Peracetic acid (PAA) and performic acid (PFA) for water disinfection

Ravi Kumar Chhetri Postdoc Introduction

Peracetic acid (PAA) is one of the most used disinfectants in wastewater treatment. Also used in food industry and aquaculture. Peracetic acid is used as commercial solution in equilibrium with hydrogen peroxide:

+ + (Acetic acid) (Hydrogen peroxide) (peracetic acid) (water) 𝐶𝐶𝐻𝐻3𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 𝐻𝐻2𝑂𝑂2 ↔ 𝐶𝐶𝐻𝐻3𝐶𝐶𝑂𝑂3𝐻𝐻 𝐻𝐻2𝑂𝑂  Does not form toxic byproducts

 Hydrogen peroxide is a weak disinfectant.

2 Introduction

Performic acid (PFA) is one of the most used disinfectants in food and medical industries.

Performic acid is unstable and need to synthesis before use:

+ + (Formic acid) (Hydrogen peroxide) (performic acid) (water) 𝐶𝐶𝐻𝐻2𝑂𝑂2 𝐻𝐻2𝑂𝑂2 ↔ 𝐶𝐶𝐻𝐻2𝑂𝑂3 𝐻𝐻2𝑂𝑂  Newly introduced disinfectant to wastewater industy  Recently used in Combined Sewer Overflow (CSO) disinfection  Does not form toxic byproducts

3 Combined sewer overflow

Disinfectant profile in CSO

6 C0 C·t = area under curve

4 Ct (t=HRT) Ct = Ceffluent dilution on 2 release to surface water Disinfectant (mg/L)

0 0 5 10 15 20 25 Reaction time (min) 3 design parameters

• C·t=effect concentration= area -500 E.coli/100mL -200 Enterococcus/100mL under curve

• Ct =concentration after retention time (t)=Ceffluent • Residual toxicity

4 Quantification method of Peracetic acid (PAA) and performic acid (PFA)

• Modified spectrophotometric method with ABTS* for less H2O2 interference. – Mixing reagent A (ABTS) and reagent B (acetic acid buffer)

*= (2, 2’’-azino-bis [3-ethylbenzothiazoline-6-sulfonic acid] diammonium salt)

5 Quantification of Peracetic acid (PAA) and performic acid (PFA)

Kinetics of color development Calibration curve

• PAA-ABTS reaction=10 min • Color development kinetics 2.5 mg/L PAA & 2.5 mg/L H2O2

0.6 0.6 y= 0,2452x+0,01211 R2= 0.9809 • PFA-ABTS reaction=20 min PFA 0.4 0.4 • Color development H2O2 kinetics 2.5 mg/L PFA & 2.5 mg/L H2O2 PFA 0.2 0.2 H2O2 Absorbans (405nm) Absorbans (405nm)

0.0 0.0 0 10 20 30 40 0 1 2 3 4 5 6 7 8 9 10 Tid (min) mg/L 6 Concentration profiles

pH effect Matrix effect 10 A 10 E C 8 8 2 Sea water pH 8.0

6 pH 7.5 6 pH 4.16 4 4 1 PAA (mg/L) PAA (mg/L) PAA (mg/L) pH 7.5 2 2 5% raw WW 15% raw WW pH 5.18 40% raw WW 0 0 0 0 100 200 300 0 100 200 300 0 50 100 150 200 Time (min) Time (min) Time (min)

8 B 4 F D 2 6 3 Sea water

4 2 pH 3.97 5% raw WW 1 PFA (mg/L) PFA (mg/L) 15% raw WW PFA (mg/L) 2 pH 6.39 1 40% raw WW pH 7.5 pH 3.78 0 pH 8.0 0 0 0 100 200 300 0 100 200 300 0 50 100 150 200 Time (min) Time (min) Time (min)

PAA PFA Slow degradation Fast degradation Matrix dependent Matrix independent Disinfection efficiency of PAA and PFA

• 10 min contact time for Enterococcus inactivation.  Reasonable robust to matrix at 5% to 15% WW.

• Light CSO was simulated with 5% wastewater  PFA is effective on Enterococcus removal, PAA efficiency increases much more with long contact times (treatment exposure time). Optimization of PAA without H2O2

1.25 PAA 150 HP 125 1.00 H

100 2 O Different concentration of KMnO 0.75 y = - 0.003 x + 1.1 2 • 4 2 (mg/L) R = 0.936 75 was used for titration

PAA (g/L) 0.50 50 • Stability of PAA was observed for 48 h 0.25 25 • Re-apperance of H2O2 was studied 0.00 0 0 10 20 30 40 50 60 70 80 90 100

mg(KMnO4)/L

PAA and H2O2 measured at the end of titration with different concentrations of KMnO4

Solution’s characteristics before and after titration procedure.

PAA (mg/L) H2O2 (mg/L) Initial concentration 1160 150

Concentration after titration 1010 1.5

Removal 12.9% 99% Schematic diagram of RAS 11 Thank you for your attention

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