Yoshitomo Watanabe

Photosynthetic Production of Microalgal Biomass in a Raceway System under Greenhouse Conditions in Sendai City

The photosynthetic productivities of the marine microalgae Chlorophyta sp. and freshwater microalgae Chlorella sp. were investigated in a raceway system under greenhouse conditions in Sendai city. The system was constructed with a surface area of 0.986 m2 and equipped with paddle wheels (8 fins). The semicontinuous batch culture experiment was carried out for 4 months from June to October 1998 in Sendai city. The productivity of Chlorophyta sp. was ranged from 4 to 13 g.m(-2).d(-1) and the average was 8.2 g.m(-2).d(-1), which corresponded to the photosynthetic efficiency of 4.15% (PAR). The productivity of Chlorella sp. was ranged from 7 to 21 g.m(-2).d(-1) and the average was 13.2 g.m(-2).d(-1), which corresponded to the photosynthetic efficiency of 6.56% (PAR). These results indicate that stable microalgal cultivation with comparatively high photosynthetic efficiency could be obtained in a raceway system under greenhouse conditions in Sendai city located in the northern part of Japan.

Investigation of photobioreactor design for enhancing the photosynthetic productivity of microalgae

As photosynthetic efficiencies are relatively high at irradiation levels of <500 micromol m(-2) s(-1), photosynthetic productivity could be increased by redistributing strong light over a larger photo-receiving area using conical, helical, tubular photobioreactors (HTP). When Chlorella were exposed to light irradiation of 980 micromol m(-2) s(-1), the ratio of productivities was 1.00:1.13:1.23:1.66 for conical HTPs with cone angles of 180 degrees (flat type), 120 degrees, 90 degrees, and 60 degrees, respectively. This suggests that photo-redistribution technology is a highly effective and convenient approach for increasing the photosynthetic productivity of microalgae.

Isolation and determination of cultural characteristics of microalgae which functions under CO2 enriched atmosphere

A fresh-water microalgae, which functions under CO2 enriched atmosphere conditions, was isolated and its cultural characteristics were investigated. The HA-1 strain, identified as genus Chlorella, was newly isolated from a paddy field by an enrichment culture using reproduced stack gases from a thermal power plant with a concentration of CO2 and O2 of 15% and 2% respectively. It showed maximum growth at 10% CO2 enriched air flowing condition, and showed a good growth rate in a broad range of physically controllable conditions, including CO2 enriched air flow rate, temperature and pH value. The results indicated the feasibility of the HA-1 strain for mass cultivation using stack gases.

High photosynthetic productivity of green microalga Chlorella sorokiniana

The batch culture of a newly isolated strain of a green microalga, Chlorella sorokiniana, was carried out using a conical helical tubular photobioreactor. The isolate was capable of good growth at 40°C under an airstream enriched with 10% CO2. The maximum photosynthetic productivity was 34.4g of dry biomass/(m2 of installation area · d) (12-h light/12-h dark cycle) when the cells were illuminated with an average photosynthetic photon flux density (photosynthetically active radiation ([PAR] 400–700 nm) simulating the outdoors in central Japan (0.980 mmol photons/[m2·s]). This corresponded to a photosynthetic efficiency of 8.67% (PAR), which was defined as the percentage of the light energy recovered as biomass (394 kJ/[reactor·d]) to the total light energy received (4545 kJ/[reactor·d]). A similarly high photosynthetic efficiency (8.12% [PAR]) was also attained in the combined presence of 10% CO2, 100 ppm of NO, and 25 ppm of SO2. Moreover, good photosynthetic productivity was also obtained under high temperature and high light intensity conditions (maximum temperature, 46.5°C; 1.737 mmol photons/[m2·s]), when simulating the strong irradiance of the midday summer sun. This strain thus appears well suited for practical application for converting CO2 present in the stack gases emitted by thermal power plants and should be feasible even during the hot summer weather.

