Lipid Production of Heterotrophic Chlorella sp. from Hydrolysate Mixtures of Lipid-Extracted Microalgal Biomass Residues and Molasses.

This study investigated the feasibility of lipid production of Chlorella sp. from waste materials. Lipid-extracted microalgal biomass residues (LMBRs) and molasses were hydrolyzed, and their hydrolysates were analyzed. Five different hydrolysate mixture ratios (w/w) of LMBRs/molasses (1/0, 1/1, 1/4, 1/9, and 0/1) were used to cultivate Chlorella sp. The results showed that carbohydrate and protein were the two main compounds in the LMBRs, and carbohydrate was the main compound in the molasses. The highest biomass concentration of 5.58 g/L, Y biomass/sugars of 0.59 g/g, lipid productivity of 335 mg/L/day, and Y lipids/sugars of 0.25 g/g were obtained at the hydrolysate mixture ratio of LMBRs/molasses of 1/4. High C/N ratio promoted the conversion of sugars into lipids. The lipids extracted from Chlorella sp. shared similar lipid profile of soybean oil and is therefore a potential viable biodiesel feedstock. These results showed that Chlorella sp. can utilize mixed sugars and amino acids from LMBRs and molasses to accumulate lipids efficiently, thus reducing the cost of microalgal biodiesel production and improving its economic viability.

Fast microwave-assisted catalytic pyrolysis of sewage sludge for bio-oil production.

In this study, fast microwave-assisted catalytic pyrolysis of sewage sludge was investigated for bio-oil production, with HZSM-5 as the catalyst. Pyrolysis temperature and catalyst to feed ratio were examined for their effects on bio-oil yield and composition. Experimental results showed that microwave is an effective heating method for sewage sludge pyrolysis. Temperature has great influence on the pyrolysis process. The maximum bio-oil yield and the lowest proportions of oxygen- and nitrogen-containing compounds in the bio-oil were obtained at 550°C. The oil yield decreased when catalyst was used, but the proportions of oxygen- and nitrogen-containing compounds were significantly reduced when the catalyst to feed ratio increased from 1:1 to 2:1. Essential mineral elements were concentrated in the bio-char after pyrolysis, which could be used as a soil amendment in place of fertilizer. Results of XRD analyses demonstrated that HZSM-5 catalyst exhibited good stability during the microwave-assisted pyrolysis of sewage sludge.

Fast microwave assisted pyrolysis of biomass using microwave absorbent.

A novel concept of fast microwave assisted pyrolysis (fMAP) in the presence of microwave absorbents was presented and examined. Wood sawdust and corn stover were pyrolyzed by means of microwave heating and silicon carbide (SiC) as microwave absorbent. The bio-oil was characterized, and the effects of temperature, feedstock loading, particle sizes, and vacuum degree were analyzed. For wood sawdust, a temperature of 480°C, 50 grit SiC, with 2g/min of biomass feeding, were the optimal conditions, with a maximum bio-oil yield of 65 wt.%. For corn stover, temperatures ranging from 490°C to 560°C, biomass particle sizes from 0.9mm to 1.9mm, and vacuum degree lower than 100mmHg obtained a maximum bio-oil yield of 64 wt.%. This study shows that the use of microwave absorbents for fMAP is feasible and a promising technology to improve the practical values and commercial application outlook of microwave based pyrolysis.

Fast microwave-assisted catalytic gasification of biomass for syngas production and tar removal.

In the present study, a microwave-assisted biomass gasification system was developed for syngas production. Three catalysts including Fe, Co and Ni with Al2O3 support were examined and compared for their effects on syngas production and tar removal. Experimental results showed that microwave is an effective heating method for biomass gasification. Ni/Al2O3 was found to be the most effective catalyst for syngas production and tar removal. The gas yield reached above 80% and the composition of tar was the simplest when Ni/Al2O3 catalyst was used. The optimal ratio of catalyst to biomass was determined to be 1:5-1:3. The addition of steam was found to be able to improve the gas production and syngas quality. Results of XRD analyses demonstrated that Ni/Al2O3 catalyst has good stability during gasification process. Finally, a new concept of microwave-assisted dual fluidized bed gasifier was put forward for the first time in this study.

Fractionation and characterization of hemicelluloses from young bamboo (Phyllostachys pubescens Mazel) leaves.

