No description available.

As underdeveloped nations continue to industrialize and the world population continues to increase, the need for energy, natural resources, and goods will lead to ever increasing heavy metal concentrations in various waste streams that can have damaging effects on plant life, wildlife, and human health. The focus of this study is to understand the impact of individual heavy metals on Nannocholoropsis salina microalgae growth and understand the potential of microalgae to be used as a bioremediation tool for contaminated water systems. Individual metals (As, Cd, Cr, Co, Cu, Pb, Ni, Hg, Se, and Zn) were introduced into growth media. For each metal a baseline concentration was determined based on reported concentrations at various municipal and industrial wastewater sites. In addition to the baseline concentrations, experimentation was conducted at 10X and 40X the baseline to evaluate the potential for severely contaminated systems. Biological growth experimentation was performed in triplicate at the various contaminant concentrations and at 3 different light intensities. Results show nickel significantly reduced growth, while the other metal contaminated systems showed growth between 89% and 99% of the control. Increased heavy metal concentrations resulted in progressively lower growth rates. Lipid analysis shows most baseline metal concentrations slightly decrease or have minimal effects in lipid content. Metals analysis on the biomass showed the majority of the metals in the systems containing Cd, Co, Cu, and Pb were sorbed by the microalgae with minimal metals remaining in the growth media illustrating the effectiveness of microalgae to effectively bioremediate contaminated systems when contamination levels are sufficiently low to not detrimentally impact productivity. Microalgal biomass in the systems containing As, Cr, Ni, and Se showed decreased ability to sorb metal ions. Results show at moderate contamination levels, microalgae can be an effective tool for bioremediation.

The work presented here investigated two methods of improving productivity in microalgal photobioreactors: applying temperature cycles intended to maximize photosynthesis and minimize respiration, and development of a mathematical model that predicts improvements in photon utilization using temporal light dilution (flashing). The experiments conducted on diurnal temperature cycles with Dunaliella tertiolecta in 30-L outdoor photobioreactors showed that a properly chosen temperature cycle can improve mass and energy productivity by 18% over an identical photobioreactor with a constant temperature. However, excessively large temperature cycle amplitudes reduced productivity. A 4-7% increase in energy content was observed in microalgae exposed to temperature cycles. The physiological reason for this could not be established. A relationship similar to the Bush Equation was obtained that related photon utilization efficiency to flashing frequency, load factor, Photosystem II (PSII) concentration and reaction frequency, and chlorophyll content. The model was validated by the experimental data of a number of researchers.

In the quest for a feedstock for the production of biofuels, microalgae are showing potential. High photosynthetic efficiency, combined with high lipid content and low fresh water requirement, has contributed to the 'biofuels feedstock' status of microalgae. In some communities, microalgae have also been cultivated in wastewater in facultative lagoons to remove phosphorus and nitrogen through the growth of microalgae. With such systems in place, complete biological wastewater treatment can be achieved and the harvested microalgae could provide feedstock for biodiesel and various other bioproducts. Due to small cell size, low culture concentrations, and the electrostatic repulsive forces that keep the cells in suspension, harvesting microalgae entails high energy inputs and associated high costs. Of the several harvesting methods tested, chemical precipitation has been shown to be the only method to harvest microalgae on a large scale. Although effective in wastewater treatment, the use of inorganic metal coagulants for microalgae harvesting leads to high dosage requirements, excess volume of sludge, and high costs, and due to the presence of associated metal hydroxide, the harvested biomass is unsuitable as feedstock for bioproducts. The drawbacks of inorganic coagulants for microalgae harvesting can be overcome by using cationic starch. Corn and potato starch were cationized using 3-methacryloyl amino propyl trimethyl ammonium chloride and biogenic amines. Flocculation efficiencies of the cationic starches were tested in a jar test apparatus using single strain microalga, Scenedesmus obliquus, and mixed culture wastewater from the Logan City, Utah lagoons. Cationic starches showed better or comparable removal of total suspended solids compared to aluminum sulfate. Total phosphorus removal efficiencies for cationic starches were lower compared to aluminum sulfate. Effect of cationic starch harvested and alum harvested S. obliquus on biodiesel, acetone, butanol, ethanol production, and Escherichia coli growth was also studied. Results suggested significantly higher yields of bioproducts when cationic starch was used to harvest microalgae and the biomass was used as feedstock. Cationic starches are an organic, sustainable, and renewable form of coagulant/flocculant. The use of cationic starch for harvesting microalgae eliminates the need for metal salts while enhancing the production of algae-based bioproducts. Cationic starch along with advanced technologies in the processing of microalgae is the way forward in the realization of the “microalgae to biofuels” initiative.

Microalgae have many desirable attributes as a renewable energy recourse. These include use of poor quality land, high yields, and it is not a food recourse. This research focusses on the energetic and environmental impact of processing microalgae into a renewable diesel. Two thermochemical bio-oil recovery processes are analyzed, pyrolysis and hydrothermal liquefaction (HTL). System boundaries include microalgae growth, dewatering, thermochemical bio-oil recovery, bio-oil stabilization, conversion to renewable diesel, and transportation to the pump. Two system models were developed, a small-scale experimental and an industrial-scale. The small-scale system model is based on experimental data and literature. The industrial-scale system model leverages the small scale system model with scaling and optimization to represent an industrial-scaled process. The HTL and pyrolysis pathways were evaluated based on net energy ratio (NER), defined here as energy consumed over energy produced, and global warming potential (GWP). NER results for biofuel production through the industrial-scaled HTL pathway were determined to be 1.23 with corresponding greenhouse gas (GHG) emissions of -11.4 g CO2 eq (MJ renewable diesel)-1. Biofuel production through the industrial-scaled pyrolysis pathway gives a NER of 2.27 and GHG emissions of 210 g CO2 eq (MJ renewable diesel)-1. For reference, conventional diesel has an NER of 0.2 and GHG emissions of 18.9 g CO2 eq MJ-1 with a similar system boundary. The large NER and GHG emissions associated with the pyrolysis pathway are attributed to feedstock drying requirements and combustion of co-products to improve system energetics. Process energetics with HTL and pyrolysis are not currently favorable for an industrial scaled system. However, processing of microalgae to biofuel with bio-oil recovery through HTL does produce a favorable environmental impact and a NER which is close to the breakeven point of one.

