Space and time-resolved probing of heterogeneous catalysis reactions using lab-on-a-chip.

Probing catalytic reactions on a catalyst surface in real time is a major challenge. Herein, we demonstrate the utility of a continuous flow millifluidic chip reactor coated with a nanostructured gold catalyst as an effective platform for in situ investigation of the kinetics of catalytic reactions by taking 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) conversion as a model reaction. The idea conceptualized in this paper can not only dramatically change the ability to probe the time-resolved kinetics of heterogeneous catalysis reactions but also used for investigating other chemical and biological catalytic processes, thereby making this a broad platform for probing reactions as they occur within continuous flow reactors.

Reducing electrocoagulation harvesting costs for practical microalgal biodiesel production.

Electrocoagulation has shown potential to be a primary microalgae harvesting technique for biodiesel production. However, methods to reduce energy and electrode costs are still necessary for practical application. Electrocoagulation tests were conducted on Nannochloris sp. and Dunaliella sp. using perforated aluminium and iron electrodes under various charge densities. Aluminium electrodes were shown to be more efficient than iron electrodes when harvesting both algal species. Despite the lower harvesting efficiency, however, the iron electrodes were more energy and cost efficient. Operational costs of less than $0.03/L oil were achieved when harvesting Nannochloris sp. with iron electrodes at 35% harvest efficiency, whereas aluminium electrodes cost $0.75/L oil with 42% harvesting efficiency. Increasing the harvesting efficiencies for both aluminium and iron electrodes also increased the overall cost per litre of oil, therefore lower harvesting efficiencies with lower energy inputs was recommended. Also, increasing the culturing salinity to 2 ppt sodium chloride for freshwater Nannochloris sp. was determined practical to improve the electrocoagulation energy efficiency despite a 25% reduction in cell growth.

Millifluidics for time-resolved mapping of the growth of gold nanostructures.

Innovative in situ characterization tools are essential for understanding the reaction mechanisms leading to the growth of nanoscale materials. Though techniques, such as in situ transmission X-ray microscopy, fast single-particle spectroscopy, small-angle X-ray scattering, etc., are currently being developed, these tools are complex, not easily accessible, and do not necessarily provide the temporal resolution required to follow the formation of nanomaterials in real time. Here, we demonstrate for the first time the utility of a simple millifluidic chip for an in situ real time analysis of morphology and dimension-controlled growth of gold nano- and microstructures with a time resolution of 5 ms. The structures formed were characterized using synchrotron radiation-based in situ X-ray absorption spectroscopy, 3-D X-ray tomography, and high-resolution electron microscopy. These gold nanostructures were found to be catalytically active for conversion of 4-nitrophenol into 4-aminophenol, providing an example of the potential opportunities for time-resolved analysis of catalytic reactions. While the investigations reported here are focused on gold nanostructures, the technique can be applied to analyze the time-resolved growth of other types of nanostructured metals and metal oxides. With the ability to probe at least a 10-fold higher concentrations, in comparison with traditional microfluidics, the tool has potential to revolutionize a broad range of fields from catalysis, molecular analysis, biodefense, and molecular biology.

Harvesting economics and strategies using centrifugation for cost effective separation of microalgae cells for biodiesel applications.

Inefficient or energy-intensive microalgal harvesting strategies for biodiesel production have been a major setback in the microalgae industry. Harvesting by centrifugation is generally characterized by high capture efficiency (>90%) under low flow rates and high energy consumption. However, results from the present study demonstrated that by increasing the flow rates (>1L/min), the lower capture efficiencies (<90%) can be offset by the larger volumes of culture water processed through the centrifuge, resulting in net lower energy consumption. Energy consumption was reduced by 82% when only 28.5% of the incoming algal biomass was harvested at a rate of 18 L/min by centrifugation. Harvesting algal species with a high lipid content and high culture density could see harvesting costs of $0.864/L oil using the low efficiency/high flow rate centrifugation strategy as opposed to $4.52/L oil using numbers provided by the Department of Energy for centrifugation harvesting.

Evaluating coagulation pretreatment on poultry processing wastewater for dissolved air flotation.

