Odor Control

Q. Dave, how do I keep the odor at bay on a three-stage iron phosphate spray line?

The majority of the stench is in the first rinse after the cleaner phosphate. The rinse is changed at 500 ppm, second rinse at 200 ppm. Due to the economy, the washer is only being used two to three times a week. We presently use calcium chloride tablets on our e-coat washer rinses, per our paint supplier at 1–3 ppm to maintain cleanliness. We also use hydrogen peroxide as a disinfectant for our R.O. storage system, and sodium hypochlorite as a disinfectant in wastewater treatment. What do you recommend for three-stage washer rinses, and what effects will it have on paint/powder adhesion? Thank you.

Looking for some fresh air, K.P.

A. It appears that you have some options available to you to try in-house. I would stay away from the bleach since that is such a strong oxidizer and could alter the chemistry of your pretreatment system and affect the quality of your phosphating. The phosphate stage will typically be formulated with an oxidizing agent to accelerate that reaction, but introducing an uncontrolled level of another oxidizing agent to that stage is inadvisable. Additionally, I do not recommend the use of hydrogen peroxide for similar reasons.

However, if you have found the calcium chloride tablets from your e-coat washer rinses to be effective, I would extend their use to your phosphate system. Calcium chloride at the level you mention (1-3 ppm) would not affect the subsequent phosphating stages or paint quality. I expect you could go higher than this without detriment to the quality of the powder coating.

Related Content

NASF/AESF Foundation Research Project #122: Electrochemical Approaches to Treatment of PFAS in Plating Wastewater - 6th Quarterly Report

The NASF-AESF Foundation Research Board has selected a project on addressing the problem of PFAS and related chemicals in plating wastewater streams, studying PFAS destruction via electrooxidation and electrocoagulation. This sixth quarter report covers the continued assessment of eight perfluoroalkyl acids PFAAs most commonly found in wastewaters, by electro-oxidation with a Magnéli phase Ti4O7 anode across a range of anodic potentials in solutions, exploring the reaction mechanisms. To summarize, the PFAAs start to exhibit degradation behavior when the anodic potential reaches a level where water oxidation occurs, suggesting that the hydroxyl free radicals generated via water oxidation play a role in PFAA degradation.
NASF/AESF Foundation Research Project #122: Electrochemical Approaches to Treatment of PFAS in Plating Wastewater - 12th Quarterly Report

This NASF-AESF Foundation research project report covers the 12th quarter of project work (October – December 2023) at the University of Georgia. In our previous report, we described our work on performance and effect of surface fluorinated Ti4O7 anodes on PFAS degradation in reactive electrochemical membrane (REM) mode. This quarter, our experiments involved utilizing porous Ti4O7 plates serving both as anodes and membranes. Tests compared pristine and F-18.6 Ti4O7 anodes at current densities of 10 mA/cm2 and 40 mA/cm2. This 12th quarterly report discusses the mechanisms of the effects on EO performance by anode surface fluorination.
NASF/AESF Foundation Research Project #120: Electrochemical Destruction of Perfluorooctanesulfonate in Electroplating Wastewaters - April 2022-March 2023

This NASF-AESF Foundation research project report covers project work from April 2022 to March 2023 at the University of Illinois at Chicago. The overall objective of this work is to utilize a cost-effective reactive electrochemical membrane (REM) for the removal of PFAS from synthetic electroplating wastewater. Initial results for the oxidation of PFOA with three different catalysts are discussed.