Effect of ozone, ozone/hydrogen peroxide and hypoclorite on natural organic matter and oxidation by-products content in water after coagulation, floculation and adsorption procesess

Cilj ovog rada je bio da se ispita uticaj ozona i ozon/vodonik-peroksida na efikasnost uklanjanja POM i prekursora oksidacionih nusproizvoda, procesima koagulacije, flokulacije i adsorpcije. Posebna pažnja posvećena je ispitivanju uticaja navedenih procesa na sadržaj prekursora oksidacionih nusproizvoda hlora (trihalometana i halosirćetnih kiselina), kao i na uticaj hipohlorita na formiranje ovih jedinjenja u tretiranoj vodi. Analiza hemijskih karakteristika sirove podzemne vode korišćene u ispitivanjima pokazuje da sadrži visok nivo POM pretežno hidrofobnog karaktera (PB = 37,7±0,60 mg KMnO4/l; DOC = 9,27±0,92 mg C/l; UV254 = 0,497± 0,015 cm-1; SUVA = 5,36±0,49 1 mg-1 m-1; PFTHM = 555±128 µg/l; PFHAA = 245±54,9 µg/l), kao i visoku koncentraciju arsena (51,7±16,4 µg/l). Poređenjem uticaja dve ispitivane vrste koagulanata (FeCl3 i FeCl3/PACl) utvrđeno je da imaju različite mehanizme uklanjanja POM i prekursora oksidacionih nusproizvoda. FeCl3/PACl omogućava smanjenje sadržaja POM izraženih preko vrednosti DOC, PB, UV254 apsorbancije i SUVA za 54%, 71%, 88% i 74%, u odnosu na sirovu vodu respektivno, dok se koagulacijom sa FeCl3 postiže smanjenje DOC, PB, UV254 apsorbancije i SUVA za 51%, 48%, 61% i 21%, respektivno. U vodi nakon koagulacije sa FeCl3 zaostaju POM hidrofobnog karaktera (SUVA = 5,12 l m-1 mg-1), dok se POM u koagulisanoj vodi sa FeCl3/PACl, mogu okarakterisati kao hidrofilne (SUVA = 1,70 l m-1 mg-1). Koagulacija sa FeCl3 i FeCl3/PACl omogućila je smanjenje sadržaja arsena u vodi za preko 95%, pri čemu su koncentracije As u koagulisanoj vodi bile niže od 10 µg/l. Ozon i O3/H2O2 proces pokazuju sličnu efikasnost u smanjenju sadržaja POM i prekursora oksidacionih nusproizvoda. Poređenjem kombinovanih tretmana koji obuhvataju oksidacioni predtretman i koagulaciju, utvrđeno je da efikasnost koagulacije sa FeCl3 i FeCl3/PACl u smanjenju vrednosti DOC, PB, UV254, SUVA, PFTHM i aldehida, uglavnom zavisi od mehanizma delovanja samih koagulanata, dok ozon i O3/H2O2 proces doprinose smanjenju vrednosti ovih parametara kroz oksidaciju i izdvajanje lako isparljivih komponenti iz vode stripingom gasa. Sa aspekta promene sadržaja prekursora HAA, ozon i O3/H2O2 proces omogućavaju povećanje efikasnosti procesa koagulacije sa FeCl3 i FeCl3/PACl, u odnosu na koagulaciju bez oksidacionog predtretmana. Kada se uzmu u obzir vrednosti svih navedenih parametara, kao i primenjenje doze oksidacionih sredstava i koagulanata, najbolji rezultati u uklanjanju POM i prekursora oksidacionih nusproizvoda (smanjenje vrednosti DOC za 55%, UV254 i SUVA za više od 90%, u odnosu na sirovu vodu; PB = 7,70 mg KMnO4/l; PFTHM =158-188 µg/l; PFHAA = 33,0-53,8 µg/l i sadržaj aldehida 16,7-17,9 µg/l) postižu se primenom tretmana koji obuhvataju oksidacioni predtretman ozonom (3,0 g O3/m3), odnosno O3/H2O2 (3,3 g O3/m3; H2O2:O3 =1:1), koagulaciju (30 g FeCl3/m3 / 30 g Al/m3) uz recirkulaciju flokulacionog mulja i adsorpciju na zeolitu, flokulaciju, sedimentaciju i filtraciju na peščano/antracitnom filtru. Za završnu obradu vode GAU filtracijom pre procesa dezinfekcije, na osnovu svih ispitivanih parametara, kao najefikasniji u uklanjanju POM i prekursora oksidacionih nusproizvoda (THM, HAA i aldehida) pokazao se GAU Norit Row 0,8 Supra. Hlorisanjem u simuliranim uslovima dezinfekcije, utvrđeno je da voda dobijena nakon GAU filtracije u ispitivanim tretmanima, ima zadovoljavajući kvalitet sa aspekta sadržaja THM i HAA (sadržaj THM je 69,7-77,4 µg/l; koncentracija DCAA je < MDL) čije su maksimalno dozvoljene koncentracije regulisane u vodi za piće (100 µg/l za THM i 50 µg/l za DCAA). Statističkom obradom podataka iz laboratorijskih i pilot ispitivanja utvrđene su empirijske zavisnosti koje se mogu primenjivati za predviđanje koncentracije THM i HAA u tretiranoj vodi nakon tretmana ispitivanih na pilot postrojenju. Da bi se mogle primeniti za druge vrste vode i drugačije dizajnirane tetmane, neophodno je izvršiti validaciju primenom nezavisnog seta podataka. Svi rezultati dobijeni u toku istraživanja ukazuju na neophodnost primene oksidacionih sredstava u tretmanu ispitivane podzemne vode. Zbog različitog mehanizma delovanja, neophodno je izvršiti odabir odgovarajuće vrste i doze oksidacionog sredstva, kao i koagulanta u tretmanu vode za piće, uzimajući u obzir karakteristika sirove vode i efikasnost koja se želi postići. Primena optimalnih doza ozona i O3/H2O2 omogućava povećanje efikasnosti uklanjanja POM i prekursora oksidacionih nusporizvoda, procesima koagulacije, flokulacije i adsorpcije. Odabirom