Qian Fu

Kinetic characteristics and modeling of microalgae Chlorella vulgaris growth and CO2 biofixation considering the coupled effects of light intensity and dissolved inorganic carbon.

Understanding and optimizing the microalgae growth process is an essential prerequisite for effective CO2 capture using microalgae in photobioreactors. In this study, the kinetic characteristics of microalgae Chlorella vulgaris growth in response to light intensity and dissolved inorganic carbon (DIC) concentration were investigated. The greatest values of maximum biomass concentration (Xmax) and maximum specific growth rate (μmax) were obtained as 2.303 g L(-1) and 0.078 h(-1), respectively, at a light intensity of 120 μmol m(-2) s(-1) and DIC concentration of 17 mM. Based on the results, mathematical models describing the coupled effects of light intensity and DIC concentration on microalgae growth and CO2 biofixation are proposed. The models are able to predict the temporal evolution of C. vulgaris growth and CO2 biofixation rates from lag to stationary phases. Verification experiments confirmed that the model predictions agreed well with the experimental results.

A thermophilic gram-negative nitrate-reducing bacterium, Calditerrivibrio nitroreducens, exhibiting electricity generation capability.

To exploit the potential diversity of thermophilic exoelectrogens, two-chamber microbial fuel cells (MFCs) were inoculated with thermophilic anaerobic digester sludge and operated at 55 °C without supplementing with exogenous redox mediator. The MFC generated a maximum power density of 823 mW m(-2) after 200 h of operation. Molecular phylogenetic analyses suggested that the microbial population on the anode was dominated by a species closely related to a thermophilic nitrate-reducing bacterium Calditerrivibrio nitroreducens, for which a strain (Yu37-1) has been isolated in pure culture. Thus, a pure culture of the C. nitroreducens strain Yu37-1 was inoculated into MFC to examine the electricity generation capability. Without an exogenous mediator, MFCs stably produced electricity with a maximum power density of 272 mW m(-2) for >400 h of operation. The MFC current recovered to the original level within few hours after medium replacement, suggesting that the electricity generation was caused by the anodic microorganisms. Cyclic voltammetry indicated that redox systems (E3 and Ec) with similar potentials (-0.14 and -0.17 V) made the main contributions to the exoelectrogenic activities of the sludge-derived consortium and C. nitroreducens Yu37-1, respectively. This study undertook the bioelectrochemical characterization of C. nitroreducens as the first example of a thermophilic Gram-negative exoelectrogen.

Bio-electrochemical property and phylogenetic diversity of microbial communities associated with bioelectrodes of an electromethanogenic reactor.

Electromethanogenesis is a new bio-electrochemical reaction potentially useful for energy conversion. As a first step toward its technical application, electromethanogenic reactors were built, and their bio-electrochemical properties were analyzed. Comparisons of the microbial compositions of the electromethanogenic cathode and the current-producing anode suggested an electromethanogenic pathway mediated by exoelectrogenic bacteria.

Integrating planar waveguides doped with light scattering nanoparticles into a flat-plate photobioreactor to improve light distribution and microalgae growth.

Industrially manufactured planar waveguides doped with light scattering nanoparticles, which can dilute and redistribute the intense incident light within microalgae suspension more uniformly, were introduced into a flat-plate photobioreactor (PBR) with a width of 25cm to alleviate the adverse effect of poor light penetrability on microalgae growth. Compared with the flat-plate PBR without waveguides, the illumination surface area per unit volume in the proposed PBR was increased by 10.3 times. During the whole cultivation period, the illuminated volume fractions in the proposed PBR were 21.4-410% higher than those in the flat-plate PBR without waveguides. Consequently, attributed to the optimized light distribution in the proposed PBR, a 220% improvement in biomass production was obtained relative to that in the flat-plate PBR without waveguides. Furthermore, higher light output intensities emitted from the planar waveguide surfaces and increased microalgae growth rates were achieved by decreasing the length of planar waveguides.

Enhancement of microalgae production by embedding hollow light guides to a flat-plate photobioreactor

To offset the adverse effects of light attenuation on microalgae growth, hollow polymethyl methacrylate (PMMA) tubes were embedded into a flat-plate photobioreactor (PBR) as light guides. In this way, a fraction of incident light could be transmitted and emitted to the interior of the PBR, providing a secondary light source for cells in light-deficient regions. The average light intensity of interior regions 3-6cm from surfaces with 70μmolm(-2)s(-1) incident light was enhanced 2-6.5 times after 3.5days cultivation, resulting in a 23.42% increase in biomass production to that cultivated in PBR without PMMA tubes. The photosynthetic efficiency of microalgae in the proposed PBR was increased to 12.52%. Moreover, the installation of hollow PMMA tubes induced turbulent flow in the microalgae suspension, promoting microalgae suspension mixing. However, the enhanced biomass production was mainly attributed to the optimized light distribution in the PBR.

