Mechanistic Insight for the N- Nitrosodimethylamine (NDMA) Formation Potential of Amine-based Water Treatment Polymers

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1 Mechanistic Insight for the - itrosodimethylamine (DMA) Formation Potential of Amine-based Water Treatment Polymers Sang-Hyuck Park a, Shuting Wei b, Boris Mizaikoff b, Amelia E. Taylor c, Mustafa Aral a, and Ching-Hua Huang a a School of Civil & Environmental Engineering, GT b School of Chemistry & Biochemistry, GT c Polychemie Inc., a subsidiary of SF March 29, 27

Introduction - DMA H 3 C H 3 C O -nitrosodimethylamine (DMA) An emerging disinfection by-product (DBP) generated during chlorine-based disinfection Formation mechanism can be

2 Introduction - DMA H 3 C H 3 C O -nitrosodimethylamine (DMA) An emerging disinfection by-product (DBP) generated during chlorine-based disinfection Formation mechanism can be explained by UDMH oxidation-based pathway or specialized nitrosation pathway rather than traditional nitrosation pathway (Mitch & Sedlak, 22; Choi & Valentine, 22, 23; Schreiber & Mitch 25, 26)

3 Introduction - DMA Reasonably anticipated to be a human carcinogen (ational Toxicology Program in DHHS, 24) More toxic and challenging to detect than traditional DBPs EPA DBP regulations Total THMs 5 Haloacetic acids Bromate Chlorite MCL (µg/l) DMA advisory guidelines 1-6 Cancer Risk Level (EPA) otification Level (CA).1 Public Health Goal (CA)* draft.3 MAC (Ontario, Canada) Conc. (µg/l).7.9 Listed in UCMR 2 (Unregulated Contaminant Monitoring Regulation) for drinking water systems (US EPA, 25)

4 Introduction - Water Treatment Polymers Used to help separate particles from water in coagulation, flocculation and sludge dewatering in drinking water and wastewater treatment Electrostatic repulsion Charge eutralization = Coagulation Intermolecular Bridging = Flocculation e.g. Coagulants: polydadmac, polyamine, Flocculants: Mannich polymer, cationic polyacrylamide

5 Research Statement Amine-based water treatment polymers have recently been suggested as DMA precursors because they contain dimethylamine-based functional groups in their structures Research Objectives To understand mechanistically how DMA may form from amine-based water treatment polymers during disinfection processes. To develop means to reduce DMA formation potential of amine-based water treatment polymers

6 ( 2 Step 1 Materials and Methods Cl H O Allyl chloride Epichlorohydrin 2 2 a Polymers 2 Cl investigated 3 Cl - ) 2n Poly(dimethylamine epichlorohydrin): Polyamine (H 2 C H C H 2 C 2 Cl - Polymerization H 3 C H C 2 ) n Poly(diallyldimethylammonium 3 Cl chloride): - I : Initiator radical, ( 2 PolyDADMAC e.g., 2 S 2 O - ) n 3 Cl Haq. Dimethylamine Dimethylamine Allyl Cl chloride Cl - 2 Step 2 H 3 C O Diallyldimethyl DMA-epichlorohydrin ammonium chloride adduct (DADMAC) Polymerization DMA-epichlorohydrin adduct ( 2 HC 2 ) n at high temperature H I 2 C 2 Cl - H 3 C PolyDADMAC I M I-M Low 2 temperature 2 Allyldimethylamine 2 HCl Radical chain - I Cl Polyamine n I-M n M m -I I-M nm -I I: Initiator such as persulfate and azo compounds n

7 Materials and Methods (continued) Experimental set-up Buffers for ph control : ph 7.5 and ph 5 9 (ph 5: acetate, ph 6: bicarbonate, ph 7-8: phosphate, and ph 9: borate) Polymers and intermediate compounds:.5-1 mg/l as active Preformed monochloramine: 4-1 mg as Cl 2 /L Reaction quenching by ascorbic acid Reaction for 24 hrs or other given times

