Yecong Li

ANAEROBIC DIGESTED DAIRY MANURE AS A NUTRIENT SUPPLEMENT FOR CULTIVATION OF OIL-RICH GREEN MICROALGAE CHLORELLA SP

The present study was to investigate the effectiveness of using digested dairy manure as a nutrient supplement for cultivation of oil-rich green microalgae Chlorella sp. Different dilution multiples of 10, 15, 20, and 25 were applied to the digested manure and algal growth was compared in regard to growth rate, nutrient removal efficiency, and final algal fatty acids content and composition. Slower growth rates were observed with less diluted manure samples with higher turbidities in the initial cultivation days. A reverse linear relationship (R(2) = 0.982) was found between the average specific growth rate of the beginning 7 days and the initial turbidities. Algae removed ammonia, total nitrogen, total phosphorus, and COD by 100%, 75.7-82.5%, 62.5-74.7%, and 27.4-38.4%, respectively, in differently diluted dairy manure. COD in digested dairy manure, beside CO(2), proved to be another carbon source for mixotrophic Chlorella. Fatty acid profiles derived from triacylglyceride (TAG), phospholipid and free fatty acids showed that octadecadienoic acid (C18:2) and hexadecanoic acid (C16:0) were the two most abundant fatty acids in the algae. The total fatty acid content of the dry weight increased from 9.00% to 13.7% along with the increasing dilution multiples. Based on the results from this study, a process combining anaerobic digestion and algae cultivation can be proposed as an effective way to convert high strength dairy manure into profitable byproducts as well as to reduce contaminations to environment.

Characterization of a microalga Chlorella sp. well adapted to highly concentrated municipal wastewater for nutrient removal and biodiesel production.

The feasibility of growing Chlorella sp. in the centrate, a highly concentrated municipal wastewater stream generated from activated sludge thickening process, for simultaneous wastewater treatment and energy production was tested. The characteristics of algal growth, biodiesel production, wastewater nutrient removal and the viability of scale-up and the stability of continuous operation were examined. Two culture media, namely autoclaved centrate (AC) and raw centrate (RC) were used for comparison. The results showed that by the end of a 14-day batch culture, algae could remove ammonia, total nitrogen, total phosphorus, and chemical oxygen demand (COD) by 93.9%, 89.1%, 80.9%, and 90.8%, respectively from raw centrate, and the fatty acid methyl ester (FAME) content was 11.04% of dry biomass providing a biodiesel yield of 0.12 g-biodiesel/L-algae culture solution. The system could be successfully scaled up, and continuously operated at 50% daily harvesting rate, providing a net biomass productivity of 0.92 g-algae/(L day).

Local bioprospecting for high-lipid producing microalgal strains to be grown on concentrated municipal wastewater for biofuel production

Mass cultivation of microalgae for biofuel production depends heavily on the performance of the microalgae strains used. In this study, 60 algae-like microorganisms collected from different sampling sites in Minnesota were examined using multi-step screening and acclimation procedures to select high-lipid producing facultative heterotrophic microalgae strains capable of growing on concentrated municipal wastewater (CMW) for simultaneous energy crop production and wastewater treatment. Twenty-seven facultative heterotrophic microalgae strains were found, among which 17 strains were proved to be tolerant to CMW. These 17 top-performing strains were identified through morphological observation and DNA sequencing as Chlorella sp., Heynigia sp., Hindakia sp., Micractinium sp., and Scenedesmus sp. Five strains were chosen for other studies because of their ability to adapt to CMW, high growth rates (0.455-0.498 d(-1)) and higher lipid productivities (74.5-77.8 mg L(-1)d(-1)). These strains are considered highly promising compared with other strains reported 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).

Integration of algae cultivation as biodiesel production feedstock with municipal wastewater treatment: Strains screening and significance evaluation of environmental factors

The objectives of this study are to find the robust strains for the centrate cultivation system and to evaluate the effect of environmental factors including light intensity, light-dark cycle, and exogenous CO2 concentration on biomass accumulation, wastewater nutrient removal and biodiesel production. The results showed that all 14 algae strains from the genus of Chlorella, Haematococcus, Scenedesmus, Chlamydomonas, and Chloroccum were able to grow on centrate. The highest net biomass accumulation (2.01 g/L) was observed with Chlorella kessleri followed by Chlorella protothecoides (1.31 g/L), and both of them were proved to be capable of mixotrophic growth when cultivated on centrate. Environmental factors had significant effect on algal biomass accumulation, wastewater nutrients removal and biodiesel production. Higher light intensity and exogenous CO2 concentration with longer lighting period promote biomass accumulation, biodiesel production, as well as the removal of chemical oxygen demand and nitrogen, while, lower exogenous CO2 concentration promotes phosphorus removal.

