1. Frank Qiao and Michael Wang
Cost-effective Data Mining from SCADA system to Replace Flow Monitoring
Predicting H2S Corrosion “Hotspot” in Large Sewer Collection System
Frank Qiao and Michael Wang
March 27, 2018

2. Outline Process of H2S Formation First Lesson Case Study
Observation and Conclusion

3. Process of H2S Formation
Sulfate
Sulfide (l)
Sulfide (g)
Sulfuric
Acid
Pipe Crown
Liquid
Bio/Chemical
Physical
Bacteria
reduction
oxidation

4. First Lesson Constructed in 1986 to a build out capacity of 8 MGD
~ 17,000 LF 30" Force Main
~ 13,000 LF 24" Force Main

5. Profile

6. Permanent Dry Area in Transition Zone Most Risky

7. 24 inch DIP

8. Polybond Liner Failure

9. Recent Study
14 mile FM

10. Typical H2S Gas (ppm)

12. Higher pH limits H2S-L Formation
H2S-G (ppm)

13. H2S-G to H2S-L Ratio Varies by Location
Location Matters a lot
More pumping
More FM discharge
More downstream
More H2S formation

14. H2S-G to H2S-L Ratio

15. Physics plays a big role
Henry’s Law
Equilibrium needs lots of energy

16. Henry’s Law Constant

17. Carbon Can H2S In (ppm)

18. 14 Mile Long Force Main

20. FM TRANSITION GRAVITY AV2 AV3 AV8 AV9 AV10 AV4 AV7 AV11 AV5 AV6 AV12

22. More Extreme Cases

23. Conclusion H2S formation is very high in transition zone
H2S-L to H2S-G plays an important role in H2S formation
High pressure, long detention time and more turbulence from pumping/hydraulic jump leads to higher H2S-G to H2S-L ratio
Bi-oxide may not be a good treatment strategy
pH adjustment and H2S treatment strategy (H2O2/Fe) may be more effective