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Efekti odabranih unapredenih procesa oksidacije i koagulacije na sadržaj prirodnih organskih materija u vodi / The effects of selected advanced oxidation processes and coagulation on natural organic matter content in water

Cilj ovog rada bio je da se u laboratorijskim uslovima ispitaju efekti odabranih unapredenih procesa oksidacije (Fenton proces, ozonizacija, TiO2-katalizovana ozonizacija, perokson proces i TiO2-katalizovan perokson proces) i koagulacije na sadržaj i strukturu prirodnih organskih materija u vodi, kao prekursora dezinfekcionih nusprodukata hlora. Karaterizacija POM frakcionisanjem pre i nakon navedenih oksidacionih tretmana i koagulacije izvr&scaron;ena je u cilju ispitivanja mehanizama oksidacije i uklanjanja POM, kao i utvrdivanja promene reaktivnosti prekursorskog materijla DBP (trihalometana i halosircetnih kiselina, kao najvi&scaron;e zastupljenih DBP, i haloacetonitrila, hlorpikrina i haloketona, kao nedovoljno istraženih, visoko prioritetnih &bdquo;DBP u razvoju“). Analizom hemijskih karakteristika prirodnog matriksa utvrdeno je da voda sadrži visoke koncentracije prirodnih organskih materija (DOC sirove iznosi 9,92±0,87 mg/L) uz dominaciju materija hidrofobnog karaktera (14% huminskih i 65% fulvinskih kiselina). U slucaju sintetickog matriksa (sadržaj DOC 11,2±0,37 mg/L) zastupljena je samo frakcija huminske kiseline, te je iz tog razloga sinteticki matriks znatno hidrofobniji u odnosu na prirodni. Veci stepen hidrofobnosti sintetickog matriksa u poredenju sa prirodnim matriksom, rezultovao je i vecim sadržajem prekursora najzastupljenijih dezinfekcionih nusprodukata hlora, THM i HAA. Vrednosti za PFTHM iznose 438±88,2 μg/L za prirodni matriks, odnosno 3646±41,3 μg/L za sinteticki matriks, dok PFHAA prirodnog matriksa iznosi 339±68,9 μg/L, odnosno 559±20,5 μg/L za sinteticki matriks. Sadržaj HAN, CP i HK je znatno niži u poredenju sa prekursorima THM i HAA. PFHAN iznosi 3,65 μg/L za prirodni, odn. 7,98 μg/L za sinteticki matriks, dok prekursori CP nisu detektovani. Prekursori HK su zastupljeni samo u strukturi POM prirodnog matriksa i PFHK iznosi 46,9±5,08 μg/L. Hidrofoban materijal, kao dominantan u strukturi POM ispitivanih matriksa, je ujedno i osnovni prekursorski materijal THM i HAA, dok su prekursori haloacetonitrila i haloketona u navecoj meri zastupljeni u hidrofilnoj frakciji. Ispitivanjem uticaja Fenton procesa na sadržaj POM, pri optimalnim reakcionim uslovima (pH 5, reakciono vreme od 15 min. i brzina me&scaron;anja 30 o/min), postignuto je u zavisnosti od primenjene doze Fe2+, molarnog odnosa Fe2+ i H2O2 i matriksa 80-95% smanjenja saržaja DOC, 70-99% PFTHM, 37-92% PFHAA. Kao posledica uklanjanja POM oksidaciojom i koagulacijom, zabeležene su blage fluktuacije u sadržaju prekursora HAN, CP i HK. Ispitivanjem uticaja ozonizacije u vodi pri razlicitim pH na sadržaj i strukturu POM utvrdeno je da je ozonizacija u baznoj sredini efikasnija za uklanjanje POM u odnosu na ozonizaciju u kiseloj sredini. Katalizovanje procesa ozonizacije primenom TiO2 u vodi razlicitim pH unapreduje smanjenje sadržaja kako ukupnih organskih materija, tako i specificnih prekursora DBP u poredenju sa ozonizacijom. Najefikasnije smanjenje sadržaja POM postignuto je TiO2-O3 procesa u baznoj sredini primenom 3,0 mg O3/mg DOC i 1,0 mg TiO2/L (30% DOC, 92-100% PFTHM, PFHAA, PFHAN i PFHK). TiO2-O3 proces pri svim pH vrednostima produkuje manji sadržaj CP u odnosu na ozonizaciju. Veca efikasnost primenjenih procesa u