How SewTreat’s Plants Work

SewTreat’s range of Biological Wastewater Treatment Plants are developed to meet the demand for cost-effective, environmentally compliant solutions for the treatment of wastewater. As specialists in this field, SewTreat offers a customised solution that encompasses consultation, design, manufacturing, installation, construction and operational support. To understand more about the sewage treatment process, click on the phases below.

Screening is done at the point of entrance in the BWWTP. This can be done with either a manual or automated screen.

There are two anaerobic phases. The first phase allows for digestion of sewage and the separation of solids by means of specific gravity as some solids will settle at the bottom whilst others will settle at the top. The middle of the two sludge blankets has relatively low solids and flow through to the next phase is done by means of a middle cut. The second phase breaks down the fine sewage particles and alters the carbon dioxide and water. This ideal effluent passes to the aerobic phase. The de-nitrification cycle takes place in this phase. This function is responsible for breaking down of nitrates to nitrogen gas.

This phase is called aerobic digestion or in simpler terms, bioreactor. In this phase the digestion takes place in an aerated environment. This phase can be divided into two or three bioreactors following on each other, depending on the type of installation and the daily flow rate. The type of bacteria used in this environment is called aerobic bacteria and it is essential that dissolved oxygen transfer is optimal in this phase to ensure sufficient bacterial growth and efficiency. In this phase nitrification also takes place. Ammonia is broken down to nitrites and in turn the nitrites to nitrates. Fixed bed bio media (cross flow media) is used to enhance bacterial colonization. The bio media assists in oxygen transfer and hydraulic retention time which is effective in reducing BOD and nitrification.

The phase is also called the re-activated sludge cycle or clarifier phase. The cell material and settle able solids settle in this phase and form the so-called ‘sludge blanket’. The sludge blanket is critical to the process. When the blanket matures it is re-circulated to the anaerobic phase one to ‘seed’ or inoculate the raw sewage entering the plant and to alter the nitrates to nitrogen gas. This phase ensures that no sludge extraction is required as the bacterium continually break down the sludge, in essence creating a zero waste plant. The return of activated sludge eliminates the need for drying beds.

In the fifth and final phase, effluent is prepared for discharge. The effluent is disinfected or sterilized to prevent and harmful bacteria from entering the environment. The primary disinfection method used by SewTreat is ozone sterilization as this has no residual effect in the water. Chlorination or ultra violet systems may also be used, dependent on requirements.

Use of micro bubble diffusion allows optimal transfer of dissolved oxygen into water ensuring optimal biological action.

No need for final discharge effluent filtration by means of mechanical filtration as the final effluent is within legislative discharge requirements for discharge into the environment or use for non-potable uses.

The modularity of our systems offers a huge advantage for international clients. Plants can be added on to as needs increase.

The final effluent emerging from a SewTreat BWWTP contains no chemicals and is safe for re-use in terms of irrigation, dust suppression and discharge to the environment.

No permanent labour required to operate the plant.

Low electricity consumption.

Low operating and maintenance costs.

Plants range in size from those suitable for single households up to large industrial systems.

Minimal footprint and reduced land requirement.


4 Chopin Street,



South Africa


+27 13 590 6683

Addie de Wit (Sales): 079 045 1527

Theunis Coetzer (Technical Sales): 082 383 1178