Kisay Lee

Ammonia removal from anaerobic digestion effluent of livestock waste using green alga Scenedesmus sp.

The green alga Scenedesmus was investigated for its ability to remove nitrogen from anaerobic digestion effluent possessing high ammonium content and alkalinity in addition to its growth characteristics. Nitrate and ammonium were indistinguishable as a nitrogen source when the ammonium concentration was at normal cultivation levels. Ammonium up to 100ppm NH(4)-N did not inhibit cell growth, but did decrease final cell density by up to 70% at a concentration of 200-500ppm NH(4)-N. Inorganic carbon of alkalinity in the form of bicarbonate was consumed rapidly, in turn causing the attenuation of cell growth. Therefore, maintaining a certain level of inorganic carbon is necessary in order to prolong ammonia removal. A moderate degree of aeration was beneficial to ammonia removal, not only due to the stripping of ammonium to ammonia gas but also due to the stripping of oxygen, which is an inhibitor of regular photosynthesis. Magnesium is easily consumed compared to other metallic components and therefore requires periodic supplementation. Maintaining appropriate levels of alkalinity, Mg, aeration along with optimal an initial NH(4)(+)/cell ratio were all necessary for long-term semi-continuous ammonium removal and cell growth.

Lipid production by Chlorella vulgaris after a shift from nutrient-rich to nitrogen starvation conditions

A two-stage process, composed of growth under nutrient-rich conditions followed by cultivation under nitrogen starvation and controlled conditions of phosphate, light intensity, aeration, and carbon sources was applied for lipid production by the green alga Chlorella vulgaris. Using conditions without addition of nitrogen, 2mg/L PO(4)-P, light intensity of 100μmol/m(2)/s and 0.25vvm of air, about 43% of dry cell weight accumulated as lipids after 12h, which equates to a lipid productivity of 77.8mg/L/d. In a medium containing 5mg/L NO(3)-N and 2mg/L PO(4)-P, and at a light intensity of 100μmol/m(2)/s and 0.25vvm of 2% CO(2), about 53% of dry cell weight consisted of lipids after 24h, representing a lipid productivity of 77.1mg/L/d. The low amount of nutrients, moderate aeration and light intensity were helpful for increasing lipid productivity.

Influence of Nitrate Feeding on Carbon Dioxide Fixation by Microalgae

In this study, the effects of nitrate feeding on microalgal growth and associated CO2 fixation were evaluated, as a strategy to enhance carbon fixation by increasing the duration of the exponential phase of cell growth in the batch operation of a photobioreactor. Two species of green algae, Chlorella and Scenedesmus, and two species of cyanobacteria, Microcystis ichthyoblabe and Microcystis aeruginosa, were used after adaptation to a 15% (v/v) CO2 environment. In the absence of nitrate feeding, nitrate concentrations declined rapidly and soon became a limiting factor. Nitrate feeding, administered in fed-batch mode to maintain 15–20 ppm of NO3-N, allowed for an extension of the exponential growth phase by more than 3 days, as well as a higher cell density, which subsequently resulted in an increase in photoautotrophic carbon fixation. The increases in the carbon fixation rate were in the ranges of 56.1–56.6% for the green algae, and between 68.2–68.8% for the cyanobacteria. The results indicated that intermittent nitrate feeding was a viable strategy for the augmentation of fixation productivity, and may thus be effectively applied as a substitute for conventional medium change, which has traditionally been employed in order to prolong the active growth duration.

Hydrogen peroxide interference in chemical oxygen demand during ozone based advanced oxidation of anaerobically digested livestock wastewater

It is known that hydrogen peroxide interferes with chemical oxygen demand analysis by consuming oxidation agents such as potassium dichromate, thus leading to overestimation of the chemical oxygen demand measurements. The objective of the study was to investigate the effects of hydrogen peroxide interference and to determine true chemical oxygen demand values on interpreting treatment performance during ozone-based advanced oxidation of livestock wastewater in which hydrogen peroxide concentration and chemical oxygen demand values are dynamically changing. According to the chemical oxygen demand monitoring data, chemical oxygen demand values were always higher than the initial chemical oxygen demand load when hydrogen peroxide was involved and the treatment performance with ozone alone or ozone/ultraviolet was better than with coupled hydrogen peroxide. The extent of overestimation was proportional to the remaining hydrogen peroxide concentration and the average overestimation ratio in livestock wastewater was in the range of 0.50∼0.58 mg per 1 mg of hydrogen peroxide, depending upon the quality of the wastewater treated. True chemical oxygen demand values were estimated by correlating the extent of overestimation with the remaining hydrogen peroxide concentration during treatment. The extent of overestimation decreased to zero gradually as the amount of hydrogen peroxide also approached zero as oxidation proceeded. The corrected chemical oxygen demand values indicated underlying tendency of oxidation, which could not be seen in the original chemical oxygen demand monitoring data. Application of ozone/hydrogen peroxide was more efficient for reducing chemical oxygen demand than ozone alone, as was ozone/hydrogen peroxide/ultraviolet compared to ozone/ultraviolet. When coupled with ozone, ultraviolet irradiation was more efficient than hydrogen peroxide for decreasing chemical oxygen demand during treatment of livestock wastewater.

Life cycle analyses of CO2, energy, and cost for four different routes of microalgal bioenergy conversion.