smanjenju sadržaja POM sintetickog matriksa u odnosu na prirodni ukazuju da je frakcija huminske kiseline podložnija oksidacionom tretmanu u odnosu na fulvinsku, kao dominantnu frakciju POM prirodnog matriksa. Kada je u pitanju mehanizam oksidacije POM ispitivanih matriksa, primenom ozonizacije i TiO2-O3 procesa, pri svim pH postignuta je potpuna oksidacija frakcije huminske kiseline do fulvinske kiseline i hidrofilnih jedinjenja. U slucaju ozonizacije, sa povecanjem pH vrednosti sredine, usled povecane produkcije hidroksil radikala iz ozona, povecao se i udeo odnosno sadržaj DOC u hidrofilnoj frakciji ozonirane vode (86%-90%). Raspodela DOC nakon TiO2-O3 procesa pri svim pH vrednostima je oko 70% i 50% u hidrofilnoj frakciji prirodnog i sintetickog matriksa, redom. Frakcija koja se dominantno formira nakon navedenih oksidacionih tretmana je hidrofilna nekisela frakcija. Frakcionisanjem POM nakon oksidacionih tretmana je utvrdeno da su prekursori THM i HAA kako hidrofobne aromaticne strukture, tako i hidrofilna polarna jedinjenja, dok je najreaktivniji prekursorski materijal HAN, CP i HK sadržan u hidrofilnoj frakciji POM. Uvodenjem H2O2 u proces ozonizacije (O3/H2O2 i iO2-O3/H2O2) u slabo baznoj sredini (pH 7-7,5) postignut je jo&scaron; veci stepen oksidacije POM i povecanje udela hidrofilnih struktura (oko 88%) ispitivanih matriksa u odnosu na ozonizaciju i iO2-O3 (oko 70%), primenom 3,0 mg O3/mg DOC; O3:H2O2=1:1 i 1,0 mg iO2/L. Povecanje sadržaja prekursora THM i HAA samo u slucaju prirodnog amtriksa posledica je povecanja reaktivnosti frakcije fulvinske kiseline nakon O3/H2O2 i iO2-O3/H2O2 procesa, u kojoj su ujedno i prekursori HK najzastupljeniji. Najveci sadržaj azotnih DBP (HAN i CP) sadrži hidrofilna frakcija POM. Ispitivanjem kombinovanih procesa ozonizacije i TiO2-O3 i koagulacije utvrdeno je da oksidacioni tretmani imaju pozitivne efekte u uklanjaju POM koagulacijom. Maksimalna efikasnost smanjenja sadržaja DOC od 32% postignuto je primenom 3,0 mg O3/mg DOC i 200 mg FeCl3/L, dok su ne&scaron;to niže doze ozona pogodne za uklanjanje prekursora DBP (80- 89% PFTHM, PFHAA, PFHAN i PFHK, primenom 0,7-1,0 mg O3/mg DOC i 200 mg FeCl3/L). Prekursori CP koji se formiraju ozonizacijom zaostaju u vodi nakon koagulacije. Rezultati dobijeni tokom istraživanja ukazuju da se primenom razlicitih oksidacionih i unapredenih oksidacionih procesa može smanjiti sadržaj POM i prekursora DBP do odredenog stepena. Kao najefikasniji u uklanjaju kako ukupnih organskih materija, tako i specificih prekursora DBP se pokazao Fenton proces. Kada su u pitanju unapredeni procesi oksidacije zasnovani na primeni ozona, uvodenje katalizatora ili H2O2 kao oksidanta u proces ozonizacije, kao i odabir optimalne pH vrednosti procesa može unaprediti oksidabilnost organskih molekula. Pri tom, poznavanje mehanizama oksidacije POM iz razlicitih izvora primenom ozona i/ili hidroksil radikala, kao i mehanizma uklanjanja POM koagulacijom može se primeniti za odabir i optimizovanje odgovarajuceg procesa u tretmanu vode za pice, a u zavisnosti od kvaliteta sirove vode. / The aim of this work was to examine under laboratory conditions the effects of certain advanced oxidation processes (Fenton process, ozonation, TiO2-catalyzed ozonation, peroxone process and TiO2-catalyzed peroxone process) and coagulation on the content, structure and role of natural organic matter in water as the precursors of chlorine disinfection byproducts. The NOM was characterized by fractionation before and after these oxidation treatments