With aerobic solutions we define the bioreactors where we need oxygen for the removal of pollutants. More precise it’s about the systems where we aim to oxidise carbon and nitrogen to CO₂ and N₂ respectively on one hand. On the other hand, in such systems we will produce a sludge also containing carbon and nitrogen compounds. Furthermore, phosphorous and many other compounds will be in the sludge too. Resulting in emitting to the sky + removal with the sludge = clean effluent to be discharged or reused.

The term ‘aerobic’ comes from the first systems that were operated at aerobic conditions only. Nowadays, various redox conditions (anaerobic, anoxic, and aerobic) are applied to remove organic matter and nutrients more efficiencly.

Different from the anaerobic solutions (without input of oxygen) these aerobic solutions require oxygen. Over the years different types of reactors and processes are developed, like:

Activated sludge solutions

In such Activated Sludge Processes (ASP) the sludge is kept in suspension by mixing or aeration. The sludge is named Mixed Liquor Suspended Solids (MLSS). By feeding influent that sludge or MLSS will flow out of the reactor. To keep a high amount of sludge in the system the sludge is separated from the treated water and pumped back to the bioreactor. The water will be discharged (or further treated, polished or reused). It could be systems like:

• Classical Activated Sludge (CAS). Having a final clarifier in the end to separate the sludge from the treated water. The sludge is recirculated back to the bioreactor. And some grown sludge will be disposed. The effluent is basically fully treated water clean enough to be discharged to the environment.
• Sequence Batch Reactor (SBR). In line with the CAS system, with as main difference that all takes place in just 1 reactor. Phases are time separated. Typical phases are Feeding, Reaction, Settling, Decanting.
• Membrane BioReactor (MBR). Here membranes are used to keep the sludge in the system. Benefits with CAS or SBR are the higher MLSS concentration possible resulting in smaller reactors. Also the applicable UF or MF membranes will create an effluent very low in particles. An effluent with high potential for reuse applications!

Biofilm solutions

Attached growth or biofilm formation like MBBR Moving Bed BioReactor or FBBR Fixed Bed BioReactor. A fixed or moving ‘carrier’ is added into the water, where the biomass can grow on. The benefits of such systems is the ability to increase loading rate resulting in smaller reactors. Also much less sludge is to be separated from the treated water, resulting in smaller needed equipment to separate the sludge from the final effluent.

Granular solutions

Granular growth, like DEMON® Anammox, BIOCOS® inDENSE and Nereda®. Basically such systems have the same benefits as above mentioned biofilm growth. Noticeably more interesting for such systems is that no external ‘carrier’ is needed, while the bacteria will grow in granules by themselves, or for BIOCOS® with the inDENSE gravimetric selection technology to favor dense granules maintained in the reactor.