8 Materials and Methods (continued) Analytical Methods DMA: Solid Phase Extraction (SPE) GC/MS DMA: Derivatization Liquid Liquid Extraction (LLE) GC/MS Polymer intermediate compounds: LC/MS Free chlorine and monochloramine: DPD-FAS titration Polymer structure analysis: FT-IR and Raman spectroscopy

9 Results (1): DMA formation potential tests in conditions similar to water treatment plants DMA [ng/l] PolyDADMAC [mg/l as active] Test conditions: Coagulation: raw waters with ppm alum and varying amount of polydadmac Monochloramine: 4 mg as Cl 2 /L Chloramination time: 2 hrs ph 7.9 and 23 C

10 Mechanistic Study Outline Effect of polymer purification Effect of ph Polymer structure change analysis during chloramination (FT-IR & Raman) Effect of molecular weight of polymers Polymer intermediate compounds Comparison of DMA formation potential of polyamine and polydadmac

11 Results (2): Effect of Purification (A) DMA [ng/l] DMA [ng/l] 5 Because DMA water formation treatment polymer 25 (B) 25 solutions DMA measurement can contain impurities such 2 as monomer, catalyst and other intermediate compounds, purification process was 5 conducted by using dialysis membrane 15 of MW cut-offs. DMA [µg/l] 1 DMA [µg/l] 5 DMA i DMA f Unpurified Polyamine Dialyzed Polyamine w/ salt Dialyzed Polyamine Unpurified PDADMAC Dialyzed PDADMAC w/ salt Dialyzed PDADMAC Unpurified Polyamine Dialyzed Polyamine w/ salt Dialyzed Polyamine Unpurified PDADMAC Dialyzed PDADMAC w/ salt Dialyzed PDADMAC Reaction conditions: Polymer: 1 mg/l as active ingredient Monochloramine: 1 mg as Cl 2 /L Reaction time: 24 hrs at ph 7.5, 23 C

12 Results (3): Effect of ph DMA [ng/l] DMA formation Polyamine PolyDADMAC DMA [µg/l] DMA measurement Polyamine PolyDADMAC ph ph Reaction conditions Polymer: 1 mg/l of purified polymers as active ingredient Monochloramine: 1 mg as Cl 2 /L Reaction time: 24 hrs at ph 5 9, 23 C

13 Results (4) Polymer Structure Analysis by FT-IR and Raman Spectroscopy High concentration set-up for polymer structure analysis: 1 g/l polymer 2 mg/l MCA for 24 hrs at ph 7.5 DMA analysis Drying and other pretreatment for IR and Raman analysis Observation of polymer structure change before and after reactions by IR and Raman

14 Results (4) (Continued) IR of polyamine Raman of polyamine Before rxn Before rxn After rxn ( 2 2 ) n Cl - After rxn Oxidation of - group: occurrence of C=O band (1722 cm -1 ) in IR; decrease of C-O stretching (165 cm -1 ) in Raman. Cleavage of 2 - bond: decrease of C- stretching (1134 cm -1 ) in Raman. Polymer chain change: decrease of 572/512 cm -1 (/ 2 rocking) in Raman.

15 Results (4) (Continued) IR of polydadmac Raman of polydadmac Before rxn Before rxn After rxn After rxn ( 2 HC 2 ) n H 2 C 2 Cl - H 3 C Ring Cleavage opening: of ( decrease of cyclic 2 stretching (327/2934 cm - 3 ) 2 group: decrease of deformation ( ) cm in -1 IR/Raman ), and C-C skeletal vibration (573 cm -1 ) Raman; 3 - stretching (1268 cm -1 ) and 2 - stretching (794 decrease cm -1 ) in IR; of decrease 3 deformation of (1478 cm-1), ring C-H deformation 3 asymmetric deformation (148 cm - ( ) in Raman. cm -1 ), and shift of 2 - band (1156 cm -1 ) in IR.

