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topic 51966

Theory of ED (electrodeposition/e-coating): anolyte, ultrafiltration, constituents, bacterial growth

A discussion started in 2005 & continuing through 2017


Q. Shall I add any of the following chemicals in the anolyte tank to reduce the Bacterial growth in E.coat process?
1. Silver Nitrate
2. 5-Chloro 2-methyl-4-Isothiazolin-3-one
3. Hydrogen Peroxide 33%

or Shall I put U.V sterilizer in the D.M water line to control bacteria ?

or Can you tell me best method to sort out the issue?

SARAVANAN [last name deleted for privacy by Editor]
wheels - Chennai, Tamil nadu, India


A. Before adding any chemicals you should seek the advice of your paint supplier.

The simplest way is to add Hydrogen peroxide and circulate for a few hours before draining the entire anolyte and refilling with fresh. Hydrogen peroxide will break down into water and nascent oxygen and will not be a threat to the paint bath.

Thereafter keep a close watch on the pH and maintain in within the range specified by the paint supplier.

Gurvin Singh
Coatec India
supporting advertiser
Mohali, Punjab, India
coatec india


Q. We are leading automotive wheel manufactured in india. Recently we are facing the following problem in our process plant. The problem was heavy algae formation in the anolyte solution. For that we are taking the following measures.

Electrocoating: a Guidebook for Finishers

1. Sent the algae to biological lab for test to know what type of algae.

2. Sent query to anode supplier for compatible in between anolyte and electrode membrane

3. How frequency it is growth

4. Sent query to chemical supplier.

During study we observed the algae formation started when the fresh solution preparation after 52 hrs circulation.

Anolyte flow rate drastically declined during this period from 2lit/min to 0.5 lit /min

Lab study shows the algae not water based it is sulphate reduced type algae.

UV sterilized only will kill water based algae only.

For that now we are doing instead of 7 days once cleaning the tank we reduced the frequency of 3 days.

I request to know more about to avoid the algae formation in the anolyte solution please sent suitable technical solution.


Fungus is growing in anolyte compartment of CED bath

CED is an acronym for Cathodic Electro Deposition, i.e., electrocoating or electropainting where the work is cathodic. The anodes are in in a compartment separated from the rest of the solution by semi-permeable membranes; the solution in the anode compartment is called "anolyte".


Q. Dear sir,
In my acrylic CED bath, the anolyte solution is continuously recirculated, in which I am maintaining pH <3 and conductivity >300 and <5500 for anolyte solution as per the acrylic resin product supplier specification. While bath ages, conductivity increases slowly and pH decreases correspondingly. Due to acidic pH, fungus are forming in the anolyte tank which leads to flowmeter and pipe line through which anolyte solution passing is blocked after few days. From your site I came to know that maintaining the anolyte conductivity in higher range will reduce the fungus formation.
1. Really it is true (high conductivity will reduce the fungus formation)?
2. If so, how to increase the conductivity of anolyte solution.

- Mumbai, India

July 10, 2013

A. Install a conductivity controller and sensor. This will maintain conductivity near a desired set-point by activating a fresh DI water valve.

Dan Mack
- Horicon, Wisconsin

Relation between thickness of CED coating and anolyte conductivity?

Handbook of Electropainting Technology


Q. Thickness problem: Is there any relation between thickness of CED coating & an anolyte conductivity

Avinash Vidhate
Director - Nashik, Maharashtra, India


A. There is no relationship between CED film thickness and anolyte conductivity as long as your CED bath conductivity and anolyte conductivity is with in the spec.

Anions(CH3COO-) are generated during CED process and it is moving to Anolyte system through semi permeable membrane at the anodes there by the conductivity of anolyte increases and replenished with DI (maintained with in the spec between 400 - 400 microsiemens). If anolyte system not removing the Anions then it will be remain in CED bath then the conductivity of bath slowly increases make difference in film formation.

Please check paint supplier for Bath conductivity and Anolyte conductivity spec.

P.M.Saravanan P.M.Saravanan
   paint shop manager
Chennai, Tamilnadu, India

April 24, 2009

Q. What is anolyte, theory of ultra filtration for ED paint, constituents of ED paint? -- because I am doing work In CED line.

Liaqat Bashir
Automotive - Tehran, Iran

May 12, 2009

A. Anolyte is a solution of DI water and an acid. The pH and conductivity of this is specified by the E-coat paint supplier. The acid to be added is normally called pH controller and is also supplied by the E-coat paint supplier. The function of anolyte is to conduct the charge from the anode to the paint and to carry away the acid generated in the anode cell into the anolyte reservoir.

The theory of ultrafiltration is much like the function of the kidney in the human body. The UF membrane removes water along with solvent and solublizer from the E-coat bath and this solution is called permeate. The permeate is recycled back into the E-coat bath after utilizing it for paint recovery. If it is drained it leads to unbalance of solvent and solublizer in the bath as well as the permeate tanks.

The constituents of ED paint is not part of public domain and will be covered under IPR. That in any case is not useful information for a user.

Gurvin Singh
Coatec India
supporting advertiser
Mohali, Punjab, India
coatec india

June 15, 2009

A. In addition to Mr Gurvin

E coat Paint is combination of D.I Water _ 85% + Emulsion + Paste _13% (Mainly Black, Grey primer)+ Solvent 2%.


What is the major function of anode cells in CED?

January 21, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Please anyone explain what is major functions of anode cells in CED bath?

vinodh Balu
- chennai,TN,INDIA

January 2015

A. Hi Vinodh. I don't know a lot about ED, but the major function of the anode cells is to complete the circuit since the work is the cathode :-)

Gurvin's explanation of the anolyte and ultrafiltration explains the situation a bit further.


Ted Mooney, Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

Can't get electrocoating voltage high enough

February 3, 2016

Q. Dear Experts,

Currently I'm facing voltage drop for my ED paint Anolyte Membrane.

Voltage using is 240 VDC to 350 VDC.

When testing without the load, it can reach the voltage that I set. But with load it can reach only 290 VDC even I set at Max side.
I suspect maybe our RECTIFIER is having a problem; please give advice on this matter.
One more thing, can anyone share the correct method to check whether Anolyte membrane Cell is Okay or NG?


August 18, 2017





September 25, 2017

A. Check with your paint supplier about using a small amount of biocide in the anolyte. Once you have bacteria, it needs to be mechanically removed (brushes, hosed out, etc.) You will know it when you have it because it resembles cabbage in the return tubes.

You can check for internal leaks by shutting off the anolyte pump and closing the supply and return for each membrane. The anolyte level in the leaking membranes will equalize with the level in the paint tank.

Dan Mack
- Horicon, Wisconsin

DI Water solution and Quality in E-Coating

October 9, 2017

Q. Hi ... I'm new to this and put into the deep end at my work place, concerning the e-coat line.

What is the water called, DI or DIY?
I know acids Hydrochloric Acid and Caustic must be added and the conductivity must be at a certain level. To get to the desired/acquired quality of DIY water.

Nico Schultz
Handyman / Maintenance - Port Elizabeth, South Africa.

How to heat E-coat tank for single shift operation?

November 9, 2017

I'm having problems with keeping the e-coat tank warm. We are only running one shift so the e-coat does not run during the night shift. What can I does to keep the temperature up?

Mark Grajewski
- Dayton Ohio

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