Biological wastewater treatment

Biological systems use bacteria, in either aerobic or anaerobic conditions, to break down organic matter into carbon dioxide and cellular mass.

Packaged treatment plant are typically suitable for population equivalents under 400. They range from plants for single houses to systems for housing estates, caravan parks or leisure applications.

Engineered systems tend to be specified for population equivalents over 400, and particularly in industrial applications. Engineered systems can consist of a modular arrangement of packaged plant.

Submerged aerated filters (SAF) are small footprint units with few moving parts. They are designed for treating municipal wastewater, producing effluent <20mg/l BOD, <20mg/l TSS and <5mg/l NH3.

Membrane bioreactors (MBRs) combine a submerged membrane filtration process with a bioreactor. They are compact and produce a high-quality effluent, generally <2mg/l BOD, <2mg/l TSS and <0.6mg/l NH3.

Other technologies include biological aerated filters (BAF), sequencing batch reactors (SBR), moving bed biofilm reactors (MBBR) and continuous flow reactors (CFR).

Reedbeds and constructed wetlands  are an alternative biological treatment system that use bacteria attached to the surface of soild, sand or gravel media to treat wastewater, run-off, sewage and other contaminants.