Two-stage anaerobic reactors are being widely used in the organic waste management industry. In these reactors, up to one-third of the chemical oxygen demand (COD) content is naturally pre-acidified in a first stage pre-acidification (PA) and then fed to a second stage digester for conversion to methane. Traditionally, all the generated gases from the PA tank will be vented to the atmosphere. Hydrogen and carbon dioxide are the main gases generated in the PA tank. A pilot-scale of two-stage anaerobic expanded granular sludge bed reactor was fabricated and used to investigate the impact of the PA gas injection into the second stage. The gas from the PA reactor was captured and stored in the storage tank. The tests were run under two temperature ranges and five organic loading rates (similar to 2, 3, 4, 5, and 6 g COD/L.day). For mesophilic range, the biogas production and energy yield increased by 10-90% and 40-130%, respectively, from without PA gas injection case compared to with PA injection case. For thermophilic range, the biogas production and energy yield increased by 12-40% and 90-140%, respectively, from without PA gas injection compared to with PA injection case. For each OLR, the gas production and energy yield were 90 to 160% more in thermophilic range than the mesophilic range for the cases with and without the PA gas injection. This implies that a higher temperature range has a significant impact on energy yield in a digester. One of the important findings was the amount of the PA gas injected into the EGSB reactor should be less than 50% of the theoretically calculated hydrogen gas based on ethanol substrate assumption.

The urea-selective catalyst reduction system implemented in commercial vehicles facilitates ensuring compliance with the NOx regulation limit. A significant challenge in urea injection is to comprehend its decomposition chemistry that often leads to the formation of unfavorable deposits in the exhaust system unit. Due to the complex interaction of the multiphase fluid flow and transport processes, a significant degree of uncertainty is associated with the identification of the interacting factors that control the deposit initiation and their growth. A systematic investigation was conducted through numerous experiments to study the factors controlling the urea deposit that guide innovation for new product development. For the first time, the effect of pressure on urea deposits was investigated by heating an aqueous urea solution in a closed system maintained between 30 and 200 psi. Chemical characterization procedure was conducted using liquid chromatography-multiple reaction monitoring (LC-MRM). Additionally, deposit test was conducted on a typical after-treatment system layout. Deposit-initiating temperature were identified at different operating conditions. The results indicated that the deposit initiation occurred in a narrow temperature range. The critical diesel exhaust fluid injection rate, as a function of temperature, was plotted, and the effect of gas flow rate on urea deposit formation was studied. Further, experiments were conducted on a liquid film to identify the timescale and chemical composition of the generated deposits. The experiment concluded that higher temperatures within a liquid film facilitated early deposit initiation and formed compounds that require extremely high temperature to decompose.

Bubble point tests are widely used for assessing the integrity of sterilizing-grade membrane cartridge filters. While many authors have considered the limitations of bubble point tests as applied to cartridge filters, the level of bacterial retention assurance provided by this test as conducted with automated integrity testers (AITs) has not, until now, been quantified. Contrary to the notion that filter leaks result in a depressed bubble point, it was shown that the bubble point as reported by AITs was insensitive to defect size up until the point where the AIT either determined a gross leak failure or was not able to return a valid result. For the three AITs used in this study, the minimum laser hole defect diameter in 10-inch (25.4 cm) sterilizing-grade cartridge filters that resulted in a failing bubble point test was between about 30 and 60 µm, depending on the filter type and test conditions. These defect sizes were associated with bacterial log reduction values in the 4.0 to 4.5 range. This study supports the generally recommended practice of pairing the bubble point test (which does confirm proper pore size rating) with a complementary gas–liquid diffusion test (better suited for detecting defects) to achieve a more comprehensive assessment of filter integrity.