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CASE STUDY #3 – TREATING MIB IN SQUAW PEAK WTP INFLUENT WATER

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60

7.4 CASE STUDY #3 – TREATING MIB IN SQUAW PEAK WTP INFLUENT WATER

7.4.1 Process Control Monitoring

By late July 2001 MIB concentrations entering Squaw Peak WTP were approaching 30

ng/L (Figure 7-5). During July 2001 no PAC was added.

MIB in the Squaw Peak WTP

8/1

8/16

8/30

9/13

9/27

10/18

11/2

11/15

MIB, ng/L

Inlet

Outlet

Figure 7-5. MIB in raw (SP-IN) and finished (SP-OUT) water at the Squaw Peak WTP

7.4.2 Diagnosis

Options to minimize MIB production in the upstream canal were being implemented.

However, elevated MIB levels (> 30 ng/L) still entered the WTP. It was determined that

in-plant MIB control was required.

7.4.3 Treatment Selection

Squaw Peak WTP had no documented in-plant production of MIB, therefore chlorine or

copper addition in the WTP would not be effective at reducing MIB levels. Squaw Peak

WTP does not have ozone or chlorine dioxide feed capabilities. Since the WTP feeds

chlorine prior to filtration, biological filtration was not an option. This left powdered

activated carbon (PAC) addition as the only means of MIB treatment.

7.4.4 Treatment Application

Squaw Peak WTP had residual Norit HDB PAC in slurry storage tanks and used that

supply up by the end of July. Norit 20B was ordered; this PAC was deemed more

effective at removing MIB from the local water source based upon laboratory

performance comparisons. However, Norit HDB was delivered and had to be used

during early September. PAC ran out around September 20, 2001, and no MIB removal

was achieved. It is important to monitor PAC supplies and coordinate new deliveries

accordingly. Once Norit 20B was delivered the PAC dose was calculated based upon

laboratory dose-removal nomographs (Figure 5-10) verified the prior year at Val Vista

WTP in full-scale tests. The following equation can be used for PAC dose calculation:

C/C

= 0.95 x EXP (-0.18 x PAC_Dose)

Equation 7.1

Equation 7.2

An example Norit B PAC dose calculation for September 12, 2001, to achieve 10 ng/L

of MIB in finished water (C) when a MIB concentration of 55 ng/L was present in the raw

water (C

)

follows:

C = 10 ng/L

= 55 ng/L

PAC Dose (mg/L) = - [ ln(0.95 *10/55) ] / 0.079 = 22 mg/L

The WTP was operating near capacity (120 MGD) and detention time in the

presedimentation basins where the PAC was added was only one hour. However, the

nomographs were developed based upon a three-hour contact time. Revised

nomographs for shorter contact times were required to determine PAC doses.

7.4.5 Follow-up Monitoring

PAC (8 to 16 mg/L doses) removed MIB, but not to below 10 ng/L (Figure 7-5). PAC

doses of greater than 16 mg/L were necessary to achieve 10 ng/L MIB in the finished

water, but the PAC feed facilities were not rated for a feed rate this high.

Recommendation: improve and increase capacity of PAC feed system.

Once, after November 2001, Norit 20B was used and detention times in the

presedimentation basins were above 1.25 hours the observed and predicted MIB

removal was adequate and the target of 10 ng/L of MIB in finished water was achieved.

The experience suggested that slight refinements in PAC dose-removal nomographs

may be necessary to account for varying hydraulic retention times, and that scheduling

delivery of PAC was critical.

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C

C

Dose

PAC

62

REFERENCES

American Public Health Association, American Water Works Association and Water

Environment Federation. (1999) Standard Methods for the Examination of Water and

Wastewater. 20

Edition.

Baker, L., Westerhoff, P., Sommerfeld, M., Bruce, D., Dempster, T., Qiang, H. and

Lowry, D. (2000) Multiple barrier approach for controlling taste and odor in Phoenix's

water supply system, Water Quality Technology Conference, Salt Lake City, Utah,

November, 2000.

Baker, L. A., Westerhoff, P. and Sommerfeld, M. (1999) Multibarrier concept for taste

and odor control, North American Lake Management Society Conference, Reno,

Nevada, Dec. 1-4, 1999.

Bruce, D., Westerhoff, P., Sommerfeld, M., Baker, L., Nguyen, M. L., Lowry, D.,

Dempster, T. and Hu, Q. (2000) Occurrence of MIB and geosmin in Arizona drinking

waters, Arizona Water Pollution Control Association Conference, May 4-5, 2000.

Lloyd, S. W., Lea, J. M., Zimba, P. V., and Grimm, C. C. (1998) Rapid analysis of

geosmin and 2-methylisoborneol in water using solid phase micro extraction

procedures. Wat. Res. 37(7):2140-2146.

