optimal disinfection of water distribution networks following a contamination event
DESCRIPTION
My presentation at WDSA 2014, Bari, Italy: Water distribution systems are prone to be contaminated. Following a contamination event the contaminated section of the water distribution system should be identified, isolated and cleaned before it is returned to service. The cleaning process includes flushing and disinfection. While there are number of disinfection methods (for example: tablet, continuous and slug) they all require that the disinfectants will have minimal contact time (T) in a predefined concentration (C) with the pipe. The regulatory agencies such as the ministry of health in Israel publishes procedures for the disinfection of water mains in which usually a short part of a single main is considered and no specific procedures are given for larger portions of the water system. This study presents an optimal operation plan for disinfection of water distribution systems taking into account the locations where the disinfectants should be injected into the network, their concentration, injection times, flow rate and drainage locations. The method is a GA-EPANET framework. It is demonstrated on a small real-world network section.TRANSCRIPT
WDSA 2014, Bary, Italy, 14-17 July
OPTIMAL DISINFECTION OF WATER DISTRIBUTION
NETWORKS FOLLOWING A CONTAMINATION EVENT
Avi Ostfeld, TechnionElad Salomons, OptiWater
WDSA 2014, Bary, Italy, 14-17 July
Acknowledgment
This study was supported by the joint Israeli Office of the Chief Scientist (OCS) Ministry of Industry, Trade and Labor (MOITAL) and by the German Federal Ministry of Education and Research (BMBF), under project number GR_2443
WDSA 2014, Bary, Italy, 14-17 July
Network wide contaminations events• Water outage of several days• Caused by chemicals, sewage, backflow, human
errors …• Fortunately they are rare• Unfortunately they have a wide effect making life
very difficult• Well, not as difficult as having a slow Internet
connection…
WDSA 2014, Bary, Italy, 14-17 July
Must have a cat…
WDSA 2014, Bary, Italy, 14-17 July
Kiryat Motzkin, Israel, 2011
• E. Coli detected in water samples• Effected 47,000 residents• 8 days without potable water• Treatment: flushing
WDSA 2014, Bary, Italy, 14-17 July
Elk River, US-WV, 2014
• Chemical spill (4-Methylcyclohexanemethanol)
• Effected >300,000 residents• 6 days without potable water• Tens hospitalized• Treatment: flushing and Carbon
WDSA 2014, Bary, Italy, 14-17 July
So …
If there is a system wide contamination,
what about a system wide disinfection?(following a contamination, not regular operation)
WDSA 2014, Bary, Italy, 14-17 July
Regulation and standards
• In Israel the regulation are by the Ministry of Health – “Potable water distribution systems cleaning regulations” (sorry, only in Hebrew)• The regulations are for water tanks\reservoirs and a
single water main.• No regulations for networks.• In general, the regulations define “Ct”, where• C is the disinfectant minimum concentration, and• t is the minimum contact time with the water\pipe
WDSA 2014, Bary, Italy, 14-17 July
read this way
methodCtapplication
mg/LhrFully fill the pipe with Chlorine solution,seal it, wait and flush
WDSA 2014, Bary, Italy, 14-17 July
AWWA Standard C651-05
• “Disinfecting Water Mains”• Different disinfection methods:• Tablet – 25mg/L for 24 hours• Continuous feed – 25mg/L for 24 hours• Plug – 100mg/L for 3 hours
• Appendix C – Disposal of Heavily Chlorinated Water• Check with local sewer department…• Chlorine residual of water … will be neutralized….
WDSA 2014, Bary, Italy, 14-17 July
Simple explanation
source
Injection point50mg/L
“dead-end”drain
drain
WDSA 2014, Bary, Italy, 14-17 July
Problem formulation
• Objective:• disinfect the network in minimum time, or• disinfect the network with minimum disinfectant
• Decision variables:• disinfectant injection locations and flows• drainage locations and flows
• Constraints:• number of drainage locations• minimum concentration throughout the network (C)
WDSA 2014, Bary, Italy, 14-17 July
Power generator Hypochlorite tank Dosing pumps
Image courtesy of MODOtec LTD.
WDSA 2014, Bary, Italy, 14-17 July Image courtesy of MODOtec LTD.
WDSA 2014, Bary, Italy, 14-17 July
The real network
Image removed.
WDSA 2014, Bary, Italy, 14-17 July
WDSA 2014, Bary, Italy, 14-17 July
The modified network
WDSA 2014, Bary, Italy, 14-17 July
Simplified problem
WDSA 2014, Bary, Italy, 14-17 July
Methodology
• Genetic Algorithm linked with EPANET• Simple binary representation• Select 2 drainage locations (out of 6 options)• Select 5 drainage flows (2 for new locations + 3
fixed)• Minimum concentration at all junctions – 50mg/L
WDSA 2014, Bary, Italy, 14-17 July
The program
WDSA 2014, Bary, Italy, 14-17 July
Sensitivity analysis
1 2 3 4 5 62
3
4
5
6
7
Number of drainage locations
Ope
ratio
n tim
e (h
r)
WDSA 2014, Bary, Italy, 14-17 July
Further research
• Different disinfection methods• Time based drainage• Multiobjective formulation• And more…