and coagulation, in order to investigate NOM oxidation mechanisms and identify the changes in the reactivity of DBP precursor material (trihalomethanes and haloacetic acids, as the most abundant DBP, and haloacetonitriles, chloropicrin and haloketones, as underresearched, high priority “emerging DBP”). Through analysis of the chemical characteristics of the natural matrix, it was found that the water contains high concentrations of natural organic matter (raw water DOC was 9.92 ± 0.87 mg/L) dominated by substances with a hydrophobic character (14% humic and 65% fulvic acids). The synthetic matrix studied (DOC content of 11.2 ± 0.37 mg/L) contained only the humic acid fraction, and was therefore significantly more hydrophobic compared to the natural one. The greater degree of hydrophobicity in the synthetic matrix relative to the natural matrix resulted in a higher content of precursors of the most frequent chlorine disinfection byproducts, THM and HAA. The THMFP of the natural matrix was 438±88.2 mg/L, compared to 3646±41.3 mg/L for the synthetic matrix, while the HAAFP of the natural matrix was 339±68.9 mg/L, compared to 559±20.5 mg/L for the synthetic matrix. The contents of HAN, CP, and HK precursors were much lower than the THM and HAA precursors. HANFP were 3.65 mg/L for natural, and 7.98 mg/L for the synthetic matrix, whilst CP precursors were not detected. HK precursors were present only in the structure of the natural NOM matrix, with a HKFP of 46.9±5.08 mg/L. Hydrophobic material, as the dominant structure in the investigated NOM matrix, is the basic precursor material of THM and HAA, while the precursors of haloacetonitriles and haloketones are represented mostly in the hydrophilic fraction.Whilst examining the influence of the Fenton process on the NOM content, under optimal reaction conditions (pH 5, reaction time of 15 min and stirring speed of 30 rpm), depending upon the applied dose of Fe2+, the molar ratio of Fe2+ and H2O2, and the matrix, reductions in the DOC content of 80-95%, in the THMFP of 70-99%, and in the HAAFP of 37-92%, were achieved. As a result of removing NOM by oxidation and coagulation, mild fluctuations in the contents of HAN, CP and HK precursors were recorded. The investigation into the effects of ozonation at different pH levels on the content and structure of NOM has shown that ozonation under alkaline conditions is more effective at removing NOM than ozonation under acidic conditions. Catalyzing the ozonation process using TiO2 in water with different pH promotes the reduction of both total organic matter and specific DBP precursors in comparison with ozonation alone. The most effective NOM reduction was achieved using the TiO2-O3 process in alkaline conditions using 3.0 mg O3/mg DOC and 1.0 mg TiO2/L (30% DOC, 92-100% THMFP, HAAFP, HANFP and HKFP). The TiO2-O3 process produces lower amounts of CP at all pH values, relative to ozonation. The applied processes showed increased efficacy in reducing the NOM content of the synthetic matrix compared with the natural matrix, which shows that the humic acids fraction is more susceptible to oxidation treatments than the fulvic acids which are the dominant faction of the natural NOM matrix. Regarding the NOM oxidation mechanism in the investigated matrices, using ozonation and the TiO2-O3 process, complete oxidation of the humic acid fraction to fulvic acids and hydrophilic compounds was achieved at all pH levels. In the case of ozonation, increasing the pH in the matrix lead to an increase in