Phenol degradation using 20, 300 and 520 kHz ultrasonic reactors with hydrogen peroxide, ozone and zero valent metals

The extent of phenol degradation by the advanced oxidation process in the presence of zero valent iron (ZVI) and zero valent copper (ZVC) was studied using 20, 300 and 520 kHz ultrasonic (US) reactors. Quantification of hydrogen peroxide has also been performed with an aim of investigating the efficacy of different sonochemical reactors for hydroxyl radical production. It has been observed that the 300 kHz sonochemical reactor has the maximum efficacy for hydroxyl radical production. Phenol degradation studies clearly indicate that degradation of phenol is intensified in the presence of the catalyst and hydrogen peroxide, which can be attributed to enhanced production of hydroxyl radicals in the system. Experimental data shows that with ZVI, when the reaction was subjected to 300 kHz, complete phenol removal and 37% TOC mineralization was achieved within 25 min, whereas, in the case of 20 kHz US treatment no phenol was detected after 45 min and 39% TOC mineralization was observed. This novel study also investigated the use of zero valent copper (ZVC) and results showed that with 20, 300 and 520 kHz ultrasonic rectors, phenol removal was 10–98%, however, the maximum TOC mineralization achieved was only 26%. A comparative study between hydrogen peroxide and ozone as a suitable oxidant for Fenton-like reactions in conjunction with zero valent catalysts showed that an integrated approach of US/Air/ZVC/H2O2 system works better than US/ZVC/O3 (the ZOO process)

Decomposition of PPCPs by ultrasound-assisted advanced Fenton reaction: A case study with salicylic acid (Reprinted from Ultrasonics Sonochemistry, vol 39, pg 243-249, 2017)

The study is about the degradation of a widely used pharmaceutical and personal care product-salicylic acid by sonocatalysis, and the experimental design of the reaction system. The first part of the study consists of sonication (572 kHz) in the presence of zero-valent iron (ZVI) with or without H2O2 to select and optimize the operational parameters as frequency, time, initial solute concentration, dose of reagents and pH. The second part consists of the use of response surface methodology and multiple regression to develop an experimental design modeland to assess the individual and interactive effects of pH, power (P-o), ZVI dose and H2O2. The results showed that the optimal conditions predicted by the model without defining any restrictions are: pH = 2.0, P-o = 120 W, ZVI = 24 mg L-1, which provide total salicyclic acid and 48% TOC decay. However, the prediction implies intensive consumption of energy and reagents, and must therefore be modified by restricting the value of TOC decay to a lower value and that of pH to a higher one. Cross-validation tests showed that the prediction accuracy of the model was considerably high with 5.0-9.4% deviation from the experimental data

Sonochemical and sonocatalytic destruction of methylparaben using raw, modified and SDS-intercalated particles of a natural clay mineral

The first part of the study is about the degradation of a common PPCP-methylparaben by high-frequency ultrasound to highlight the operation parameters, the reaction sites, the oxidation byproducts and the role of OH radicals. The second part covers the catalytic effect of a highly abundant and cost-effective clay mineral-sepiolite, and investigates the role of surface modification and SDS-composites of the clay in improving the efficiency of the degradation reactions. It was found that the compound (C-0 = 10 mg L-1) was readily and totally decomposed by 30-min sonication at neutral pH, producing phenolic and aliphatic intermediates, but with insignificant mineralization. The major reaction site was the bubble-liquid interface, where the reactions were governed by OH radical attack. Modification of the sepiolite surface by pre-sonication in an ultrasonic bath improved the rate of reaction and the degree of TOC decay, Further modification by the synthesis of 20-min sonicated (200 kHz bath) SDS-intercalates of the clay was found to yield significant enhancement in the rate of target compound decomposition and the fraction of TOC decay, provided that the reaction was operated at acidic pH

Optimization of methylparaben degradation by sonocatalysis

Sonocatalytic degradation of methylparaben (MPB) in the presence of a low-cost clay mineral (sepiolite) was optimized using a multivariable center composite design protocol based on response surface methodology (RSM). Using the data generated with varying MPB concentrations, pH, frequency and catalyst dose, two semi-empirical expressions were developed to describe the relation between the apparent reaction rate constant of the parent compound and the most significant control variables. It was found that ultrasonic power, pH, sepiolite dose and its interactions with time and pH were the most significant parameters influencing the rate of MPB decay under high frequency ultrasound. The models also showed that the rate constant was a convex function of time, as it decreased during the first 35-min of sonolysis and increased thereafter, indicating the formation and depletion of competing oxidation byproducts. Finally, the models predicted that the rate of MPB decay was a maximum either at alkaline pH and a high sepiolite dose (k = 1.68 x 10(-1) min(-1)), or at acidic pH and a considerably lower dose of the mineral (k = 1.48 x 10(-1) min(-1))

Decomposition of PPCPs by ultrasound-assisted advanced Fenton reaction: A case study with salicylic acid

The study is about the degradation of a widely used pharmaceutical and personal care product-salicylic acid by sonocatalysis, and the experimental design of the reaction system. The first part of the study Consists of sonication (572 kHz) in the presence of zero-valent iron (ZVI) with or without H2O2 to select and optimize the operational parameters as frequency, time, initial solute concentration, dose of reagents and pH. The second part consists of the use of response surface methodology and multiple regression to develop an experimental design modeland to assess the individual and interactive effects of pH, power (P-o), ZVI dose and H2O2. The results showed that the optimal conditions predicted by the model without defining any restrictions are: pH = 2.0, P-o = 120 W, ZVI = 24 mg L-1, which provide total salicyclic acid and 48% TOC decay. However, the prediction implies intensive consumption of energy and reagents, and must therefore be modified by restricting the value of TOC decay to a lower value and that of pH to a higher one. Cross-validation tests showed that the prediction accuracy of the model was considerably high with 5.0-9.4% deviation from the experimental data