No description available.

No description available.

Microalgae have been in the center of research for several years due to their high production rates. The use of fresh-water algae in the production of biofuels coupled with wastewater treatment has become a topic of modern research. While most algal farming is performed in warm and sunny climate, this project focused on naturally occurring microalgae in Northern Sweden and their ability to reclaim wastewater and produce lipids. The four microalgae Chlorococcum sp. (MC1), Scotiellopsis reticulata (UFA-2), Coelastrella sp. (3-4) and Chlorella vulgaris (13-1) were grown under mixotrophic conditions in municipal wastewater (MWW), pulp and paper wastewater (PnP) and mixtures of both. Except of UFA-2, I found the growth of the tested species to be limited in pure PnP, however, mixtures of PnP and MWW were suitable for algal growth. The removal rates of total nitrogen achieved the goals regulated by the Swedish government for wastewater reclamation. Phosphorus, of which maximal levels according the Swedish regulations need to be below 0.5 mg/L, was efficiently removed by the strain 3-4 in PnP and in MWW + PnP (ratio 3+1) as well as by the strain 13-1 in MWW + PnP (ratio 3+1). The tested microalgae are therefore appropriate candidates to be used in sustainable wastewater treatment. The algal biomass composition was determined with the help of Fourier-transform infrared spectroscopy and an increase in the spectra for biomass grown in wastewaters within the fingerprint region (800 – 1800 cm-1) was observed. From this, I conclude that the lipid content was elevated in the biomass received after growth in PnP and all mixtures of MWW and PnP compared to the in BG11 grown biomass, which acts as a control group. A quantitative lipid analysis performed on the biomass of the strains UFA-2 and 3-4 confirmed higher lipid amounts after growth in PnP wastewater compared to growth in BG11. These findings show that the examined microalgae might have the potential to be used as a potential feedstock for biofuel productions after cultivation in local wastewaters.

Microalgal biomass is a candidate feedstock for biofuel production. To improve the sustainability of algae biofuel production, following biofuel recovery, the biomass nutrients should be recycled for additional algae growth. Anaerobic digestion of algae or oil-extracted algae is a means of recovering carbon and other nutrients, while offsetting algae production electricity demand. The major limiting factor in microalgae digestion is the low biodegradability of the cell walls. In the present study, various pretreatment technologies were tested at bench scale for their ability to improve raw, non-lipid-extracted algae biodegradability, which was assessed in terms of methane yield, volatile solids destruction, and solubilization of N, P, and K. The microalgae were harvested by sedimentation from outdoor wastewater-fed raceways ponds operated in coastal southern California. Four pretreatment methods (sonication, high-pressure homogenization, autoclaving, and boiling) were used on the algae slurries, each followed by batch anaerobic digestion (40 days at 35oC). Biomass sonication for 10 minutes showed the highest methane yield of 0.315 L CH4/ g VSIN, which is a 28% increase over the untreated control. Conversely, autoclaved algae slurry inhibited methane production (0.200 vs. 0.228 L CH4/ g VSIN for the treatment and control). A preliminary energy balance indicated that none of the pretreatments led to a net increase in energy conversion to biomethane. However, pretreatment did increase the initial N and P solubilization rates, but, after digestion, the ultimate N and P solubilization was nearly the same among the treatments and controls. After 40 days of digestion, solubilization of N, P, and K reached, respectively, 50-60% of average total Kjeldahl N, 40-50% of average total P, and 80-90% of average total K. Descriptive first-order models of solubilization were developed. Overall, certain pretreatments marginally improved methane yield and nutrient solubilization rate, which cast doubt on the efficacy of, or even the need for, algae biomass pretreatment prior to anaerobic digestion.

This thesis explores the treatment of municipal wastewater using pilot-scale raceway ponds and looks specifically at the capability of the raceways in removing BOD and nitrogen. Nine 33 square-meter algal raceway ponds were used to conduct research at the San Luis Obispo Water Resources Recovery Facility. Main objectives of this study were to increase the removal of total ammonia nitrogen (NH3-N plus NH4+-N) from municipal wastewater through increased assimilation and nitrification. Raceway ponds with CO2 addition were operated in series with an intermediate settling step and a total hydraulic retention time (HRT) of 4 days to measure the increase in nitrogen removal through assimilation by two rounds of algae growth. A single round of treatment with a 4 day HRT was also operated and compared to the two rounds. The two rounds of treatment and 1 round of treatment removed on average 36.6 mg-N/L and 35.2 mg-N/L of TAN, with respective standard deviations of 6.3 mg-N/L and 5.3 mg-N/L. No statistical significant difference was found between two treatment methods for TAN (mg-N/L) removal (t = -0.64, DF = 23.3, P =0.28), % TAN removal (t = -1.18, DF = 22.6, P = 0.25), and TAN (mg-N/L) of final effluent (t = 1.11, DF = 23.6, P = 0.28). Raceway ponds were aerated at night to keep nighttime DO from dropping to concentrations inhibitory to nitrification. The rates of nitrification with night aeration were measured. The nitrification rates were compared to a model based on Monod kinetics. The Monod model did not correspond with performance results of ponds.