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The Science of Particle Removal

Coagulation and flocculation are essential physicochemical processes that transform microscopic, stable particles into larger, settleable flocs that can be efficiently removed from water.

Colloidal Stability

Natural particles in water carry like charges that keep them suspended. Understanding this stability is key to effective treatment.

Charge Neutralisation

Coagulants introduce opposite charges that neutralise particle surfaces, destabilizing colloids and enabling aggregation.

Bridging Mechanism

Long-chain polymers physically bridge between particles, creating larger flocs that settle rapidly.

Enmeshment

Hydroxide precipitates formed by metal coagulants physically trap and sweep particles from solution.

From Colloids to Settleable Flocs

Coagulation

Rapid mixing of coagulant with water to destabilise colloidal particles through charge neutralisation.

Mixing Time: 10-60 seconds
G-Value: 300-1000 s-1

Flocculation

Gentle mixing promotes particle collisions, allowing microflocs to aggregate into larger, visible flocs.

Mixing Time: 15-30 minutes
G-Value: 20-80 s-1

Separation

Large flocs settle by gravity or are removed by flotation, leaving clarified water.

Options: Sedimentation, DAF, Filtration

Types of Coagulants & Flocculants

Aluminium Sulphate (Alum)

Traditional coagulant effective over a wide pH range (5.5-7.5). Economical choice for municipal and industrial applications.

Best for: General purpose, drinking water

Ferric Chloride

Highly effective coagulant that works at lower pH and temperatures. Produces dense, fast-settling flocs.

Best for: Cold water, phosphorus removal

Polyaluminum Chloride (PAC)

Pre-polymerized aluminium coagulant with lower alkalinity consumption and reduced sludge production.

Best for: Low alkalinity water, reduced sludge

Ferric Sulphate

Alternative iron-based coagulant with good performance across pH range 4-11.

Best for: Industrial wastewater, colour removal

Anionic Polymers

Negatively charged polymers ideal for inorganic solids and mineral slurries. High molecular weight for effective bridging.

Best for: Mining, sand washing, mineral processing

Cationic Polymers

Positively charged polymers effective for organic solids and biological sludge conditioning.

Best for: Municipal sludge, food wastewater

Key Design Parameters

Rapid Mixing Time10 - 60 seconds
Rapid Mixing G-Value300 - 1000 s-1
Flocculation Time15 - 30 minutes
Flocculation G-Value20 - 80 s-1
Coagulant Dose (typical)5 - 50 mg/L
Polymer Dose (typical)0.5 - 5 mg/L
Optimum pH Range (Alum)5.5 - 7.5
Optimum pH Range (Ferric)4.0 - 7.0
Temperature EffectHigher doses needed at low T

Why Coagulation-Flocculation Works

High Removal Efficiency

Achieves 90-99% removal of suspended solids, turbidity, and associated pollutants.

Pathogen Reduction

Removes 90-99% of bacteria and viruses attached to particles.

Rapid Treatment

Complete process in 30-45 minutes compared to hours for advanced biological treatment.

Compact Footprint

Physicochemical systems require significantly less space than biological alternatives.

Related Equipment & Systems

Chemical Dosing Systems

Precision coagulant and polymer dosing equipment for accurate chemical delivery.

View Dosing Systems

Rapid Mixers

High-intensity mixers for rapid dispersion of coagulants throughout the water stream.

Flocculation Basins

Designed for gentle, controlled mixing to promote floc growth without shear damage.

DAF Systems

Dissolved air flotation for removing light flocs and oils that don't settle easily.

View DAF Systems

Lamella Clarifiers

High-rate sedimentation for efficient floc removal in a compact footprint.

View Clarifiers

Polymer Stations

Automated polymer preparation systems for optimal flocculant activation.

View Polymer Stations

Coagulation Science & Equipment Guides

In-depth physics, chemistry and equipment guides for coagulation and flocculation

Electrical Double Layer & DLVO

Zeta potential, the double layer and the DLVO balance of attraction and repulsion that keep colloids stable.

View Guide

Charge Neutralisation & Sweep Floc

The four coagulation mechanisms and the dose, pH and mixing that select between them.

View Guide

Mixing Energy, G & Camp Number

Velocity gradient G, the Camp number Gt, Smoluchowski kinetics and tapered flocculation design.

View Guide

Jar Testing & Dose Optimisation

Dose and pH matrices, mixing simulation and translating bench results to plant set-points.

View Guide

Coagulant & Polymer Selection

Alum, ferric, PACl and polymers compared by optimum pH, dose, sludge and acid demand.

View Guide

Mixing & Clarification Equipment

Flash mixers, flocculators, lamella and conventional clarifiers, DAF and polymer make-up systems.

View Guide

Related Pages

Daf Automated Operation

Fully automated DAF systems with PLC and SCADA control.

View Page

Daf Design Sizing Guide

Complete engineering guide to DAF system design including hydraulic loading, air-to-solids ratio, saturator sizing, coagulation.

View Page

Daf Food Processing

DAF systems for food processing wastewater treatment.

View Page

Daf Hydraulic Loading

Design DAF systems for correct hydraulic loading.

View Page

Daf Manufacturing

DAF systems for manufacturing wastewater treatment.

View Page

Daf Micro Bubble Technology

Advanced microbubble generation for superior DAF performance.

View Page

Option H: EC Containerised

Containerised electrocoagulation systems for heavy metals, emulsified oils, colloidal solids, paint wastewater.

View Containerised Option

Process Tanks

Flash mix and flocculation tanks for rapid coagulant dispersion and gentle floc growth.

Flash Mix TanksFlocculation Tanks

Optimise your coagulation process

Our engineers can help you select the right chemicals and design the perfect system.

Industries We Serve

Our expertise spans multiple industries with sector-specific water treatment solutions.