Isabelle Papineau, Ph.D., École Polytechnique de Montréal Yves Dionne (V de G) and Benoit Barbeau (EPM) 16 th Canadian National Conference on Drinking Water October 28th 2014
1. Background City of Gatineau operates a total of four surface water treatment plants (WTP): 1. Gatineau 2. Aylmer 3. Buckingham 4. Hull All WTPs are currently being brought up to standards Some treatment trains will be upgraded Bench scale assays were conducted prior to the retrofit of the Hull WTP to inform decision makers on the most promising treatment alternatives from a water quality stand point 2
1.2 Background Hull Water Treatment Plant Built in 1971 Treatment scheme: 1. Alum coagulation 2. Sedimentation/Granular filtration 3. Post chlorination 4. ph adjustment Source : Ottawa River Sludge Blanket Clarifiers Granular Filters Low alkalinity ( 20 40 mg CaCO 3 /L) Fairly high TOC concentrations (> 7 mg C/L) Ottawa River Capacity: 85 980 m 3 /d Population: 70 000 pers. Requirement of the MDDELCC (Gvt of Québec) to conduct Ottawa River Reservoir Cl treatability assays if Alum source water 2 TOC concentrations >7 mg C/L Lime 3
1.3 Background Hull WTP: Goals of the Retrofit 1. Increase disinfection by product (DBP) precursor removal 2. Reinforce primary disinfection performance 3. Include a process capable of oxidizing: Cyanotoxins Microbial metabolites which cause taste and odors: MIB & Geosmine Pesticides Other compounds of emerging concern (CEC) 4. Review and upgrade water storage capacity to respond to fire fighting needs 4
1.4 Background Objectives of Bench Scale Assays 1. Assess the possible benefits of optimized coagulation Removal of Natural Organic Matter (NOM) Limit aluminium and iron concentrations in filtered water 2. Identify optimal conditions for ozonation Minimise BDOC concentrations and bromate formation Reduce the DBP formation potential Remove CEC in warm water Assess the impact of O 3 location (inter vs post O 3 ) on water quality 3. Assess the impact of incubation conditions on DBP formation 4. Assess performance both in cold and warm waters 5
2.1 Methodology: Coagulation Optimisation 1. Coagulant Type: Alum, Ferric Sulfate, PASS 10, PAX XL6 Cationic Polymer (Superfloc, 0.25 mg/l) 2. Selection of tested coagulant dose: Aluminium based coagulants Alum dose used by the WTP the day of sampling ± 0.15 meq/l Ferric Sulfate: 2.1 mg Fe/L 1.0 mg Al/L 3. Characterization of settled and filtered waters: ph, alkalinity, turbidity, DOC, UV 254 Aluminium, iron and manganese concentrations 4. Selection of the optimal coagulant dose: Use of enhanced coagulation optimisation criteria (USEPA, 1999) Optimal dose : Threshold where an dosage increase of 10 mg/l provides less than 0.3 mg C/L TOC removal 6
2.2 Methodology: Ozonation 1. Simulations of pre, inter and post ozonation Impact on natural organic matter (NOM): UV 254, DOC, BDOC Impact on DBP formation potential (THM, HAA, Bromate) 2. Predictions of CEC removal in warm water (22 C): Geosmine, MIB, cyanotoxins, pharmaceutical products, hormones & pesticides C C 1 K CT N 1 K R CT N Vincent et al., 2010 Molecular O 3 Hydroxyl radicals (OH ) Were N= 6.68 which corresponds to a T 10 /T= 0.5 7
2.2 Methodology: Ozonation: Experimental Design Type of water 4⁰C O 3 (mg/l) 22⁰C Source water 3 mg/l Settled water (Optimal coagulant dose) Filtered water (Optimal coagulant dose) 1 mg/l 2 mg/l 3 mg/l 1 mg/l 2 mg/l 3 mg/l 1 mg/l 2 mg/l 3 mg/l 1 mg/l 2 mg/l 3 mg/l 8
