Maria Teresa Gutierrez-Wing

Effect of dopant concentration on visible light driven photocatalytic activity of Sn1−xAgxS2

Tin(iv) sulfide (SnS2), as a mid-band-gap semiconductor shows good potential as an excellent photocatalyst due to its low cost, wide light spectrum response and environment-friendly nature. However, to meet the demands of large-scale water treatment, a SnS2 photocatalyst with a red-shifted band gap, increased surface area and accelerated molecule and ion diffusion is required. Doping is a facile method to manipulate the optical and chemical properties of semiconductor materials simultaneously. In this work, SnS2 photocatalysts with varied Ag doping content are synthesized through a facile one-step hydrothermal method. The product is characterized by XRD, SEM, TEM and UV-Vis spectrometry. The photocatalytic activity of the as-prepared Sn1-xAgxS2 is studied by the degradation of methylene blue (MB) dye under solar light irradiation. It is found that increasing the Ag dopant concentration can effectively increase the solar light adsorption efficiency of the photocatalyst and accelerate heterogeneous photocatalysis. The optimal concentration of Ag dopant is found to be 5% with the highest rate constant being 1.8251 hour-1. This study demonstrates that an optimal amount of Ag doping can effectively increase the photocatalytic performance of SnS2 and will promote the commercialization of such photocatalysts in the photocatalytic degradation of organic compounds.

Impact of light quality and quantity on growth rate kinetics of Selenastrum capricornutum

Microalgal biomass produced in indoor photobioreactors can be used as inoculum for large‐scale outdoor cultures or directly for the production of high‐value bioproducts due to the higher control of these cultures compared with outdoor systems. One of the main costs of indoor microalgal cultures is the illumination. This work can be used as a basis for the optimization of the light source for indoor microalgal biomass production, based on the light source type, irradiance, productivity, growth rate, attenuation coefficients, and contaminant growth on the reactors side‐walls. Four commercially available near 400‐W artificial light sources for microalgal cultures (metal halide (MH), high‐pressure sodium (HPS), Son Agro®, and fluorescent) were compared. The light elevation and the surface scalar irradiance were shown to have a linear relationship. The attenuation coefficient in air (ka) was highest with Son Agro®. A linear partition of the attenuation coefficient between the water and biomass and an exponential relationship between average scalar irradiance and depth were found. An empirical overall scalar attenuation coefficient for each light source was obtained. The lowest maximum observed growth rate was obtained with fluorescent light (0.98 d−1) and the highest with Son Agro® (2.39 d−1). The highest growth on the reactors wall was obtained with Son Agro®. Further studies resulted in a higher maximum specific growth rate and optimum irradiance for HPS (2.37 d−1 and 460 μmol s−1 m−2) compared with those observed with MH (1.73 d−1 and 391 μmol s−1 m−2).

Anaerobic biodegradation of polyhydroxybutyrate in municipal sewage sludge.

Anaerobic biodegradation in sewage sludge of polyhydroxybutyrate (PHB) was investigated. Evolved gaseous carbon was measured to assess biodegradability according to ASTM D5210. Mass-loss experiments were performed to determine degradation kinetics. Changes in the polymer properties were investigated. The impact of a natural plasticizer [tributyl citrate (TBC)] on biodegradation was determined. Polylactic acid was also biodegraded for comparison. Melt-pressed plates of PHB (with thicknesses of 0.24, 0.5, 1.2, 3.5, and 5.0 mm) were biodegraded to investigate the relationship between initial mass:initial surface area ratios and decay rates. Scanning electron microscopy micrographs of degraded specimens were recorded for visual illustration of the degradation process. A relationship between initial mass:initial surface area and degradation rates indicates that the thickness and surface area of the material affect its degradation. The degradation rates were impacted by the sewage sludge activity. TBC additive hindered PHBs rate of degradation. Thermal properties, molecular bonding, and molecular weight measured by differential scanning calorimetry, Fourier transform infrared, and size exclusion chromatography, respectively, were only slightly affected by biodegradation, indicating that recycling PHB will not affect its performance.

