Degradation of chloroethenes in aqueous solution by ultrasound

Ultrasonics Sonochemistry, 2011

Sonochemistry is a technique that offers promise for pollutant degradation, but earlier studies on various chlorinated substrates do not give a definitive view of the effectiveness of this methodology. We now report a thorough study of ultrasonic operational variables upon perchloroethylene (PCE) degradation in water (variables include ultrasonic frequency, power and system geometry as well as substrate concentration) and we attempt to close the mass balance where feasible. We obtained fractional conversions of >97% showing very effective loss of pollutant starting material, and give mechanistic proposals for the reaction pathway based on cavitational phenomena inducing pyrolytic and free radical processes. We note major products of Cl À and CO 2 /CO, and also trichloroethylene (TCE) and dichloroethylene (DCE) at ppm concentrations as reported earlier. The formation at very low (ppb) concentration of small halocompounds (CHCl 3 , CCl 4 ) and also of higher-mass species, such as pentachloropropene, hexachloroethane, is noteworthy. But of particular importance in our work is the discovery of significant quantities of chloroacetate derivatives at ppm concentrations. Although these compounds have been described as by-products with other techniques such as radiolysis or photochemistry, this is the first time that these products have been identified in the sonochemical treatment of PCE; this allows a much more effective account of the mass balance and may explain earlier inconsistencies. This reaction system is now better identified, but a corollary is that, because these haloacetates are themselves species of some toxicity, the use of ultrasound here may not sufficiently diminish wastewater toxicity.

… science & technology, 1992

H This work describes the sonochemical degradation at 530 kHz of pentachlorophenate (PCP) in aqueous solutions saturated with different gases: air, oxygen, and argon. The main features of the sonochemical transformation are as follows: fast cleavage of the carbon-chlorine bond releasing C1-, mineralization of PCP to COz when the solution is saturated with air or oxygen, CO production if argon is the saturating gas, nitrite and nitrate formation when the reaction is conducted with aerated solutions. It has also been shown that PCP disappearance is followed by a decrease in the toxicity of the medium for the green algae Scenedesmus subspicatus.

Ultrasonics Sonochemistry, 2008

The degradation of 4-chlorophenol (4-CP) in aqueous media by 516 kHz ultrasonic irradiation was investigated in order to clarify the degradation mechanism. The degradation of concentrated 4-CP solution by means of ultrasound, UV irradiation and their combined application was also studied. The obtained results indicate that Å OH radical are the primary reactive species responsible for 4-CP ultrasonic degradation. Very little 4-CP degradation occurs if the sonolysis is carried out in the presence of the Å OH radical scavenger tert-butyl alcohol, also indicating that little or no pyrolysis of the compound occurs. The dominant degradation mechanism is the reaction of substrate with Å OH radicals at the gas bubble-liquid interface rather than high temperature direct pyrolysis in ultrasonic cavities. This mechanism can explain the lower degradation rate of the ionic form of 4-CP that is partly due to the rapid dissociation of Å OH radicals in alkaline solutions. The sonochemical destruction of concentrated 4-CP aqueous solution is obtained with low rate. Coupling photolysis with ultrasound irradiation results in increased efficiency compared to the individual processes operating at common conditions. Interestingly, the photosonochemical decomposition rate constant is greater than the additive rate constants of the two processes. This may be the result of three different oxidative processes direct photochemical action, high frequency sonochemistry and reaction with ozone produced by UV irradiation of air, dissolved in liquid phase because of the geyser effect of ultrasound streaming. Additionally, the photodecomposition, at 254 nm, of hydrogen peroxide produced by ultrasound generating Å OH radical can partly explain the destruction enhancement.

