avon lake corrosion control study and orthophosphate ... · background avon lake water filtration...
TRANSCRIPT
Avon Lake Corrosion
Control Study and
Orthophosphate
Implementation
Andrew Skeriotis, Stantec
Greg Yuronich, Avon Lake Regional Water
Agenda
1 History and Background of Avon Lake
2 Lead and Copper in Water
3Avon Lake Corrosion Control Study
4 Implementation
5 Questions
Background
Avon Lake Water Filtration Plant
– Built in 1926- originally a 2 MGD
plant serving 1,000 people
– Serves 225,000 people in a 680-
square mile service area
– 85% of the water produced
goes outside of Avon Lake
– Seasonal approved capacity of
50 MGD in the summer and 40
MGD in the winter.
• 3 Million Gallons
• Scheduled to be in operation
November of this year
• Will compliment the new 3 million
gallon clearwells that went in to
service December 2016 to provide
increase in finished water storage
Plant Layout
LEAD…• Ever since Flint, lead is something no one
wants to hear mentioned in the same
sentence as their water system.
HOSPITAL IN FLINT, MI OCTOBER 2015
Avon Lake Pb and Cu SamplingMonitoring Period No. of Sites 90% Pb (μg/L) 90% Cu (μg/L)
1992 60 9.0 61.0
1993 60 6.1 96.8
1994 30 2.5 116
1995 30 < 2.2 75.2
1996 30 2.4 38.6
1999 30 5.6 80.0
2001 30 < 3.0 28.4
2004 30 < 3.0 90.8
2007 30 6.5 93.0
2010 30 < 3.0 49.5
2013 30 < 3.0 60.9
2016 30 < 3.0 52.0
• Neither Avon Lake Regional Water nor any of our
bulk customers have ever had a problem with
lead exceeding the action level.
• One action level exceedance would be one too
many and we wanted to make sure we maintain
the highest level of safety for our customers.
• After much internal discussion and debate, we
decided to start looking into ways we could
further safeguard our water…
Lead News Not Going Away
Anytime Soon…
Lead in Water
Sources of Lead and Copper:
1. Lead is rarely found in source water.
2. Lead release typically occurs in lead
service lines and household plumbing.
Factors that Influence CorrosionFactor Effect
Physical
- Flow- Corrosion rates have been observed to increase withincreasing and/or fluctuating water velocity
- Temperature - Increases corrosion rates and precipitation of CaCO3
Chemical
- pH- Low pH may increase corrosion rate; high pH mayprotect pipes and decrease corrosion rates
- Alkalinity- May help form protective CaCO3 coating; helps controlpH changes, reduces corrosion
- Dissolved oxygen- Increases rate of many chemical reactions, typically
increases corrosion, absence of DO can lead toanaerobic biological corrosion
- Chlorine residual Increases metallic corrosion, may form Pb coating
- Total dissolved solids (TDS) - High TDS increase conductivity and corrosion rate
- Hardness (calcium and magnesium)- Ca may precipitate as CaCO3 and thus provideprotection and reduce corrosion rates
- Chloride, sulfate- High levels increase corrosion of iron, copper andgalvanized steel
- Hydrogen sulfide - Increases corrosion rates
- Silicate, phosphates - May form protective films
- Natural color, organic matter - May decrease or increase corrosion
- Iron, zinc or manganese- May react with compounds on interior of pipe to formprotective coating
Biological
- Aerobic and anaerobic bacteria - May induce corrosion
Reference: (AWWARF/DVGW 1985 and USEPA 1984)
Corrosion Control Alternatives
• Calcium Carbonate Precipitation
• pH/Alkalinity/DIC Adjustments
• Phosphate Inhibitors• Silicate Inhibitors
Corrosion Control Alternatives
Carbonate PassivationOptimal Conditions (pH=9.3)
- Lowest theoretical lead solubility
- Extremely low copper solubility
- High pH values impact compliance with DBP regulations
- Very depositing water; potential for scale deposition in water pipes
- Reduced chlorine efficiency for disinfection
Calcium Carbonate PrecipitationOptimal Conditions (CCPP=6)
- Option is effective for corrosion control
- Sloughing off of deposits could result in periodic higher lead concentrations
- Difficult to maintain a uniform film throughout the distribution system
- Lines closed to WTP need to be flushed periodically
Polyphosphate Inhibitor - Tends to revert to orthophosphate reducing lead solubility
- Beneficial for other water quality concerns (sequestering agent)
- Potential for reduced lead solubility
- Uncertain effectiveness for corrosion control
- Potential for lead solubilizationif orthophosphate is not present
- Effectiveness depends on formulation characteristics
- Uncertain effectiveness for corrosion control
Treatment Option Advantages Disadvantages
Corrosion Control Alternatives
Orthophosphate Inhibitor - Effective for lead and copper corrosion control in similar systems
- Raw water is suitable for orthophosphate addition
- Lower pH value (lower TTHMs may increase
HAAs)- Lower chemical feed
requirements- Reduced corrosion
rates for various pipe types (iron, asbestos-cement, galvanized pipes, etc.)
