A fluorescence-based sensing scheme exploiting an environment-sensitive fluorophore embedded in a hydrogel has been developed for measurement of relative humidity (RH). The fluorophore, dapoxyl sulfonic acid (DSA), is incorporated into two different hydrogel films, agarose and a copolymer of acrylamide and 2-(dimethylamino)ethyl methacrylate (DMAEM) cross-linked with N,N'-methylenebisacrylamide. The swelling and contracting of the hydrogels in response to relative humidity alters the polarity of the environment of DSA, stimulating a shift in the emission wavelength. From 0 to 100% RH, acrylamide-DMAEM sensors exhibited a 40 and 15 nm wavelength shift in still air and flowing gas, respectively. Agarose sensors showed a 40 nm wavelength shift from 0 to 100% RH in still air and a 30 nm shift from 0 to 70% RH in flowing gas. Response times for both sensors were 15 min in still air and less than 5 min in flowing gas. The sensing approach is straightforward and cost-effective, yields sensors with characteristics suitable for commercial measurement of RH (i.e., sensitivity, response times, reproducibility), and allows ease of adaptability to specific RH measurement requirements. The results support the potential extension of the method to a wide variety of analytes in the vapor phase and aqueous solution by incorporation of functionalized "smart" hydrogels.

A portable infrared attenuated total reflection (IR-ATR) spectrometer was developed for analyzing CO2 and CH4 in geosequestration scenarios. This infrared-based online sensor system is suitable for monitoring, detecting, and differentiating carbon dioxide and methane at different pressures (i.e., up to 11 MPa) in saline aquifer and/or synthetic brine environments. The design of the sensor system eliminates the present problems in such measurement scenarios of either portability or capability operating at harsh conditions, and especially at elevated pressures for in-field deployment of current available IR systems. It is demonstrated that the detection and quantification of dissolved CO2 and CH4 at pressurized conditions is feasible at relevant saline downhole conditions present within the piping of the present injection wells serving as an online/in-line monitoring tool.

Mid-infrared sensors based on ATR spectroscopy provide a robust and reliable platform for the quantification of organic molecules dissolved in water.

This study developed a strategy to control effluent ammonia from an activated sludge system, using oxidation-reduction potential. By controlling effluent ammonia concentrations, disinfection of treated wastewater is more cost effectively achieved by chloramination rather than break-point chlorination. The system under consideration was an extended aeration oxidation ditch. The study takes into account the concepts of nitrification and denitrification, as well as intrinsic characteristics of oxidation-reduction potential, while also keeping ease of operation in mind. Data were gathered by varying the rate of aeration of the basin from two extremes, while collecting samples along the timeline. Oxidation-reduction potential, dissolved oxygen concentration and ammonia concentration data were collected for evaluation. Using these data a preliminary control strategy was developed. The control strategy focused on operating the system in a continuous flow and varying aeration scenario. Two attempts to control the oxidation ditch were made. Using oxidation-reduction potential as an indicator, adjustments were made to the aerator controls in order to accommodate changes in organic loading, and maintain a constant effluent ammonia concentration. The first attempt was met with success and used to fine tune the strategy for the second attempt. The second attempt experienced more success than the first in controlling effluent ammonia concentrations, thus confirming the original hypothesis of the study.