Health Based Targets Application of Log Reduction Values. Phillip Fasham Manager Water Quality Regulations and Verification

Transcription

1 Health Based Targets Application of Log Reduction Values Phillip Fasham Manager Water Quality Regulations and Verification

2 Contents Log Credits & Treatment Barriers Typical Treatment Components and Critical Control Point Limits Coagulation, Flocculation, Sedimentation or Dissolved Air Flotation Direct Filtration Conventional treatment Micro & Ultra Filtration Secondary Stage Filtration Chlorination & Chloramination Ultraviolet Disinfection Ozone Example Korong Vale WTP 2

3 Goal of a Water Treatment Professional To produce water that is both safe for consumption and aesthetically pleasing. We are here today to talk about pathogen risks in drinking water and the water treatment barriers required. Target is 1 micro DALY. Water treatment barriers required depend on the raw water Source Category (i.e. the poorer the catchment the more barriers). Note: you may also require processes for metals, organics, salt, taste and odour and algae removal 3

4 Log Reduction Values and Treatment Barrier It is common practice to have multiple treatment processes/barriers at water treatment plant. Individual treatment barriers have differing levels of performance when reducing the risks of Bacteria, Virus and Protozoa in drinking water. Each barrier can be used as a building block to achieve the required Log Reduction Values The WSAA Manual for the Application of Health-Based Treatment Targets details the differing levels of risk reduction for each barrier based on log reduction values. 4

5 Typical Treatment Processes Coagulation, Flocculation, Sedimentation or Dissolved Air Flotation Conventional Treatment Secondary Stage Filtration Direct Filtration Ozone Micro/Ultra Filtration Ultraviolet Chlorination/Chloramination 5

6 Coagulation, Flocculation, Sedimentation or Dissolved Air Flotation Process Coagulation, Flocculation & Dissolved Air Flotation Coagulation, Flocculation & Sedimentation Bacteria Virus Protozoa Critical Limits Log reduction value Under- Float or settled water <2 NTU for 95% of the Month or Alternative target is 70% reduction in turbidity over the month where raw water is very high Note: Appendix D of the WSAA manual provides a broader range of log reduction values for all treatment processes. 6

7 Direct Filtration Process Direct Filtration Bacteria Virus Protozoa Critical Limits Log reduction value Individual filter turbidity 0.3 NTU for 95% of the month and not >0.5 NTU for 15 minutes. Combined filtrate turbidity <0.2 NTU for 95% of the month and not >0.5 NTU for 15 minutes Individual filter turbidity 0.2 NTU for 95% of the month and not >0.5 NTU for 15 minutes. Individual filter turbidity 0.15 NTU for 95% of the month and not >0.3 NTU for 15 minutes. 7

8 Conventional Treatment Process Conventional Treatment Bacteria Virus Protozoa Critical Limits Log reduction value Individual filter turbidity 0.3 NTU for 95% of the month and not >0.5 NTU for 15 minutes. Combined filtrate turbidity <0.2 NTU for 95% of the month and not >0.5 NTU for 15 minutes Individual filter turbidity 0.2 NTU for 95% of the month and not >0.5 NTU for 15 minutes. Individual filter turbidity 0.15 NTU for 95% of the month and not >0.3 NTU for 15 minutes. Note: Applying more stringent operational limits (CCP s) Log Reduction Values can being increased. 8

9 Micro & Ultra Filtration Process Micro- Filtration Ultra- Filtration Bacteria Virus Protozoa Critical Limits Log reduction value Individual filter turbidity 0.1 NTU for 95% of the month and not >0.15 NTU for 15 minutes. Membrane Integrity to manufacturer s specification for the required LRV and/or certified to a recognised standard Individual filter turbidity 0.1 NTU for 95% of the month and not >0.15 NTU for 15 minutes. Membrane Integrity to manufacturer s specification for the required LRV and/or certified to a recognised standard 9

10 Secondary Stage Filtration Process Bacteria Virus Protozoa Critical Limits Log reduction value Secondary Stage Filtration Individual filter turbidity 0.15 NTU for 95% of the month and not >0.3 NTU for 15 minutes. 10

11 Chlorination and Chloramination Disinfection Process Chlorination Chloramination Bacteria Virus Protozoa Critical Limits Log reduction value Ct >15 mg/l.min with ph <8.5 at all water temps. Feed water turbidity <1.0 NTU Ct >857 mg/l.min with ph 6-9 water temperature 5ºC Ct >1988 mg/l.min with ph 6-9 water temperature 5ºC 11

12 Ultraviolet Disinfection Process Ultraviolet Disinfection Bacteria Virus Protozoa Critical Limits Log reduction value UV dose >40 mj/cm 2 UV dose >60 mj/cm 2 UV dose >190 mj/cm 2 Feed Water: Turbidity <1.0 NTU UVT%> Manufacture s Specification 12

13 Ozone Disinfection Process Ozonation Bacteria Virus Protozoa Critical Limits Log reduction value Ct >0.6 mg/l.min with ph <8, turbidity <1.0 NTU water temperature 5ºC Ct >1.2 mg/l.min with ph <8, turbidity < 1 NTU water temperature 5ºC 13

