Zhenhong Yuan

Nutrient removal and biodiesel production by integration of freshwater algae cultivation with piggery wastewater treatment.

An integrated approach, which combined freshwater microalgae Chlorella zofingiensis cultivation with piggery wastewater treatment, was investigated in the present study. The characteristics of algal growth, lipid and biodiesel production, and nutrient removal were examined by using tubular bubble column photobioreactors to cultivate C. zofingiensis in piggery wastewater with six different concentrations. Pollutants in piggery wastewater were efficiently removed among all the treatments. The specific growth rate and biomass productivity were different among all the cultures. As the initial nutrient concentration increased, the lipid content of C. zofingiensis decreased. The differences in lipid and biodiesel productivity of C. zofingiensis among all the treatments mainly resulted from the differences in biomass productivity. It is worthy of note that the diluted piggery wastewater with 1900 mg L(-1) COD provided an optimal nutrient concentration for C. zofingiensis cultivation, where the advantageous nutrient removal and the highest productivities of biomass, lipid and biodiesel were presented.

Two-step liquid hot water pretreatment of Eucalyptus grandis to enhance sugar recovery and enzymatic digestibility of cellulose

A two-step liquid hot water pretreatment (TSLHW) was developed with the objective of achieving complete saccharification of both hemicellulose and cellulose of Eucalyptus grandis, thereby avoiding the problems associated with the use of strong acid catalysts. The first step of the pretreatment was studied in the temperature range 180-200 degrees C, and the highest yield of total xylose achieved was 86.4% after 20 min at 180 degrees C. The second-step of the pretreatment was studied in the temperature range 180-240 degrees C and for lengths of time of 0-60 min. The conversion rate of glucan was more sensitive to temperature than time. The optimum reaction conditions for the second step of the pretreatment with minimal degradation of sugars were 200 degrees C for 20 min. the total sugar recovery from E. grandis with the optimized pretreatment and 72 h enzymatic digestion, reached 96.63%, which is superior to the recovery from a single-step pretreatment with hot water or dilute acid.

Improved biogas production from rice straw by co-digestion with kitchen waste and pig manure.

In order to investigate the effect of feedstock ratios in biogas production, anaerobic co-digestions of rice straw with kitchen waste and pig manure were carried out. A series of single-stage batch mesophilic (37±1 °C) anaerobic digestions were performed at a substrate concentration of 54 g/L based on volatile solids (VS). The results showed that the optimal ratio of kitchen waste, pig manure, and rice straw was 0.4:1.6:1, for which the C/N ratio was 21.7. The methane content was 45.9-70.0% and rate of VS reduction was 55.8%. The biogas yield of 674.4 L/kg VS was higher than that of the digestion of rice straw or pig manure alone by 71.67% and 10.41%, respectively. Inhibition of biogas production by volatile fatty acids (VFA) occurred when the addition of kitchen waste was greater than 26%. The VFA analysis showed that, in the reactors that successfully produced biogas, the dominant intermediate metabolites were propionate and acetate, while they were lactic acid, acetate, and propionate in the others.

Liquid hot water pretreatment of sugarcane bagasse and its comparison with chemical pretreatment methods for the sugar recovery and structural changes

Liquid hot water (LHW), dilute hydrochloric acid (HCl) and dilute sodium hydroxide (NaOH) were applied to sugarcane bagasse (SB). Application of the same analytical methods and material balance approaches facilitated meaningful comparisons of glucose and xylose yields from combined pretreatment and enzymatic hydrolysis. All pretreatments enhanced sugar recovery from pretreatment and subsequent enzymatic hydrolysis substantially compared to untreated sugarcane bagasse. Adding Tween80 in the enzymatic hydrolysis process increased the conversion level of glucan/xylan by 0.3-fold, especially for the low pH pretreatment where more lignin was left in the solids. The total sugar recovery from sugarcane bagasse with the coupled operations of pretreatment and 72 h enzymatic digestion reached 71.6% for LHW process, 76.6% for HCl pretreatment and 77.3% for NaOH pretreatment. Different structural changes at the plant tissue, cellular, and cell wall levels might be responsible for the different enzymatic digestibility. Furthermore, a combined LHW and aqueous ammonia pretreatment was proposed to reduce energy input and enhance the sugar recovery.

Scale-up potential of cultivating Chlorella zofingiensis in piggery wastewater for biodiesel production

Scale-up potential of cultivating Chlorella zofingiensis in piggery wastewater for simultaneous wastewater treatment and biodiesel production was tested. The cultivation of C. zofingiensis with autoclaved wastewater and NaClO-pretreated wastewater, cultivation of algae indoors and outdoors, and stability of semi-continuous feeding operation were examined. The results showed that C. zofingiensis cultivated in piggery wastewater pretreated by autoclaving and NaClO had no evident difference in the performance of nutrient removal, algal growth and biodiesel production. The outdoor cultivation experiments indicated that C. zofingiensis was able to adapt and grow well outdoors. The semi-continuous feeding operation by replacing 50% of algae culture with fresh wastewater every 1.5 days could provide a stable net biomass productivity of 1.314 g L(-1) day(-1). These findings in this study can prove that it is greatly possible to amplify the cultivation of C. zofingiensis in piggery wastewater for nutrient removal and biodiesel production.

