Hiroyasu Nagase

Biological elimination of nitric oxide and carbon dioxide from flue gas by marine microalga NOA-113 cultivated in a long tubular photobioreactor

Nitric oxide (NO) and carbon dioxide (CO2) were simultaneously eliminated from a model flue gas using a marine microalga, strain NOA-113, cultivated in a long tubular photobioreactor. About 40 mg of NO and 3.5 g of CO2 were eliminated per day in a 4-l reactor column with aeration of 300 ppm (v/v) NO and 15% (v/v) CO2 in N2 at a rate of 150 ml/min. This reactor system is thought to be suitable for evaluating NO elimination by microalgae. The effects of NO concentration, gas flow rate, and light conditions on NO elimination were investigated using this system.

Uptake pathway and continuous removal of nitric oxide from flue gas using microalgae

Abstract Nitric oxide (NO), a major constituent of NOx in fossil fuel flue gas, can be removed by the microalga, Dunaliella tertiolecta, in a bubble-column-type bioreactor. The uptake pathway of NO was investigated, and it was found that little NO was oxidized in the medium before its uptake by algal cells and that NO mostly permeated directly into the cells by diffusion based on the mass balance of nitrogen and the change in nitrate and nitrite concentration in the medium in batch culture. For further application of this system, it is necessary to remove NO over a long duration, and the stability of NO removal is important. NO removal rate of about 50–60% could be maintained stably for 15 days in continuous culture under the light condition. Because the consumption of nitrate was reduced by the amount of taken NO, NO rather than nitrate is preferentially utilized as a nitrogen source for cell growth. Therefore, this algal system is useful for continuous NO removal and production of algal biomass using NO as a nitrogen source.

Removal of hazardous phenols by microalgae under photoautotrophic conditions

Various algae were screened for their ability to decrease the concentration of 2,4-dinitrophenol (DNP), as a model compound of hazardous phenols, under photoautotrophic conditions. Chlorella fusca var. vacuolata and Anabaena variabilis grew well and showed high DNP removal ability over the concentration range of 5 to 40 microM. Their abilities to remove various phenols were investigated. More than 90% of 40 microM o- and m-nitrophenol and DNP was removed during the cultivation period of 5 d. o-, p-Chlorophenol and 2,4-dichlorophenol could be removed, but not to a significant extent. C. fusca also removed 85% of bisphenol A, suspected to be an endocrine disrupter. It was found that microalgae would be applicable to the removal of hazardous phenols without the addition of any organic carbon sources.

Characteristics of Biological NOx Removal from Flue Gas in a Dunaliella tertiolecta Culture System

Abstract A system for the biological removal of NOx from fuel flue gas was investigated using the unicellular microalga Dunaliella tertiolecta . When nitric oxide (NO), the main component of NOx in flue gas, was supplied to the algal culture in a bioreactor with a 2-m column in the light at concentrations ranging from 25 to 500 ppm, about 65% of the NO was removed. Under these conditions, cell growth was not affected by the concentration of the NO supplied, and about 1.6% O 2 was constantly evolved by photosynthesis. About 30% of the NO was removed by the medium without cells at 2% O 2 , in which case the NO was probably photochemically oxidized by Fe 3+ present in the medium. In cell cultures without Fe 3+ , however, 65% NO removal was achieved. In the dark, on the other hand, the rate of NO removal was governed by the amount of O 2 supplied in the inlet gas, i.e. , achievement of a NO removal rate similar to that achieved in the light required the presence of O 2 at 2% or more, and NO removal did not occur without the supply of O 2 . It is thus clear that both algal cells and O 2 are essential in the reactor system. NO removal is assumed to proceed as follows: NO in the gas is first dissolved in the aqueous phase, after which it is oxidized and assimilated by the algal cells. The results of investigations under various culture conditions indicate that the dissolution of NO in the aqueous phase is the rate-limiting step in this reactor system.

Improvement of Microalgal NOx Removal in Bubble Column and Airlift Reactors

Nitric oxide (NO), a major nitrogen oxide component in fossil fuel flue gas, was removed by the green alga Dunaliella tertiolecta cultivated in bubble column and airlift reactors. As NO removal was enhanced by increasing the dissolution of NO in water, increasing the gas-liquid contact area and time was deemed as an effective method for improving NO removal. The highest level of NO removal, 96%, was achieved with a counter-flow type airlift reactor when 100 ppm NO was aerated with smaller bubbles.

