A municipal wastewater treatment plant recently faced challenges in its sludge dewatering system, where belt filter press performance had declined, resulting in high sludge moisture, excessive polymer consumption, and unstable cake formation.

By introducing Hengfeng Cationic 9802 and optimizing the conditioning process, the plant significantly improved dewatering efficiency, reduced operating costs, and achieved stable, continuous operation.

Site Overview

Industry: Municipal wastewater treatment
Sludge type: Mixed primary and secondary (biological) sludge
Treatment capacity: 1,800–2,200 m³/day (sludge processing line)

Sludge characteristics:
High organic content, poor dewaterability, sludge concentration 0.8–1.2%, with high extracellular polymeric substances (EPS), making flocculation difficult.

Dewatering system configuration:

· Belt filter press units

· Polymer prepared at 0.1% concentration

· Gravity thickening + pressure zone dewatering

Initial Issues

· Sludge cake moisture content remained high at 82–85% 

· Filtrate turbidity was high, with visible solids carryover

· Flocs were small and weak, breaking easily under shear

· Polymer consumption was high, yet performance remained unstable

· Belt blinding and clogging occurred frequently, increasing cleaning frequency

Problem Analysis

After on-site evaluation, several key issues were identified:

1. Inadequate Polymer Performance

The previously used flocculant had insufficient charge density and molecular weight, leading to poor charge neutralization and weak bridging ability. Flocs formed were loose and easily destroyed in the press zone.

2. Poor Sludge Conditioning

The sludge was not fully conditioned before entering the belt press. Mixing intensity and reaction time were insufficient, resulting in incomplete floc formation.

3. High Organic Content Interference

Municipal biological sludge contains high levels of EPS and organic matter, which increases viscosity and water retention, requiring stronger cationic polymers for effective dewatering.

4. Non-Standardized Operation

Polymer preparation and dosing lacked consistency. Solution aging time was insufficient, and operators relied heavily on experience rather than structured control, leading to fluctuating performance.

Technical Solution

Optimized Polymer Selection

Hengfeng recommended Cationic Polyacrylamide 9802, featuring:

· Optimized cationic charge density

· High molecular weight for strong bridging

· Excellent adaptability to biological sludge

The product significantly improved floc size, density, and resistance to shear.

Process Optimization

Polymer preparation:

· Concentration increased to 0.15% 

· Aging time extended to 45–60 minutes to ensure full dissolution

Dosage control:

· Adjusted to 4.0–5.5 kg/t DS (dry sludge) 

· Fine-tuned based on cake dryness and filtrate clarity

Mixing optimization:

· Improved flocculation tank mixing to ensure sufficient reaction time

· Reduced shear before entering the belt press

Equipment Operation Adjustment

· Optimized belt speed and pressure distribution

· Balanced gravity drainage and الضغط zones

· Reduced over-squeezing, which previously caused floc breakage

Operator Training & Standardization

Hengfeng technical team provided on-site guidance to:

· Standardize polymer preparation procedures

· Establish visual floc evaluation standards

· Train operators to adjust dosage based on real-time performance

· Implement routine monitoring and record-keeping

This ensured stable and repeatable operation.

Performance Results

After implementation and continuous monitoring:

· Sludge cake moisture reduced to 75–78% 

· Filtrate became clear, with significantly reduced suspended solids

· Polymer consumption decreased by 15–20% 

· Flocs became large, dense, and resistant to shear

· Belt clogging was eliminated, reducing downtime and cleaning frequency

· Overall system achieved stable, continuous operation

Project Outcome

Through optimized polymer selection, improved sludge conditioning, and standardized operation, Hengfeng successfully enhanced belt filter press performance in municipal sludge dewatering.

This case highlights that effective sludge dewatering depends not only on equipment, but also on selecting the right flocculant and implementing proper process control.