Flocculation and Sedimentation Water Treatment

Flocculation and sedimentation are technological processes used by Veolia Water Technologies South Africa (Veolia) within water treatment cycles to make water safe to drink or for water reuse. Flocculation and sedimentation cannot occur without coagulation, and some of Veolia’s patented Hydrex® water treatment chemicals are used to facilitate all of these processes. 

Coagulation, flocculation and sedimentation processes in wastewater treatment and water treatment are significant. Coagulation destabilises particles through chemical reaction between coagulant and colloids, and flocculation transports the destabilised particles that causes collisions with flocs. Essentially, a coagulant is added to water in order to gather any waste in the water such as dust, earth particles, fish eggs, etc., into flocs. As these flocs are heavier than water they settle at the bottom of the sedimentation tank resulting in the removal of 90% of the suspended matter.



A process wherein colloids come out of suspension in the form of floc, either spontaneously or due to the addition of a clarifying agent. It is used in applications like water purification, sewage treatment, cheese production and brewing, for example.


When particles suspended in fluid, such as dust and pollen or solutions of single molecules like proteins and peptides, settle out of the fluid and come to rest against a barrier. This action is in response to gravitational forces, centrifugal acceleration or electromagnetism.


A chemical process that involves a neutralising charge on the particles. This occurs when a coagulant is added to water to destabilise colloidal suspensions. The coagulation and flocculation in water and wastewater treatment processes can be used as a preliminary or intermediary step between other water or wastewater treatment processes like filtration and sedimentation.

Image of an Actiflo® plant with discharge in action.

Veolia’s patented Hydrex™ range of water treatment chemicals optimises the entire water cycle while reducing treatment plants’ operating and maintenance costs. 

Hydrex® Chemicals For Water & Wastewater Treatment

Veolia’s range of patented Hydrex® chemicals used in drinking water treatment, potable water treatment and wastewater treatment are ISO certified, with selected products carrying the SABS Food Grade mark of approval.

Used in both municipal water treatment and industrial water treatment, the Hydrex 3000 Series is the approved filtration in water treatment for potable water applications, while its sister series, the Hydrex 6000 range, is used in sewage treatment plants, industrial processes and industrial wastewater treatment, aiding in flocculation in wastewater treatment. Both the Hydrex 3000 and 6000 allow for sedimentation with coagulation.

Hydrex™ 3000 series: Flocculants and polymers

Primarily used for potable water clarification in bottling plants and sewage water treatment systems, they provide advanced sedimentation in water treatment for mining and industrial applications and provide clarification of water streams as well as removing turbidity and solids cost-effectively. It makes dirty water cleaner and therefore covers a wide spectrum of applications.

The product series includes scale and corrosion inhibitors, flocculants, coagulants and Green chemistry. 

Hydrex™ 6000 series: Wastewater chemicals

With emulsions, organic & inorganic coagulants, and powders & beads that deliver state-of-the-art clarification and wastewater chemistry and application exposure, this product series includes coagulants, flocculants, antifoaming agents, odour control, metal removal and Green chemistry.

Veolia provides full technical, operations and maintenance support so your plant remains in peak operating condition and the water meets all required standards.

Water Clarification Treatment

Cross-section schematic of Actiflo® technology in

Clarification water treatment is used as a pre-treatment to other purification processes used in municipal wastewater and drinking water, as well as in industrial effluent. It can also be used as a specialised application to remove oil and grease in industrial effluents.

To ensure the optimum use of space and speed of water clarification with increased efficiency, Veolia uses and advocates its patented high rate clarification treatment Actiflo® and Multiflo™ water clarification systems. Each can be retrofitted into existing water purification systems to increase plant capacity, and they can also be supplied as a pre-package system.

Actiflo® and Actiflo® Turbo

  • Actiflo® is a high-rate compact water clarification process in wastewater treatment and water treatment. Microsand enhances robust floc formation and acts as ballast, helping to increase their settling velocity. The microsand ballasted flocs allow for short retention time clarifier designs and high rise rates. Its compact system footprints are up to 50 times smaller than other similar capacity clarification processes.
  • Actiflo® Turbo is referred to as the ‘Ultimate Clarifier’. It incorporates the best in water clarification performance, and is compact, fast and flexible. The process covers many applications and can be integrated into more than one treatment chain to produce potable water of high quality. The system is equipped with a flocculation tank that contains a Turbomix™ draft tube reactor which reduces the footprint of ACTIFLO® and MULTIFLO™. It also enables the addition of water softening chemistry for a variety of applications.

Multiflo™ and Multiflo™ Trio

  • Multiflo™ is an advanced clarification technology incorporating chemical precipitation with sludge thickening. Extremely efficient at removing high quantities of precipitated solids from water, other operational benefits include a small footprint, low concentration of suspended solids in treated water, low sensitivity to operational upsets and lower operational costs when compared to conventional clarifiers.
  • Multiflo™ Trio provides a solution to remove high levels of arsenic and heavy metals from water and combines the coagulation, flocculation and settling stages in an efficient process. In addition, it removes suspended solids and colour, produces a high thickened sludge concentration, softens water and is easy to build and operate.

All of Veolia’s products and components are sourced from reputable suppliers and OEMs locally and internationally, providing our customers with the highest quality products that achieve the highest possible water quality.

Case Studies

Tubatse Ferrochrome smelter

A R100 million project that turned the Tubatse ferrochrome smelter in Steelpoort into a zero effluent plant to conserve the water in the Steelpoort River. It does this by assisting with the reuse of wastewater without the risk of salinating process water. The plant treats all water outflows on the smelter's site including industrial effluent containing a high concentration of dissolved salts, industrial storm water, treated sewage water and contaminated groundwater. These sources are contained in a balancing dam and then fed to Veolia’s patented high-rate package plant Actiflo® clarifiers to remove suspended solids and some precipitated salts. Click here to read the full case study.

Sasol South Africa

Veolia was responsible for the design, construction and commissioning of a cooling towers blowdown reuse construction of water treatment plant and water purification installations. Multiflo™ 300 was used for flocculated water and cold lime softener and other technologies and solutions, including submersible membrane, ion exchange softening, reverse osmosis and a mixed bed polisher. Read more about this case study here.

Evander Gold Mine

A full operation and maintenance agreement where Veolia manages the entire water treatment system. Veolia supplied 12 new treatment solutions, including new chemical dosing stations; flocculants, coagulants, anti-scalant and micro-biocide chemical treatment; a semi-automated duplex flocculent plant; and coagulant plants to address the water treatment challenges. A Veolia specialist remains onsite for the duration of the contract providing 24/7 technical direction, support and consultancy. Read the full case study here.

Jozini-Ingwavuma Bulk Water Supply project

A government initiative to create a sustainable solution to the uMkhanyakude District Municipality's (KwaZulu-Natal) water shortages. Veolia supplied a turnkey water treatment plant, addressing all facets of water treatment from sedimentation and clarification to filtration and disinfection, to produce 20 ML of potable water a day at the Shemula Water Treatment Plant. Veolia was responsible for phase 1B, which entails a turnkey water treatment solution, including civil, mechanical and electrical work. The full case study can be accessed here.

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