Ultrasonics Sonochemistry, 2011

The effects of frequency in chlorobenzene, chloroform, and carbon tetrachloride have been experimentally investigated in this study. The irradiation frequencies were 35, 74, 170, 300 and 1000 kHz. The degradation rates of chlorobenzene, chloroform, and carbon tetrachloride were highest at 300 kHz. The results of between formation of hydrogen peroxide concentration and degradation of chlorinated compounds were not a coincidence. Methods of the sonochemical efficiency were needed to review. The concentration of total organic carbon was remained after 4 h of sonication. High power intensity, longer sonication time, addition of catalysts and combination of the AOP process, were needed for the degradation of TOC. The formation of chloride ion in aqueous solution was evident for the degradation of chlorinated compounds. However, the theoretical concentration of chloride ion was higher than the measured concentration. This means that the remaining chlorinated contaminants in each solution cannot complete dechlorination and some intermediated were produced.

Ultrasonics Sonochemistry, 2001

Although most papers in the ®eld of sonochemical degradation of volatile organics in aqueous media describe experiments at the millimolar concentration range, this study focuses on the degradation kinetics of chlorobenzene (CB) and trichloroethylene (TCE) in the micromolar range. It was found that the reaction kinetics increase with decreasing initial substrate concentrations. For example, the pseudo-®rst-order reaction rate constant of CB increases by a factor of 14.3, if the initial concentration drops from 3440 to 1 lM. Previous work in the millimolar range has shown that the degradation of these volatiles is mainly due to pyrolytic reactions. The enhancement of the reaction kinetics at lower concentrations, in this work, could no longer be explained by this mechanism, even by taking into account the eect of the concentration of the solutes on the reaction temperature. Therefore, a new model was developed, incorporating gas phase OH radical induced degradation, next to pyrolysis. The model, ®tting the experimental results, illustrated that at micromolar concentrations the OH radical induced degradation becomes signi®cant. Simulations showed that at initial concentrations of CB > 1000 lM degradation is due to pyrolysis for over 99.97%, but it was also demonstrated that at concentrations between 1 and 5 lM, the OH radical mechanism contributed 48.5% of the total degradation.

International Journal of Procurement Management, 2019

This study examines the extent to which the Colleges of Education (COEs) in Ghana comply with one of the key provisions; transparency in the Public Procurement Act 663 of Ghana. A questionnaire survey was conducted among 53 tender committee members in seven COEs in Ashanti Region, Ghana. Respondents were interviewed using tools for assessing transparency which were spelt out in five thematic areas. Data obtained was analysed through percentages, mean scores and relative importance indices. Findings show that the average percentage level of compliance with the transparency provisions in Act 663 among the COEs is 77.4%, indicating that the COEs complied with the transparency provisions in the Act 663. Findings from this study should encourage people in managerial positions in all sectors where procurement is carried out within Ghana to ensure that they comply with the transparency provisions in the act to help fight the menace of corruption.

Following the Minimum Food Security Quota (MFS-Quota) proposed by Ruiz Estrada, Ndoma, and Park (2016) to evaluate and determine the food sustainability of any given developing and least developed countries in the event of any famine this paper sets out to apply the MFS-Quota to test Guatemala's food storage and supply readiness for any potential famine that may critically affect the socioeconomic and political wellbeing of the developing and least developed countries. The primary objective of the MFS-Quota is to calculate the approximate amount of annual food storage that any developing and least developed countries needs in order to subsist through any potential famine. As such, any developing and least developed country could build its own MFS-Quota based on its agriculture production system(s) and national food policy focus.

Página 3 ANEXO I: Reglas 24-26, Apéndices I -III, Interpretaciones unificadas del ANEXO I y Apéndices 1-7 de las interpretaciones unificadas Página 4 ANEXO I: Apéndices 8-9 de las interpretaciones unificadas ANEXO II: Reglas 1-15