Enhanced biofilm distribution and cell performance of microfluidic microbial fuel cells with multiple anolyte inlets.

A laminar-flow controlled microfluidic microbial fuel cell (MMFC) is considered as a promising approach to be a bio-electrochemical system (BES). But poor bacterial colonization and low power generation are two severe bottlenecks to restrict its development. In this study, we reported a MMFC with multiple anolyte inlets (MMFC-MI) to enhance the biofilm formation and promote the power density of MMFCs. Voltage profiles during the inoculation process demonstrated MMFC-MI had a faster start-up process than the conventional microfluidic microbial fuel cell with one inlet (MMFC-OI). Meanwhile, benefited from the periodical replenishment of boundary layer near the electrode, a more densely-packed bacterial aggregation was observed along the flow direction and also the substantially low internal resistance for MMFC-MI. Most importantly, the output power density of MMFC-MI was the highest value among the reported µl-scale MFCs to our best knowledge. The presented MMFC-MI appears promising for bio-chip technology and extends the scope of microfluidic energy.

An annular photobioreactor with ion-exchange-membrane for non-touch microalgae cultivation with wastewater

To eliminate the negative impacts of pollutants in wastewater (such as suspended solids, excess N, P, heavy metals) on microalgae growth, an annular ion-exchange-membrane photobioreactor (IEM-PBR) was proposed in this study. The IEM-PBR could avoid direct mixing of algae cells with wastewater by separating them into two chambers. In the IEM-PBR, the nutrients (mainly N and P) in wastewater continuously permeated into microalgae cultures through the ion-exchange-membrane for microalgae growth, while the pollutants hardly permeated into microalgae cultures. Three types of representative wastewater were investigated to evaluate the performance of the IEM-PBR. When cultivated with wastewater containing excess nutrients, high turbidity and excess heavy metals, microalgae biomass concentrations were significantly improved from 2.34, 2.15 and 0gL(-1) in the traditional PBR to 4.24, 3.13 and 2.04gL(-1) in the IEM-PBR. Correspondingly, the removal efficiencies of N and P in wastewater were also greatly improved by using the IEM-PBR.

Electrochemical and phylogenetic analyses of current-generating microorganisms in a thermophilic microbial fuel cell.

To explore diversity of thermophilic exoelectrogens, a thermophilic microbial fuel cell was constructed. Population analysis of the anodic microorganisms suggested possible involvement of Caloramator-related bacteria in electricity generation. Pure culture of Caloramator australicus showed electricity-generating ability, indicating that the bacterium is a new thermophilic exoelectrogen.

Comparison of Chlorella vulgaris biomass productivity cultivated in biofilm and suspension from the aspect of light transmission and microalgae affinity to carbon dioxide

To investigate light transmission and cells affinity to CO2, Chlorellavulgaris was attached to microfiltration membrane that laid on the solidified BG11 medium compared to that in suspended cultivation mode in this study. The results showed that C. vulgaris showed a 30.4% higher biomass production (103gm-2) in attached than in suspend system. The upper layer of biofilm with a thickness of 41.31μm (the corresponding areal density of 40gm-2) was effectively illuminated under light intensity of 120μmolm-2s-1 and more than 40% of the microalgal cells were in light even the areal density was high to 100gm-2. While only 2.5% of the cells were effectively illuminated in the suspended cultivation system. Furthermore, microalgae cells in biofilm showed a higher affinity to CO2 compared with that in suspension, and CO2 saturation point of microalgae cells in biofilm was 1.5% but 4.5% in suspension.

Improvement on light penetrability and microalgae biomass production by periodically pre-harvesting Chlorella vulgaris cells with culture medium recycling

To improve light penetrability and biomass production in batch cultivation, a cultivation mode that periodically pre-harvesting partial microalgae cells from suspension with culture medium recycling was proposed. By daily pre-harvesting 30% microalgae cells from the suspension, the average light intensity in the photobioreactor (PBR) was enhanced by 27.05-122.06%, resulting in a 46.48% increase in total biomass production than that cultivated in batch cultivation without pre-harvesting under an incident light intensity of 160μmolm(-2)s(-1). Compared with the semi-continuous cultivation with 30% microalgae suspension daily replaced with equivalent volume of fresh medium, nutrients and water input was reduced by 60% in the proposed cultivation mode but with slightly decrease (12.82%) in biomass production. No additional nutrient was replenished when culture medium recycling. Furthermore, higher pre-harvesting ratios (40%, 60%) and lower pre-harvesting frequencies (every 2, 2.5days) were not advantageous for the pre-harvesting cultivation mode.