With a target production of 1000 ton of dry algae/yr, lipid content of 30 wt.%, and productivity of 30 g/m(2)-d in a 340-day annual operation, four common scenarios of microalgae bioenergy routes were assessed in terms of cost, energy, and CO2 inputs and outputs. Scenario 1 (biodiesel production), Scenario 2 (Scenario 1 with integrated anaerobic digestion system), Scenario 3 (biogas production), and Scenario 4 (supercritical gasification) were evaluated. Scenario 4 outperformed other scenarios in terms of net energy production (1282.42 kWh/ton algae) and CO2 removal (1.32 ton CO2/ton algae) while Scenario 2 surpassed the other three scenarios in terms of net cost. Scenario 1 produced the lowest energy while Scenario 3 was the most expensive bioenergy system. This study evaluated critical parameters that could direct the proper design of the microalgae bioenergy system with an efficient energy production, CO2 removal, and economic feasibility.

Biohydrogen production by immobilized Chlorella sp. using cycles of oxygenic photosynthesis and anaerobiosis.

Hydrogen production was studied using immobilized green alga Chlorella sp. through a two-stage cyclic process where immobilized cells were first incubated in oxygenic photosynthesis followed by anaerobic incubation for H2 production in the absence of sulfur. Chlorella sp. used in this study was capable of generating H2 under immobilized state in agar. The externally added glucose enhanced H2 production rates and total produced volume while shortened the lag time required for cell adaptation prior to H2 evolution. The rate of hydrogen evolution was increased as temperature increased, and the maximum evolution rate under 30 mM glucose was 183 mL/h/L and 238 mL/h/L at 37 °C and 40 °C, respectively. In order to continue repeated cycles of H2 production, at least two days of photosynthesis stage should be allowed for cells to recover H2 production potential and cell viability before returning to H2 production stage again.

Growth of microalgae in diluted process water of the animal wastewater treatment plant.

The growth of microalgae was investigated using diluted process water from an animal waste treatment plant as a substrate. Batch experiments were carried out to determine the growth characteristics of three microalgae strains: Microcystis aeruginosa, Chlorella vulgaris and Euglena gracilis. The two types of process water with different dilution rates were used for the experiments. The biokinetic parameters of each culture were estimated from the logistic growth curves for comparative analysis. In aerobic effluent, most growth parameters were significantly better than in anaerobic effluent regardless of the dilution rates. This suggests that the concentration of organic matter, such as volatile fatty acids, affects microgal growth. Euglena gracilis, which was the largest in size, had the highest growth rates among the three species in both pure and mixed cultures.

Effects of electric field directions on surfactant enhanced electrokinetic remediation of diesel‐contaminated sand column

Abstract The removal of diesel from a sandy soil column was conducted by surfactant enhanced electrokinetic remediation process to study the effects of the electric field direction on the diesel removal efficiency. Anionic surfactant SDS(sodium dodecyl sulfate) was fed to one of the electrode chambers driven by electrokinetics and/or a pump. When an electric current was applied while SDS was fed to anode chamber at a constant rate by pump, an effluent flowrate higher than the feeding rate was obtained at cathode side because the directions of electroosmosis and pumped convective flow were identical. Meanwhile, when SDS was fed to cathode chamber by pump in the presence of an electric current, a lowered effluent flowrate was obtained, where the directions of electroosmosis and pumped flow were opposite. In this case, however, the diesel removal rate and total recovered amount of diesel were substantially increased compared to the case that SDS was fed to anode side. Results implied in SDS transport through...

Influence of the CO2 absorbent monoethanolamine on growth and carbon fixation by the green alga Scenedesmus sp.

The influence of monoethanolamine (MEA) as a CO(2) absorbent on photoautotrophic culture of CO(2)-fixing microalgae was investigated. When 300 ppm MEA (4.92 mM) was added to blank culture medium, the dissolved inorganic carbon and the molar absorption ratio increased to 51.0mg/L and 0.34 mol CO2 = mol MEA, respectively, which was an almost 6-fold increase in CO(2) solubility. When free MEA up to 300 mg/L was added to a green alga Scenedesmus sp. culture that was supplied 5% (v/v) CO(2) at 0.1 vvm, both cell growth rate and final cell density were enhanced compared to when no MEA was added. The cell growth rate reached 288.6 mg/L/d, which was equivalent to 539.6 mg-CO(2)/L/d as a CO(2)-fixation rate and enhancement of about 63.0% compared to not adding MEA. Chlorophyll-a content and nitrate consumption rate increased correspondingly. MEA doses higher than 400mg/L inhibited cell growth, probably due to toxicity of the carbamate intermediate.

Bio-hydrogen production by Chlorella vulgaris under diverse photoperiods.

The hydrogen production by Chlorella vulgaris exposed to four different light patterns was explored. Cultures of immobilized, sulfur-deprived cells were purged with N2 and either kept in the dark for 72 h, kept in the dark for 24 h before being exposed to light (intensity of 120 μ mole/m2/s) for 72 h, exposed to light for 72 h, or kept in the light for 24h before being subjected to darkness for 48 h. The latter condition provided for the highest total hydrogen production of 530±5 ml/l of medium and a maximum hydrogen release rate of 34.8 ml/h/l. Growth for 72 h under partial light conditions was essential for continuous and enhanced hydrogen production. The addition of glucose to the sulfur-deficient medium increased hydrogen production by 18 times under partial light condition. To increase the hydrogen productivity, a carbon source may be added to enhance hydrogen production.