Light irradiance and spectral distribution effects on microalgal bioreactors

The irradiance and light spectral distribution affect the growth and productivity of microalgal cultures. In extensive open pond cultures, the light control has limited options, mainly the culture depth. In photobioreactors, besides the culture depth, the light source, configuration of the reactor, light pathway, and flow rate can be used to control the characteristics of the light available to the cultures. The change of light conditions can also be used to modify the composition of the microalgal biomass produced to optimize the production of bioproducts of interest. Additionally, in mixed cultures, the species composition can be influenced by the light quantity and quality. Determining the effect of the light quantity and quality in photosynthetic cultures will help to develop strategies to optimize the production of biomass, lipids, pigments, proteins, and other compounds of interest in photosynthetic microorganisms. Information obtained from bench scale cultures can rarely be applied directly to large‐scale bioreactors. Nonetheless, determining the kinetic parameters of microalgal cultures at bench scale will reduce the time needed to optimize the cultures in photobioreactors. In this work, a review of the main factors is presented, along with specific examples of the effect of light quality and quantity in cultures with single and multiple species. Additionally, some models to predict the effect of light on microalgal productivity are discussed.

Homogeneous detection of cyanobacterial DNA via polymerase chain reaction

Aims:  To design a primer set enabling the identification through PCR of high‐quality DNA for routine and high‐throughput genomic screening of a diverse range of cyanobacteria.

POLYHYDROXYALKANOATES AS A CARBON SOURCE FOR DENITRIFICATION OF WATERS

Polyhydroxybutyrates (PHB; a bacterially produced biodegradable plastic) was used as a carbon source for biological denitrification of water. The use of a solid, nonwater soluble bioplastic in the denitrification process reduces the need for monitoring and dosing of the carbon source. Denitrification rates at four different salt concentrations (0, 5, 15 and 30 ppt) using synthetic salt water were determined. The mean denitrification rates varied from 2.4 to 3.2 kg-NO3N/m 3 -day, with the highest rate in water with a salinity of 15 ppt. While differences in denitrification rates were observed, they were not statistically significant. Additionally, denitrification rates were higher at higher nitrate concentrations. The denitrification rates had no significant differences with PHA of different molecular weights. Hydrogen sulfide production was not observed in any of the studies, even 45 days after the depletion of nitrates. The mean bioplastic consumption was 2.92 ± 2.70 mg/mg of NO3-N reduced.

A continuous microwave system for prevention of invasive species during de-ballasting operation--death kinetics.

A continuous microwave heating system was tested for its effectiveness at removing potentially invasive organisms during deballasting operations. Four different organisms, namely Nan-nochloropsis oculata (microalgae), Artemia nauplii, Artemia adults and Crassosstrea virginica (oyster larvae) normally found in ballast water were investigated in a controlled study to quantify their survival after continuous microwave heating of synthetic ballast water. The experiments were performed in the microwave system using a 2 x 2 factorial design with power (2.5 and 4.5 kW) and flow rate (1.0 and 2.0 Ipm) and the organisms subsequently subjected to different holding times. The control treatment was performed in a water bath using the same temperatures and holding times as in the case of the microwave treatment. Overall, the results obtained indicated that the microwave system was more effective in eliminating the organisms when compared with the control treatment. In most cases there were no survivors present after the microwave treatment at holding times above 100 s, and temperatures as low as 50°C particularly for oyster larvae and Artemia adults. The results are promising, indicating that this technology has the potential to be an effective tool in controlling/preventing the introduction of invasive species into native environments.

Impact of light quality on a native Louisiana Chlorella vulgaris/Leptolyngbya sp. co-culture

Light effect on cultures of microalgae has been studied mainly on single species cultures. Cyanobacteria have photosynthetic pigments that can capture photons of wavelengths not available to chlorophylls. A native Louisiana microalgae (Chlorella vulgaris) and cyanobacteria (Leptolyngbya sp.) co‐culture was used to study the effects of light quality (blue–467 nm, green–522 nm, red–640 nm and white–narrow peak at 450 nm and a broad range with a peak at 550 nm) at two irradiance levels (80 and 400 μmol m−2 s−1) on the growth, species composition, biomass productivity, lipid content and chlorophyll‐a production. The co‐culture shifted from a microalgae dominant culture to a cyanobacteria culture at 80 μmol m−2 s−1. The highest growth for the cyanobacteria was observed at 80 μmol μmol m−2 s−1 and for the microalgae at 400 μmol m−2 s−1. Red light at 400 μmol m−2 s−1 had the highest growth rate (0.41 d−1), biomass (913 mg L−1) and biomass productivity (95 mg L−1 d−1). Lipid content was similar between all light colors. Green light had the highest chlorophyll‐a content (1649 μg/L). These results can be used to control the species composition of mixed cultures while maintaining their productivity.