and degradation of lignocellulosic components of rice straw by combined biological and chemical pretreatment.

In order to determine eco-friendly pretreatment method, the combination of different pretreatment reagents such as: CaO, ammonia solution (AS), liquid fraction of digestate (LFD), CaO-AS and CaO-LFD were used in this study. The features of physico-chemical structures and anaerobic digestion (AD) performance of rice straw were investigated using different combined biological and chemical pretreatment methods. The results showed that CaO-LFD bio-chemical pretreatment achieved the best effect among different pretreatment conditions. The removal rate of lignocellulosic components from CaO-LFD pretreated rice straw was 20.73% higher than that of the control sample. The ether and ester bonds between lignin and hemicellulose were ruptured during pretreatment. Moreover, the methane yield from CaO-LFD pretreated rice straw was 274.65 mL gVS-1, which was 57.56% more than the control. Compared with the untreated rice straw, T80 decreased by 42.86%. CaO-LFD combined pretreatment has advantages as both biological and chemical pretreatment, which complement each other to improve the degradation of the rice straw. Meantime, AD performance was improved and excellent economic viability was achieved. Therefore, this study provides sustainable insight for exploring efficient pretreatment strategy to stabilize and enhance AD performance for further application.

Serial completely stirred tank reactors for improving biogas production and substance degradation during anaerobic digestion of corn stover.

Several completely stirred tank reactors (CSTR) connected in series for anaerobic digestion of corn stover were investigated in laboratory scale. Serial anaerobic digestion systems operated at a total HRT of 40days, and distribution of HRT are 10+30days (HRT10+30d), 20+20days (HRT20+20d), and 30+10days (HRT30+10d) were compared to a conventional one-step CSTR at the same HRT of 40d. The results showed that in HRT10+30d serial system, the process became very unstable at organic load of 50gTS·L-1. The HRT20+20d and HRT30+10d serial systems improved methane production by 8.3-14.6% compared to the one-step system in all loads of 50, 70, 90gTS·L-1. The conversion rates of total solid, cellulose, and hemicellulose were increased in serial anaerobic digestion systems compared to single system. The serial systems showed more stable process performance in high organic load. HRT30+10d system showed the best biogas production and conversions among all systems.

Biomethane production and physicochemical characterization of anaerobically digested teff (Eragrostis tef) straw pretreated by sodium hydroxide.

The biogas production potential and biomethane content of teff straw through pretreatment by NaOH was investigated. Different NaOH concentrations (1%, 2%, 4% and 6%) were used for each four solid loadings (50, 65, 80 and 95 g/L). The effects of NaOH as pretreatment factor on the biodegradability of teff straw, changes in main compositions and enhancement of anaerobic digestion were analyzed. The result showed that, using 4% NaOH for pretreatment in 80 g/L solid loading produced 40.0% higher total biogas production and 48.1% higher biomethane content than the untreated sample of teff straw. Investigation of changes in chemical compositions and physical microstructure indicated that there was 4.3-22.1% total lignocellulosic compositions removal after three days pretreatment with NaOH. The results further revealed that NaOH pretreatment changed the structural compositions and lignin network, and improved biogas production from teff straw.

Improving Biomethane Production and Mass Bioconversion of Corn Stover Anaerobic Digestion by Adding NaOH Pretreatment and Trace Elements.

This research applied sodium hydroxide (NaOH) pretreatment and trace elements to improve biomethane production when using corn stover for anaerobic digestion. Full-factor experimental tests identified the best combination of trace elements with the NaOH pretreatment, indicating that the best combination was with 1.0, 0.4, and 0.4 mg·L(-1)·d(-1) of elements Fe, Co, and Ni, respectively. The cumulative biomethane production adding NaOH pretreatment and trace elements was 11,367 mL; total solid bioconversion rate was 55.7%, which was 41.8%-62.2% higher than with NaOH-pretreatment alone and 22.2%-56.3% higher than with untreated corn stover. The best combination was obtained 5-9 days shorter than T90 and maintained good system operation stability. Only a fraction of the trace elements in the best combination was present in the resulting solution; more than 85% of the total amounts added were transferred into the solid fraction. Adding 0.897 g of Fe, 0.389 g of Co, and 0.349 g of Ni satisfied anaerobic digestion needs and enhanced biological activity at the beginning of the operation. The results showed that NaOH pretreatment and adding trace elements improve corn stover biodegradability and enhance biomethane production.

Promoting anaerobic biogasification of corn stover through biological pretreatment by liquid fraction of digestate (LFD).

A new biological pretreatment method by using liquid fraction of digestate (LFD) was advanced for promoting anaerobic biogasification efficiency of corn stover. 17.6% TS content and ambient temperature was appropriate for pretreatment. The results showed that C/N ratio decreased to about 30, while total lignin, cellulose, and hemicellulose (LCH) contents were reduced by 8.1-19.4% after pretreatment. 3-days pretreatment was considered to be optimal, resulting in 70.4% more biogas production, 66.3% more biomethane yield and 41.7% shorter technical digestion time compared with the untreated stover. The reductions on VS, cellulose, and hemicellulose were increased by 22.1-35.9%, 22.3-35.4%, and 19.8-27.2% for LFD-treated stovers. The promoted anaerobic biogasification efficiency was mainly attributed to the improved biodegradability due to the pre-decomposition role of the bacteria in LFD. The method proved to be an efficient and low cost approach for producing bioenergy from corn stover, meanwhile, reducing LFD discharge and minimizing its potential pollution.

Using feature objects aided strategy to evaluate the biomethane production of food waste and corn stalk anaerobic co-digestion.

Feature objects aided strategy was used to predict and evaluate the biomethane production of food waste and corn stalk anaerobic co-digestion. The kinetics of co-digestion and mono-digestion of food waste and/or corn stalk was also analyzed. The results indicated that the compositions of food waste and corn stalk were significantly different. The anaerobic digestion of three feature objects at different mixing ratios showed the different biomethane yields and kinetic constants. Food waste and corn stalk co-digestion enhanced the digestion rate and achieved 22.48% and 41.55% higher biomethane production than those of food waste and corn stalk mono-digestion, respectively.

Improving the mixing performances of rice straw anaerobic digestion for higher biogas production by computational fluid dynamics (CFD) simulation.

As a lignocellulose-based substrate for anaerobic digestion, rice straw is characterized by low density, high water absorbability, and poor fluidity. Its mixing performances in digestion are completely different from traditional substrates such as animal manures. Computational fluid dynamics (CFD) simulation was employed to investigate mixing performances and determine suitable stirring parameters for efficient biogas production from rice straw. The results from CFD simulation were applied in the anaerobic digestion tests to further investigate their reliability. The results indicated that the mixing performances could be improved by triple impellers with pitched blade, and complete mixing was easily achieved at the stirring rate of 80 rpm, as compared to 20-60 rpm. However, mixing could not be significantly improved when the stirring rate was further increased from 80 to 160 rpm. The simulation results agreed well with the experimental results. The determined mixing parameters could achieve the highest biogas yield of 370 mL (g TS)(-1) (729 mL (g TS(digested))(-1)) and 431 mL (g TS)(-1) (632 mL (g TS(digested))(-1)) with the shortest technical digestion time (T 80) of 46 days. The results obtained in this work could provide useful guides for the design and operation of biogas plants using rice straw as substrates.