Siva Sarathy and Mihaela Stefan

Transcription

1 Siva Sarathy and Mihaela Stefan Trojan Technologies, London, ON, Canada

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3 Combination of UV and H 2 O 2 providing enhanced oxidative degradation of pollutants in water via highly reactive species, such as the hydroxyl radical ( OH). Performance highly dependent on various factors, one of which is water quality parameters Oxidative processes may impact the water quality through the byproducts generated from water matrix constituents, including NOM. PWN ANDIJK, NETHERLANDS SAN GABRIEL VALLEY, CALIFORNIA

4 NOM Absorbs UV photons Scavenges OH NOM + OH reaction causes observable changes in NOM (e.g., molecular weight distribution, aromaticity) NOM + OH reaction products may affect water quality particularly with respect to Biological stability Literature reports potential formation of oxygenated by products Potential for increase in AOC and BDOC Chlorinated disinfection by products NOM transformation may alter water matrix reactivity towards chlorine Mixed reports on whether DBP formation is affected Both are dependent on source water and NOM characteristics

5 The bacterial regrowth potential in drinking water distribution systems. Two key metrics: assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC). AOC fraction of DOC ( %; van der Kooij, 1990) metabolized by microbial community resulting in biomass growth; Assayed through the amount of microbial cells grown aldehydes, ketones, carboxylic acids, aminoacids, etc. No drinking water standard for AOC; but monitored by water utilities AOC levels for biostable water (literature data): Van der Kooij (1982): heterotrophic bacteria do not increase in nonchlorinated water with AOC<10 g/l LeChevallier et al (1987): AOC< g/l and 3 6 mg/l chlorine may limit coliform regrowth

6 O OH OH O O O HO O O O OH HO OH O O HO O OH O OH O HO OH Typical Humic acid structure Fulvic acid structure (Leenheer et al. 1998) O O OH, O 3 reactive sites Protein chain O 3 reactive sites OH reactive sites NDOM Complex heterogeneous mixture of organic compounds of aquatic and terrestrial origins, with highly diversified structures, properties and

7 Monitored and regulated DBPs: THMs (80 µg/l) and HAAs (60 µg/l) THMs formation Ring opening and hydroxylation of aromatic rings can increase species reactivity towards chlorine HAAs formation Acetaldehyde could be chlorinated and then hydrolyzed to acid

8 Activated carbon serves as support for microbial growth Very long operation duration (e.g. 20 years at Zurich, Paris) 2 cm 2 cm 40 X 280 µm Fresh GAC 10.4 µm 20 years later Microbial presence Cylindrical shaped preserved Macroporous structure 600 X Velten et al. (2007)Rapid and direct estimation of active biomass on GAC through ATP determination. Wat Res 41 p Installed in numerous drinking water plants to ensure biostable water Empty bed contact time (EBCT) is the primary design parameter Full scale hydraulic loading rates between 5 15 m/h

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10 Water delivered to Trojan Water delivered to Trojan

11 Swift 2L12 reactor setup BAC column B 80 ml/min 10 m/h HLR BAC column A 120 ml/min 15 m/h HLR BAC column C 40 ml/min 5 m/h HLR Untreated water tank Feed water tank

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13 [Fanshawe Pond] 1 micron filter blending UV/H 2 O 2 TOC: 2.3 mg/l T 254nm,1cm : 92.4% Trojan In-House Method Stefan and Sarathy. (2011) A method for quantifying the assimilable organic carbon in UV/H 2 O 2 biological activated carbon filtration treated water. IOA IUVA World Congress & Exhibition, Paris, France May 23-27, 2011

14 [Fanshawe Pond] 1 micron filter blending UV/H 2 O 2 TOC: 2.3 mg/l T 254nm,1cm : 92.4%

15 [Lake Erie ultrafiltration] UV/H 2 O 2 TOC: 1.8 mg/l T 254nm,1cm : 95.7%

16 [Fanshawe Pond] 1 micron filter blending UV/H 2 O 2 TOC: 2.3 mg/l T 254nm,1cm : 92.4%

17 [Lake Erie ultrafiltration] UV/H 2 O 2 TOC: 1.8 mg/l T 254nm,1cm : 95.7%

18 Oxidative conditions during UV/H 2 O 2 led to increase in AOC NOM oxidation may lead to an increase in DBP precursors (dependent on NOM characteristics). Potential increase in DBP formation not necessarily an increase over/above regulatory limits.

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20 Fed blended surface water to activated carbon columns for 3 months. Monitored activated carbon column s adsorption capacity and biological activity. Raw Fanshawe Lake Water Blended Fanshawe Lake Water T 254nm,1cm 69 71% 89 91% Turbidity 2 8 NTU < 1 NTU TOC mg/l mg/l

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22 Day 13 Day 41

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24 [Fanshawe Pond] 1 micron filter blending UV/H 2 O 2 TOC: 2.3 mg/l T 254nm,1cm : 92.4% Trojan In-House Method Stefan and Sarathy. (2011) A method for quantifying the assimilable organic carbon in UV/H 2 O 2 biological activated carbon filtration treated water. IOA IUVA World Congress & Exhibition, Paris, France May 23-27, 2011

25 [Lake Erie ultrafiltration] UV/H 2 O 2 2 day Cl 2 BAC 2 day Cl 2

26 [Lake Erie ultrafiltration] UV/H 2 O 2 2 day Cl 2 BAC 2 day Cl 2

27 Small/short design BAC (EBCT 4 min) is capable of reducing AOC below untreated water levels If DBP formation surpasses regulatory limits, short BAC is capable of sufficient reduction. Greater reduction at longer EBCT (20 min, still reasonable)

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29 Only approx % of the initial concentration (3 10 mg/l) of H 2 O 2 is consumed in the UV/H 2 O 2 process (direct photolysis and OH reactions) H 2 O 2 residual is currently removed in North America through chlorination (2.1:1 Cl 2 :H 2 O 2 mass ratio) 15 m/h 10 m/h 5 m/h 15 m/h 10 m/h 5 m/h

30 Potential for nitrite formation by UV/H 2 O 2 (through nitrate photolysis) USEPA nitrite Maximum Contaminant Level: 3.3 mg/l as NO 2 EU Directive nitrite parametric value: 0.1 mg/l as NO 2 Hydraulic Loading Rate

31 The potential for formation of AOC after UV/H 2 O 2 can be addressed by NOM pre treatment and proper UV/H 2 O 2 treatment sizing Increase in DBP formation after UV/H 2 O 2 was not likely to surpass regulatory limits BAC, at very short contact times, was observed to be effective and sustainable at addressing potential water quality issues post UV/H 2 O 2

32 The authors gratefully acknowledge Trojan colleagues help with pilot setup, sample and data analysis.