Liandong Zhu

Nutrient removal and biodiesel production by integration of freshwater algae cultivation with piggery wastewater treatment.

An integrated approach, which combined freshwater microalgae Chlorella zofingiensis cultivation with piggery wastewater treatment, was investigated in the present study. The characteristics of algal growth, lipid and biodiesel production, and nutrient removal were examined by using tubular bubble column photobioreactors to cultivate C. zofingiensis in piggery wastewater with six different concentrations. Pollutants in piggery wastewater were efficiently removed among all the treatments. The specific growth rate and biomass productivity were different among all the cultures. As the initial nutrient concentration increased, the lipid content of C. zofingiensis decreased. The differences in lipid and biodiesel productivity of C. zofingiensis among all the treatments mainly resulted from the differences in biomass productivity. It is worthy of note that the diluted piggery wastewater with 1900 mg L(-1) COD provided an optimal nutrient concentration for C. zofingiensis cultivation, where the advantageous nutrient removal and the highest productivities of biomass, lipid and biodiesel were presented.

Scale-up potential of cultivating Chlorella zofingiensis in piggery wastewater for biodiesel production

Scale-up potential of cultivating Chlorella zofingiensis in piggery wastewater for simultaneous wastewater treatment and biodiesel production was tested. The cultivation of C. zofingiensis with autoclaved wastewater and NaClO-pretreated wastewater, cultivation of algae indoors and outdoors, and stability of semi-continuous feeding operation were examined. The results showed that C. zofingiensis cultivated in piggery wastewater pretreated by autoclaving and NaClO had no evident difference in the performance of nutrient removal, algal growth and biodiesel production. The outdoor cultivation experiments indicated that C. zofingiensis was able to adapt and grow well outdoors. The semi-continuous feeding operation by replacing 50% of algae culture with fresh wastewater every 1.5 days could provide a stable net biomass productivity of 1.314 g L(-1) day(-1). These findings in this study can prove that it is greatly possible to amplify the cultivation of C. zofingiensis in piggery wastewater for nutrient removal and biodiesel production.

Temperature dependence of optical gain, quantum efficiency, and threshold current in GaAs/GaAlAs graded-index separate-confinement heterostructure single-quantum-well lasers

The temperature dependence of the optical gain in graded-index separate-confinement heterostructure single-quantum-well lasers with different quantum-well widths were investigated. The observed dependence of the kink temperature on cavity loss and quantum-well width and the differential quantum efficiency minimum at the kink temperature were analyzed in terms of the temperature variation of the gain spectra and peak gain curves. Dependences of the characteristic temperature T/sub 0/ on the quantum-well width, cavity loss, and temperature range are discussed in terms of the variation of the peak modal gain versus current relation with temperature and quantum-well width. >

Comparison of vertical-flow constructed wetlands with and without supplementary aeration treating decentralized domestic wastewater

Constructed wetlands (CWs) are efficient in reducing excessive contamination from wastewaters. However, oxygen inside CW beds is frequently low especially when substrate clogging problems appear after long-term operation, and this may become a limited factor for the treatment of wastewaters. Aimed at dealing with the issue of a low oxygen content in CW systems, two laboratory-scale vertical-flow constructed wetlands (VFCWs) with and without an aeration device (called VFCW-a and VFCW-c, respectively) were designed in this study to test the contribution of supplementary aeration to the treatment of decentralized domestic wastewater. Results showed that under the intermittent operation of about 45 days, two VFCW units were successfully started up by using activated sludge as seed sludge. Compared to VFCW-c, VFCW-a had a better resistance ability to organic shock loads and its removal function could be effectively recovered within a short period after the introduction of organic shock loads. Under intermittent operation with a 12 h idling time, the ideal hydraulic retention time (HRT) of VFCW-a was 42 h, about 6 h shorter than that of VFCW-c. Likewise, under intermittent operation with 42 h HRT, the ideal idling time of VFCW-a was 12 h, still about 6 h shorter than that of VFCW-c. Under intermittent operation with HRT-42 h and an idling time of 12 h, SS, COD, TN and TP removal efficiencies in VFCW-a could reach 81.2%, 85%, 89.9% and 77.9%, respectively. The VFCW unit with supplementary aeration is an efficient innovation for the treatment of decentralized domestic wastewater.

