BioStability of New York Citys Distribution Water WSTC
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 Water Quality Water New York City Department of of Environmental Protection New Bureau of Water Supply
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. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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 Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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/cm 2 CFU: colony forming unit Water Quality New York City Department of Environmental Protection Bureau of Water Supply
HPC Plates Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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 prefinished water samples. • The HPC levels were categorized by concentrations: <1, 1 -100, 101 -200, 201 -500, >500 cfu/m. L. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
The following Tables and Charts present some of the HPC results from New York City’s Distribution system Water Quality New York City Department of Environmental Protection Bureau of Water Supply
# of Samples Analyzed by Water Type Years Water Type Pre-Finished Distribution Total Samples 1990 -1994 3047 7643 10690 1995 -1999 8198 22157 30355 2000 -2004 7992 35372 41045 2005 -2008 7856 18750 26606 Total 27093 83922 108696 Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Percent HPC Levels by Years Water Quality New York City Department of Environmental Protection Bureau of Water Supply
HPC Levels by Years HPC (cfu/ml) 1990 -1994 1995 -1999 2000 -2004 2005 -2008 <1 30. 98% 75. 24% 86. 49% 89. 18% 1 -100 61. 88% 23. 33% 12. 87% 10. 76% 101 -200 5. 45% 0. 55% 0. 18% 0. 01% 201 -500 0. 95% 0. 41% 0. 15% 0. 01% >500 0. 74% 0. 47% 0. 31% 0. 03% Total 100. 00% Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Pre-Finished Water Percent HPC Levels by Years Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Distribution Water Percent HPC Levels by Years Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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% Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Does HPC Correlate with Residual Chlorine? • Small Negative Correlation for Pre-finished Sample Sites but none for Distribution Sample Sites Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Correlation Between Residual Chlorine and HPC in Pre-Finished Sample Sites (2000 -2004) Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Correlation Between Residual Chlorine and HPC in Distribution Sample Sites (2000 -2004) Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Does HPC Correlate with Temperature? • No Correlations for Pre-Finished or Distribution Sample Sites Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Correlation Between Temperature and HPC in Pre-Finished Sample Sites (2000 -2004) Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Correlation Between Temperature and HPC in Distribution Sample Sites (2000 -2004) Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Identification of HPC >50 cfu/ml Dominated Species 2000 2001 2002 2003 2004 2005 2006 2007 2008 Acinetobacter spp 22 6 6 14 10 1 3 3 3 Aeromonas spp 18 1 43 3 6 0 0 0 4 Enterobacter spp 10 1 9 5 5 1 1 0 1 Pseudomons spp 2 3 8 0 1 0 0 0 5 183 13 13 5 9 3 6 1 30 Other Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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/m. L, but the proportion of samples in the other categories >1 cfu/m. L also declined significantly. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Is the Decrease in HPC Associated with Nutrients - BDOC? BDOC: Biodegradable Organic Carbon A Biofilm Study Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
What Do Biofilms Looks Like? Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Continuous Regrowth Annular Biofilm Reactor Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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 1 ml through a series of 6 bacterial glass tubes with 9 ml of phosphate buffer. • 1 ml of diluted sample from each tube was add to PAC agar in duplicate by spread method and incubated at 35 o. C for 48 hrs. • HPC count for each dilution sample was converted into cfu/cm 2. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
HPC Results from Bioreactor in 2006 -2007 Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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/cm 2 on iron surfaces. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Conclusions: Biofilm Study • 2006 -2007 Bioreactor study showed that BDOC supported HPC of 105 to 106 cfu/cm 2 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. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Summary • HPC density decreased significantly in New York City’s Distribution System over the past 18 years • 90% of all samples are <1 (nondetect) for HPC • BDOC limits HPC re-growth in the distribution system • New York City’s distribution system is biologically stable. Water Quality New York City Department of Environmental Protection Bureau of Water Supply
Questions? Thank You Water Quality New York City Department of Environmental Protection Bureau of Water Supply
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