Biodegradation of bisphenol a and disappearance of its estrogenic activity by the green alga Chlorella fusca var. vacuolata

Bisphenol A (BPA) is known as an endocrine disruptor and often is found in landfill leachates. Removal of BPA by green alga, Chlorella fusca, was characterized, because we previously found that various phenols were well removed by this strain, including BPA. Chlorella fusca was able to remove almost all BPA in the concentration range from 10 to 80 microM for 168 h under continuous illumination at 18 W/m2. At the low light intensity of 2 W/m2, 82% of 40 microM BPA was removed, and only 27% was removed in the dark. Moreover, C. fusca could remove 90% of 40 microM BPA under the 8:16-h light:dark condition, which was almost as high as that under the continuous-light condition. The amount of BPA contained in the cells was less than the amount of BPA removed from the medium. Monohydroxybisphenol A was detected as an intermediate of BPA degradation. Moreover, estrogenic activity that originated from BPA in the culture medium also completely disappeared. Based on these results, BPA was finally degraded to compounds having nonestrogenic activity. Therefore, C. fusca can be considered a useful organism to remove BPA from landfill leachates.

A novel method using cyanobacteria for ecotoxicity test of veterinary antimicrobial agents.

The effect of antimicrobial agents for veterinary use on the growth of cyanobacteria was investigated by measuring minimum inhibitory concentration, medium effective concentration (EC50), and no-observed-effect concentration of seven antimicrobial agents for eight cyanobacteria. The results demonstrated that the seven antimicrobial agents, even at low concentrations, inhibited the growth of cyanobacteria. Microcystis aeruginosa and Synechococcus sp. had the highest sensitivity to the antimicrobial agents used in the present study. It is considered that the utilization of cyanobacteria would enable easy and highly sensitive assessment of the toxicity of such chemicals as antimicrobial agents. We suggest that cyanobacteria be used for ecotoxicity test in addition to the hitherto established method that uses green algae.

Removal of cadmium from aqueous solution by the filamentous cyanobacterium Tolypothrix tenuis

Cadmium removal was investigated using the filamentous cyanobacterium, Tolypothrix tenuis, which exhibited a high level of Cd tolerance and had the highest Cd removal ability among 17 cyanobacterial strains obtained in Thailand. The removal of Cd was equilibrated within 30 min, and the type of Cd removal could be described by the Langmuir isotherm. Cadmium removal by T. tenuis is thus suggested to be caused by adsorption of Cd onto the cell surface. T. tenuis showed consistent Cd adsorption ability over a wide range of temperature and pH. The adsorption of Cd was not strongly affected in the presence of Na, K, Ca, and Mg ions. These results suggest that T. tenuis may be applicable to the removal of Cd from surface and ground water in certain outdoor situations.

Ability of a Microbial Consortium to Remove Pesticide, Carbendazim and 2,4-Dichlorophenoxyacetic Acid

A bacterial consortium capable of simultaneously degrading the fungicide, carbendazim, and the herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) was obtained by enrichment of soil samples collected from paddy fields in Japan. This consortium was acclimated in a continuously fed culture with 20 μM carbendazim and 2 mM 2,4-D as sole carbon sources using a glass column reactor. By denaturing gradient gel electrophoresis, we observed changes in the bacterial population following the degradation of the both pesticides. This acclimated consortium completely degraded up to 100 μM carbendazim and 3 mM 2,4-D within 36 and 24 h, respectively, in batch culture, but a lag time was observed after precultivation in a rich medium. The immobilization of the consortium on a polyester support enhanced the degradation ability of this consortium compared with the use of free cells. This microbial consortium could be useful for bioremediation at sites contaminated with these pesticides.

Selective cadmium removal from hard water using NaOH-treated cells of the cyanobacterium Tolypothrix tenuis

Abstract Cadmium removal from water in the presence of Ca2+ or Mg2+ was investigated using the filamentous cyanobacterium Tolypothrix tenuis. Untreated cells of T. tenuis exhibited a low degree of selectivity with respect to the removal of Cd in the presence of Ca2+ or Mg2+. Pretreatment of cells with 0.1 M NaOH, however, greatly increased the level of their Cd adsorption. Langmuir parameters were calculated and the amounts of Cd adsorbed were compared for different concentrations of Ca2+. The results showed that NaOH pretreatment of cells increased their Cd adsorbing ability in the presence of Ca2+. Pretreatment with NaOH was also shown to be applicable to other cyanobacterial strains. It is thought that the biomass of filamentous cyanobacteria treated by NaOH could be utilized as a novel biosorbent for Cd removal, even from hard water containing a high concentration of Ca2+ and/or Mg2+.