1. Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering Multiple Barriers, Multiple Exposures Perspectives from the North and the South

2. Multi-Barrier Approach  If we implement multiple barriers, then failure in any one barrier won’t result in catastrophic failure of the overall process  Multiple barriers increase the reliability of the overall process  The concept of multiple barriers is often used to refer to water purification steps, but it can also be extended to any interventions used to break pathogen exposure routes

3. Barriers: The Water Purification Perspective  Watershed protection  Particle removal  Coagulation, flocculation and sedimentation  Filtration  Disinfection  Distribution system  Cross contamination protection  Residual disinfectant

4. Treatment Train Comparison  Alternative 1- one unit process, which, when it operates properly, achieves 6 logs of removal ____________________  Alternative 2 - three independent unit processes in series, each of which, when it operates properly, achieves only 2 logs of removal  ______________________ Membrane filtration Conventional filtration Chlorination UV disinfection

5. Barriers with Failure  Let’s also assume that each unit process completely fails 1% of the time  “Normally”, both trains produce 6 logs of removal but, let’s look closer 6 log removal really means that pf = 6 Negative log of the fraction remaining

6. 263 hours 158 min. 32 sec. 361 days 350 days 87.6 hours Comparison of one and three barrier trains with same nominal removal

7. Relative performance  Increasing the number of process barriers substantially reduces the risk of __________ in return for a small compromise in the time at which the nominal design performance is achieved  This analysis assumes failures are independent events!  Imagine if every electrical power failure resulted in everyone in your city becoming ill! total failure

8. Add It Up to Meet the Target Protection Level  Multiple Barrier approach as codified in EPA regulations  Treatment technique summation  Barrier trading  Choose which barrier to implement  Can trade different approaches

9. Crypto Requirements for Filtration Plants 1 (40 CFR 141.709 and 40 CFR 141.720) 2 Systems may use any technology or combination of technologies from the microbial toolbox. 3 Systems must achieve at least 1 log of the required treatment using ozone, chlorine dioxide, UV, membranes, bag/cartridge filters, or bank filtration. 4 Total Cryptosporidium treatment must be at least 4.0 log. 5 Total Cryptosporidium treatment must be at least 5.0 log. 6 Total Cryptosporidium treatment must be at least 5.5 log. If your Cryptosporidium concentration (oocysts/L) is...binpf And if you use the following filtration treatment in full compliance with existing regulations, then your additional treatment requirements are... Conventional Filtration Treatment (includes softening) Direct FiltrationSlow Sand or Diatomaceous Earth Filtration Alternative Filtration Technologies < 0.07513No additional treatment > 0.075 and < 1.024.01 log treatment 2 1.5 log treatment 2 1 log treatment 2 As determined by the State 2,4 > 1.0 and < 3.035.02 log treatment 3 2.5 log treatment 3 2 log treatment 3 As determined by the State 3,5 > 3.045.52.5 log treatment 3 3 log treatment 3 2.5 log treatment 3 As determined by the State 3,6 DRAFT - LONG TERM 2 ENHANCED SURFACE WATER TREATMENT RULE TOOLBOX GUIDANCE MANUAL

10. EPA Crypto  Maximum oocyst concentration is 0.0001/L  So for every 10,000 liters of water consumed, one person could contract Cryptosporidiosis…  But not all oocysts are viable…

11. Filtration Credit for Crypto  The total Cryptosporidium treatment required for Bins 2, 3, and 4 is 4.0 log, 5.0 log, and 5.5 log, respectively  The additional treatment requirements are based on a determination that conventional, slow sand, and diatomaceous earth filtration plants in compliance with the IESWTR or LT1ESWTR achieve an average of 3 log removal of Cryptosporidium  Therefore, conventional, slow sand, and diatomaceous earth filtration plants will require an additional 1.0 to 2.5 log additional treatment to meet the total removal requirement, depending the source water contamination DRAFT - LONG TERM 2 ENHANCED SURFACE WATER TREATMENT RULE TOOLBOX GUIDANCE MANUAL Why isn’t Crypto pf measured for each plant?