Photocatalytic Destruction of Caffeine on Sepiolite-Supported TiO2 Nanocomposite

The study is about the degradation of a common pharmaceutical and personal care product (PPCP) caffeine by photocatalysis under UV-visible light using pristine TiO2 (P-25) and a lab-made nanocomposite of sepiolite-TiO2. It was found that the dark adsorption of caffeine on P-25 was insignificant, but considerably high on the nanocomposite, owing to the high porosity and unique structure of sepiolite. The degradation of the compound in the presence of P-25 and Sep-TiO2 followed the pseudo-first order and exponential decay kinetics, with a rate constant of 0.12 min(-1) and 0.50 min(-1), respectively. The efficiency of both catalysts for carbon mineralization was better at acidic pH, but that of the nanocomposite was significantly higher at all pH than that of the unmodified P-25 (36.1 against 9.6% at pH 6.0). The loading of TiO2 on sepiolite was an important factor in the activity of the catalyst, as the maximum activity was observed at a loading ratio of 12.5 mmol per g sepiolite, which decreased at higher ratios of the semiconductor to sepiolite. Exposure of the treated samples to high-frequency ultrasound at pH 6 was found to enhance the degree of mineralization to 65.1 and 52.1% in the presence of the nanocomposite and P-25, respectively. The outcome was attributed to the unique properties of ultrasound for the cleaning of solid surfaces, for enhancing the mass transfer of solutes to heterogeneous interfaces, and for generation of excess hydroxyl radicals. Finally, the nanocomposite was found to be considerably stable, as it was easily recovered and used four times without a significant loss in activity

Catalytic ozonation of caffeine with sepiolite: Effects of impregnation with zero-valent iron and ultrasound

The study is about the oxidative destruction and mineralization of caffeine by catalytic ozonation using sepiolite, which is a low-cost natural clay mineral found abundantly in Anatolia. The results showed that while ozonation alone at pH 6.0 (the natural pH of the test solution) provided 72% caffeine decay and 18% carbon mineralization during 10-min and 60-min reaction, respectively; catalytic ozonation with sepiolite provided 96% conversion and 30% mineralization during equivalent pH and reaction times. The activity of the catalyst was further improved by immobilization of zero-valent iron (ZVI) on its surface to produce a nanocomposite (ZVI/SEP) with a massive surface area and a much more reactive surface. Integration of the process with high-frequency ultrasound (US) was found to further enhance the rate of caffeine degradation and the degree of carbon mineralization via the unique properties of ultrasound for enhancing the rate of mass transfer to the catalyst surface and the generation of hydroxyl radicals (HO center dot) via thermal fragmentation of water molecules in the collapsing cavity bubbles. Maximum process efficiency was obtained under the following optimized conditions: pH = 6.0, O-3 (aq.) = 4 mg L-1, SEP/ZVI = 1.0 g L-1, US frequency = 577 kHz, t = 5-min and 60-min for 100% caffeine and 57% TOC decay, respectively. The nanocomposite was also highly stable, for it was used consecutively in four cycles without significant loss in activity

Pretreatment of Sewage Sludge by Low-frequency Ultrasound

The key point of waste activated sludge (WAS) pretreatment is to rupture the cell wall for allowing the release of intracellular matter that acts as a bioavailable substrate in anaerobic digestion processes. In this regard, ultrasonic irradiation has been one of the most effective tools owing to the unique properties of ultrasound to produce extreme conditions in heterogeneous liquids such as waste activated sludge. The present study investigates the impact of short-frequency ultrasound on disintegration, biodegradability and dewatering characteristics of sewage sludge by monitoring soluble chemical oxygen demand (sCOD), dissolved organic carbon (DOC), soluble proteins, total dissolved nitrogen, particle size and dewaterability of raw and sonicated sludge samples to optimize the operating parameters. The results showed that short wave ultrasound is a highly effective method of WAS treatment, because it provides high degrees of disintegration and biomass transfer from sludge solids to the aqueous phase, thus resulting in enhanced biodegradability

Oxidative decomposition and mineralization of caffeine by advanced oxidation processes: The effect of hybridization

The study consists of a detailed investigation of the degradability of the emerging water contaminant-caffeine by homogeneous and heterogeneous Advanced Oxidation Processes (AOP's), estimation of a synergy index for each hybrid operation thereof, and proposing the most plausible reaction mechanisms that are consistent with the experimental data. It also encompasses evaluation of the effect of the water matrix represented by carbonate species and humic acids, as strong scavengers of hydroxyl radicals. The results showed that single AOP's such as sonolysis (577 kHz) and photolysis with H2O2 provided complete caffeine elimination, but they were insufficient for the mineralization of the compound. Hybrid AOP's were considerably more effective, particularly when operated at a heterogeneous mode using commercial TiO2. The most effective hybrid process was UV-H2O2/TiO2, which provided more than 75% TOC decay at the minimum test doses of the reagent and catalyst. While the addition of ultrasound to the process significantly increased the rate of caffeine decomposition, it reduced the overall degradation of the compound to 64% in terms of TOC decay. The antagonistic effect was attributed to the formation of excess H2O2, and the presence of cavity clouds and/or high density layers that inhibited the transmission of UV light. The effect of natural water ingredients was found to reduce the reaction rates, signifying the major contribution of hydroxyl radicals to the destruction of caffeine. The proposed reaction mechanisms based on OH radical attack and the calculated energy barriers were in good agreement with the experimentally detected reaction byproducts