hydroxyl radicals production from ozone, and the proportion or content of DOC in the hydrophilic fraction of ozonated water (86%-90%) increased. The distribution of DOC after the TiO2-O3 process at all pH values was about 70% and 50% in the hydrophilic fraction of the natural and synthetic matrices, respectively. The dominant fraction formed after the oxidation treatments was the hydrophilic non-acid fraction. By NOM fractionation after the oxidation treatments, it was shown that the THM and HAA precursors are hydrophobic aromatic structures and hydrophilic polar compounds, whilst the most reactive precursor materials for HAN, CP and HC are contained in the hydrophilic NOM fraction. Introducing H2O2 into the ozonation process (O3/H2O2 and iO2-O3/H2O2) in weak basic conditions (pH 7 to 7.5) enhances further the degree of NOM oxidation and increases the proportion of hydrophilic structures (88%) in the examined matrices in comparison to ozonation and iO2-O3 (about 70%), using 3.0 mg O3/mg DOC; O3:H2O2=1:1 and 1.0 mg iO2/L. An increase in the THM and HAA precursor contents occurred in the case of the natural matrix as a result of the increased reactivity of the fulvic acid fraction after the O3/H2O2 and iO2-O3/H2O2 processes, and HK precursors were also present. The highest content of nitrogen DBP (HAN and CP) was found in the hydrophilic NOM fraction. By examination of the combined processes of ozonation, TiO2-O3 and coagulation, it was shown that oxidative treatments have a positive effect on NOM removal by coagulation. A maximum efficacy in reducing DOC by 32% was achieved with 3.0 mg O3/mg DOC and 200 mg FeCl3/L, whereas slightly lower ozone doses are suitable for the removal of DBP precursors (80-89% THMFP, HAAFP, HANFP and HKFP, using 0.7-1.0 mg O3/mg DOC and 200 mg FeCl3/L). CP precursors which are formed during ozonation remain in the water after coagulation. The results obtained during this investigation show that the application of different oxidation and enhanced oxidation processes can reduce the contents of NOM and DBP precursors to some degree. The most effective process at removing both total organic matter and specific DBP precursors proved to be the Fenton process. With respect to enhanced oxidation processes based upon the use of ozone, by introducing catalysts or H2O2 as an oxidant in the ozonation process and by selecting the optimum pH for the process, the oxidizability of organic molecules can be improved. In addition, knowledge of the NOM oxidation mechanisms from different sources using ozone and / or hydroxyl radicals, as well as the mechanism of NOM removal by coagulation, can be used to select and optimize the most appropriate process in drinking water treatment, depending upon the quality of the raw water.

Identifer	oai:union.ndltd.org:uns.ac.rs/oai:CRISUNS:(BISIS)77387
Date	10 October 2011
Creators	Molnar Jazić Jelena
Contributors	Agbaba Jasmina, Dalmacija Božo, Klašnja Mile
Publisher	Univerzitet u Novom Sadu, Prirodno-matematički fakultet u Novom Sadu, University of Novi Sad, Faculty of Sciences at Novi Sad
Source Sets	University of Novi Sad
Language	Serbian
Detected Language	Unknown
Type	PhD thesis
Format	application/pdf

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Efekti odabranih unapredenih procesa oksidacije i koagulacije na sadržaj prirodnih organskih materija u vodi / The effects of selected advanced oxidation processes and coagulation on natural organic matter content in water

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