1. Introduction
Electrocoating (e-coat) wastewater is characterized by low pH (acidic), high COD, and the presence of resins, surfactants, and trace heavy metals. Direct discharge or conventional treatment is often challenging. During the pretreatment stage, flocculation and sedimentation are critical for removing suspended solids and colloidal substances. As a high-efficiency flocculant, the ionic type and molecular weight of Polyacrylamide (PAM) directly influence treatment performance.
This study evaluates five types of PAM (at 1‰ concentration) using real e-coat wastewater (initial pH = 4) through jar tests, aiming to provide data support and product selection guidance for engineering applications.
2. Experimental Conditions and Methods
2.1 Wastewater Sample
- Source: Comprehensive wastewater from an electrocoating line (including degreasing, phosphating, and e-coat rinsing)
- Initial pH: 4 (strongly acidic)
2.2 Conditioning Reagent
- 5% alkali solution, added at 0.3 ml per test (to adjust pH to neutral or slightly alkaline range for optimal flocculation)
2.3 PAM Products Tested (All as 1‰ aqueous solutions)
| No. | Product Code | Type |
|---|---|---|
| 1 | HRFLOC A623 | ANIONIC PAM |
| 2 | HRFLOC C8040 | Cationic PAM |
| 3 | HRFLOC C8060 | Cationic PAM |
| 4 | HRFLOC C8038 | Cationic PAM |
| 5 | HRFLOC C8038v | Cationic PAM |
2.4 Experimental Procedure
- 30 ml of wastewater was placed into a beaker.
- 0.3 ml of 5% alkali solution was added (initial pH adjustment).
- 0.1 ml of each respective PAM solution (1‰) was added.
- The mixture was gently stirred and then allowed to settle while observing floc formation and sedimentation.
3. Experimental Results
The observations showed:
All five PAM products exhibited good flocculation and sedimentation performance.
From left to right (HRFLOC A623 → HRFLOC C8038v), flocs formed rapidly, were clearly visible, the supernatant was relatively clear, and settling speed was favorable.
No significant stratification or floc breakup was observed, indicating that this e-coat wastewater has broad adaptability to PAM.
4. Discussion of Results
4.1 Characteristics of E‑Coat Wastewater Favor PAM
The main pollutants in e-coat wastewater are negatively charged organic colloids (e.g., resin particles, surfactants, emulsified oils).
PAM neutralizes these charges, compresses the double layer, and simultaneously acts as a bridging agent, aggregating fine suspended particles into dense flocs.
4.2 Importance of pH Adjustment
The original pH of 4 is acidic, which inhibits PAM flocculation activity. Adding a small amount of alkali (5% solution, 0.3 ml per 30 ml of water) raised the pH to near‑neutral conditions, significantly enhancing the hydrolysis and adsorption capacity of the PAM.
4.3 Why Multiple Products Performed Well
Although HRFLOC A623, C8040, C8060, C8038, and C8038v differ in molecular weight or cationicity, all belong to the cationic series. For this particular e-coat wastewater, the charge density and concentration of pollutants fell within the effective window of PAM, allowing all five products to respond rapidly.
5. Recommendations for Engineering Applications
Based on the experimental findings, the following practical guidance is provided:
- Flexible Selection Based on Cost and Site Conditions
Since HRFLOC A623, C8040, C8060, C8038, and C8038v showed comparable performance, the lower‑cost or faster‑dissolving product can be prioritized. - pH Pre‑adjustment is Essential
Adjust wastewater pH to 6.5–8.0 before PAM addition, using 5–10% alkali solution or lime milk. - Recommended Dosage Reference
Based on the experimental ratio (0.1 ml of 1‰ PAM per 30 ml of wastewater), the initial engineering dosage is suggested to be 2–5 mg/L (as dry powder) , to be optimized according to actual effluent quality. - Combination with Inorganic Coagulants
If wastewater contains high levels of phosphorus or heavy metals, add inorganic coagulants such as Polyaluminum Chloride (PAC) or ferrous sulfate first, followed by PAM, forming an inorganic‑organic composite flocculation system.
6. Conclusion
- This jar test validated that all five PAM products (HRFLOC A623, C8040, C8060, C8038, and C8038v) exhibited excellent flocculation and sedimentation performance for this e‑coat wastewater.
- PAM effectively treats the negatively charged organic colloids in e‑coat wastewater. When combined with pH adjustment, rapid sludge‑water separation is achieved.
- It is recommended to prioritize PAM in practical applications and select the specific product based on cost and on‑site conditions.
