Validation of Relationship Between Free Chlorine Dose and Pathogen Inactivation in Drinking Water

Transcription

1 Validation of Relationship Between Free Chlorine Dose and Pathogen Inactivation in Drinking Water Dr Arran Canning Seqwater Satiya Wati, Alex Keegan, Duncan Middleton, Duncan Shillito, Michael Bartkow

2 Contents Introduction Current guidance on virus treatment Impact of Health Based Targets Coxsackie B5 research Application of research Conclusions

3 Introduction

4 Viruses Smallest and simplest forms of infectious agents Carry their genetic material as single or double stranded DNA or RNA Not equip to replicate in isolation need host genetic machinery Common waterborne viruses Hepatitis A Norovirus Rotavirus Adenovirus Generally only sourced from humans

5 Sources Human pathogenic viruses are only sourced from humans

6 Guidance The ADWG it recommends 0.5mg/L of free chlorine for a contact time of 30 minutes. C.t of 15mg.min/L ADWG (2011) p 185

7 Guidance Australian Drinking Water Guidelines (2011) guidance on pathogen treatment

8 USEPA Guidance Based on Hepatitis A virus ph 6-9 C.t Table Temperature ( C) Inactivation log log log

9 Changes to Australian Guidance Health Based Targets

10 Health Based Targets WSAA Health Based Targets Manual 2014 For viruses Achieve 0,3,4 or 6 log reduction Based on catchment characteristics and sanitary survey Maximum of 4 log credits can be gained through chlorine disinfection

11 Health Based Targets Can claim up to 2 log through coagulation and filtration 4 log for free chlorine disinfection

12 Recent research Coxsackie B5

13 Black et. al Investigated coxsackievirus B5 as a possible reference pathogen for chlorine disinfection Coxsackievirus is one of the more chlorine resistant enteroviruses compared to viruses used in previous studies Concluded C.t of 11.5mg.min/L required for 4 log reduction at ph 7.5 and at 5 C Temperature ( C) Inactivation log log log USEPA C.t Table for free chlorine

14 Seqwater work Black work was only carried out at 5 C Southeast Queensland climate is much warmer Only limited ph range USEPA range is vague, 6-9 Black work limited ph s investigated.

15 Experimental Decided to extend previous work at a range of temperatures and ph s to better inform local conditions Temperature ( C) ph X X X 7.5 X* X X X 7.8 X X X 8 X X X 9 X* * Repeat of work by Black et. al.

16 Experimental

17 Validation of Method Experiments undertaken by Australian Water Quality Centre

18 Chlorine decay Chlorine decay curves C.t values were calculated as area under the FAC curve between time zero and time for 1, 2, 3 and 4 log 10 inactivation of CB5.

19 Viral survival The survival curves Show linear inactivation of CB5 for all ph values Linear regression equations from these graphs were used to determine time points for between 1 and 4 log 10 inactivation of viruses. C.t values were calculated as area under the FAC curve between time zero and time for 1, 2, 3 and 4 log10 inactivation of CB5 over the 30 min duration for each of the experiments.

20 Example of Log reduction vs 10 C C.t appears linear with log reduction of CB5

21 Free Chlorine C.t table for CB5 ph Log 10 inactivation Temperature ( C) 0* C.t (mg.min/l) 1 ND ND ND 2 ND ND ND 3 ND ND ND 4 ND ND ND 1 ND ND ND 2 ND ND 3 ND ND 4 ND ND 1 ND ND ND 2 ND ND ND 3 ND ND ND 4 ND ND ND 1 ND ND ND 2 ND ND ND 3 ND ND ND 4 ND ND ND 1 ND ND ND ND ND ND 2 ND 13.6 ND ND ND ND 3 ND 18.8 ND ND ND ND 4 ND 23.6 ND ND ND ND USEPA data (for comparison) 2 6.0* * *

22 Don t Extrapolate 12 C.t vs Temperature for 4 log inactivation of CB5 C.t mg.min/l Temperature ( C) In a small temperature range the relationship appears linear However at low temperatures required C.t for same log removal increases more rapidly.

23 Effect of ph on C.t 12 C.t required for 4 log reduction of CB5 at 10 C 10 C.t mg.min/l ph Effect of increasing ph on C.t for a given log reduction Well understood as shift between hypochlorous acid and hypochlorite ion HOCl OCl + H +

24 Effect on HOCl Converting FAC C.ts to HOCl C.ts As HOCl is the predominant biocide, as ph increase you would expect a constant C.t with ph This not the case Observe a decrease in C.t required to inactivate 4 Log CB5 as ph increases

25 Effect on HOCl Potential reason may be attributed to the CB5 virus being more susceptible to increased concentration of hydroxide ions. One proposed theory could be that with increased ph the clumping of CB5 may be effected. (the reason that makes it more resistant in the first place)

26 Application of the research

27 Determine Log inactivation ph (s.u) WTP Measured Data Temperature ( C) WTP Information Contact tank lowest operating volume (L) Disinfectant type Peak Hourly Flow (L/s) Residual Disinfectant Concentration (mg/l) Baffle factor Theoretical Detention Time (min) Detention Time (min) CT Tables CT calc (min.mg/l) WTP Log Inactivation

28 Conclusions New dataset has been produced using the most relevant chlorine resistant virus Demonstrated that in general higher C.ts are required than previously understood in USEPA guidance (Hep A) HOCl C.ts is not constant with ph This C.t table for CB5 has been included in the WSAA HBT manual as an alternative to USEPA or the genertic Ct 15 mg.min/l Confirmed the ADWG /WHO 15 mg.min/l is suitable as a default standard up to ph 8

29 Acknowledgements Seqwater for funding the work AWQC for undertaking the experimental work Michael Bartkow Duncan Middleton Duncan Shillito Satiya Wati Alex Keegan