1. Overview:
Biological aeration filters, or BAFs for short. It is a new type of wastewater treatment technology pioneered in the late 80s by the French company OTV. Shenzhen Guotai Environmental Technology***
The BAF biological aeration filter is a new type of high-load immersion fixed biofilm three-phase reactor, which combines the advantages of two existing wastewater biochemical treatment methods: activated sludge method and biofilm method, and combines the two treatment processes of biochemical reaction and physical filtration (i.e., biodegradation removal of BOD and solid-liquid separation removal of SS) in the same reactor. BAF biological aeration filter is especially suitable for the treatment of urban domestic sewage, and the treated effluent meets the water quality standards of domestic miscellaneous water, and can also be used as the precursor water for industrial water.
Second, the working principle:
BAF is divided into upward flow and downward flow according to the direction of water flow, the downward flow biological aeration filter adopts the process route of water vapor reverse at the same time as the water intake, so that the surface of the medium forms a biofilm, and when the sewage flow filter bed, the pollutants are first filtered and adsorbed, as the nutrient substrate of the obligate degrading bacteria of "doubling clearing", accelerating the formation of biofilm by degrading bacteria, and the biofilm further "captures" the substrate, assimilating, metabolizing and degrading it. Therefore, the biological filter can degrade organic matter at the same time, and has the role of biological coagulation and adsorption filtration. Moreover, because the biofilm is attached to the filter material and has high activity, the biofilm is not limited by mud age, which is very beneficial to the degradation of pollutants.
With the progress of the treatment process, the suspended activated sludge between the gaps of the filter material forms a sludge filter layer between the gaps of the filter material, which plays a further role in adsorption and filtration while oxidizing and degrading the organic matter in the sewage, so that the organic matter and suspended matter can be completely removed. In the upper part of the reactor, heterotrophic microorganisms are the dominant bacteria, where carbon contaminants (CODCR, BOD5 and SS) are mainly removed, while in the lower part of the reactor, autotrophic bacteria, such as nitrifying bacteria, are dominant and ammonia nitrogen is nitrified. In the biofilm, as well as in the gaps between some fillers, a large amount of activated sludge accumulates with facultative microorganisms, so that the removal of carbon pollutants can occur in the BAF, and it has the functions of nitrification and denitrification.
In the process of filter operation, with the metabolism of the biofilm, the shedding biofilm and the impurities intercepted on the filter material continue to increase, the head loss in the filter material increases, the water level rises, and the filter material needs to be backwashed for a certain period. The BAF biological aeration filter uses the clear effluent stored in the oxygenation disinfection tank as the backflush water, and there is no separate backflush tank, and the backwash wastewater is returned to the primary treatment facility through the drain pipe.
Third, the characteristics of the process.
1) The coarse and porous granular packing of BAF provides an optimal growth environment for microorganisms, so the biomass is large. The high concentration of microorganisms increases the volumetric load of the BAF, which not only reduces the volume and footprint of the tank (the volume is only 1 3-1 5 of the activated sludge method), but also shortens the honey stop time to 1-2 hours. The pool volume occupies 1 5-1 10 of the conventional secondary treatment, and the infrastructure investment is 20%-30%. (2) The granular filler in the packed bed has a huge specific surface area, on which a highly active biofilm composed of various carbonizing bacteria, ammoniating bacteria and nitrifying bacteria grows, which has excellent functions of oxidative degradation and adsorption of pollutants in the filtered water, and can remove organic matter (COD, BOD, SS, NH3-N, P, etc.) in sewage without setting up a secondary sedimentation tank. (3) Relative movement of air and water. The bubble contact area is increased, and the oxygen utilization rate is increased by 15%-20%.The contact area between the air and water and the biofilm is increased, which improves the treatment effect and reduces the operating cost. (4) High nitrification efficiency and good denitrification effect. This is something that cannot be achieved with conventional secondary treatment. (5) High-quality effluent. The effluent quality reaches the effluent quality of sand filtration** treatment, which can not only meet the environmental protection discharge standards but also meet the reuse water standards, and can be used for domestic miscellaneous water or cooling water. BAF also has a good treatment effect on low concentrations of organic wastewater, such as bath water. (6) No odor and no secondary pollution during operation. (7) Strong impact load resistance, no sludge expansion problem. Microorganisms grow on the surface of rough and porous fillers, which are immobilized microorganisms and will not be lost, so the operation and management are convenient and simple. (8) The biological aeration filter can be used in combination with other traditional processes, which can carry out technical transformation of some old factories and reduce the secondary investment cost.