14 Example - Korong Vale WTP Korong Vale 14

15 Korong Vale WTP continued Located in north central Victoria Maximum treatment capacity of 3.6ML/d Supplies a population of approximately 900 in Korong Vale and Wedderburn Conventional Water Treatment Process Coagulation Pre ph correction Clarification Dual Media Filtration Post ph Correction Chloramination } Conventional Treatment 15

16 16 Process Diagram

17 Log Reduction Requirements Results Log Reduction Requirements Korong Vale Type of Source Surface Water (Moderately Protected Catchment) Sanitary Survey Results Category Minimum pathogen log reduction required Bacteria Viruses Protozoa Raw water is sourced from Lake Bellfield which has a well protected catchment in the Grampians 17

18 WTP Performance Assessment Theoretical Assessment - what could possibly be achieved from each barrier, assuming it was optimised and working within strict performance windows Physical Assessment - a review of SCADA information to determine what barrier log removal credits are achieved under current operational practices 18

19 19 WTP Assessment Theoretical (Maximum Log Reduction Values from WSAA Manual) 2 Bacteria, 2 Virus and 4 Protozoa for Conventional Treatment, no log credits from chloramination as storage volumes are too small to achieve Ct Physical Review of twelve months of online SCADA data for both filtration (NTU) and chloramination concentration (mg/l) The data was obtained at 10 minute intervals Data only included when WTP was operational (i.e flow > 2 L/s) This exercise highlighted other issues with SCADA data integrity/ WTP functionality / instrumentation calibration and failure which all had to resolved

20 Physical Log Reduction Values LRV Conventional Treatment Manual investigation of filter turbidity NTU and length of time of any exceedance events above the allowable maximums (i.e. either 0.5 or 0.3 NTU) Chloramination LRV for chloramination is dependent on Ct values and chloramine residual monitor Baffle factor used (0.3) 20

21 Conventional Treatment Process Maximum LRV Compliance 95% Criteria duration > y NTU B V P Cell 1 Cell 2 Cell 1 Cell Individual filter turbidity 0.3 NTU for 95% of month and not > 0.5 NTU for 15 consecutive minutes. Combined filtrate turbidity < 0.2 NTU for 95% of the month and not > 0.5 NTU for 15 consecutive minutes. 99% 99% <15min <15min Conventional Treatment Individual filter turbidity 0.2 NTU for 95% of month and not > 0.5 NTU for 15 consecutive minutes Individual filter turbidity 0.15 NTU for 95% of month and not > 0.3 NTU for 15 consecutive minutes 96% 96% <15min <15min 93% 93% >15min >15min X LRV credits of 2 Bacteria, 2 Virus and 3.5 Protozoa was claimed It should be noted that 4 log protozoa was achieved for 4 months 21

22 Chloramination Ct Calculation Ct = CR.Fsc.V / Q Where Ct = contact time (min.mg/l) CR = chlorine residual (mg/l) Fsc = baffle factor V = minimum volume (m 3 ) Q = maximum hourly flow rate (m 3 /min) Minimal Ct required is 857mg/L to achieve 2 log bacteria and virus 22

23 C.t example Korong Vale WTP CR monitored after the TWS; 1.28mg/L measured during peak flow periods Fsc - assumed to be 0.3 ( single or multiple unbaffled inlets and outlets, no intra-basin baffles") V 2x 325kL TWS in series with 70% WTP Cut in (455m 3 ) Q maximum rolling hour average flow over 2012/13 and 2013/14 summer (high demand) periods = 27L/s (1.6m 3 /min) Ct = 1.28 x 0.3 x 455/1.6 Ct = 109 min.mg/l Hence no LRV credits claimed as this is well below the required Ct of 857mg/L 23

24 Summary HBT Results Summary Results Sanitary Survey Results Water Treatment Log Reduction Guidance Review of Treatment Process only Review of Treatment Process and Performance Data Water Treatment Plant Category Minimum pathogen log reduction required Pathogen LRV reductions Pathogen LRV reductions Bacteria Viruses Protozoa Bacteria Viruses Protozoa Bacteria Viruses Protozoa Korong Vale non-conforming conforming The Korong Vale WTP does not achieve the required log reduction values for Bacteria and Virus. The WTP is 3 log short for bacteria and 1 log Virus 24

25 Next Step There are three likely options to gain the extra log credits required. The preferred option will need to be assessed to determine the least life time costs. Option 1 Converting the disinfection system to free chlorination. Free chlorination with a Ct > 15mg/L will provide the additional log reduction values required (4 log bacteria and 4 log virus) 25

26 Option 2 Install a UV system A UV system with a dose of >60 mj/cm2 will provide the additional log reduction values required (4 log bacteria, 1 log virus and 4 log Protozoa) Option 3 Install an Ozone system An Ozone system with a Ct >1.2 mg/l.min will provide the additional log reduction values required (4 log bacteria and 4 log virus) 26

27 27 Questions