SBR stands for Sequence batch reactor. It is a style of wastewater treatment that was invented in England in the 70’s, but popularized in Europe during the 90’s. Early domestic SBR systems suffered from complexity issues, normally relating to the use of pumps to move water through the system. In later years, the use of air blowers to add oxygen, and move water has simplified SBR systems making them a very popular choice for homeowners looking for a sewage treatment system.
The multi chamber SBR treatment plant is the original design. Waste enters a primary chamber where sludge settles to the bottom. The treatment and final settlement processes happen within a second chamber. Because heavy solids are kept in the primary chamber, the treatment cycles can be as short as 6 hours (4 treatment cycles a day).
The normal stages of treatment are as follows:
This cycle repeats for as many times as is programmed to, typically 3 or 4 treatment cycles a day are used.
Single chamber SBR systems have become more common across Europe in the last 10 years. This is largely due to an amendment in German regulations (where SBR systems are very popular, due to their low energy usage). The change in German regulations removed the requirement to have a primary chamber in all treatment systems.
Single chamber SBR systems operate within one chamber. Therefore the feeding happens throughout the treatment process as follows:
By allowing wastewater to enter the treatment zone directly, oxygen levels in the water are maintained. This is opposed to multi chambered systems where oxygen levels drop in the primary chamber, then oxygen is added to bring the levels up, within a separate chamber. This increases efficiency and results in better nitrification. In other words, lower ammonia levels are seen in the final eater quality.
Filling refers to water entering the treatment zone. This is typically at the start of the treatment process, however in single chamber SBR systems, the treatment chamber is filled throughout the treatment process.
The treatment happens by aerating the water in the treatment zone. Aeration is normally achieved by blowing air into the water by means of an air compressor (blower). The air enters the treatment zone through a fine membrane diffuser. This adds oxygen to the water and creates turbulence, which mixes the active sludge (bacteria) and the wastewater.
This aeration happens in small, timed bursts. Allowing the bacteria to settle between aeration bursts.
SBR systems grow activated sludge, therefore fine bubble diffusers are easy to remove and clean during servicing.
This treatment phase is often 6-8 hours for multi chambered SBR systems and 12 hours for single chamber SBR’s.
This phase typically lasts 1-1.5 hours. It is a period of time where aeration stops entirely, allowing bacteria to fall to the bottom of the chamber. Once bacteria has fallen to the bottom, the cleaned water will remain on the top. Ready for the last phase
Following settlement of the bacteria (stage 3, above), clean water is decanted (discharged) out of the treatment plant. Modern SBR’s use an “air lift” which is a pipe with a hole in the side, attached to the air blower. The air blower starts, bubbling air to the base of the pipe, as the bubbles rise, water if lifted up and out of the plant. This is a very effective way to remove the cleaned water.
Often the cleaned water enters a sample pot, allowing a sample to be taken.
The Cycle repeats.
One very large benefit of SBR systems is the ability to adjust aeration (oxygen) in the system. Reducing the aeration for a system used by less people, and increasing the aeration for a system used by more people. This level of adjustment is not seen in other styles of wastewater treatment. The adjustment happens within the timer. The below graphic below shows you how this is achieved and represents one treatment cycle in a multi chamber SBR.
SBR systems are sometimes “pooh Pooh’d” by installers, who feel they are more complex than a standard 3 stage SAF (submersed aeration filter). Whilst this can be appreciated, the sheer elegance of SBR systems cannot be ignored. The simple fact that the air blower doesn’t run 24 hours a day, is a huge bonus for consumers both in terms of energy efficiency, and prolonged life of the air blower.