Bio-Stability of New York City’s Distribution Water

New York City Department of Environmental ProtectionBureau of Water Supply

Water Quality

Bio-Stability of New York City’s Distribution WaterBio-Stability of New York City’s Distribution Water

Authors: Authors: Dr. Xiaoping Wang, Assistant Director, Dr. Xiaoping Wang, Assistant Director, Distribution Laboratory DWQO, BWS Distribution Laboratory DWQO, BWS

NYCDEP NYCDEP Dr. Guo Baiying, Research Scientist, Dr. Guo Baiying, Research Scientist,

DWQO, BWS, NYCDEPDWQO, BWS, NYCDEP


Water Quality

WSTC September 15, 2009WSTC September 15, 2009

Presenter:Presenter: Salome Freud, Chief Salome Freud, Chief

Distribution Water Quality Distribution Water Quality Operations, BWS, NYCDEPOperations, BWS, NYCDEP


Water Quality

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

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

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


Water Quality

HPC Plates


Water Quality

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.


Water Quality

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

The following Tables and Charts present some of the HPC results from New

York City’s Distribution system


Water Quality

# 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

Percent HPC Levels by Years

0

10

20

30

40

50

60

70

80

90

100

%

1990-1994 1995-1999 2000-2004 2005-2008

Time

<1

1-100

101-200

201-500

>500


Water Quality

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% 100.00% 100.00% 100.00%


Water Quality

Pre-Finished Water Percent HPC Levels by Years

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

1990-1994 1995-1999 2000-2004 2005-2008

<1 1-100101-200 210-500>500


Water Quality

Distribution Water Percent HPC Levels by Years

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

1990-1994 1995-1999 2000-2004 2005-2008

<1 1-100101-200 201-500>500


Water Quality

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

Does HPC Correlate with Residual Chlorine?

•Small Negative Correlation for Pre-finished Sample Sites but none for Distribution Sample Sites


Water Quality

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

0.00E+00

1.00E+00

2.00E+00

3.00E+00

4.00E+00

Aug-

99

Nov

-99

Feb-

00

Apr-

00

Jul-0

0

Oct

-00

Dec

-00

Mar

-01

May

-01

Aug-

01

Nov

-01

Jan-

02

Apr-

02

Jul-0

2

Sep-

02

Dec

-02

Feb-

03

May

-03

Aug-

03

Oct

-03

Jan-

04

Apr-

04

Jun-

04

Sep-

04

Nov

-04

Feb-

05

May

-05

Time

Res

idu

al C

hlo

rin

e m

g/L

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

r = - 0.0995

HP

C c

fu/m

L

Residual ChlorineHPCLinear (HPC)


Water Quality

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

0.00

1.00

2.00

3.00

4.00

Jan-

00

Mar

-00

Apr-0

0

Jun-

00Au

g-00

Oct-0

0De

c-00

Feb-

01

Apr-0

1Ju

n-01

Aug-

01Oc

t-01

Dec-

01Fe

b-02

Apr-0

2Ju

n-02

Aug-

02Oc

t-02

Dec-

02Fe

b-03

Apr-0

3Ju

n-03

Aug-

03

Oct-0

3De

c-03

Feb-

04Ap

r-04

Time

chlo

rine

Res

idua

l mg/

L

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

r = - 0.010

HP

C c

fu/m

l

Residual Chlorine

HPC


Water Quality

Does HPC Correlate with Temperature?

•No Correlations for Pre-Finished or Distribution Sample Sites


Water Quality

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

0.00

10.00

20.00

30.00

Aug-

99

Nov

-99

Feb-

00

Apr-

00

Jul-0

0

Oct

-00

Dec

-00

Mar

-01

May

-01

Aug-

01

Nov

-01

Jan-

02

Apr-

02

Jul-0

2

Sep-

02

Dec

-02

Feb-

03

May

-03

Aug-

03

Oct

-03

Jan-

04

Apr-

04

Jun-

04

Sep-

04

Nov

-04

Feb-

05

May

-05

Time

Tem

per

atu

re (

C)

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

r = 0.067

HP

C c

fu/m

L

Temperature

HPC


Water Quality

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

0.00

10.00

20.00

30.00

Jan-

00Fe

b-00

Mar

-00

Mar

-00

Apr-

00M

ay-0

0Ju

n-00

Jul-0

0Au

g-00

Sep-

00N

ov-0

0D

ec-0

0Ja

n-01

Feb-

01M

ar-0

1Ap

r-01

May

-01

Jun-

01Ju

l-01

Aug-

01Se

p-01

Oct

-01

Nov

-01

Dec

-01

Jan-

02Fe

b-02

Mar

-02

Apr-

02M

ay-0

2Ju

n-02

Jul-0

2Ap

r-03

Jun-

03Se

p-03

Oct

-03

Nov

-03

Dec

-03

Feb-

04M

ar-0

4Ap

r-04

Time

Tem

per

atu

re (

C)

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

1.00E+04

r = 0.006

HP

C c

fu/m

L

HPC

Temperature ©


Water Quality

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

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

Other 183 13 13 5 9 3 6 1 30


Water Quality

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.


Water Quality

Is the Decrease in HPC Associated with Nutrients

- BDOC?BDOC: Biodegradable Organic Carbon

A Biofilm Study


Water Quality

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

What Do Biofilms Looks Like?


Water Quality

Continuous Regrowth Annular Biofilm Reactor


Water Quality

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.


Water Quality

HPC Results from Bioreactor in 2006-2007

HPC from Biofilm Samples

1.00E+01

1.00E+03

1.00E+05

1.00E+07

1.00E+09

Feb-0

6

Apr-

06

May-0

6

Jun-0

6

Jul-06

Sep-0

6

Nov-0

6

Jan-0

7

Feb-0

7

Mar-

07

Sampling Date

cfu

/cm2

Iron PVC


Water Quality

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.


Water Quality

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.


Water Quality

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.


Water Quality

Questions?

Thank You

Documents

Bio-Stability of New York City’s Distribution Water