The gabarband tradition of water management is an unsurpassed marvel of the story of a civilization. This penchant for water management finds expression in water reservoirs, drainage and sewerage systems of Sarasvati-Sindhu Civilization, dated to ca. 3000 BCE. See: Possehl, Gregory L., 1975. The chronology of gabarbands and palas in western South Asia. Expedition 17 (2): 33-37. A corollary to the gabarband water management tradition of the civilization is the drainage and sanitation system of unparalleled sophistication and hydrological initiatives evidenced in sites such as Mohenjo-daro, Dholavira, Lothal. Indus Script hieroglyph, Sign 194: koḍa 'sluice'; Rebus: koḍ 'artisan's workshop' (Kuwi). A hieroglyph Sign 194 signifies a water sluice. An overview of the sites of the civilization clearly indicates navigable waterways of Sindhu and Sarasvati rivers for ancient maritime tin-bronze trade across long distances from Ancient Far East to Ancient Near East. On these rivers water management systems, including gabarbands, were constructed. Gabarband of Sarasvati-Sindhu civilization A remarkable article by Robert L. Raikes in the Anthropologist (1961) is appended. https://anthrosource.onlinelibrary.wiley.com/doi/pdf/10.1525/aa.1961.63.2.02a00020 The prehistoric climate of Baluchisthan and the Indus Valley by Robert L.Raikes (1961). This article highlights the importance of a unique hydrological irrigation system called gabarband. This gabarband system is a precursor to the Grand stone anicut of Kallanai on Kaveri river 2000 years' old which created a stone anicut to create the Kollidam river diverting the surplus waters of Kaveri and brought an additional 5 acres of land under cultivation in the delta region. [quote] Aurel Stein and others have discovered dams built across the mountain streams in Baluchistan estimated to have been built during neolithic-calcholithic period for irrigation of lands. Wheeler also mentioned the existence of such dams in Baluchistan which are known locally as gabarband. These had been strongly built by stone rubble, even up to height of 10 to 15 feet, to hold sufficient silt and water.[Sir Mortimer Wheeler, The Indus Civilization, Cambridge University Press, 1968, Third Edition, pp.10-11.] Walter A. Fairservis also mentioned such evidence of dams in Las Bela discovered near an Amri site on the Upper Hab River that were built to catch the small annual overflow from the surrounding mountains and by storing it to render it available to normally arid silt tracts which the position of the site indicates were cultivated.[Walter A. Fairservis, “The Harappan Civilization – New Evidence and More Theory,” in, American Museum Novitates, Published by the American Museum of Natural History, New York, No. 2055, 1961, p. 5. ] He also refers to the presence of bund agriculture in southwest Sind mentioned by O.H.K. Spate and earlier by the residents of a Harappan village on the edge of the Malir oasis. All these evidences indicate that these dams were constructed as a rather desperate attempt to store the available water from small rivers and utilize for agriculture. Such bund or dam based agriculture was not unknown in the ancient world as mentioned by some authors. R.S. Bisht has also mentioned the existence of dams at three places that were raised across the Manhar and at two places across the Mansar, both the storm water runnels were embraced the site Dholavira.[ R.S. Bisht, “Dholavira and Banawali: Two Different Paradigms of the Harappan Urbis Forma,” in, Puratattva, No. 29, 1999, pp. 26-28.] The purpose of damming was to harvest water for filling the reservoir in the urban site of Dholavira. At Mehrgarh although no dam was reported, it is mentioned that there is possible evidence for the construction of irrigation ditches, which may have been helpful to agricultural intensification and, eventually population growth.[Jonathan Mark Kenoyer, “Households and Neighborhoods of the Indus Tradition: An Overview,” in, eds, Bradley J. Parker and Catherine P. Foster, New Perspectives on Household Archaeology, Eisenbrauns, Indiana, 2012, p. 381.] C. Benveniste and L. Renou first mentioned Vṛitra from purely philological consideration to mean “obstacle,” “barrage,” or “bloquage,” not a demon, with which D.D. Kosambi also agreed. [Damodar Dharmanand Kosambi, An Introduction to the Study of Indian History, Popular Prakashan, Bombay, First Published 1956, Revised Second Edition 1975, Reprinted 1985, pp. 74, 75.] Kosambi had the same view that Indra’s breaking up dams is related to the breaking of prehistoric dams, called “Gebr-band” and are still found on many water-courses in the western parts of this region. M.K. Dhavalikar mentions the connection on gabarbands to the Vṛitra whom Indra slew, burst the cloud, broke the strongholds and drove the floods.