Chain-length dependent ultrasonic degradation of perfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) have been found all over the world and are particularly persistent, potentially carcinogenic, and bioaccumulative in the environment. Degradation of short-chain perfluorinated carboxylic acids of varying carbon chain lengths (from 4 to 8 carbons), higher-chain perfluoro carboxylic acids of varying carbon chain lengths (from 9 to 14 carbons), and perfluorosulfonic acids of varying carbon chain lengths (6 and 8 carbons) were tested in a flow through ultrasonic cavitation reactor to determine the efficacy of the high frequency ultrasound process. Temperature, frequency, power density, pH, sodium chloride, and sodium bicarbonate concentrations are examined as process parameters. The frequency and length of the PFAS chain were found to be vital components in the sonolytic degradation process. Degradation of all PFAS was shown to be particularly rapid at room temperature, basic pH, and a power density of 252 W/L. At a power density of 144 W/L, all of the PFAS were degraded by more than 97% in 8 h, with the exception of perfluorobutonic acid (83%) and perfluorohexanoic acid (94%). The bond dissociation energy of C-F bonds was found to be much higher than experimental sonolytic activation energies, supporting cavitation bubble as a catalyst for thermolytic destruction of PFAS compounds. Optimizing the reactor geometry has the potential to make this approach even more appealing for treating small volumes of concentrated wastes

Synthesis and Characterization of High Viscosity Cationic Poly(Proline-Epichlorohydrin) Composite Polymer with Antibacterial Functionalities

We report microbial resistance and catalytic activity of high viscosity cationic poly(proline-epichlorohydrin) composite (PRO-EPI) in the aqueous system. The PRO-EPI was prepared by a simple polycondensation, followed by FTIR, 1H NMR, SEM, DLS, viscosity, and DSC/TGA characterization. Several concentrations of the PRO-EPI were tested against Gram-negative (E. coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) microorganisms. The antimicrobial screening revealed that PRO-EPI was a potent antimicrobial agent with the least inhibitory concentrations (MICs) of 128 µg/mL against Gram-negative microorganisms. The PRO-EPI indicated no inhibitory effect against Gram-positive microorganisms. It was determined that PRO-EPI contains polymeric-quaternary ammonium compounds that inactivate the Gram-negative microorganisms by a dual mode of action and carries domains for electrostatic interaction with the microbial membrane and an intracellular target. To study the removal of toxic industrial wastewater, congo red (CR) was tested using sodium borohydride as a reducing agent. Adsorption was achieved within 20 min at a rate constant of 0.92 ks−1. UV–vis spectra showed that the removal of CR in the reaction solution was due to the breakup of the azo (–N=N–) bonds and adsorption of aromatic fragments. PRO is biodegradable and non-toxic, and PRO-EPI was found to be both antimicrobial and also acts as a catalyst for the removal of congo red dye

Chain-length dependent ultrasonic degradation of perfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) have been found all over the world and are particularly persistent, potentially carcinogenic, and bioaccumulative in the environment. Degradation of short-chain perfluorinated carboxylic acids of varying carbon chain lengths (from 4 to 8 carbons), higher-chain perfluoro carboxylic acids of varying carbon chain lengths (from 9 to 14 carbons), and perfluorosulfonic acids of varying carbon chain lengths (6 and 8 carbons) were tested in a flow through ultrasonic cavitation reactor to determine the efficacy of the high frequency ultrasound process. Temperature, frequency, power density, pH, sodium chloride, and sodium bicarbonate concentrations are examined as process parameters. The frequency and length of the PFAS chain were found to be vital components in the sonolytic degradation process. Degradation of all PFAS was shown to be particularly rapid at room temperature, basic pH, and a power density of 252 W/L. At a power density of 144 W/L, all of the PFAS were degraded by more than 97% in 8 h, with the exception of perfluorobutonic acid (83%) and perfluorohexanoic acid (94%). The bond dissociation energy of C-F bonds was found to be much higher than experimental sonolytic activation energies, supporting cavitation bubble as a catalyst for thermolytic destruction of PFAS compounds. Optimizing the reactor geometry has the potential to make this approach even more appealing for treating small volumes of concentrated wastes

Kinetic model for sonolytic degradation of non-volatile surfactants:Perfluoroalkyl substances