odgovarajućih uslova tretmana postiže se da i nakon hlorisanja u postupku dezinfekcije, voda zadovoljava kriterijume kvaliteta vode za piće, sa aspekta sadržaja trihalometana i halosirćetnih kiselina.The aim of this work was to investigate influence of ozone and ozone/hydrogen peroxide on efficiency of coagulation, flocculation and adsorption on natural organic matter and oxidation by-products removal. Special attention was dedicated to investigation of these processes on chlorine oxidation by-products (trihalomethanes and haloacetic acids) as well as on hypochlorite influence on formation of these compounds in treated water. The analysis of chemical characteristics of raw ground water used in this investigation show that it contains high amount of NOM, mainly of hydrophobic nature (PB = 37,7±0,60 mg KMnO4/l; DOC = 9,27±0,92 mg C/l; UV254 = 0,497± 0,015 cm-1; SUVA = 5,36±0,49 1 mg-1 m-1; PFTHM = 555±128 μg/l; PFHAA = 245±54,9 μg/l) as well as high arsenic concentration (51,7±16,4 μg/l). Comparing the influences of two investigated coagulants (FeCl3 and FeCl3/PACl) it was observed that they have different mechanisms of NOM and oxidation by-products precursors’ removal. FeCl3/PACl enables reduction of DOC, PB, UV254 absorbance and SUVA value for 54%, 71%, 88% i 74%, respectively, relative to raw water. Coagulation with FeCl3 provides reduction of DOC, PB, UV254 absorbance and SUVA for 51%, 48%, 61% i 21%, respectively. In water coagulated with FeCl3 remains NOM of hydrophobic nature (SUVA = 5,12 l m-1 mg-1) while NOM in coagulated water with FeCl3/PACl can be characterized as hydrophilic (SUVA = 1,70 l m-1 mg-1). Coagulation with FeCl3 and FeCl3/PACl enables arsenic content reduction for over 95% relative to raw water, with As concentrations in coagulated water below of 10 μg/l. Ozone and O3/H2O2 process demonstrates similar efficiency in NOM and oxidation by-products precursors content reduction. Comparing combined treatment which includes oxidation pretreatment and coagulation, it was observed that efficiency of coagulation in DOC, PB, UV254, SUVA, PFTHM and aldehydes reduction mainly depends on coagulants activity mechanisms, while ozone and O3/H2O2 process contributes to reduction of these parameters through oxidation and removal of volatile compounds from water by gas stripping. Ozone and O3/H2O2 process enables increase of coagulation efficiency for HAA precursor’s removal, comparing to coagulation without oxidation pretreatment. Taking into account all measured parameters as well as applied doses of oxidation reagents and coagulants, it can be concluded that the best results in NOM and oxidation by-products precursors content reduction (decrease of DOC for 55%, UV254 i SUVA for more then 90%, related to raw water; PB = 7,70 mg KMnO4/l; PFTHM =158-188 μg/l; PFHAA = 33,0-53,8 μg/l and content of aldehydes 16,7-17,9 μg/l) can be obtained by treatments which include oxidation pretreatment with ozone (3,0 g O3/m3), as well as with O3/H2O2 (3,3 g O3/m3; H2O2:O3 =1:1), coagulation (30 g FeCl3/m3 / 30 g Al/m3), with flocculation sludge recirculation and zeolit adsorption, flocculation, sedimentation and filtration on sand/anthracite filter. For the final water treatment with GAC filtration before disinfection process, based on all parameters, GAC Norit Row 0,8 Supra was the most efficient in NOM and oxidation by-products precursors reduction (THM, HAA and aldehydes). After chlorination in simulated disinfection conditions, it was determined that water after GAC filtration in investigated treatments has satisfactory quality in terms of regulated THM and HAA (content of THM is 69,7-77,4 μg/l; concentration of DCAA is < MDL) which maximal allowable level for drinking water is established (100 μg/l for THM and 50 μg/l for DCAA). By statistical analysis of data obtained in laboratory and pilot scale experiments it was determined empirical relations for THM and HAA concentration predictions in treated water. All obtained results in this research indicate that oxidation reagents need to be applied in treatment of investigated ground water. Because of different action mechanism, it is necessary to select the adequate type and dose of oxidation reagent and coagulant in water treatment, taking into account characteristics of raw water and efficiency that needs to be achieved. Application of optimal doses of ozone and O3/H2O2 enables increase of coagulation, flocculation and adsorption efficiency in NOM and oxidation by-products precursors’ removal. Selection of adequate treatment conditions provides that after chlorination in disinfection process water satisfies drinking water quality criteria, in terms of trihalomethanes and haloacetic acids