A hetero-photoautotrophic two-stage cultivation process to improve wastewater nutrient removal and enhance algal lipid accumulation

A hetero-photoautotrophic algal growth model was studied for improved wastewater treatment and low cost algal biofuel feedstock production. The microalga, Auxenochlorella protothecoides UMN280, was grown heterotrophically on concentrated municipal wastewater and then autotrophically with CO(2) supplementation (air, 1% and 5%, respectively). Strain UMN280 was harvested by self-sedimentation after the heterotrophic stage and the supernatant was aerated with different levels of CO(2) to facilitate autotrophic growth in the second stage. The maximal biomass concentration and lipid content at the first and second stages reached 1.12g/L and 28.90%, and 1.16g/L and 33.22%, respectively. The nutrient removal efficiencies for total phosphorus, ammonia, nitrogen and chemical oxygen demand at the end of the two-stage cultivation were 98.48%, 100%, 90.60% and 79.10%, respectively. The above process can be used to treat organic-rich wastewaters (e.g. industrial and animal manure wastewaters) to achieve the dual purpose of low-cost wastewater treatment and biofuel feedstock production.

Enzymatic hydrolysis of corn stover pretreated by combined dilute alkaline treatment and homogenization.

Corn stover, the most abundant agricultural residue in the U.S., is a potential feedstock for production of bioethanol because of its high content of carbohydrates, but an efficient pretreatment is required prior to enzymatic hydrolysis. In this study, a combination of NaOH treatment and homogenization was used as a pretreatment to enhance the enzymatic hydrolysis of corn stover. The combined pretreatment increased the enzymatic hydrolysis of corn stover five times compared to the control. The effectiveness of such pretreatment was found to be a function of NaOH concentration and particle size. Within the NaOH concentration range of 0.1 to 1.0 N, best performance of this combined pretreatment was achieved at 0.3 N NaOH. There is a significant cross effect of homogenization and NaOH treatment. Among the three particle sizes tested (the particle size was not directly measured; it passed through screens with openings of 2 mm, 0.707 mm, and 0.25 mm respectively), 2 mm was found to maximize the economic benefit of the pretreatment.

Effect of light intensity on algal biomass accumulation and biodiesel production for mixotrophic strains Chlorella kessleri and Chlorella protothecoide cultivated in highly concentrated municipal wastewater

In this research, the effect of light intensity on biomass accumulation, wastewater nutrient removal through algae cultivation, and biodiesel productivity was investigated with algae species Chlorella kessleri and Chlorella protothecoide. The light intensities studied were 0, 15, 30, 60, 120, and 200 µmol m−2 s−1. The results showed that light intensity had profound impact on tested responses for both strains, and the dependence of these responses on light intensity varied with different algae strains. For C. kessleri, the optimum light intensity was 120 µmol m−2 S−1 for all responses except for COD removal. For C. protothecoide, the optimum light intensity was 30 µmol m−2 S−1. The major components of the biodiesel produced from algae biomass were 16‐C and 18‐C FAME, and the highest biodiesel contents were 24.19% and 19.48% of dried biomass for C. kessleri and C. protothecoide, respectively. Both species were capable of wastewater nutrients removal under all lighting conditions with high removal efficiencies. Biotechnol. Bioeng. 2012;109: 2222–2229.

Swine manure fermentation for hydrogen production.

Biohydrogen fermentation using liquid swine manure as substrate supplemented with glucose was investigated in this project. Experiments were conducted using a semi-continuously-fed fermenter (8L in total volume and 4 L in working volume) with varying pHs from 4.7 through 5.9 under controlled temperature (35+/-1 degrees C). The hydraulic retention time (HRT) tested include 16, 20, and 24h; however, in two pH conditions (5.0 and 5.3), an additional HRT of 12h was also tried. The experimental design combining HRT and pH provided insight on the fermenter performance in terms of hydrogen generation. The results indicated that both HRT and pH had profound influences on fermentative hydrogen productivity. A rising HRT would lead to greater variation in hydrogen concentration in the offgas and the best HRT was found to be 16 h for the fermenter in this study. The best pH value in correspondence to the highest hydrogen generation was revealed to be 5.0 among all the pHs studied. There was no obvious inhibition on hydrogen production by methanogenesis when methane content in the offgas was lower than 2%. Otherwise, an inverse linear relationship between hydrogen and methane content was observed with a correlation coefficient of 0.9699. Therefore, to increase hydrogen content in the offgas, methane production has to be limited to below 2%.

Mutual influence of light and CO 2 on carbon sequestration via cultivating mixotrophic alga Auxenochlorella protothecoides UMN280 in an organic carbon-rich wastewater

This study focusses on the assimilation of carbon in concentrated municipal wastewater rich in organic carbon using the mixotrophic microalga Auxenochlorella protothecoides UMN280 with the addition of supplemental CO2. The entire growth period of A. protothecoides UMN280 can be characterized by three phases: first, a phase where algae grew in a mixotrophic-dominated mode; second, a transition phase; and last, a phase where algae grew in a photoautotrophic-dominated mode. In this study, it was found that light intensity had a strong effect on algal biomass production; the culture system would transfer from a mixotrophic-dominated mode to a photoautotrophic-dominated mode quicker under higher light intensities. The addition of CO2 exhibited an important role in the photoautotrophic-dominated cultivation stage. At certain level of irradiance and certain range of CO2 injection rate, higher CO2 injection rate would result in a higher level of carbon fixation. It is clearly beneficial to inject exogenous CO2 in the mixotrophic wastewater algae production system when a light source is available, such as during daylight hours.