Metabolic changes of starch and lipid triggered by nitrogen starvation in the microalga Chlorella zofingiensis.

The aim of this research was to study the metabolic changes of starch and lipid biosynthesis in the microalga Chlorella zofingiensis under nitrogen starvation in comparison to nitrogen abundant condition. C. zonfingiensis showed a rapid growth and kept stable chlorophyll content when grown in nitrogen-replete medium, while a severe inhibition of cell growth and a sharp degradation of chlorophyll occurred under nitrogen depletion. Nitrogen-replete C. zonfingiensis cells possessed basal levels of starch and lipid. Upon nitrogen starvation, both starch and lipid increased greatly within cells, but starch synthesis preceded lipid accumulation. After 2 days of stress condition, starch was partially degraded, possibly to support lipid synthesis. It was speculated that starch accumulation acted as a quick response to environmental stress, whereas lipid served as long-term energy storage. Additionally, C. zonfingiensis tends to lower the degree of unsaturation in response to nitrogen starvation which is desirable for biodiesel production.

Biogas Production Potential and Kinetics of Microwave and Conventional Thermal Pretreatment of Grass

Pretreatment methods play an important role in the improvement of biogas production from the anaerobic digestion of energy grass. In this study, conventional thermal and microwave methods were performed on raw material, namely, Pennisetum hybrid, to analyze the effect of pretreatment on anaerobic digestion by the calculation of performance parameters using Logistic function, modified Gompertz equation, and transference function. Results indicated that thermal pretreatment improved the biogas production of Pennisetum hybrid, whereas microwave method had an adverse effect on the performance. All the models fit the experimental data with R2 > 0.980, and the Reaction Curve presented the best agreement in the fitting process. Conventional thermal pretreatment showed an increasing effect on maximum production rate and total methane produced, with an improvement of around 7% and 8%, respectively. With regard to microwave pretreatment, maximum production rate and total methane produced decreased by 18% and 12%, respectively.

Artificial neural network-genetic algorithm based optimization for the immobilization of cellulase on the smart polymer Eudragit L-100

Cellulase was covalently immobilized on a smart polymer, Eudragit L-100 by carbodiimide coupling. Using data of central composite design, response surface methodology (RSM) and artificial neural network (ANN) were developed to investigate the effect of pH, carbodiimide concentration, and coupling time on the activity yield of immobilized cellulase. Results showed simulation and prediction accuracy of ANN was apparently higher compared to RSM. The maximum activity yield obtained from RSM was 57.56% at pH 5.54, carbodiimide concentration 0.32%, and coupling time 3.03 h, where the experimental value was 60.87 + or - 4.79%. Using ANN as fitness function, a maximum activity yield of 69.83% was searched by genetic algorithm at pH 5.07, carbodiimide concentration 0.36%, and coupling time 4.10 h, where the experimental value was 66.75 + or - 5.21%. ANN gave a 9.7% increase of activity yield over RSM. After reusing immobilized cellulase for 5 cycles, the remaining productivity was over 50%.

Medium optimization for ethanol production with Clostridium autoethanogenum with carbon monoxide as sole carbon source

Plackett-Burman and central composite designs were applied to optimize the medium for ethanol production by Clostridium autoethanogenum with CO as sole carbon source, and a medium containing (g/L): NaCl 1.0, KH(2)PO(4) 0.1, CaCl(2) 0.02, yeast extract 0.15, MgSO(4) 0.116, NH(4)Cl 1.694 and pH 4.74 was found optimal. The optimum ethanol yields predicted by response surface methodology (RSM) and an artificial neural network-genetic algorithm (ANN-GA) were 247.48 and 261.48mg/L, respectively. These values are similar to those obtained experimentally under the optimal conditions suggested by the statistical methods (254.26 and 259.64mg/L). The fitness of the ANN-GA model was higher than that of the RSM model. The yields obtained substantially exceed those previously reported (60-70mg/L) with this organism.

Cultivation of Chlorella zofingiensis in bench-scale outdoor ponds by regulation of pH using dairy wastewater in winter, South China

Cultivation of Chlorella zofingiensis and nutrients removal in dairy wastewater were investigated in bench-scale outdoor ponds in winter, South China. The impacts of the two types of pH regulations, 5 ≈ 6% CO(2) and acetic acid (HAc) on this process were studied. After 6 days cultivation, the removal rates of total nitrogen (TN) and orthophosphate (PO(4)(3-)) using CO(2) regulation were better than those using HAc. The removal rates of PO(4)(3-) and TN were 97.5% and 51.7%, respectively using CO(2) regulation; 79.6% (TN) and 42.0% (PO(4)(3-)) were obtained using HAc regulation. Higher biomass, protein, sugar content, and stable pH control were found using CO(2) regulation. However, significantly higher lipid content (31.8%) was observed using HAc regulation. The dominant differences of fatty acids were the content of C18:1 and C18:3. The growth characteristics and environmental conditions especially during the typical logarithmic phase were also analyzed.