Treatment of real wastewater using co-culture of immobilized Chlorella vulgaris and suspended activated sludge.

The use of algal-bacterial symbiotic association establishes a sustainable and cost-effective strategy in wastewater treatment. Using municipal wastewater, the removal performances of inorganic nutrients (nitrogen and phosphorus) and organic pollutants were investigated by the co-culture system having different inoculum ratios (R) of suspended activated sludge to alginate-immobilized microalgae Chlorella vulgaris. The co-culture reactors with lower R ratios obtained more removal of nitrogen than in pure culture of C. vulgaris. The reactor with R = 0.5 (sludge/microalgae) showed the highest performance representing 66% removal after 24 h and 95% removal after 84 h. Phosphorus was completely eliminated (100%) in the co-culture system with inoculum ratios of 0.5 and 1.0 after 24 h and in the pure C. vulgaris culture after 36 h. The COD level was greatly reduced in the activated sludge reactor, while, it was increasing in pure C. vulgaris culture after 24 h of incubation. However, COD was almost stabilized after 24 h in the reactors with high R ratios such as 2.0, 5.0, and 10 due to the higher concentration of activated sludge. The growth of C. vulgaris was promoted from 0.03 g/L/d to 0.05 g/L/d in the co-culture of low inoculum ratios such as R = 0.5, implying that there exist an optimum inoculum ratio in the co-culture system in order to achieve efficient removal of nutrients.

Nitrate repletion strategy for enhancing lipid production from marine microalga Tetraselmis sp.

The cell growth rate and cellular lipid content of microalgae are affected by the nitrogen levels during cultivation. The growth rate and lipid content of marine microalga Tetraselmis sp. was found to increase under nitrate replete conditions, but not under deplete conditions. Thus, in order to enhance the lipid productivity of Tetraselmis sp., a two-stage culture process utilizing nitrate replete condition was applied. When the cells were cultivated in F/2 medium for five days in the first stage, the obtained lipid content and productivity were 22.4% and 26.7mgL(-1)d(-1), respectively. After second stage of cultivation for a further 36h under nitrate replete conditions with 8.82mM NaNO3, increased biomass concentration of 1.32gL(-1) and lipid content of 30.5% were obtained, with an enhanced lipid productivity of 47.3mgL(-1)d(-1).

Degradation and changes in toxicity and biodegradability of tetracycline during ozone/ultraviolet-based advanced oxidation.

Advanced oxidation processes (AOPs) composed of O3, H2O2 and ultraviolet (UV) were applied to degrade tetracycline (TC). Degradation efficiency was evaluated in terms of changes in absorbance (ABS) and total organic carbon (TOC). The change in biotoxicity was monitored with Escherichia coli and Vibrio fischeri. The improvement in biodegradability during oxidation was demonstrated through 5-day biochemical oxygen demand/chemical oxygen demand ratio and aerobic biological treatment. The combination of O3/H2O2/UV and O3/UV showed the best performance for the reductions in ABS and TOC. However, mineralization and detoxification were not perfect under the experimental conditions that were used in this study. Therefore, for the ultimate treatment of TC compounds, it is suggested that AOP treatment is followed by biological treatment, utilizing enhanced biodegradability. In this study, aerobic biological treatment by Pseudomonas putida was performed for O3/UV-treated TC. It was confirmed that O3/UV treatment improved TOC reduction and facilitated complete mineralization in biological treatment.

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.

Hydrogen production by immobilized Chlorella vulgaris: optimizing pH, carbon source and light.

The effects of light, pH and organic carbon sources were investigated on hydrogen production by algae. An optical fiber was examined as an internal light source. The optical fiber rendered prolonged lag time and total time of hydrogen production. The optimal pH to produce hydrogen for Chlorella sp. was 8.0. Glucose, fructose, sucrose and malt extract were compared as organic carbon sources. The optimal dose of each carbon source was 5 g/L for maximum hydrogen yield. Sucrose produced the largest hydrogen volume (1,315 ml/L), while the highest production rate (24 ml/L/h) was observed in the presence of fructose.

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 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.

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.

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.

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.

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 ionic speciation of lysine on its adsorption and desorption through a sulfone-type ion-exchange column.

Lysine produced during microbial fermentation is usually recovered by an ion-exchange process, in which lysine is first converted to the cationic form (by lowering the pH to less than 2.0 with sulfuric acid) and then fed to a cation-exchange column containing an exchanger that has a sulfone group with a weak counterion such as NH4+. Ammonia water with a pH above 11 is then supplied to the column to displace the purified lysine from the column and allow its recovery. To enhance the adsorption capacity and for a possible reduction in chemical consumption, monovalent lysine fed at pH 4 was investigated in comparison with conventional divalent lysine fed at pH 1.5. The adsorption capacity increased by more than 70% on a mass basis using pH 4 feeding compared with pH 1.5 feeding. Lysine adsorbed at pH 4 started to elute earlier than that adsorbed at pH 1.5 when ammonia water was used as the eluant solution, and the extent of early elution became more notable at lower concentrations of ammonia. Moreover, the elution of monovalent lysine fed at pH 4 displayed a stiffer front boundary and higher peak concentration. However, when the ammonium concentration was greater than 2.0 N, complete saturation of the bed was delayed during adsorption and the percent recovery yield from elution was lowered, both drawbacks that were considered inevitable features originating from the increased adsorption of monovalent lysine.

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.

A colorimetric confirmation method for DNA amplification in PCR and its application to the detection of Giardia lamblia cysts.

A simple and quick colorimetric method for confirming DNA amplification in polymerase chain reactions (PCR) is described and has been applied to the amplification of Giardia lamblia DNA. This method detects the release of pyrophosphate based on the competition between 1, 10-phenanthroline and pyrophosphate complexing with ferrous ion. When 1, 10-phenanthroline complexed with Fe2+ is added to the finished PCR solution, depending on whether or not the DNA was amplified, the mixture is, respectively, either bleached or red. The color changed optimally for 20-30 min at 60-80 degrees C, and the result could be determined by detecting an absorbancy change at 510 nm or a color change discernible to the naked eye. The extent of change in absorbance was proportional to the amount of pyrophosphate produced.

Influence of alcohol cosurfactants on surfactant-enhanced flushing of diesel-contaminated soil.

The effects of medium-chain alcohols on the surfactant-enhanced diesel removal from contaminated sandy soil were investigated. The mixture of Tween 80, which has a double bond in its hydrophobic structure, and hexanol showed the best performance of diesel removal among the combinations of surfactants (Tween 20, Tween 60, and Tween 80) and alcohols (n-butanol, n-pentanol, and n-hexanol) used in this study. The efficiency of diesel flushing increased as the alkyl-chain length of the alcohol and the alcohol fraction in the flushing solution increased. Meanwhile, the removal rate was reduced when the surfactant concentration was too high most likely due to the surfactant aggregation or emulsion formation. A pulsed pumping of flushing solution was not beneficial for improving the removal rate under the experimental conditions described in this study.