regu p. regunathan phd regunathan & associates, inc. technical consultant to wqa 10 aug 2011
TRANSCRIPT
Discussion on WHO Guidelines on Evaluation of Household Water
Treatment Options
Regu P. Regunathan PhDReguNathan & Associates, Inc.Technical Consultant to WQA
10 Aug 2011
Guidelines released • Released in June 2011 after considerable reviews
and discussions
• Intended Audiences are:• National Certifiers• Regulatory Authorities• Researchers• Manufacturers & Implementers
• Arranged in 3 short Sections and 4 detailed Appendices
Tiered ApproachOne of the most contentious subject by reviewers
Modified from original proposal but still retained the essence of the concept . Interim Target approach has been altered significantly.
Based on WHO’s regularly and extensively used target levels of DALY (Disability Adjusted Life Years)
Quantitative Microbial Risk Assessment (QMRA) was employed to estimate Health based Performance Targets
DALYMeasure to estimate burdens of disease and
injuries
Health effects weighed - 0 (good health) to 1 (death)
Years of life lost due to mortality = YLLYears of life lived with disability = YLDDALY = YLL + YLD
10⁻⁶ DALY/person/year = loss of 365 healthy days/one million/year = 1 excess case of cancer/100000 people drinking water over 70 years
Target Pathogens Selected
Bacteria - Campylobacter jejuni
Virus – Rotavirus
Protozoa - Cryptosporidium
Tiers presented
Highly Protective ----- 10⁻⁶ DALY /person/year
Protective -------------- 10⁻⁴ DALY/person/year
Interim ----------------- Achieves “protective” targets for two classes of pathogens & results in health gains in applications.
Health Based HWT Performance Targets
Target Log reduction
- Bacteria
Log reduction
- Virus
Log Reduction
- Protozoa
Highly
Protective
≥4 ≥5 ≥4
Protective ≥2 ≥3 ≥2
Interim Achieves “protective” targets for two classes of
pathogens & results in health gains
Derivation of Targets using QMRABased on known sets of data and several assumptions
Pathogens selected had been cited in GDWQ of WHO along with being involved in several outbreaks
Pathogen levels in raw water calculated on the basis of adding wastewater to a concentration of 0.01%
Daily water consumption, probability of infection by each pathogen, risk of diarrheal illness, and susceptible population were all assumed for the calculations of the DALY and thus these target levels
Technologies described in Appendices
Chemical Disinfection (chlorine, bromine, iodine, chlorine dioxide, ozone, etc.
Filters of all types (Membrane, ceramic, Granular, etc)
Solar DisinfectionUV Thermal TechnologiesCoagulation, precipitation and settlingCombination of relevant technologies
Protocol DetailsTwo types of test waters similar to EPA protocol
Differentiation of protocols based on technology
Alternate indicator microbes suggested (E. coli, MS2, C. perfringens spores, inert particles, etc.)
But not very detailed directions for carrying out the actual tests with the selected pathogens or suggested alternates
Mostly guidelines for development of national regulations and protocols along with certification approaches
Few thoughts
Potentially Simpler ApproachPresent approach for interim targets appears well thought out and
appropriate compared to earlier 1/1/1 log reductions proposed.
Had to make several assumptions to reach these two tiers and targets. Any different assumptions would have lead to very different results
Could have decided on ONE suggested goal to be reached by different countries.
10⁻⁵ DALY/person/year could have been selected as the only one approach
This approach would have lead to targets of 3/4/3 for bacteria/virus/ protozoa. If one gets 4 logs of virus reduction along with 3 logs of protozoan reduction that technology would have easily also achieved 6 logs or more of bacteria reduction. Same as EPA protocol of 6/4/3!!!