CO2 fixation by Chlorella sp. HA-1 and its utilization

Abstract Growth response of Chlorella sp. HA-1 against NOx and SOx were investigated. Chlorella sp. HA-1 was tolerant to an air containing 10% CO2 and NOx which corresponded to the stack gas from LNG thermal power plant. Chlorella sp. HA-1 cells contained 0.57g protein and 0.18g lipids per g dry cells. Its artificial digestibility was 85.9%, so high value as Chlorella cells. These results indicate that the HA-1 cells are valuable as a fodder for the livestock.

Development of a photobioreactor incorporating Chlorella sp. for removal of CO2 in stack gas

We developed a new design photobioreactor incorporating Chlorella sp. for removal of CO2 in stack gas. Photosynthetic conversion of CO2 into Chlorella biomass was investigated in a photobioreactor, which we termed a cone-shaped helical tubular photobioreactor. The laboratory scale photobioreactor (0.48 m high × 0.57 m top diameter) was set up with a 0.255 m2 installation area. The photostage was made from transparent polyvinyl chloride (PVC) tubing (1.6 cm internal diameter with 2 cm wall thickness and 27 m in length). The inner surface of the cone-shaped photostage (0.50 m2) was illuminated with a metal halide lamp, the energy input into the photostage [photosynthetically active radiation (PAR, 400–700 nm)] was 2127 KJ day−1 (12 h day / 12 h night). The maximum daily photosynthetic efficiency was 5.67% (PAR) under an air-lift operation at a flow rate of 0.3 litre min−1 10 % CO2 enriched air. Maximum increase of Chlorella biomass was 21.5 g dry biomass m−2 (installation area) day−1 or 0.68 g dry biomass litre medium−1 day−1. Also, a helical tubular photobioreactor for outdoor culture was constructed with a 1.1 m2 installation area (1.2 m top diameter) and photosynthetic productivity was investigated in July 1996.

Photosynthetic CO2 conversion technologies using a photobioreactor incorporating microalgae - energy and material balances -

Since microalgae have a high photosynthetic capability, solar energy-driven CO 2 fixation technologies using microalgae have the potential to convert CO 2 in the stack gas from a thermal power station into energy-rich biomass. We investigated a new design of photobioreator in order to achieve efficient photosynthetic performance. The system has several advantages over the conventional mass culture system of microalgae. We have investigated the energy and material balances of microalgal biomass production in a photobioreactor system both theoretically and experimentally. CO 2 conversion to microalgal biomass in the laboratory scale conical-shaped helical tubular photobioreactor incorporating Spirulina platensis was investigated. The photobioreactor system was constructed with a basal area of 0.255 m 2 .The total volume of photostage was 6.23 litre with 0.651 m 2 light absorbing area ( inner surface of cone). The photostage was illuminated with cool white fluorescent lamps, the daily energy input of the photosynthetic active radiation (PAR, 400-700nm) into the photobioreactor was 1249 kJ. The productivity of Spirulina platensis of this photobioreactor was 15.9 g dry biomass per m 2 (basal area) per day,or 0.51 g dry biomass litre -1 day -1 . This corresponded to a photosynthetic efficiency of 6.83 % (PAR). According to these results, a large scale microalgal production using a unit basic type photobioreactor (1 m 2 basal area) is discussed.

Trace-Level Mercury Ion (Hg2+) Analysis in Aqueous Sample Based on Solid-Phase Extraction Followed by Microfluidic Immunoassay

