New insights into the ultraviolet disinfection of wastewater

Transcription

1 Engineering Conferences International ECI Digital Archives Wastewater and Biosolids Treatment and Reuse: Bridging Modeling and Experimental Studies Proceedings Spring New insights into the ultraviolet disinfection of wastewater Ramin Farnood University of Toronto Follow this and additional works at: Part of the Environmental Engineering Commons Recommended Citation Ramin Farnood, "New insights into the ultraviolet disinfection of wastewater" in "Wastewater and Biosolids Treatment and Reuse: Bridging Modeling and Experimental Studies", Dr. Domenico Santoro, Trojan Technologies and Western University Eds, ECI Symposium Series, (2014). This Conference Proceeding is brought to you for free and open access by the Proceedings at ECI Digital Archives. It has been accepted for inclusion in Wastewater and Biosolids Treatment and Reuse: Bridging Modeling and Experimental Studies by an authorized administrator of ECI Digital Archives. For more information, please contact

2 New Insights into the Ultraviolet Disinfection of Wastewater Ramin Farnood Department of Chemical Engineering, University of Toronto Wastewater and Biosolids Treatment and Reuse: Bridging Modelling and Experimental Studies Otranto, June 8-14,

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4 Log (CFU/100 ml) N o Initial Slope: Free Microbes Tailing: Particle Associated Coliform Bacteria (PAC) UV Dose mj/cm 2 UV dose is corrected dose for UV absorbance, i.e. the actual dose is larger. 3

5 Log (CFU/100 ml) N o Initial Slope: Free Microbes N target Tailing: Particle Associated Coliform Bacteria (PAC) Dose 1 UV Dose mj/cm 2 Presence of particle associated coliform bacteria cause the tailing of UV DRC and increases the UV dose demand of effluent 4

6 Log (CFU/100 ml) N o Case I N target Dose 2 Dose 1 UV Dose mj/cm 2 Lowering the tailing of UV DRC improves the UV disinfection of effluent 5

7 Log (CFU/100 ml) N o Case II N target Dose UV Dose mj/cm 2 Lowering the tailing of UV DRC improves the UV disinfection of effluent 6

8 Use of upstream processes has been suggested for improving UV disinfection performance (Darby et al., 1999). Ultrasound (Blume and Neis, 2002) and filtration (Jolis et al., 2001) have been shown to improve disinfection performance. Systematic study on better quantify the impact of particle size on UV disinfectability required

9 How does the UV disinfection of suspended particles/flocs change with size? How does floc structure and composition affect its UV disinfectability? How can UV disinfectability of effluents be controlled/ improved? 8

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11 Droppo, I.

12 Bacteria EPS EPS absorbs UV light at the germicidal wavelengths The two layer model is a proposed structure of flocs which is in accordance with the tailing phenomenon Dense Core Loose outer shell Liao et al. 2002

13 Dense cores cause floc resistance to UV thereby leading to tailing Chemical composition can affect floc UV disinfectability through interactions with UV light

14 Dense cores cause floc resistance to UV thereby leading to tailing Chemical composition can affect floc UV disinfectability through interactions with UV light

15 Sieving Activated Sludge Sieving Exposure to UV Light Shearing 3500 rpm, 15 min UV Dose Response Curves

16 Shearing Original Sample Cores (after shearing)

17 N/N μm Larger particles show higher degrees of tailing μm μm Floc Size (μm) μm μm μm UV Dose (mj/cm²)

18 N/N μm Cores higher tailing than flocs. Above 45 um, UV DRC of cores did not vary with size! μm μm 0.1 Core Size (μm) μm μm μm μm UV Dose (mj/cm²)

19 Log(N/N0) UV Dosage (mj/cm2) Core Sample (sheared) μm Floc Sample (un-sheared) -3.5 For the same size, cores are harder to disinfect than flocs

20 Fraction of UV-Resistant Microorganisms (β) Flocs (Un-sheared) Cores (Sheared) Size Fraction (microns) Cores are more resist UV disinfection than flocs.

21 Loose shell Dense core Type 1: Indicator organism in the loose shell, Easier to disinfect δ S R Type 2: Indicator organism in the core, Harder to disinfect (a) Indicator organism (b) N(R) /N o (R) = ( o δ S f (δ,r) dδ) e k 1 D + ( δs δ f (δ,r) dδ) e k 2 D 20

22 N / No Core Volume Core Diameter 70% (53 μm) µm flocs No core UV Dose (mj/cm 2 ) 40% (44 μm) 10% (28 μm) Core Volume % 21

23 N / No μm 70μm 60μm 40 μm Core size UV Dose (mj/cm 2 ) Good qualitative and semi-quantitative agreement. 22

24 Dense cores cause floc resistance to UV thereby leading to tailing Chemical composition can affect floc UV disinfectability through interactions with UV light, i.e. advanced oxidation 23

25 BNR-UCT CAS Identical influent conditions. 24

26 Log (N/N0) 0-1 Final Effluents BNR - UCT CAS -2 CAS BNR- UCT UV Dose (mj/cm²) BNR-UCT effluent is disinfected more readily. 25

27 Particle Number % 10 8 BNR-UCT CAS Floc Size (μm) BNR-UCT flocs are smaller. 26

28 BNR-UCT flocs contain polyphosphates 27

29 % Discoloration of MB MB + UV + Na3P3O9 MB + UV + TiO2 Polyphosphates could act as a photocatalyst in producing highly oxidative hydroxyl radicals under UV irradiation 15 5 MB + UV + Na3P3O9 + MeOH MB + UV Exposure to UV (minutes) 28

30 % Discoloration of MB MB + UV + Na3P3O9 35 MB + UV + TiO MB + UV + Na3P3O9 + MeOH MB + UV Exposure to UV (minutes) BNR-UCT flocs may have two UV disinfection mechanisms: Direct UV damage to the DNA Cell membrane damage by oxidative species (advanced oxidation) 29

31 N(R, δ) /N o (R, δ) = o R f (R, δ) e (k eff,uv (δ) + k eff, OH (δ))d dδ 30

32 UV disinfection kinetics of flocs can be explained using a simple structural model Cores are harder to disinfect than flocs of the same size, i.e. higher tailing level Naturally occurring polyphosphate may act as a photocatalyst and accelerate UV disinfection in the BNR-UCT flocs 31

33 Yaldah Azimi TC Tan Lucile Paez Benoit Barroso Yao Wang Sara Kirchner Daphne Wilson Dr. Bill Cairns (Trojan UV) Dr. Ted Mao (Trojan UV) Scott Dunlop (Environment Canada) Dr. Peter Seto (Environment Canada) 32