- Potential for bacteria increase in distribution system (PO4 is a nutrient)
- Relatively long detention times for film formation
- Requires periodic flushing of distribution system
Treatment Option Advantages Disadvantages
Study Objectives
1. Present an overview of the LCR,
2. Analyze the stability of the raw and
finished water from Avon Lake
Regional Water,
3. Evaluates viable corrosion control
treatment alternatives, and
4. Outline a recommended corrosion
control plan for Avon Lake Regional
Water and their consecutive systems.
Overview of LCR
Avon Lake Water Quality Parameters
• Potassium permanganate 0.12 mg/L;
• Alum 27.5 mg/L;
• PAC 0.5 to 8.5 mg/L (on an as needed basis);
• Lime 3.5 mg/L;
• Chlorine 3.5 mg/L; and
• Sodium silicofluoride 1.3 mg/L.
Parameter Raw Water (Lake Erie)
WTP Finished Water
pH 7.8 7.3 Temperature, oC 11 11
Alkalinity, mg/L as CaCO3 91 81 Total Hardness, mg/L as CaCO3 120 124
Calcium Hardness, mg/L as CaCO3 109 114 Total Dissolved Solids (TDS), mg/L 167 170
Dissolved Inorganic Carbonate (DIC), mg/L as C 22 22
Avon Lake Corrosivity Parameters
OUTPUT
Calculated Parameters
Ca++
Hardness (mg/L as CaCO3)
Alkalinity (mg/L as CaCO3)
pH
CCPP* (mg/L CaCO3)
* Calcium Carbonate Precipitation Potential
Langelier Index
Buffer Capacity (mg/L-pH)
Acidity (mg/L as CaCO3)
Dissolved Inorganic Carbonate (mg C/L)
Ryznar Index
101
91
7.84
-3.65 -27.11
-1.17
30.86
110.03
8.59 9.43
22.6 22.6
Before
Chemical Adiition
After
Chemical Addition
-0.37
8.00
96.95
107.25
77.93
7.08
Treatment Alternatives
DescriptionAlkalinity and pH
Adjustment
Corrosion Inhibitor
Treatment
Inhibition
MechanismPassivation Passivation
Critical Water
Quality
Parameters
pH, Alkalinity, Dissolved
Inorganic Carbonate
(DIC), Total Dissolved
Solids (TDS), and
Temperature
pH, Alkalinity, DIC,
Metals of Interest,
Hardness, and
Temperature
Determining OCCT
Determining OCCT
Lead Solubility Diagram at various PO4
Doses (pH=7.5, I=0.005, T=25 ° C)
Considerations
Recommendations• Initiate the procedure for designing and installing
orthophosphate storage-and-feed facilities in accordance
with requirements of the RSWW.
• Ohio EPA (i.e., a backup feed pump and 30-days of storage).
• Develop the protocol for a rigorous program for initially
flushing the distribution system including coordination with
consecutive PWSs utilizing unidirectional flushing before the initial orthophosphate dose.
• Initiate a public educational program to inform the customers
for expected changes in the finished-water quality, especially during the initial application of the corrosion inhibitor. These
changes may be discoloration, red-water, sediment, and
taste and odor issues, however, the initial unidirectional
flushing will help alleviate many water quality issues. Keeping a customer comment log will help the PWSs target problem
areas.
Recommendations
• Inform the local wastewater treatment facilities
for the expected changes in the finished-water
quality and coordinate with the wastewater
treatment facilities (including the consecutive
PWSs) to minimize the potential problems
associated with the presence of phosphate and
the potential presence of zinc in the finished
water.
Implementation• Apply an initial orthophosphate dose of approximately 2 mg/L for a
3-month period; then reduce the dose to 0.5 to 1.0 mg/L.
Implement a partial-system testing program (coordinating with
consecutive PWSs) for corrosion control:
• After 3 months from the initiation of orthophosphate feed, flush the
system to remove any corrosion byproducts and tuberculation
utilizing unidirectional flushing coordinating with the consecutive
PWSs.
• After the system has settled down, collect 30, first-draw samples from
consumers’ taps in accordance with the LCR.
• These samples are to be used as the baseline for the current
treatment practice for corrosion control. Sample collection shall
also be coordinated with the consecutive PWSs.
Unidirectional Flushing vs.
Conventional Flushing
It has
begun!
Questions
Thank you for your time!