2.3 Methodology: DBP Formation Potential 1. CTTEP (Québec regulatory approach): ph = 7.5, 22 C, Residual Cl 2 = 0.5 ±0.2 mg Cl 2 /L 2. Simulated Distribution System (SDS) Specific conditions of the Hull distribution system Cl 2 dose applied at the WTP the day of sampling Incubation= 7, 24 & 48 hours 3. In parallel, samples were collected on the distribution system to validate results obtain in lab scale experiments To allow a direct comparison of THM and HAA concentrations Incubation times were determined through hydraulic modeling (City of Gatineau) 9
3.1 Results: Overview of Coagulation Performance TYPE OF COAGULANT TURBIDITY (UTN) DOC (mg C/L) DOSES (meq/l) 4⁰C 22⁰C 4⁰C 22⁰C 4⁰C 22⁰C ALUM 1.16 0.42 2.85 2.68 0.50 0.50 Fe 2 (SO 4 ) 3 0.47 0.32 1.97 2.27 0.67 0.52 PAX XL6 0.26 3.02 0.60 PASS 10 0.42 3.15 0.60 10
3.1 Results: Coagulation Optimization in Warm Waters 1. Ferric sulfate outperformed all other coagulants but alum also offered good performances 2. DOC removal in cold water: Alum > pre hydrolyzed coagulants (PASS 10 and PAX XL6) 3. Alum dose used for subsequent experiments = 0.5 meq/l Dose > 0.5 meq/l Offered no additional gains in DOC removal (4⁰C & 22⁰C) No longer corresponded to the optimum ph (4⁰C) Increased residual aluminium concentrations in filtered effluent (4⁰C and 22⁰C). Increased filtered effluent turbidity (22⁰C) 11
3.2 Results: Impact of Ozonation on BDOC Concentrations Biological dissolved organic carbon (BDOC) 1.50 1.25 COLD (4⁰C) Source Water: 0.66 mg C/L 1.50 1.25 WARM (22⁰C) Source Water: 0.49 mg C/L BDOC (mg C/L) 1.00 0.75 0.50 Typical zone for biological filtration Inter O3 BDOC (mg C/L) 1.00 0.75 0.50 Typical zone for biological filtration 0.25 Post O3 0.25 Inter O3 0.00 0 1 2 3 Dose (mg O 3 /L) Pre O3 0.00 0 1 2 3 Dose (mg O 3 /L) Post O3 BDOC concentrations increased with the applied O 3 dose 12
3.2 Results: Impact of Ozonation on Chlorine Demand Chlorine demand assessed after 24 hours Chlorine Demand (mg Cl 2 /L) 3.5 3.0 2.5 2.0 1.5 1.0 COLD (4⁰C) Source Water: 9.9 mg/l Inter O3 Post O3 Pre O3 0 1 2 3 Dose (mg O 3 /L) Chlorine Demand (mg Cl 2 /L) 3.5 3.0 2.5 2.0 1.5 1.0 WARM (22⁰C) SourceWater: 7.82 mg/l Inter O3 Post O3 0 1 2 3 Dose (mg O 3 /L) No significant increase of the chlorine demand for O 3 doses 2 mg/l 13
3.2 Results: Impact of Ozonation on THM Formation 80 80 THM CTTEP (µg/l) 60 40 20 COLD (4⁰C) Inter O3 Post O3 Pre O3 Source Water : 288 µg THM/L THM CTTEP (µg/l) 60 40 20 Inter O3 Post O3 WARM (22⁰C) Source Water: 292 µg THM/L 0 0 1 2 3 Dose (mg O 3 /L) 0 0 1 2 3 Dose (mg O 3 /L) A dose of 1 mg O 3 /L seems optimal to reduce THM formation No significant differences amongst inter and post ozonation 14
3.2 Results: Impact of Ozonation on HAA Formation HAA CTTEP (µg/l) 60 40 20 COLD (4⁰C) Source Water: 258 µg HAA/L Inter O3 Post O3 Pre O3 HAA CTTEP (µg/l) 60 40 20 WARM (22⁰C) Source Water: 269 µg HAA/L Inter O3 Post O3 0 0 1 2 3 Dose (mg O 3 /L) 0 0 1 2 3 Dose (mg O 3 /L) A dose of 1 mg O 3 /L seems optimal to reduce HAA formation 15
3.3 Results: Prediction of CEC Removals by Ozonation Removal (%) at 22⁰C Compound Description Inter O 3 (mg O 3 /L) Post O 3 (mg O 3 /L) 1 2 3 1 2 3 17 α Ethinylestradiol Hormone >99.9 >99.9 >99.9 >99.9 >99.9 >99.9 Anatoxin a Algaltoxin >99.9 >99.9 >99.9 >99.9 >99.9 >99.9 Microcystin Algal toxin >99.9 >99.9 >99.9 >99.9 >99.9 >99.9 Naproxen Anti inflammatory >99.9 >99.9 >99.9 >99.9 >99.9 >99.9 Carbamazepine Anticonvulsant >99.9 >99.9 >99.9 >99.9 >99.9 >99.9 Salicylic Acid Pain relief 97 >99.9 >99.9 99 >99.9 >99.9 Geosmine Odorous compound 51 84 93 64 82 93 2 Methylisoborneol Odorous compound 46 81 91 59 78 91 Alachlor Herbicide 41 76 87 53 72 87 Atrazine Herbicide 21 49 63 29 46 64 16
