Dissolved Air Floatation (DAF)

Dissolved Air Flotation clarifier utilises air floatation technology as clarification method. Our clarifier is designed based on ‘zero velocity’ water distribution and recovery concept to produce perfect clarification at high flows with minimum hydraulic turbulence. Zero velocity means that the speed at which the water enters the unit equals the speed at which it is discharged. The efficiency of the flotation is therefore greatly increased to near the maximum theoretical limits due to the least amount of turbulence in the tank.

The oil, solid and liquid separation occurs in the DAF clarifier. As the flocculated wastewater flows into the clarifier, it will combine with the dissolved air generated from Air Saturation Tube (AST). Bubbles will be released and will rise to the surface of water which carrying the suspended solids.

The trapped-solids will float on the top surface of water and will be collected by sludge spiral scoop for removal from the unit. The sludge will then be transferred to a holding facility for further treatment.

In practice, the water depth of open tank is only 400 mm, which means that better clarification can be carried out to have higher solid capture rate. At this operating level, the sludge collection scoop can remove higher volume of floated sludge without varying the scoop rate. The retention time for DAF clarifier is very low, water is processed from inlet to outlet in just 2-3 minutes only.

Advantages and key features of DAF system :

  • High loading rates, small footprint and significantly lower building costs.
  • Excellent oil and grease, colour and algae removal, final turbidity less than 1 NTU.
  • Independent settled sludge removal mechanism from scum removal at the top, reducing turbulence in clarified water zone.
  • Lower chemical usage, low operation cost.
  • Quick start-up and tolerant of changing raw water conditions.
  • Quiet, simple and easy-to-operate with minimal operator intervention.
  • Pre-assembled and pre-tested packaged plant often saves 50% or more over in-situ construction.
  • Automatic controls and monitoring systems customised to meet individual needs.

Sequential Batch Reactor (SBR)

SBR is a type of suspended growth activated sludge system. Specific bacteria are cultured in the SBR tanks to digest the dissolved organic matter. SBR system does not operate on a continuous cycle whereby a tank is required for each process. SBR is ‘fill and draw’ activated sludge system in which aeration, sedimentation and separation processes are carried out in the same tank but sequentially in alternate tanks.

SBR offers high flexibility, better control, easier monitoring, less prone to upset and higher organic removal efficiency for biological treatment.

SBR system consists of 5 processes phases as below

1.  Fill (Aerate)

At the beginning of the process, the reactor is at the minimum level and influent fills the reactor. Depending on the operating mode selected, oxygen can be supplied during the fill period or at the beginning of the react period.

2.  React         

During this period, aeration starts until complete biodegradation of BOD and nitrogen is achieved. After the substrate is consumed famine stage starts. During this stage some microorganisms will die due to lack of food and will help reduce the volume of settling sludge. The length of the aeration period determines the degree of BOD consumption.

3. Settle

After the preset oxygen concentration or cycle is reached, the aerators are shut off and the settling period begins. At this stage, the reactor functions as a quiescent clarifier with no internal movement or fluid flow, solid separation takes place, leaving clear treated effluent above the sludge blanket.

4. Decant

For decant, the discharge valve opens and the effluent withdrawal mechanism collects the clarified effluent. This removal must be done without disturbing the settled sludge. When the minimum water level is reached the discharge valves close. 

5. Idle

The reactor is not in use at this stage, until the cycle is repeated. The time in this stage can be used to de-sludge if necessary The frequency of de-sludging ranges between once each cycle to once every 2 to 3 months depending upon system design.

Rationales and Advantages of SBR

SBR system offers the following advantages to suit the purpose of providing the most economically suitable biological treatment system.

  • No secondary clarifier is required, thus no floating sludge or sludge carry-over problems.
  • More effective sedimentation under stagnant condition resulting in better Suspended Solid, BOD and COD in final effluent results.
  • Longer mean cell retention time, less sludge yield rates and is equivalent to Extended Aeration System.
  • Batch system provides more data for better control, monitoring and trouble shooting.
  • Oxygen supply can be cut off when reaction is complete and reduce energy consumption.
  • Aeration time (Reaction Time) can be varied by changing the time allocated to each stage as required.
  • Batch system provides self-equalization for each batch, which will homogenize the loading. In continuous system, variation of flow will upset the secondary clarifier.
  • Less maintenance on SBR system because only PLC and pneumatic valves are involved.
  • As with BOD removal, nitrification can be accomplished in attached growth biological processes along with BOD removal in the same single process.
  • The modified SBR system is able to employ double anoxic denitrification process by using BOD in the influent wastewater and the aid of additional carbon source. Nitrate removal may occurs in SBR during non-aerated settle and decant periods.


Ranhill Water Technologies Sdn. Bhd.
Suite 1203, Level 12, Plaza Permata,
No.6 Jalan Kampar, Off Jalan Tun Razak, 50400 Kuala Lumpur, Malaysia
Tel: +603-2716 5625/5606/5621 Fax: +603-2716 5626 Email: