Constant Transfer

The Constant Transfer process represents a significant advance in the biological treatment of raw sewage. The simple and efficient operation of these plants has been proven worldwide with the additional benefit of uncomplicated construction. Choice of the optimum plant configuration can be made to serve populations between 200 and 15000 people.

Operation
The raw sewage flows directly into the aeration tank where an automatically variable level ensures that the inevitable fluctuation of flow does not affect the rate of treatment. The mixture of treated sewage and active bacteria is moved at a constant rate from aeration to gravity settlement and this is fundamental to the Constant Transfer system design.

Thus the plant works at a sure steady pace with obvious benefits in efficiency. All the power for aeration, mixing and airlift transfer pumping is provided by low pressure air from an electrically driven air blower in a machinery house, together with the control panel which provides fully automatic control of the plant.

Construction
Constant Transfer plants are constructed from prefabricated units and can be installed on the site with supervised, local unskilled labour. No on-site fabrication or welding is required. Construction can be from reinforced concrete tanks or glass coated steel panel tanks on reinforced concrete bases.

In addition to the basic plant comprising aeration tank(s), settlement hopper(s) and machinery house equipment, facilities can be provided for sludge consolidation, effluent storage, effluent disinfection and pumping. The plant may also require a separate pumping chamber to transfer raw sewage from existing drainage facilities.

Performance
The Constant Transfer plant provides treated effluent to a quality of at least 20 mg/l BOD and 20mg/l suspended solids. Higher quality standards can be achieved with the addition of tertiary treatment equipment. The process is odour free and therefore there are no restrictions on the plant location and it is viable to install the plant inside buildings if required.

Modular design of the plant facilitates the addition of further treatment capacity as and when required to suit local development.

Basic Plant
The simplest configuration comprises an aeration cell containing the settlement hopper and a separate machinery house.

Raw sewage enters the aeration stage directly and the treated effluent is discharged by gravity.

Complete System
As basic plant plus components for pumping raw sewage and for the pumping and storage of both effluent and sludge. Tertiary treatment and effluent disinfection can also be included if required.

Construction
The plant can be constructed in circular glass coated steel tanks or in rectangular reinforced concrete tanks as shown here. This is a typical twin cell plant arrangement.

The Constant Transfer Process

Pumping Station
This option uses two raw sewage pumps in a self contained, fully automatic system and includes covers and lifting tackle, for easy servicing.

Aeration Tank
The aeration tank, containing the free-standing settlement hopper forms the heart of the process. One or more tanks are supplied, each providing an ample volume of over 200 litres per person served. The hopper supports maintenance free, coarse bubble diffusers and a constant rate mixed liquor transfer airlift.

Machinery House
Housing blowers, controls and any pumps (such as the constant pressure irrigation system illustrated) separate from the rest of the plant for ease of operation and maintenance.

Effluent Storage Tank
An option for retention of clear, treated effluent, allowing its use for irrigation or further treatment. This tank is also used to provide Chlorine contact for effluent disinfection.

Sludge Consolidation Tank
This option facilitates the process of aerobic digestion to give a thick, inert sludge suitable for fertiliser and reduces the volume for disposal by two thirds.