3.4 Results: THM concentrations Simulated Distribution System (SDS) THM SDS (µg/l) 100 80 60 40 COLD (4⁰C) Hull Distribution System SDS: Sed.+Filtration SDS: Post O3 (2 mg/l) SDS: Inter O3 (2 mg/l) THM SDS (µg/l) 100 80 60 40 WARM (22⁰C) Regulatory sampling point 20 20 0 0 0 12 24 36 48 Time (h) 0 12 24 36 48 Time (h) Ozonation conditions in Simulated Distribution System = 2 mg O 3 /L Chosen according to UV 254 as DOC concentrations were not yet available 17
3.4 Results: HAA Concentrations Simulated Distribution System (SDS) 60 COLD (4⁰C) 60 WARM (22⁰C) HAA SDS (µg/l) 40 20 Hull Distribution System SDS: Sed.+ Filtration SDS: Post O3 (2 mg O3/L) SDS: Inter O3 (2 mg O3/L) HAA SDS (µg/l) 40 20 Regulatory sampling point 0 0 0 12 24 36 48 Time (h) 0 12 24 36 48 Time (h) Ozonation conditions in Simulated Distribution System = 2 mg O 3 /L Chosen according to UV 254 as DOC concentrations were not yet available 18
Summary of Results 1. Optimized Coagulation: Ferric sulfate was most promising Alum (0.5 meq/l) also offered good UV 254 and DOC removals 2. Ozonation: O 3 reduced DBP formation potential Bromate formation was a non issue No significant increase of chlorine demand for doses 2 mg O 3 /L Similar initial demand and half life were observed for inter and post O 3 CEC Removal > 99.9% removal of cyanotoxins at 1 mg O 3 /L 1.5 2 mg O 3 /L would reduce taste & odors < detection ( 10 ng/l) 3. DBP formation potential: Reduced by ozonation (1 mg O 3 /L) Would be further improved if biological filtration was used subsequent to inter O 3 to reduce BDOC concentrations prior to Cl 2 19
Retained Treatment Scheme for the Retrofit of the Hull WTP 1. Alum coagulation 2. Inter Ozonation (dose of 1.5 mg O 3 /L) Reduce the DBP formation potential Oxidize CECs No redundancy of ozone generators No inactivation credits 3. Biological filtration (GAC/sand filters) Reduce the DBP formation potential Reduce chlorine demand Improve the stability of treated waters 4. Post chloration Primary disinfection 5. ph adjustment Lime to improve the Langelier Index in contrast with caustic soda 20
Acknowledgements City of Gatineau Martin Dompierre, Mario Renaud Technical staff of the NSERC Industrial Chair on Drinking Water Julie Philibert, Mélanie Rivard, Yves Fontaine, Jacinthe Mailly, Mireille Blais, Marcellin Fotsing 21
isabelle.papineau@polymtl.ca 22
1.2 Background Hull WTP: Source Water Characteristics PARAMETER April 2013 AUGUST 2013 ALCALINITY (mg CaCO 3 /L) 34 26 ph 7.14 7.55 TURBIDITY (UTN) 11.3 1.95 UV ABSORBANCE (cm 1 ) 0.235 0.228 DOC (mg/l) 7.79 7.28 SUVA (cm 1. mg 1.L) 3.2 3.1 TOTAL Al (µg/l) 402 307 TOTAL Requirement Fe (µg/l) of the MDDELCC 468 (Government of Québec) 192 TOTAL Mn to (µg/l) conduct treatability assays 27 if source water TOC 11 DISOLVED Mn (µg/l) concentrations exceed 5 7 mg C/L 4 23
3.2 Results: Ozonation Type of water Dose O 3 (mg/l) Half life (min) Cold (4⁰C) Initial Demand (% dose) Half life (min) Warm (22⁰C) Initial Demand (% dose) Pre O 3 3.0 0.22 39 % Inter O 3 2.0 14.8 13 % 3.35 39 % 3.0 16.3 17 % 5.64 36 % 1.0 7.5 25 % 1.31 48 % Post O 3 2.0 14.2 9 % 3.61 33 % 3.0 23.1 6 % 6.24 25 % 1.0 11.6 23 % 1.59 33 % 24