Optical gain in GaAs/GaAlAs graded-index separate-confinement single-quantum-well heterostructures

Optical model gain in both the TE and TM polarizations of graded-index separate-confinement single-quantum-well heterostructure lasers measured at various levels of injection current on samples with different quantum-well widths is discussed. Lasers with wide quantum wells (>or=120 AA) have emission and gain spectra which exhibit two peaks, caused by the n=1 and n=2 subband transitions. With ordinary cavity parameters, the saturation gain of the n=1 subband transitions is lower than the cavity loss of the laser, and the lasers always lase at the n=2 transitions. Reducing the quantum-well width increases the saturation gain of the n=1 transitions enough to allow lasing from them, even in cases of higher cavity loss. Further, for a fixed cavity loss, reduction of the quantum-well width decreases the threshold current density for n=1 lasing transitions, while that for n=2 lasing increases. The superlinear increase of the material gain with the decrease of the well width reduces the minimum cavity length for n=1 subband lasing. Narrower quantum wells with higher mirror reflectivity allow shorter cavity lengths while retaining n=1 lasing, resulting in low threshold current. >

Oil production from pilot-scale microalgae cultivation: An economics evaluation

ABSTRACT Of the potential sources of renewables, the most promising one is microalgae, which are viewed as a biofuel feedstock and technological solution for CO2 sequestration. Among microalgae-derived biofuels, biodiesel is one of the best application choices since microalgae have substantial amounts of oils. Nonetheless, microalgal biodiesel production is still in its infancy, since there is no commercial production on a large scale. The economic data and evaluation related to microalgal biodiesel production are incomplete and out of date, although lots of technological research has been carried out. This article demonstrates the pilot scale cultivation of microalgae in photobioreactors and evaluates the economics of producing oil from microalgae, including net energy ratio and cost-effectiveness evaluation. The contribution of this article lies in the presentation of an updated analysis of economic conditions for pilot scale microalgal oil production, which can provide the direction for future development of this important biofuel process.

Using magnetic materials to harvest microalgal biomass: evaluation of harvesting and detachment efficiency

ABSTRACT Using naked iron oxide (Fe3O4) and yttrium iron oxide (Y3Fe5O12) nanoparticles as flocculants, the harvesting efficiency of Chlorella vulgaris biomass was investigated. The harvesting process includes two steps, which are the separation of microalgae from the culture solution with the magnetic nanoparticles and then the separation of the algae from the magnetic nanoparticles. The optimal dosages and pH values for the magnetic harvesting of microalgal biomass were determined. Results showed that Y3Fe5O12 nanoparticles were more efficient in microalgal biomass harvesting than Fe3O4 nanoparticles. In an effort to achieve more than 90% of harvesting efficiency, optimal dosages for Fe3O4 and Y3Fe5O12 to harvest microalgal biomass were 10 and 2.5 g/L, while the appropriate pH values were 6.2 and 7.3, respectively. The harvesting efficiency of Fe3O4 and Y3Fe5O12 nanoparticles increased as the pH value decreased. The experimental results also showed that under a higher pH value Fe3O4 nanoparticles were much easier to be separated from the flocs than Y3Fe5O12. 62.9% of Fe3O4 nanoparticles could be de-attached from the aggregates, when the floc pH value reached 12.3.

Biomass Accumulation of Chlorella Zofingiensis G1 Cultures Grown Outdoors in Photobioreactors

The complicated and changeable weather conditions and pest invasion increase difficulties in outdoor microalgae cultivation. In this paper, outdoor microalgae cultivation experiments were investigated in Foshan city, South China. During June and August when the temperature is high, the cooling system-water spray combined shade tarpaulin can effectively reduce the temperature to 4–7˚C in the 40 L vertical tubular outdoor photobioreactors. Under 300 mg/L urea and 200 mg/L ammonium bicarbonate conditions, Chlorella zofingiensis G1 had the largest biomass accumulation. Addition of acetic acid to adjust the pH of the medium can effectively improve the C. zofingiensis G1 biomass in the photobioreactor, which was four times more than that only through air ventilation conditions. The biomass accumulation of C. zofingiensis G1 was essentially unchanged during night time.