Means, E. G. and McGuire, M. J. (1986) An early warning system for taste and odor

control. Journal AWWA: March, 1986, 77-83.

Nguyen, M. L. (2002) Sources and characteristics of dissolved organic carbon in arid

region water supplies, Ph.D. Dissertation, Civil and Environmental Engineering, Tempe,

Arizona State University, .

Nguyen, M. L., Baker, L. A. and Westerhoff, P. (2002) Sources of DOC and DBP

precursors in western U.S. watersheds and reservoirs. J. Am. Water Works Assoc.

94(5):98-112.

Suffet, I. H., Khiari, D. and Bruchet, A. (1999) The drinking water taste and odor wheel

for the millenium: beyond geosmin and 2-methylisoborneol. Wat. Sci. Tech. 40(6):1-13.

Taylor, W. D., Losee, R. F., Isaguirre, G., Crocker, D. J., Otsuka, D. J., Whitney, R. D.,

Kemp, J. and Faulconer, G. (1994) Application of limnological principles for

management of taste and odor in drinking water reservoirs: a case study, Water Quality

Technology Conference, San Francisco, CA, Nov. 6-10, 1994.

Watson, S. B., Brownlee, B., Satchwill, T., and Hargesheimer, E. E. (2000) Quantitative

Analysis of trace levels of geosmin and MIB in source and drinking water using

headspace SPME. Wat. Res. 34(10): 2818-2828.

63

APPENDIX A

SAMPLE DATA SHEETS FOR LAKE, CANAL AND WTP SAMPLES

Taste and Odor Project – Lake Sampling

Site #: ____________ Location: _________ Date: __________Time: ________

Personnel: __________Weather: ____________________________ Elevation: ___

Description of water:

Description: ______________________________________ Water Depth ____________ m

(circle): Turbid clear

green blue-green brown yellow-brown

white floc

white foam

Secchi Disk Reading 1 __ m Secchi Disk Reading 2 __m Average Reading ___m

Field measurements:

Depth (m)

T (

o

C - D.O.)

D.O. (mg/L)

sample (yes/no)

comments

Description of phytoplankton (free-floating):

____________________________________________________________________________

Color (circle): Green Brown

yellow-brown Blue-green Pink Other:

____________________

Visible clumps: yes no

Comments: ________________________________

Water Odor Characteristics:

Odor in epilimnion composite water sample:

Odor strength (circle one): Strong Medium Weak Absent

Odor (circle): musty earthy moldy fishy sulfidic grassy chlorine Other

Comments:

______________________________________________________________________

Odor in hypolimnion composite water sample:

Odor strength (circle one): Strong Medium Weak Absent

Odor (circle): musty earthy moldy fishy sulfidic grassy chlorine Other

Comments:

______________________________________________________________________

Samples collected:

Comments:

____________________________________________________________________________

65

Taste and Odor Project – Canal Sampling

Site #: Specify Site ID Location: Specify location Date: ____________Time: ________

Personnel: ____________Weather: ___________________________ Elevation: _____

Description of water:

Description:

____________________________________________________________________________

(circle): Turbid clear

green blue-green brown yellow-brown

white floc

white foam

Description of phytoplankton (free-floating):

Description: _______________________________________________________________

Color (circle): Green Brown/yellow-brown Blue-green Pink Other:

Visible clumps: yes no Comments: _______________________________

Description of periphyton (attached to canal walls):

Description:

______________________________________________________________________

Depth less than 15 cm:

Approximate thickness of mat: _____ cm Comments: ________________________

Color of mat (circle): Green Blue-green Brown or goldish-brown Black Other:

________________

Depth 15 – 30 cm:

Approximate thickness of mat: __________ cm Comments: __________________

Color of mat (circle): Green Blue-green Brown or goldish-brown Black Other:

________________

Depth greater than 30 cm:

Approximate thickness of mat: ______ cm Comments: ______________________

Color of mat (circle): Green Blue-green Brown or goldish-brown Black Other:

________________

Field measurements:

Temp (

C - DO): ______ D.O. (mg/L): ______ Temp (

C - pH meter): ________ pH: ______

Odor in water sample:

Odor strength (circle one): Strong Medium Weak Absent

Odor (circle): musty earthy moldy fishy sulfidic grassy chlorine Other

66

Samples collected:

Used scraping device? (yes or no) _________ # of scrapes (2 if possible) _____________

Comments:

____________________________________________________________________________

67

APPENDIX B

DESIGN AND OPERATION OF PERIPHYTON SAMPLER

A periphyton sampler was designed for this project. The periphyton sampler is a

rectangular chamber, measuring 25 cm long, 18 cm wide and 18 cm high. The upper

part of the chamber is made of a clear PVC plate, whereas the bottom is a metal plate

with a 10 x 15 cm open area (0.015 m

). The side of the chamber facing the canal bank

is a small slot through which a wire pool brush inside the chamber is attached to a

telescoping pole. The upstream side of the chamber has a large opening that is

covered by a fine plastic screen that allows water to flow through the chamber. The

downstream side of the chamber is a large circular opening with an attached plankton

net (80 um mesh). Two people are required to collect samples. The sampler is placed

on the canal wall and held into position with the telescoping pole by one person. A

second individual brushes the wall a predetermined number of times. As periphyton

mats are removed from the canal wall, they are carried by water flow into the plankton

net. Because vertical zonation of periphyton is evident on canal walls, sampling is done

at three depths (just below the surface and at 30 cm intervals. The three samples are

composited and stored in a sterile whirl-pak bag at 4

C until laboratory analysis.

Diagram of the periphyton sampler. Sampler consists of A, a rectangular chamber with an open window

(10 x 15 cm) on the bottom plate; B, a plankton net; C, a plastic screen with metal frame (D); E, two

telescoping poles; and F, a wire pool brush.

68

APPENDIX C

SPME METHOD FOR MEASURING MIB AND GEOSMIN

Twelve (12) ml of sample is added to a 25 ml septum capped vial that contains 4 g

desiccated sodium chloride. An internal standard (10 ng/L IPMP, Sulpelco #47527 U) is

added through the septum and the vial is placed in a heat block 50

1.5

C. A SPME

fiber (Supelco # 57348 U) is introduced into the head space through the septum and the

sample is shaken for 30 minutes. The fiber is removed from the vial and inserted into

the gas chromatograph injector at 250

C for 5 minutes. The fiber is then retracted into

the holder, removed from the GC inlet and reused for the next sample. Compounds

from the fiber are desorbed in the column gas chromatograph (MDN-5 capillary column;

Supelco, Pennsylvania) and eluted into a mass spectrometer set for selective ion

monitoring (selective m/z values: MIB = 95, geosmin = 112 and IPMP = 124, 136).

Calibration curves are generated using MIB and geosmin standards (mixture standard:

Supelco # 47525 U). Analysis of MIB and geosmin was performed on a Varian Star

3400 CX gas chromatograph and mass spectrometer (GC/MS). (QA/QC analysis of

MIB measurements by the City of Phoenix and ASU labs has shown a nearly 1:1

correlation (actual slope was 0.95), and a statistical R

value of 0.72 for approximately

150 samples since inception of the project.) The method detection limit (MDL) for MIB

and geosmin is ca. 1ng/L ng/L.

69

APPENDIX D

TEST PROTOCOL FOR EVALUATING

PAC MIB ADSORPTION CAPACITY

A PAC slurry should be prepared by adding 1000 mg of PAC to 1 liter of 0.45

m filtered

water and allowed to hydrate overnight while being mixed with a magnetic stir. Filter

approximately 2 liters of raw water and spike with MIB and geosmin to give a

representative concentration (e.g., 30 ng/L). Fill amber glass bottles (no headspace;

250 mL) with this water sample. The hydrated PAC slurry will have a PAC

concentration of 1 mg/ml. Select representative PAC doses for the performance-based

experiments (e.g., 15 mg/L). Calculate the volume of PAC slurry (V

PAC

) required for

addition to the 250mL sample (e.g., a PAC dose of 15 mg/L would equate to 3.75 mL of

PAC slurry); remove and add V

PAC

of the PAC slurry to the 250 mL amber bottle. Using

a magnetic stir or wrist-shaker, rapidly agitate the bottle containing the water sample

and PAC for a desired period representative of average HRT of the presedimentation

basins (e.g., 1 to 4 hours). Immediately after the prescribed agitation period use a

syringe-filter (0.2

m) and filter the water sample/PAC mixture. Collect the filtrate in a

100 mL amber vial (no headspace). Conduct MIB and geosmin analysis on the filtrate.

Repeat for each PAC brand, and repeat for a blank (no PAC added). Calculate the

fraction of MIB remaining: C/C

where C

is the MIB or geosmin concentration in the

blank and C is the concentration after contact with the PAC. Compute the Index Value

based upon the fraction of MIB remaining (C/C

) and the unit cost of the PAC (e.g.,

$/lb):

Index Value = [C/C

] x [PAC unit Cost]

Equation D.1

The PAC brand with the lowest Index Value is the most cost-effective. This assumes

that there are no limitations to PAC feed rates. For example, to achieve a desired MIB

removal, one PAC brand may require 40 mg/L of PAC while a more expensive PAC

brand may only require 30 mg/L of PAC feed. Therefore, the actual fraction removed

(C/C

) should be examined. High PAC feed rates can increase the frequency of PAC

shipments, sludge production, handling costs and maintenance on equipment, etc.

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