Eleven metal coagulants and one polyelectrolyte were assessed for their suitability in assisting a dissolved air flotation (DAF) system aimed at treating poultry processing wastewater. Preliminary jar tests determined that a combination of 800 mg/L of FeCl(3) (ferric chloride) and 900 mg/L of Floccin 1115 would provide the best treatment by removing at least 98% of the total suspended solids (TSS) and 97% of the volatile suspended solids (VSS), while providing a 97% increase in water clarity. Final flotation tests suggested that the flocculated particles could be carried to the surface with 40% recycle ratio of the DAF. The resulting supernatant indicated 94.7% increase in clarity (± 1.4%), 97.3% reduction in TSS (± 0.5%), 96.6% reduction in VSS (±1.1%), 91% reduction in chemical oxygen demand (COD), and nearly 100% removal of fats, oils, and greases (FOGs). Despite the high removal efficiencies, flotation was found not to be critically necessary for treatment because the high concentration of coagulants caused settling of the flocs to occur just as rapidly. Potential coagulant overdosing is suspected at the higher end of the tested coagulant concentrations due to limited alkalinity in the wastewater. However, lack of residual metal (coagulant) ions in water may be linked to reactions leading to phosphate precipitation. The exact effect of the competing phosphate reaction on treatment efficiency is not clearly evident from this present study.

Hydrothermal liquefaction of separated dairy manure for production of bio-oils with simultaneous waste treatment.

A bench scale hydrothermal liquefaction (HTL) system was tested using dairy manure to explore biooil production and waste treatment potential. Carbon monoxide was used as the process gas and sodium carbonate (Na(2)CO(3)) as catalyst. At a 350°C process temperature, the HTL unit produced 3.45 g (± 0.21) of acetone soluble oil fractions (ASF), with an average Higher Heating Value of 32.16 (± 0.23) MJ kg(-1). A maximum ASF yield of 4.8 g was produced at a process temperature of 350°C and 1g of catalyst. The best ASF yield corresponded to 67.6% of energy contained in the raw manure. GC-MS analysis of ASF indicated that the highest quantities of phenolic compounds were formed when 1g catalyst was used. Chemical Oxygen Demand (COD) reduction in the dischargeable slurry was as high as 75%. The results point to an alternative dairy waste treatment technology with a potential to generate transportable biooils.

Oxygen electrode-based single antibody amperometric biosensor for qualitative detection of E. coli and bacteria in water.

Design and performance of an amperometric biosensor for E. coli O157:H7 that is based on a common dissolved oxygen probe is discussed. Anti-E. coli O157:H7 antibody was conjugated to horseradish peroxidase and immobilized on a nitrocellulose membrane that was placed over the oxygen probe membrane using a custom-fabricated polyvinyl chloride (PVC) insert. Upon bacterial cell binding, a decrease in enzyme activity resulted in a change in oxygen concentration that was detected with a Clark-type oxygen electrode probe. Validation experiments determined the effect of the outer membrane and insert on the Clarke electrode performance and linearity, and the effects of stirring on sensor response. The mechanism of enzymatic disruption is presumably steric hindrance due to binding of the bacterial cell and conformational change in antibody structure. Sampling various dilutions of heat-sterilized E. coli O157:H7 cells in water, as little as 50 bacterial cells/mL could be detected in approximately 20 minutes of sampling and processing procedures. Bacterial concentrations from 0 to 5000 cells/mL were tested, with 2.52 mg/L +/- 0.37 mg/L equivalents of oxygen produced from as few as 50 cells/mL, versus 6.26 +/- 0.64 mg/L when no cells were present in solution. Overall, the developed amperometric biosensor technology offered an efficient means of detection primarily due to its ease of use, cost-effectiveness, portability, and amenability to incorporation at existing water quality gaging stations.

Toxicity and biouptake of lead and arsenic by Daphnia pulex.

Acute and chronic toxicity studies were conducted on Daphnia pulex using synthetic lead and arsenic water samples. For acute studies, solutions with 0.25, 0.5, 1.0, 2.0, 5.0 mg/L lead and arsenic along with a control were used. The chronic studies were conducted for 21 days using 0.25, 0.5, 1.0 mg/L lead and arsenic solutions along with a control. Results indicated that the LC50 (48 hour) was 4.0 and 3.4 mg/L for lead and arsenic, respectively. Results from chronic studies suggest that the exposure to lead solutions significantly (P < 0.05) impaired the reproduction rates of Daphnia at the 1 mg/L concentration. However, the reproduction rates were enhanced at low concentrations of arsenic (up to 0.5 mg/L). A second chronic study was conducted to confirm this finding. Results from the second study indicated that lead exhibited significantly higher (P < 0.05) toxicity at 0.5 mg/L concentration, while reproduction rates in all concentrations of arsenic solutions were not significantly different from the controls. Metal analysis on exposed Daphnia, following nitric acid digestion procedures, indicated that Daphnia bio-accumulated 75.3-97.2% of the lead added to the experimental containers. This high lead biouptake coupled with the fast growth, high reproduction rates, and short life cycle all suggest that a Daphnia-based remediation (growth and partial harvest) may a viable treatment alternative that is worth considering. However, further field studies have to be conducted to verify this alternative. Biouptake or sequestration by Daphnia of arsenic at all tested concentrations was negligible, thereby, suggesting selective uptake or sequestration by daphnia under the tested pH and temperature conditions.