optimal disinfection of water distribution networks following a contamination event

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…

WDSA 2014, Bary, Italy, 14-17 July

Thank you

Questions?

selad@optiwater.com