Biological filter

Aerated biological filter

1、 Working principle of biological aerated filter

Biological Aerated Filters (BAF) are developed based on biofilm methods such as conventional biofilters, high load biofilters, biofilters, and biological contact oxidation, and are known as the third generation biofilters. In the development process, we fully drew on the design ideas of sewage treatment contact oxidation method and water supply fast filter, which require aeration, high filtration speed, interception of suspended solids, and regular backwashing. The process principle is to fill a certain amount of granular filter material with smaller particle size in the filter tank, with highly active biofilm growing on the surface of the filter material, and aeration inside the filter tank. When sewage flows through, the high concentration biofilm oxidation degradation ability brought by the high specific surface area of the filter material is utilized to rapidly purify the sewage, which is the process of biological oxidation degradation; At the same time, when the sewage flows through, the filter material is in a compacted state. By utilizing the small particle size of the filter material and the biological flocculation effect of the biofilm, suspended solids in the sewage are intercepted, and the detached biofilm is ensured not to float out with the water, which is the interception effect; After running for a certain period of time, due to the increase in head loss, it is necessary to backwash the filter tank to release the trapped suspended solids and update the biofilm, which is the backwashing process.

Generally speaking, aerated biofilters have the following characteristics:
(1) Using granular fillers as biological carriers, such as ceramic particles, quartz sand, activated carbon, etc.
(2) Different from general biofilters and biofilters, aeration is required for the removal of BOD and ammonia nitrogen.
(3) High hydraulic load, high volumetric load, and high biofilm activity.
(4) It has dual functions of biological oxidation degradation and SS interception, and there is no need to set up a secondary sedimentation tank after the biological treatment unit.
(5) Regular backwashing is required to clean the SS trapped in the filter and update the biofilm.

2、 The main advantages of the biological aerated filter process
(1) Aerated biofilter is a third-generation biofilter that uses filter materials with small particle size and large specific surface area, significantly increasing biological concentration; The combination of biological treatment and filtration treatment eliminates the need for a secondary sedimentation tank; Adopting backwashing method eliminates the possibility of blockage and improves the activity of biofilm; The combination of biofilm and biological floc treatment is adopted, which simultaneously utilizes the advantages of biofilm method and activated sludge method. Greatly improved the effluent quality and treatment load.
Aerated biofilters have both biological oxidation degradation and filtration functions, thus achieving high effluent quality and meeting the standards for recycled water quality. For industrial wastewater, even in the case of weak biodegradability, the treatment effect of aerated biological filter is better than that of general processes, because the treatment of organic matter by aerated biological filter not only relies on biological oxidation, but also has significant biological adsorption and filtration effects, because it can remove larger particle sizes and adsorb and remove some substances with weak biodegradability. Due to the interception of the filler itself and the biological flocculation of the surface biofilmThe effluent SS is very low, generally not exceeding 10mg/l,The effluent is very clear and transparent; Due to continuous backwashing, the biofilm is effectively renewed, manifested as a thin biofilm (usually around 110 microns) with high activity. Highly active biofilms are not only reflected in biological oxidation and degradation, but also in biological flocculation and adsorption. For some difficult to degrade substances, they can be adsorbed and retained in the pool for removal.
Aerated biofilter has a high treatment load: hydraulic load and volumetric load are significantly higher than traditional sewage treatment processes(Water)The force load can reach 6-8m3/m2h; The volumetric load can reach 3-6kgBOD5/m3d, and the residence time is short (single stage can reach 0.5-0.66h).
(2) Small footprint and low infrastructure investment. After the biological aerated filter, there is no need to set up a secondary sedimentation tank, which can save the land occupation and investment of the secondary sedimentation tank.The footprint of the biological aerated filter is only 1/10-1/5 of that of conventional processesThe processing load is high and the residence time is short, resulting in a smaller pool capacity and a savings of at least 20-30% in infrastructure investment compared to conventional processes.
(3) Low operating costs. The energy consumption of gas supply accounts for a considerable proportion of the operating costs of all aerobic biological treatments. The aeration biological filter process has high efficiency in oxygen transmission and utilization, small aeration volume, and low power consumption for oxygen supply.The utilization efficiency of oxygen can reach 20-30%. Engineering practice has shown that the aeration rate is 1/20 of traditional activated sludge method, 1/6 of oxidation ditch, and 1/4-1/3 of SBR1,It greatly saves operating costs. The head loss of the biological aerated filter is relatively small, the remaining sludge volume is small and easy to handle, and the maintenance amount is minimal, which will ensure low operating costs.
(4) Strong shock load resistance and low temperature resistance. Operating experience has shown that aerated biofilters can operate under short-term shock loads 2-3 times the normal load, with minimal changes in effluent quality. On the one hand, this depends on the high specific surface area of the filter material. When the external organic load increases, the biomass on the surface of the filter material can rapidly increase; On the other hand, it depends on the buffering capacity of the overall aerated biofilter. In addition, once the biofilm formation is successful, the biological aerated filter can operate at a water temperature of 6-10 ℃ and has good operational performance.
(5) Easy to hang film, fast to start. The biological aerated filter can complete the membrane formation process in 2 to 3 weeks at a water temperature of around 15 ℃. When not in use temporarily, the operation can be turned off. At this time, the biofilm on the surface of the filter material does not die, but exists in the form of spores. Once water is supplied for aeration, it can quickly return to normal. The sewage temperature is around 15 ℃, and the operation is stopped for half a month (with the filter column drained of water and no aeration). After resuming operation, it fully returns to normal after three days. This feature makes the aerated biological filter very suitable for sewage treatment in areas with large water volume changes. In tourist areas, the amount of sewage is greatly affected by the season and the number of tourists. During the off-season of tourism, it is possible to completely shut down some of the aeration biofilters to reduce unnecessary operating costs. Once needed, the designed treatment capacity can be restored in a very short period of time.
(6) The aerated biological filter adopts a modular structure, which is convenient for later renovation and expansion. There is a common drawback in the existing domestic sewage and wastewater treatment processes: when adding new sewage and wastewater treatment capacity, it is necessary to make thorough modifications to the original processes, mainly because these processes are not modular structures. The fully modularized aerated biological filter is very conducive to later expansion and renovation. Only the number of filters needs to be increased in parallel, without affecting the operation of existing processes.
(7) Adopting automated control, easy to manage. The biological aerated filter can be fully automated and managed with ease. At the same time, due to its relatively simple structure, there is no need for complex self-control equipment or extensive personnel technical training.
(8) No foul odor and high environmental quality. The environmental quality of existing sewage treatment plants in China is generally poor, with foul odors and a high number of insects such as flies. Aerated biofilters do not produce foul odors, and sewage plants using this process have high environmental quality.