Sonolytic degradation kinetics of non-volatile surfactant perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) were investigated over a range of concentration, considering active cavity as a catalyst. The Michaelis-Menten type kinetic model was developed to empirically estimate the concentration of active cavity sites during reactions. Sonolytic degradation of PFOA and PFOS, as well as the formation of its inorganic constituents, fluoride, and sulfate, follows saturation kinetics of pseudo-first order at lower concentration (23.60 µM). Nitrate and hydrogen peroxide formations were 0.53 ± 0.14 µM/min and 0.95 ± 0.11 µM/min, respectively. At a power density of 77 W/L and frequency of 575 kHz, the empirically estimated maximum number of active cavity sites that could lead to the sonolytic reaction were 89.25 and 8.8 mM for PFOA and PFOS, respectively. This study suggests that a lower number of active cavity sites with higher temperature needed to degrade PFOS might be the reason for lower degradation rate of PFOS compared to that of PFOA. Diffusion of non-volatile surfactants at the cavity-water interface is found to be the rate-limiting step for the mineralization of perfluoroalkyl substances

Power density modulated ultrasonic degradation of perfluoroalkyl substances with and without sparging Argon

The power density modulates the dynamics of the chemical reactions during the ultrasonic breakdown of organic compounds. We evaluated the ultrasonic degradation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) at various power densities (30 W/L–262 W/L) with and without sparging Argon. We observed pseudo-first-order degradation kinetics at an initial PFASs concentration of 100 nM over a range of power density. The rate kinetics of degradation shows a non-linear increase with an increase in power density. We proposed a four-parameter logistic regression (4PLR) equation that empirically fits the degradation rate kinetics with the power density. The 4PLR equation predicts that the maximum achievable half-life of PFOA and PFOS sonochemical degradation are 1 and 10 min under a given set of experimental conditions. The high bulk-water temperature (i.e., 30 °C) of the aqueous sample helps increase the degradation rate of PFOA and PFOS. The addition of oxidants such as iodate and chlorate help enhance PFOA degradation in an argon environment at an ultrasonic frequency of 575 kHz

POSET-RL: Phase ordering for Optimizing Size and Execution Time using Reinforcement Learning

The ever increasing memory requirements of several applications has led to increased demands which might not be met by embedded devices. Constraining the usage of memory in such cases is of paramount importance. It is important that such code size improvements should not have a negative impact on the runtime. Improving the execution time while optimizing for code size is a non-trivial but a significant task.The ordering of standard optimization sequences in modern compilers is fixed, and are heuristically created by the compiler domain experts based on their expertise. However, this ordering is sub-optimal, and does not generalize well across all the cases.We present a reinforcement learning based solution to the phase ordering problem, where the ordering improves both the execution time and code size. We propose two different approaches to model the sequences: one by manual ordering, and other based on a graph called Oz Dependence Graph (ODG). Our approach uses minimal data as training set, and is integrated with LLVM.We show results on x86 and AArch64 architectures on the benchmarks from SPEC-CPU 2006, SPEC-CPU 2017 and MiBench. We observe that the proposed model based on ODG outperforms the current Oz sequence both in terms of size and execution time by 6.19% and 11.99% in SPEC 2017 benchmarks, on an average. © 2022 IEEE

Combined Ozone and Ultrasound for the Removal of 1,4-Dioxane from Drinking Water

<p>Ozone, ultrasound, and ozone/ultrasound processes were evaluated for the removal of 1,4-dioxane from tap water using a continuous flow reactor with on-line aqueous ozone measurement. The addition of ultrasound to ozone was found to significantly boost removal. The removal of 1,4-dioxane by ozone/ultrasound process exceeded the sum of the removals from ozone alone and ultrasound alone. Ultrasound alone showed less than 20% removal of 1,4-dioxane. The effects of reactor pressurization and bicarbonate as a hydroxyl radical scavenger were also studied. It was observed that at constant aqueous ozone concentration, additional pressure in the reactor tended to mute the 1,4-dioxane removal boost noted in the ozone/ultrasound process, while additional pressure did not affect 1,4-dioxane removal via ozone alone. The removal of 1,4-dioxane was found to be dependent on the consumption of aqueous ozone, and the consumption of ozone was found to be increased by either the addition of ultrasound or by increasing pH. Rate constants were calculated for various ozone concentrations for the ozone and ozone/ultrasound processes and the systems were fitted to a Chick–Watson model.</p