12. Barrier Equivalency  Mathematically correct (adding pf is like multiplying fraction remaining)  Are removal and inactivation equivalent? Achieving pf for Crypto We need to understand how each of these technologies work!

13. Barrier Order of Operation  The underlying assumption is that the barrier fraction remaining can be multiplied  Does order of operation matter?  Mathematically: ____  Water treatment: ________________________ = YES! Ask for proof after treatment technologies NO!

14. Cryptosporidium Treatment Credit Source Toolbox Components Watershed control program0.5 log credit Pre-Filtration Toolbox Components Bank filtration0.5 log credit for 25 foot setback; 1.0 log credit for 50 foot setback. Presedimentation basin with coagulation 0.5 log credit for new basins with continuous operation and coagulant addition. Two-stage lime softening0.5 log credit for two-stage softening with coagulant addition. Treatment Performance Toolbox Components Combined filter performance0.5 log credit for combined filter effluent turbidity ≤ 0.15 NTU in 95% of samples each month. Individual filter performance1.0 log credit for individual filter effluent turbidity ≤ 0.1 NTU in 95% of daily maximum samples each month (excluding 15 minutes following backwash) and no filter >0.3 NTU in two consecutive measurements taken 15 minutes apart. Additional Filtration Toolbox Components Bag filters1 log credit with demonstration of at least 2 log removal efficiency in challenge test; Cartridge filters2 log credit with demonstration of at least 3 log removal efficiency in challenge test; Membrane filtrationLog removal credit up to the lower value of the removal efficiency demonstrated during the challenge test Second stage filtration0.5 log credit for a second separate filtration stage; treatment train must include coagulation prior to first filter. Slow sand filters2.5 log credit for second separate filtration process. No disinfectant residual present in influent.

15. Additional Barriers  Wastewater treatment  New water distribution systems disinfected prior to use  Distribution system always pressurized to prevent infiltration  Prevention of siphoning  Vigilance against cross connections  Residual chlorine  Protection against recontamination (in the home or in the distribution system)  Providing residual protection against microbial regrowth  Are these microbes pathogens?  Is there a health risk to microbial regrowth? Research!

16. No Absolute Barriers?  Did you notice that each barrier is given a pf rating?  No barriers have absolute protection  Any claims that a treatment technology provides an absolute barrier (100% removal) should be evaluated skeptically  Usually “100% removal” means the detection limit was too high  There is a world of difference between 99% removal and 100% removal pf = 2 vs. pf = infinity!

17. Barrier Summary  Don’t depend on a single barrier  The protection from each barrier can be characterized by its pf  EPA’s pf values may be overly simplistic, but the concept of additive pf values is useful  A fundamental understanding of how each process achieves its pf is required to understand how processes can be combined into treatment trains Coming soon!

18. Multiple Exposures: Pathogen load  Watersheds:  Inhabited  Agriculture including Livestock and Poultry  Households  Latrines (or lack thereof)  Hand washing (not as convenient)  Livestock and Poultry

19. Multiple Exposures  Water treatment  Urban areas  Conventional centralized water treatment (large scale similar practices in the North)  Incomplete coverage  Rationing  Small communities and underserved urban areas  Inadequate central treatment  Unreliable point of use treatment  Distribution system  Water rationing  Cross contamination  Household storage

20. Global South Context  Honduras  Urban: Tegucigalpa (1 million)  Central water treatment  Sanitation and water supply in the poor neighborhoods  Rural poor: Vara de Cohete (300)  Mexico  Urban: Mérida (1 million)

21. Coagulation

22. Sedimentation (Lamella)

23. Filter beds

24. Filter Controls

25. Chlorination

26. Tegucigalpa Latrines

27. Pila

28. Rainwater

29. Vara de Cohete

30. Masa Stone

31. Corn Grinder

32. Fuego y Cal

33. Laundry day

34. Rural Latrine

37. Mérida

38. Urban Household Water Tanks