16 Results (5): Effect of Molecular Weight DMA [ng/l] Low MW Polyamine Lowest MW Polyamine DMA formation High MW Polyamine Low MW PDADMAC High MW PDADMAC DMA [µg/l] DMA measurement Lowest MW Polyamine Low MW Polyamine High MW Polyamine Low MW PDADMAC High MW PDADMAC DMA i DMA f Reaction conditions Polymer: 1 mg/l as active ingredient Monochloramine: 1 mg as Cl 2 /L Reaction time: 24 hrs at ph 7.5, 23 C Cl I n Cl I n

17 Results (6): Polyamine Intermediate Compound DMA [ng/l] DMA formation Polyamine DMA-Epi -DMA Step 1 2 DMA [µg/l] 6 2 DMA measurement H 8 DMA i DMA f 4 3 Cl Step 2 Reaction conditions Polymer: 1 mg/l as active ingredient Intermediate compound: 1 mg/l Monochloramine: 1 mg as Cl 2 /L Reaction time: 24 hrs at ph 7.5, 23 C O 2 Epichlorohydrin Cl DMA-epichlorohydrin adduct Polyamine DMA-Epi -DMA Cl Dimethylamine H 3 C H 3 C n O DMA-epichlorohydrin adduct Polymerization at high temperature H 3 C H 3 C ( 2 Low temperature 2 2 DMA-epichlorohydrin-DMA DMA-epichlorohydrin-DMA HCl ) n Polyamine Cl -

18 Results (7): PolyDADMAC Intermediate Compounds DMA [ng/l] PolyDADMAC DMA formation DADMAC monomer Allydimethylamine 2 2 Cl H Allyl chloride Allyl chloride DMA [µg/l] Reaction conditions Polymer: 1 mg/l as active ingredient Intermediate compound: 1 mg/l Monochloramine: 1 mg as Cl 2 /L Reaction time: 24 hrs at ph 7.5, 23 C DMA measurement 2 2 ( 2 HC 2 ) n H 2 C 2 PolyDADMAC Cl - H 3 C PolyDADMAC Dimethylamine DMA i a DMA f aq. H 3 C DADMAC monomer 2 2 Cl - Diallyldimethyl ammonium chloride (DADMAC) Allydimethylamine I Allyldimethylamine Radical chain - Polymerization Cl I n I: Initiator such as persulfate and azo compounds

19 Why does polyamine produce more DMA than polydadmac? 1. Polyamine has tertiary amine at the end of polymer chain. Cl n Polyamine 2. Repeating unit of polyamine has higher DMA formation potential than that of polydadmac. 3. Polyamine has less rigid polymer chain than polydadmac so that polyamine is more flexible and moves more freely in aqueous solution. This may give more chance to react with monochloramine. I Cl PolyDADMAC I n

20 Conclusions This study was conducted under conditions that maximize DMA formation in order to gain insights for the mechanisms in which amine-based polymers can act as DMA precursors. Preliminary results show that the DMA formation potential of the polymers under conditions in line with those in typical water treatment plants was lower than the current advisory levels. The mechanistic study, however, provide useful results that can be the basis for designing polymers of minimized DMA formation potential: 1) Polymer purification reduces DMA formation potential for polyamine and polydadmac, while does not eliminate the polymers DMA formation potential.

21 Conclusions (continued) 2) Direct reaction of polyamine and polydadmac with monochloramine can result in polymer degradation in several functional groups and release of DMA. DMA formation potential is closely related to these two phenomena. 3) Polymer chain end plays the major role in polyamine s DMA formation potential, while degradation of quaternary ammonium group and residual DMAcontaining intermediate are the significant factors in PolyDADMAC s DMA formation potential.

22 Acknowledgments Financial Support: SF Holding Company People: Shuting Wei (GT) Dr. Boris Mizaikoff (GT) Dr. Mustafa Aral (GT) Dr. Amelia Taylor (SF) Dr. Cédrick Favero (SF) Dennis Marroni (SF)

A STUDY OF THE EFFECT OF POLYMERS ON POTENTIAL N-NITROSODIMETHYLAMINE (NDMA) FORMATION AT WATER AND WASTEWATER TREATMENT PLANTS

A STUDY OF THE EFFECT OF POLYMERS ON POTENTIAL N-NITROSODIMETHYLAMINE (NDMA) FORMATION AT WATER AND WASTEWATER TREATMENT PLANTS Sang Hyuck Park, Shuting Wei Ching-Hua Huang, Boris Mizaikoff, Mustafa M.