CITY OF PITTSBURG

Water Treatment Plant

Operations and Modifications

Presenters:

Walter Pease, Director of Water Utilities

Ana Corti, WQA / Lab Director

Treatment Plant Characteristics

• Water Treatment

• 16,500 service connections (some of which provide water to commercials and industrial users).

• 9 employees at Water Treatment Plant

Innovation

Description

• New SCADA System, installation of sludge collection system, Water Treatment Plant upgrade, and conversion to Chlorine Dioxide as pre-oxidant.

Type of Innovations

• Increased use of Information Technology

• New treatment process

• Optimization of existing resources

MOTIVATION FOR INNOVATION AND BENEFITS

Historical Demand

Water treatment Plant Phases.

• 1953 8 MGD

• 1973 16 MGD

• 1990 32 MGD

Motivation for Innovations

Preparing for 50 percent growth in Water Treatment Plant demand

Benefits

• Will achieve better water quality and probably lower treatment costs

Water Sources

Our water Sources.

– Contra Costa Water District canal (surface water) – Lake – Rossmoor and Bodega Wells (groundwater)

• The water comes in through pipelines. We can take water from either the wells, lake or just directly from the canal.

• We can blend sources for best treatment results.

Our Challenge on Water Treatment

1. Physical. Material that do not dissolve in water and make the water appear “dirty”.

2. Chemicals. Substances dissolved in the water from both natural and man made. (Iron and Manganese removal)

3. Biological. Viruses, bacteria, algae and other small living organisms. (Seasonal Algae Blooms Causing Water Taste and Odor Issues)

Water Treatment Process

Large particles

and debris are

removed from the

raw water by

travelling screens

as the water

enters into the

treatment plant at

the headwork

Coagulation

• Rapid mixing of chemicals known as coagulation

COAGULANTS

• ALUM ( Al2(SO4)3

• POLYMER

groups of chemicals know as

polyelectrolytes large positive

charged attract negative charged

(like clay particles).

Flocculation

• In our flocculator basins, the water is gentle mixed. This allows the proper conditions for our floc to form.

• Next, the water is slowed down as it travels through the sedimentation basins. These big basins allow the water to stand still long enough that the floc can settle out.

Sedimentation

• The flocculated water flows into a sedimentation basin, where the water flows slowly so floc can settle to the bottom by gravity.

Filtration

• After sedimentation, the water passes through the filter to remove the remaining suspended impurities and floc.

• The filter materials are made of anthracite carbon and sand with support gravel

DISINFECTION.

FLUORINATION

We add additional fluoride after the filtration to raise the level to 0.8 mg/L.

Sodium Hydroxide.

The pH of the water is raised from approximately 7.5 to range 8.4 to 8.5 by adding NaOH

We use chloramine for our disinfection proses.

Chloramines are formed during a reaction between chlorine (Cl2) and ammonia (NH3).

Finished Water

• Two cover tanks storage the water before it enter the distribution system.

(1MG and 5MG)

• Storage ensures enough time for the chloramines provide adequate disinfection

Laboratory

• This is the laboratory where we do several different tests on the water. Each day we test for hardness, pH, alkalinity, Total Dissolved Solids, Conductivity and more. We also perform bacteriological tests 2 times a day on the finished water. Some testing is done every 4 hrs.

The Benefits of Chlorine Dioxide in Water Treatment

Presentation Outline

• Benefits of Chlorine Dioxide in Water Treatment

• City of Pittsburg WTP Iron/Manganese Problem

• Proposed ClO2 Facilities

• Bench-Scale Testing Results and Conclusions

• Summary and Recommendations

Introduction

• Chlorine dioxide (ClO2) is a soluble gas but is very volatile

• ClO2 is an USEPA- and CDPH-approved alternative disinfectant (>800 installations in North America)

• ClO2 is more effective than Cl2 for inactivating Giardia and Cryptosporidium

• ClO2 is a selective strong oxidant

• MCL of chlorine dioxide is 0.8 mg/L

• MCL of chlorite (ClO2-) is 1.0 mg/L

Benefits of ClO2 in Water Treatment

• Strong disinfectant @ pH 2-10

• THM and HAA Reduction

• Effective for Fe/Mn Oxidation

• Taste and odor reduction

• Algae control

• Enhance coagulation-flocculation-filtration

• Nitrification prevention in distribution systems

• Much lower capital cost vs. ozone (O3)

IPMP: ClO2 > Cl2 > MnO2 > O3 > KMnO4

IBMP: ClO2 > Cl2 > MnO2 > O3 > KMnO4

MIB: ClO2 > O3 > Cl2 > MnO2 > KMnO4

TCA: ClO2 > MnO2 > O3 > Cl2 > KMnO4

Geosmin: ClO2 > O3 > MnO2 > Cl2 > KMnO4

Taste and Odor Removal Oxidant Comparison

Brown and Caldwell 18

City of Pittsburg WTP Fe/Mn Problems.

