Project Description

Process Terms and Descriptions

Intelligent Flow Balancing (IFB)

Our IFB system offers a holding tank combined with float switch and PLC controlled pump(s) to forward feed a balanced flow to the sewage treatment plant thus ensuring optimal flow to the plant which can either help an existing system perform more efficiently or reduce the required size of a new plant.


Submerged Aerated Filter (SAF)

The submerged aerated filter (SAF) is a settling tank to clarify the solids that slough from the filter rather than using back-washing. The plant typically has a 1-4m deep bed of filter media on which to grow a biomass. A blower sends air to the bottom of the bed to provide oxygen for the biomass to support the oxidation process. The air stream promotes both efficient mixing of the effluent and disturbance of any excess solids from the filter medium.

Whether used as an addition to existing failing treatment plant, a new stand-alone system or for nitrification, the SAF process is made up of a number of biological treatment stages to ensure a high biological removal rate to guarantee the wastewater is treated to the required standards. This technology offers a very cost effective method of treatment.

Dissolved Air Flotation (DAF )

The Dissolved Air Flotation (DAF) is a water treatment process that treats wastewater by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at atmospheric pressure in a flotation tank or basin. The released air forms tiny bubbles which adhere to the suspended matter causing the suspended matter to float to the surface of the water where it may then be removed by a skimming device.

A portion of the clarified effluent water leaving the DAF tank is pumped into a small pressure vessel (called the air drum) into which compressed air is also introduced. This results in saturating the pressurized effluent water with air. The air-saturated water stream is recycled to the front of the float tank and flows through a pressure reduction valve just as it enters the front of the float tank, which results in the air being released in the form of tiny bubbles. Bubbles form at nucleation sites on the surface of the suspended particles, adhering to the particles. As more bubbles form, the lift from the bubbles eventually overcomes the force of gravity. This causes the suspended matter to float to the surface where it forms a froth layer which is then removed by a skimmer. The froth-free water exits the float tank as the clarified effluent from the DAF unit.

Moving Bed Bio film Reactor (MBBR)

The MBBR process is efficient, compact and easy to operate and often offers a very good solution as a stand-alone process within a single bespoke tank.  Similarly, it can be used to specifically enhance or upgrade treatment potential of activated sludge processes.

Uses moving, random media to treat the effluent with blowers. Care required when tankering to not suck up the media, and ideally the dip pipes between the zones should be capped with perforated dips to help prevent the media escaping forwards. This can be retro fitted with netting of mesh over the dips to allow effluent and some solids to travel forwards but not allow media to escape.


Sequencing Batch Reactor (SBR) technology

The SBR is an activated sludge process designed to operate under non-steady state conditions with the ability to treat a wide variance of influent volumes.  The SBR operates in a true batch mode with aeration and sludge settlement both occurring within the same tank.  They are able to offer a degree of flexibility and produce high quality effluents with a low sludge production.

SBR reactors treat wastewater such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches. Oxygen is bubbled through the mixture of wastewater and activated sludge to reduce the organic matter (measured as biochemical oxygen demand (BOD) and chemical oxygen demand (COD).

Membrane Bio-Reactor (MBR)

MBR systems combine clarification, aeration and filtration into a simple and cost-effective process that reduces capital and operating costs.  The result is consistent, high quality effluent (5:5:5mg/l (BOD:SS:NH4-N)) suitable for particularly sensitive discharges and for any discharge or water reuse application.

Primary Settlement Tank (PST)

Initial stage of treatment. Normally 2 stages of PST but can be single or three stage. Requires fully emptying at regular services to remove rags and any build up. The PST should capture most heavy items and fat/ oil and grease but this depends on the flow and incoming characteristics of the effluent.

 Humus Settlement Tank (HST)

Final stage of secondary treatment- before discharge unless tertiary treatment is required. Will require some tankering depending on solid build up but shouldn’t have much sludge build up in the tank if the system is operating correctly and not overloaded.

Rotation Biological Reactor(RBC)

These units are normally very reliable with little running costs. However when a problem arises they are very difficult and expensive to repair, often requiring specialist skills. The design of the units means that they require specialist lifting equipment for some repairs. At one site we recently helped repair where there was damage to the shaft we had to use a crane to left the shaft up. The components are very costly and also require a lot of labour for repairs (we had to use a four man crew). Also the health and safety checks during repairs need considering. These rotate on a drum shaped system, instead of a trickling filter type rotation (if that makes sense). The systems work by using fixed media on the drum which are exposed to the air for periods of time to become oxygenated. Should an RBC stop operating they can be problematic to restart due to the system’s design. The liquid flows off the discs (media) which are in the air and then the systems become bottom heavy. Therefore there is often a lot of extra energy required to restart them which can trip our control panels. In many cases these have to be physically ‘walked’ around to get restarted by someone inside the unit

Bucket Lift Elevator (BLE)

Now mostly replaced by Pumping Stations, although reliable the BLEs are harder to maintain and repairs are potentially very costly. If these need repairs it can mean using specialist lifting equipment to raise the equipment from the ground. Can be up to 4m of height required on the lifting equipment.

Pumping Stations

Final Effluent Pumping Stations

Final Effluent Pump Stations are designed to pump final effluent (fully treated effluent) to the designated discharge point or soakaway, and are installed downstream of a sewage treatment plant.


Raw Sewage Pumping Stations

These pumping stations are designed to pump raw sewage (non treated, and not settled sewage) to a sewage treatment plant or foul drain. These require solids handling pumps and also face problems from ragging


Settled Sewage Pumping Stations

These pumping stations are designed to pump settled sewage to a higher level where treatment can take place or to a soakaway.


Storm Attenuation Pumping Stations

Designed to assist in the management of surface water runoff and prevention of flooding, these pumping stations are becoming increasingly popular.

Due to variation and intensity of rainfall and the amount of building work that has taken place over the last two decades the management of surface water runoff and the prevention of flooding forms an integral part of any new build development within the UK.  Attenuation of storm water by the means of storage and pumping is one method that can be employed on Sustainable Urban Drainage Schemes (SUDS).



One other note which may be useful is the difference between flat shaped floats vs pear shaped (sewage) floats.

At EnSo we only use pear shaped floats as these are more reliable for raw sewage. The floats need to be able to sink slightly in the system to allow the levels to register.

Flat floats can sometimes sit on top of the sewage, especially sites with heavy FOG build up, or thick crusts. In order to send signals to the control panel or pumps, the floats have to be able to manipulate the cable attached to trigger the change of status. If flat floats are just sitting on the top of the effluent no movement is detected in the cable.