Sewage treatment plants (STPs) treat domestic wastewater from buildings, residential communities, hotels, hospitals, labour camps and the domestic side of industrial sites. The treated water is discharged or, increasingly, reused for toilet flushing, cooling or irrigation.
Most STPs rely on biological treatment, so the choice of process and the quality of the aeration equipment largely decide both effluent quality and running cost.
Common STP technologies
- Activated sludge and extended aeration
- Aeration tank followed by a clarifier with sludge returned to the aeration tank. Robust and well understood, with a larger footprint.
- Sequencing batch reactor (SBR)
- Fill, aerate, settle and decant in the same tank on a timed cycle. Compact and flexible, but relies on reliable automation.
- Moving bed biofilm reactor (MBBR)
- Plastic carriers in the aeration tank grow biofilm, allowing more treatment in a smaller volume. Popular for upgrades and compact sites.
- Membrane bioreactor (MBR)
- Submerged membranes replace the clarifier and produce high-quality effluent suited to reuse. Smallest footprint, but higher energy use and membrane replacement costs.
- Package plants
- Factory-built FRP or steel units for small flows, delivered largely assembled.
Specifications to compare before you request quotes
- Design flow and population
- Population equivalent or m³/day, plus the peak factor assumed. Ask how the plant performs at your starting load as well as at full occupancy.
- Treated effluent quality
- Guaranteed BOD, TSS, ammonia or total nitrogen, phosphorus and faecal coliforms, matched to your local discharge standard or reuse requirement.
- Blowers
- Type (for example rotary lobe or screw), duty and standby arrangement, power draw and noise level in dB(A), which matters in residential and hospitality settings.
- Diffusers
- Fine-bubble disc or tube diffusers, membrane material and expected replacement interval. Diffuser efficiency has a direct effect on blower power.
- Energy use
- kWh per m³ treated at design load. Aeration is usually the largest single energy consumer in an STP.
- Sludge and odour
- Expected sludge quantity, how it is dewatered and removed, and what odour control is included.
- Automation and monitoring
- Level of automation, alarms and whether remote monitoring is available.
Information to send suppliers with your enquiry
- Occupancy or population, and measured or estimated water use per person.
- Where treated water goes and the standard it must meet.
- Available area, and whether the plant can be below ground or must be above ground.
- Noise and odour constraints from neighbours or building occupants.
- Any phasing, for example a building that will fill up over several years.
Common sourcing mistakes
- Sizing for final occupancy with no plan for low initial loads. Underloaded biological plants often perform poorly, so ask about modular trains or turndown.
- No standby blower or pump, so one failure stops treatment.
- Ignoring blower noise and odour close to occupied buildings.
- Buying the plant without an operation plan. STPs need trained operators and regular sampling.