• Design capacity – 32 mgd (conventional processes) • Raw water – mostly 80 % Contra Costa Canal water, 10-20%

well water and recycled backwash water • Fe/Mn from two wells • KMnO4 used for Fe/Mn Oxidation • Chloramine as primary disinfectant (no free Cl2 contact) to

control THM and HAA5 • KMnO4 generates extra MnO2 (Manganese oxide) in sludge • Mn re-solubilizes in sed basins and backwash storage pond • Proposed to replace KMnO4 (Potassium permanganate) with

ClO2 for Fe/Mn oxidation with other benefits in WTP upgrade

Existing PFD of Pittsburg WTP

Brown and Caldwell 21

Proposed PFD of Pittsburg WTP

Brown and Caldwell 22

Proposed Site Plan

Proposed ClO2 Generation System

Location of New ClO2 Generators

Bench-Scale Testing

• Testing required by CDPH for new ClO2 use

• Pilot or full-scale testing not feasible

• Objectives of bench-scale testing

– Verify ClO2 demand

– Verify Fe/Mn oxidation

– Effects on THM and HAA5 formation

– Effects on NDMA formation

Bench-Scale Testing Plan

Previous ClO2 Demand Result

Sample Time (minutes)

Initial ClO2 (mg/L)

Residual ClO2 (mg/L)

ClO2 Demand (mg/L)

Raw Water 0 0.0 0.07 ---

10 0.47 0.15 0.32

10 1.00 0.64 0.36

10 1.47 1.09 0.38

Average 0.35

New ClO2 Demand Results Time of Reaction, min ClO2 Dosage, mg/L ClO2 Residual, mg/L ClO2 Demand, mg/L

5 1.5 1.02 0.48

10 1.5 0.96 0.54

15 1.5 0.84 0.66

30 1.5 0.77 0.73

Average 0.60

5 1.0 0.52 0.48

10 1.0 0.49 0.51

15 1.0 0.41 0.59

30 1.0 0.36 0.64

Average 0.56

5 0.5 0.20 0.30

10 0.5 0.18 0.32

15 0.5 0.17 0.33

30 0.5 0.16 0.34

Average 0.32

Typical Fe and Mn Oxidation Results

Sample Total Fe, mg/L

Dissolved Fe, mg/L

Total Mn, mg/L

Dissolved Mn, mg/L

WTP Influent 0.23 <0.05 0.059 0.040

Treated with 1.5 mg/L ClO2

0.23 <0.05 0.058 0.0078

Treated with 1.0 mg/L ClO2

0.21 <0.05 0.056 0.0070

Treated with 0.5 mg/L ClO2

0.23 <0.05 0.056 0.0053

DBP Formation Effects

Results of September 25, 2013 DBP Formation Effects Tests

Sample

Total Organic Carbon

TOC, mg/L

Trihalomethanes

TTHM, µg/L

Haloacetic Acids

HAA5, µg/L

N-

Nitrosodimethyla

mine

NDMA, ng/L

Chlorine dioxide

ClO2, mg/L

Free Cl2, mg/L Chlorite, mg/L

WTP Influent 2.88 NA NA NA NA NA <0.01

ClO2 Treated 2.51 32.45 13.6 14 0.21 0.00 0.55

No ClO2 Treated 2.65 34.79 23.6 22 NA 0.00 <0.01

DBP Formation Effects 2/2 Results of November 13, 2013 DBP Formation Effects Tests

Sample TOC, mg/L TTHM, µg/L HAA5, µg/L NDMA, ng/L ClO2, mg/L

Free Cl2, mg/L

Chlorite, mg/L

WTP Influent 2.77 NA NA NA NA NA NA

ClO2 Treated 2.40 28.89 16.5 15 0.38 0.00 0.57

No ClO2 Treated 2.58 36.16 25.6 15 NA 0.00 0.015

ClO2 Treated at Lower Cl2 Dose

2.54 28.22 21.2 22 0.40 0.00 0.61

ClO2 Treated without Polymer

2.62 28.80 17.9 22 0.42 0.00 0.57

No ClO2 Treated Without Polymer

2.69 33.06 27.3 35 NA 0.00 0.008

Conclusions of Bench-Scale Testing

• ClO2 demand depends on dosage and reaction time

• ClO2 is effective for Fe and Mn oxidation

• A ClO2 dosage of 1.0 mg/L is appropriate

• ClO2 pre-oxidation reduces THM and HAA5 formation (more effective for HAA5 than THMs)

• ClO2 effect on NDMA reduction is neutral to positive

• Free Cl2 contact has more pronounced effect on NDMA reduction than ClO2

• Polymer used at the WTP does not appear to contribute to NDMA formation but helps to reduce NDMA via better coagulation to remove NDMA precursors

Summary and Recommendations

• Use of ClO2 for Fe and Mn oxidation at the WTP is effective and can provide other benefits such as DBP formation reduction, taste and odor reduction, and nitrification prevention

• Fe and Mn oxidation and DBP reduction have been verified by bench-scale testing

• ClO2 and free Cl2 contact can be used in conjunction to control NDMA, THM and HAA5 formation prior to chloramination

• Use of ClO2 to replace KMnO4 is recommended for implementation

CITY OF PITTSBURG WATER TREATMENT PLANT

• We are here to make sure the process is working and the water is safe before it leaves the plant.