[M.K. Dhavalikar, The Aryans: Myth and Archaeology, Munshiram Manoharlal Publishers Pvt. Ltd., New Delhi, 2007, pp. 100,101.] He mentions “This interpretation is more plausible because it prevents the water flowing down where the Aryans were living in the Indus plains.” On this ground it can be suggested that artificial irrigation based on building dams on rivers was employed in the Indus Civilization to increase the agricultural production which was essential for the subsistence of the huge number of the people living in the Indus-Saraswati Valley in so many settlements distributed throughout the vast region. Till now there is no intensive study conducted on the river based irrigation system of the Harappan people which is related to the subsistence agriculture. It can be assumed that the Harappan people built dams on the rivers to impound water and then sent them to distant places through cannels to irrigate agricultural lands. It can also be surmised that there were sluicegates at the dams to control the river waters as required for the irrigation purpose to distribute water to different communities of people. Sluicegates were not unknown to the Harappan people as its existence is mentioned from dockyard of Lothal where there was an arrangement of sliding wooden door in the recesses of the spill-way to control water level at the dock[S.R. Rao, (1979), Lothal: A Harappan Port Town (1955-62), Volume I, Published by the Archaeological Survey of India, New Delhi, 1979, p.126.] and the wooden sluicegate or grill at the drains of Harappa[Jonathan Mark Kenoyer, Ancient Cities of the Indus Valley Civilization, 1998, p. 61]. The water management for the irrigation system was solely controlled by the Harappan state, which was a very sensitive task and requires some kind of control and authority over the whole population living under its jurisdiction[unquote] https://www.ongshumali.com/en/decline-of-indus-civilization-and-vedic-upheaval-chapter-4/ Lothal: Sanitary drainage at the acropolis "The most unique aspect of planning during the Indus Valley civilization was the system of underground drainage. The main sewer, 1.5 meters deep and 91 cm across, connected to many north-south and east-west sewers. It was made from bricks smoothened and joined together seamlessly. The expert masonry kept the sewer watertight. Drops at regular intervals acted like an automatic cleaning device. A wooden screen at the end of the drains held back solid wastes. Liquids entered a cess poll made of radial bricks. Tunnels carried the waste liquids to the main channel connecting the dockyard with the river estuary. Commoner houses had baths and drains that emptied into underground soakage jars." (Dinesh Shukla) An elaborate sanitary and drainage system, a hallmark of ancient Indus cities, is in evidence everywhere at Lothal. "The proximity of the seat of power to the warehouse may have ensured that the ruler and his entourage could inspect stocks easily. An ivory workshop in the acropolis suggests that elephants may have been domesticated to produce the raw material." (Dinesh Shukla) https://www.harappa.com/category/slide-subject/sanitation Near the warehouse, also on a high plinth, is the upper town or acropolis which spans 128 by 61 meters and has extensive drainage systems. This bathing area in Harappa today is identical to ancient bathing areas. Many of the buildings at Mohenjo-daro had two or more stories. Water from the roof and upper storey bathrooms was carried through enclosed terracotta pipes or open chutes that emptied out onto the street, such as this one on a house in DK-G Area. (See a modern example of this type of open drain chute in Slide 100). harappa.com In the modern town of Harappa, a covered drain built along the outside of a house takes sewage water from a second storey latrine and bathroom to the street level drain without splashing people passing by on the street. A bathing platform in UM area with blocked up doorway leading into the room. The brick floor was made with carefully fitted flat paved bricks and a smaller catchment drain along the side of the platform. A small step was placed at one side of the platform, and a ledge of finely fitted bricks protected the base of the wall.