Usually, biological treatment to remove dissolved organic loads contained in the primary effluent. Aeration is used to stimulate aerobic degradation of the organic matter (biological process). There are 3 main types of processes:
Aerobic treatment – bio-filtration
Aerobic: Oxygen dependent wastewater treatment requiring the presence of oxygen for aerobic bacterial breakdown of waste.
Aerobic treatment – Fixed Biofilm and MBR
Membrane Biological Reactor (MBR): This process combines a biological treatment using activated sludge with a physical separation treatment using submerged membranes (instead of secondary clarifier).
Biofiltration: Microorganisms are fixed to a media support and wastewater flows through it to be treated. Media acts as a physical support for the growth of microorganisms. Microorganisms form a biological layer of biofilm where water contaminants are degraded.
Trickling bed consists of a fixed bed of media over which pretreated wastewater is sprayed. Media = stones, plastic shapes, wooden salts.
Aerobic treatment – activated sludge
Activated sludge treatment: It is a biological reactor, in which the microorganisms responsible for treatment are kept in suspension and aerated. Liquid – solids separation is required and done using a clarifier. There is a recycle system for returning solids removed from the liquid-solids separation unit back to the reactor. An important feature of the AS process is the formation of flocculent settleable solids that can be removed by gravity settling. Activated sludge process utilizes fluidized microorganisms, mixed growth organisms, aerobic conditions.