Drew W. Johnson

Evaluation of hydrogen sulphide concentration and control in a sewer system

This study focused on monitoring hydrogen sulphide (dissolved and atmospheric) generation and wastewater volumetric flow in a 21.4 km sewer line of the City of San Antonio, Texas. The results were used to evaluate daily and seasonal trends of atmospheric and dissolved sulphide, and to better apply sulphide control using ferrous sulphate to prevent odour and sewer pipe deterioration. As part of this study, the evaluation of a cost-effective dosing strategy with ferrous sulphate was performed to better control the sulphide contents in wastewater. Dosing studies were performed in the laboratory to find the required ratio of ferrous sulphate for acceptable sulphide removal. The results indicate a 1.25 mole ratio requirement, to reduce sulphide by 93%. Over a typical daily diurnal cycle, necessary dosing rates to maintain sulphide concentrations below 2 mg varied between 0 and 36,777 mol d−1 with a daily average rate of 14,438 mol d−1. If, instead of dosing at the maximum required rate, dosing was matched over the diurnal cycle, chemical savings would amount to 22,339 mol d−1 while achieving sulphide control. The approximate cost of the ferrous sulphate solution dosed is

Soil-Strength Enhancements from Polymer-Infused Roots

0.14 per mol and this amount of chemical savings translates into roughly

Aggregated Nanoparticle Morphology Effects on Membrane Filtration

2923 per day. Actual dosing cost for the hypothetical average day will be

Strength enhancement of plant roots through polymer infusions

1889 per day. These cost savings can easily recoup the required instrumentation costs to achieve this diurnal dose matching.

Historical data review and source analysis of PCBs/Arochlors in the Lower Leon Creek Watershed

AbstractThis research investigates the use of polymer-infused roots for soil-improvement applications. By infusing polymer through the easily accessible above-surface plant stems, polymer-infused roots can be created without subsurface excavations. Evaluation of this technique involves identifying the improvements from polymer-infused roots by measuring in situ shear strength of soil using a vane shear apparatus and by measuring the tensile strength using split-tension tests in the laboratory. Roots of Ruellia squarrosa and Artemisia annua plants were infused with a mixture of epoxy resin and polyoxyalkylamine blend hardener. Compared with noninfused roots, polymer-infused roots provided an additional 22 kPa (28%) of shear strength for elastic silt and an additional 13.1 kPa (25%) of shear strength for low-plasticity clay with a corresponding 13.6-kPa (55%) increase in tensile strength for the low-plasticity clay. Acid hydrolysis testing was performed to ascertain the potential durability of the polymer-i...

Mass transfer in SiO2 nanofluids: A case against purported nanoparticle convection effects

Nanoparticles are considered potential environmental contaminants because of reported toxicity to biota in the environment. As such, there is interest in understanding how to remove nanoparticles from waters. This study investigated membrane filtration behaviors of 70-nm alumina oxide nanoparticle when aggregated under diffusion limited aggregation and reaction limited aggregation regimes. In this study, nanoparticles were aggregated under conditions of high and low ionic strength to form aggregates of different morphology. Aggregates were filtered using a hydrophilic polyvinylidene fluoride membrane with a pore size of 0.22 µm, 100% nanoparticle removal efficiencies were obtained regardless of aggregation conditions used. Aggregate morphology was quantified by measured fractal dimensions. Fractal structure differences coincided with measured filtration resistance values. Low porosity aggregates provided a filtration resistance 43% greater than high porosity aggregates of the same effective size. Model predictions for measured specific resistance values were improved through incorporation of compressibility indexes. In order to obtain a porous structure with less resistance, a fast coagulation process is suggested for nanoparticle removal.

The occurrence and characterization of fouling during membrane evaporative cooling

By infusing a thermoset epoxy polymer into the root system of a plant, we aim to create an in situ plant-polymer composite material of high tensile strength resistant to biodegradation and suitable for soil stabilization applications. Microscopy imaging, volume and mass measurements, thermogravimetric analysis, and tensile testing were conducted to characterize the effects of infusing polymer into the plant system. The polymer appears to travel predominantly through xylem vessels of the plant system during infusions. Maximum tensile strength and modulus of elasticity are increased by 107% and 92%, respectively, with a polymer content of 59% by mass after infusions were conducted.

Characterization of dispersed and aggregated Al2O3 morphologies for predicting nanofluid thermal conductivities

PCBs have been banned since the late 1970s, but concentrations still exist in sediments and riverine fish and continue to exceed regulatory limits which can result in negative health effects. This study looks at historical records of PCB and Arochlor concentrations in surface water, sediments, and fish tissue for the Lower Leon Creek, Bexar County in Texas. Temporal analysis on the concentrations of PCBs and Arochlors was conducted for detection and exceedance of selected screening criteria. In addition, the half-lives of select PCB congeners were calculated for 2007–2012 data to ascertain differences in PCB concentrations with their hydrophobicity. Source analysis was conducted to determine the potential contributing sources of PCB contamination using source data (landfills, outfalls, etc.) and the PCB exceedance data. For sediment and fish tissue sampling results, historic data shows high concentrations of PCB/Arochlors over the course of several decades. The historical data is characterized as being widely variable for detections in Arochlors and concentrations between years, with a dramatic drop in concentrations detected starting in 2009. Overall, the sampling locations adjacent to and downstream from the former Kelly Air Force Base have the highest concentrations of PCB/Arochlors over the longest period of time. The results of this work will aid regulatory agencies in addressing impairment.