Mercury is considered the most important heavy-metal pollutant, because of the likelihood of bioaccumulation and toxicity. Monitoring widespread ionic mercury (Hg(2+)) contamination requires high-throughput and cost-effective methods to screen large numbers of environmental samples. In this study, we developed a simple and sensitive analysis for Hg(2+) in environmental aqueous samples by combining a microfluidic immunoassay and solid-phase extraction (SPE). Using a microfluidic platform, an ultrasensitive Hg(2+) immunoassay, which yields results within only 10 min and with a lower detection limit (LOD) of 0.13 μg/L, was developed. To allow application of the developed immunoassay to actual environmental aqueous samples, we developed an ion-exchange resin (IER)-based SPE for selective Hg(2+) extraction from an ion mixture. When using optimized SPE conditions, followed by the microfluidic immunoassay, the LOD of the assay was 0.83 μg/L, which satisfied the guideline values for drinking water suggested by the United States Environmental Protection Agency (USEPA) (2 μg/L; total mercury), and the World Health Organisation (WHO) (6 μg/L; inorganic mercury). Actual water samples, including tap water, mineral water, and river water, which had been spiked with trace levels of Hg(2+), were well-analyzed by SPE, followed by microfluidic Hg(2+) immunoassay, and the results agreed with those obtained from reduction vaporizing-atomic adsorption spectroscopy.

Microfluidic heavy metal immunoassay based on absorbance measurement.

A simple and rapid flow-based multioperation immunoassay for heavy metals using a microfluidic device was developed. The antigen-immobilized microparticles in a sub-channel were introduced as the solid phase into a main channel structures through a channel flow mechanism and packed into a detection area enclosed by dam-like structures in the microfluidic device. A mixture of a heavy metal and a gold nanoparticle-labeled antibody was made to flow toward the corresponding metal through the main channel and make brief contact with the solid phase. A small portion of the free antibody was captured and accumulated on the packed solid phase. The measured absorbance of the gold label was proportional to the free antibody portion and, thus, to the metal concentration. Each of the monoclonal antibodies specific for cadmium-EDTA, chromium-EDTA, or lead-DTPA was applied to the single-channel microfluidic device. Under optimized conditions of flow rate, volume, and antibody concentration, the theoretical (antibody K(d)-limited) detection levels of the three heavy metal species were achieved within only 7 min. The dynamic range for cadmium, chromium, and lead was 0.57-60.06 ppb, 0.03-0.97 ppb, and 0.04-5.28 ppb, respectively. An integrated microchannel device for simultaneous multiflow was also successfully developed and evaluated. The multiplex cadmium immunoassay of four samples was completed within 8 min for a dynamic range of 0.42-37.48 ppb. Present microfluidic heavy metal immunoassays satisfied the Japanese environmental standard for cadmium, chromium and, lead, which provided in the soil contamination countermeasures act.

Label-free impedimetric immunoassay for trace levels of polychlorinated biphenyls in insulating oil.

A rapid, ultrasensitive, and practical label-free impedimetric immunoassay for measuring trace levels of total polychlorinated biphenyls (PCBs) in insulating oil was developed. First, we developed a novel monoclonal antibody (RU6F9) for PCBs by using a designed immunogen and characterized its binding affinity for a commercial mixtures of PCBs and its main congeners. A micro comblike gold electrode was fabricated, and the antibody was covalently immobilized on the electrode through a self-assembled monolayer formed by dithiobis-N-succinimidyl propionate. The antigen-binding event on the surface of the functionalized electrode was determined as the change in charge transfer resistance by using electrochemical impedance spectroscopy. The resulting impedimetric immunoassay in aqueous solution achieved a wide determination range (0.01-10 μg/L) and a low detection limit (LOD) of 0.001 μg/L, which was 100-fold more sensitive than a conventional flow-based immunoassay for PCBs. By combining the impedimetric immunoassay with a cleanup procedure for insulating oil utilizing a multilayer cleanup column followed by DMSO partitioning, an LOD of 0.052 mg/kg-oil was achieved, which satisfied the Japanese regulation criterion of 0.5 mg/kg-oil. Finally, the immunoassay was employed to determine total PCB levels in actual used insulating oils (n = 33) sampled from a used transformer containing trace levels of PCBs, and the results agreed well with the Japanese official method (HRGC/HRMS).