Bamboo leaves are considered as an important source of bioactive molecules. In this work, leaves from young bamboo (Phyllostachys pubescens Mazel) aged 3 months were subjected to aqueous extraction and 2% NaOH solution extraction followed by precipitation in ethanol-water medium with different ethanol concentrations. The dissolved hemicellulosic polysaccharides presented a total recovery of 67.83% based on the total hemicellulose content in bamboo leaves. Chemical analysis of the fractions was performed by sugar composition analysis, Fourier-transform infrared spectrometry, and 1D nuclear magnetic resonance imaging. The results revealed that all polysaccharide fractions contained xylose, arabinose, glucose, galactose, ribose, and uronic acid. The polysaccharides from young bamboo leaves mainly consisted of arabinoxylans, arabinogalactans, and non-cellulosic ß-D-glucans having (1→3)- and (1→4)-glucosidic linkages. The content of these polysaccharides was found to vary among the fractions depending on the separation method. Finally, the thermal behavior was also discussed.

Catalytic pyrolysis of microalgae and their three major components: carbohydrates, proteins, and lipids.

To better understand the pyrolysis of microalgae, the different roles of three major components (carbohydrates, proteins, and lipids) were investigated on a pyroprobe. Cellulose, egg whites, and canola oil were employed as the model compounds of the three components, respectively. Non-catalytic pyrolysis was used to identify and quantify some major products and several reaction pathways were proposed for the pyrolysis of each model compound. Catalytic pyrolysis was then carried out with HZSM-5 for the production of aromatic hydrocarbons at different temperatures and catalyst to feed ratios. The aromatic yields of all feedstocks were significantly improved when the catalyst to biomass ratio increased from 1:1 to 5:1. Egg whites had the lowest aromatic yield among the model compounds under all reaction conditions, which suggests that proteins can hardly be converted to aromatics with HZSM-5. Lipids, although only accounted for 12.33% of Chlorella, contributed about 40% of aromatic production from algal biomass.

Novel fungal pelletization-assisted technology for algae harvesting and wastewater treatment.

A novel fungi pelletization-assisted bioflocculation technology was developed for efficient algae harvesting and wastewater treatment. Microalga Chlorella vulgaris UMN235 and two locally isolated fungal species Aspergillus sp. UMN F01 and UMN F02 were used to study the effect of various cultural conditions on pelletization process for fungi-algae complex. The results showed that pH was the key factor affecting formation of fungi-algae pellet, and pH could be controlled by adjusting glucose concentration and fungal spore number added. The best pelletization happened when adding 20 g/L glucose and approximately 1.2E8/L spores in BG-11 medium, under which almost 100% of algal cells were captured onto the pellets with shorter retention time. The fungi-algae pellets can be easily harvested by simple filtration due to its large size (2-5 mm). The filtered fungi-algae pellets were reused as immobilized cells for treatment wastewaters and the nutrient removal rates of 100, 58.85, 89.83, and 62.53 % (for centrate) and 23.23, 44.68, 84.70, and 70.34% (for diluted swine manure wastewater) for ammonium, total nitrogen, total phosphorus, and chemical oxygen demand, respectively, under both 1- and 2-day cultivations. The novel technology developed is highly promising compared with current algae harvesting and biological wastewater treatment technologies in the literature.

Microwave-assisted pyrolysis of microalgae for biofuel production.

The pyrolysis of Chlorella sp. was carried out in a microwave oven with char as microwave reception enhancer. The results indicated that the maximum bio-oil yield of 28.6% was achieved under the microwave power of 750 W. The bio-oil properties were characterized with elemental, GC-MS, GPC, FTIR, and thermogravimetric analysis. The algal bio-oil had a density of 0.98 kg/L, a viscosity of 61.2 cSt, and a higher heating value (HHV) of 30.7 MJ/kg. The GC-MS results showed that the bio-oils were mainly composed of aliphatic hydrocarbons, aromatic hydrocarbons, phenols, long chain fatty acids and nitrogenated compounds, among which aliphatic and aromatic hydrocarbons (account for 22.18% of the total GC-MS spectrum area) are highly desirable compounds as those in crude oil, gasoline and diesel. The results in this study indicate that fast growing algae are a promising source of feedstock for advanced renewable fuel production via microwave-assisted pyrolysis (MAP).

Physical and chemical properties of bio-oils from microwave pyrolysis of corn stover.

This study was aimed to understand the physical and chemical properties of pyrolytic bio-oils produced from microwave pyrolysis of corn stover regarding their potential use as gas turbine and home heating fuels. The ash content, solids content, pH, heating value, minerals, elemental ratio, moisture content, and viscosity of the bio-oils were determined. The water content was approx 15.2 wt%, solids content 0.22 wt%, alkali metal content 12 parts per million, dynamic viscosity 185 mPa.s at 40 degrees C, and gross high heating value 17.5 MJ/kg for a typical bio-oil produced. Our aging tests showed that the viscosity and water content increased and phase separation occurred during the storage at different temperatures. Adding methanol and/or ethanol to the bio-oils reduced the viscosity and slowed down the increase in viscosity and water content during the storage. Blending of methanol or ethanol with the bio-oils may be a simple and cost-effective approach to making the pyrolytic bio-oils into a stable gas turbine or home heating fuels.