Bio-Stability of New York City’s Distribution Water

1. Water Quality New York City Department ofEnvironmentalProtection Bureau of Water Supply Bio-Stability of New York City’s Distribution Water WSTC September 15, 2009 Presenter: Salome Freud, Chief Distribution Water Quality Operations, BWS, NYCDEP Authors: Dr. Xiaoping Wang, Assistant Director, Distribution Laboratory DWQO, BWS NYCDEP Dr. Guo Baiying, Research Scientist, DWQO, BWS, NYCDEP

2. Introduction • The ability to limit re-growth in drinking water is referred to as biological stability (bio-stability) and is dependant on the concentration of the substrates required for the growth of microorganisms. • The bio-stability of New York City’s distribution system water was assessed by evaluating HPC (heterotrophic plate count) levels in distribution water and biofilms from a laboratory bioreactor.

3. What is HPC? The heterotrophic plate count (HPC), formerly known as the standard plate count, is a procedure for estimating the number of live heterotrophic bacteria (requiring organic compounds of carbon and nitrogen for nourishment) in water. This test can provide useful information about water quality

4. Analytical Methods • Total HPC count method (SM 9215 with PCA Medium), reported in cfu/ml. • Biofilm samples growth in a Bench top Bioreactor, reported as cfu/cm2 CFU: colony forming unit

5. HPC Plates

6. HPC Evaluation The HPC levels in the drinking water were compared in 5 year increments with data from 1990 to 2008. HPC levels were measured in drinking water from the distribution system and in pre-finished water samples. The HPC levels were categorized by concentrations: <1, 1-100, 101-200, 201-500, >500 cfu/mL.

7. Types of Water • Pre-Finished Water • Water that has been disinfected with chlorine to meet SWTR requirements for Giardia, coliform and viruses but has not received all chemical treatment including secondary disinfection or corrosion inhibitors. Some pre-finished water is exposed to the atmosphere in Hillview Reservoir. • Distribution Water • Water from the distribution system which has received all treatment and has since been under pressure in tunnels and water mains.

8. The following Tables and Charts present some of the HPC results from New York City’s Distribution system

9. # of Samples Analyzed by Water Type

10. Percent HPC Levels by Years

11. HPC Levels by Years

12. Pre-Finished Water Percent HPC Levels by Years

13. Distribution Water Percent HPC Levels by Years

14. HPC in New York City’s Water From 1990 to 2008 the Fraction of Samples with: • HPC >500 cfu/ml decreased 90% • HPC <1 cfu/ml increased 50% • HPC 1-100 cfu/ml decreased 80% • HPC 101-200 cfu/ml decreased 99% • HPC 201-500 cfu/ml decreased 99%

15. Does HPC Correlate with Residual Chlorine? • Small Negative Correlation for Pre-finished Sample Sites but none for Distribution Sample Sites

16. Correlation Between Residual Chlorine and HPC in Pre-Finished Sample Sites (2000-2004)

17. Correlation Between Residual Chlorine and HPC in Distribution Sample Sites (2000-2004)

18. Does HPC Correlate with Temperature? • No Correlations for Pre-Finished or Distribution Sample Sites

19. Correlation Between Temperature and HPC in Pre-Finished Sample Sites (2000-2004)

20. Correlation Between Temperature and HPC in Distribution Sample Sites (2000-2004)

21. Bacterial Species Changes over Time • All HPC samples >50 cfu/ml were speciated by an automatic bacterial ID system (Vitek). • The most frequently isolated HPC bacteria in the system (Acinetobacter spp and Aeromonas spp) greatly decreased from 2000 to 2008.

22. Identification of HPC >50 cfu/ml

23. Conclusions: HPC Monitoring in NYC Distribution System • HPC levels in distribution declined between 1990 and 2008. • The greatest decrease was observed in the samples with the highest levels of HPC, >500 cfu/mL, but the proportion of samples in the other categories >1 cfu/mL also declined significantly.

24. Is the Decrease in HPC Associated with Nutrients - BDOC? BDOC: Biodegradable Organic Carbon A Biofilm Study

25. What is Biofilm? A biofilm is a complex aggregation of microorganisms growing on a solid substrate. Biofilms are formed in distribution system pipelines when microbial cells attach to pipe surfaces and multiply to form a film or slime layer on the pipe.

26. What Do Biofilms Looks Like?

27. Continuous Regrowth Annular Biofilm Reactor

28. Measurement of Biofilm • Coupons of PVC and iron used inside the bioreactor. • Coupons were removed after 2 weeks to measure HPC. • Dipped coupons in 50 ml of phosphate buffer removing the biofilm. • Suspension liquid was further diluted down to log 6 by transferring 1ml through a series of 6 bacterial glass tubes with 9ml of phosphate buffer. • 1ml of diluted sample from each tube was add to PAC agar in duplicate by spread method and incubated at 35oC for 48 hrs. • HPC count for each dilution sample was converted into cfu/cm2.

29. HPC Results from Bioreactor in 2006-2007

30. 1995-96 Biofilm Studies In 1995-1996 the mean BDOC value in New York City’s Distribution System was 376 ug/L. This supported HPC levels of 106 to 107 cfu/cm2 on iron surfaces.

31. Conclusions: Biofilm Study • 2006-2007 Bioreactor study showed that BDOC supported HPC of 105 to 106 cfu/cm2 on iron for a two week growth period. • The density of HPC on PVC was a factor of 10 lower than on iron. • The 1995-1996 study found HPC density a factor of 10 higher than the 2006-2007 Bioreactor study. • Based on HPC growth levels one can assume a decrease in BDOC levels which infer improved source water quality.

32. Summary • HPC density decreased significantly in New York City’s Distribution System over the past 18 years • 90% of all samples are <1 (non-detect) for HPC • BDOC limits HPC re-growth in the distribution system • New York City’s distribution system is biologically stable.

33. Questions? Thank You