Sewage Treatment

Typical modern extended aeration package treatment plant

Sewage treatment involves creating a habitat where bacteria can develop. The bacteria use the incoming polluting material as a nutrient and food source. The environment is very specific, and most of the bacteria which develop do not arise from the human intestinal tract.

Settlement tanks will remove any solids, including bacteria, washed through the treatment process to leave a clear effluent. Settlement tanks and screens may also be used before the biological stage to remove gross solids.

Treatment works are divided into attached and suspended processes. Attached processes provide a fixed environment for the bacteria to develop. These include traditional percolating filters, rotating biological contactors (RBC) and submerged aerated filters which have recently come to prominence. Gross solids must be removed before the sewage enters most of the attached process plants.

Suspended process plants are typified by the activated sludge process, where the bacterial mass is free-floating in contact with the polluting flow, and is returned from a final settlement tank to the reactor vessel. These plants can deal with whole sewage.

Anaerobic processes are also available, typically for high strength industrial wastes.

Traditional sewage treatment plants were:

• massive concrete installations;
• accompanied by fly / smell nuisance;
• expensive to install.
• difficult to modify to cope with changing flows and discharge requirements

Modern technology in sewage treatment permits treatment to higher standards in less space with less nuisance. Sewage treatment plants range from the major installations for a large city to individual plants for a single property.

Treatment plants can be designed for your site conditions to meet the requirements of discharge consents. These plants can either be fabricated to order or constructed on site, whether you are a householder, industrialist, property developer, utility or Water Service Company.