Biofilm process is an aerobic biological treatment technology of wastewater in parallel with activated sludge process. It is a fixed membrane method and an artificially enhanced soil self-purification process. ● Mainly remove soluble and colloidal organic pollutants in wastewater; ● Main category: biological filter? Common biofilter, high-load biofilter, tower biofilter, etc. Biological turntable; Biological contact oxidation method; Aerobic biological fluidized bed etc.

Edit the specific introduction of biofilm method in this paragraph.

summary

Biofilm method is a method to treat organic sewage by using microorganisms (biofilm) attached to the surface of some solid objects. Biofilm is an ecosystem composed of highly dense aerobic bacteria, anaerobic bacteria, facultative bacteria, fungi, protozoa and algae, and the solid medium attached to it is called filter material or carrier. Biofilm can be divided into gas-producing layer, aerobic layer, attached water layer and moving water layer from the filter material. The principle of biofilm method is that the biofilm first absorbs the organic matter attached to the water layer, then it is decomposed by aerobic bacteria in the aerobic layer, and then it enters the anaerobic layer for anaerobic decomposition. The flowing water layer washes away the aging biofilm and grows new biofilm, thus achieving the purpose of purifying sewage. Biological treatment of microorganisms growing along the surface of solid (which can be called carrier) in wastewater. It is named after the microbial population grows into mucous membrane along the solid surface. When wastewater comes into contact with biofilm, pollutants are transferred from the water to the membrane, thus being treated. Its basic mechanism can be found in the biological treatment of water. Biofilm process (Figure 1) The bioreactor in a typical process flow can be a biofilter, a biological turntable, an aerated biofilter or an anaerobic biofilter. The first three are used in aerobic biological treatment process, and the latter is used in anaerobic process. The earliest biofilm biological devices were intermittent sand filter and contact filter (full of debris). Their operation is intermittent, and filtration-leisure or water intake-contact-drainage-leisure constitutes a working cycle. They are the development of sewage irrigation, based on the phenomenon of soil self-purification. Then there is a continuous biological filter. After the advent of new plastics, there have been new developments.

biofilter

One of the most commonly used biological devices in biofilm process. The biological carrier used is small pieces (such as gravel and plastic filler) or plastic blocks, which are piled up or stacked to form a filter bed, so it is often called filter material. Different from the general filter in water treatment, the filter bed of biological filter is exposed to the air, and wastewater will be spilled on the filter bed. There are many forms of water distributor, including fixed and mobile. Rotary water distributor is the most widely used. It takes two or more symmetrically arranged horizontal perforated pipes as the main body and can rotate around the center of the pool. The perforated pipe clings to the surface of the filter bed, and water flows out of the hole. The work of the water distributor is continuous, but the water application to the local bed surface is intermittent, which inherits the concept of intermittent irrigation with sewage irrigation. Below the filter bed is a water collecting layer paved with bricks, special pottery blocks and concrete blocks. Below is the bottom of the pool. The water collecting layer is communicated with the outside of the pool, which not only drains water but also ventilates it. When working, the wastewater flows down the filter bed from top to bottom along the surface of the carrier, and is in close contact with a large number of microorganisms and attached water growing on the surface of the carrier for material exchange. Pollutants enter the biofilm and metabolites enter the water flow. Effluent with detached biofilm fragments needs to be separated by sedimentation tank. Dissolved oxygen required by biofilm is obtained directly from air or through water flow. In common biofilter, the biofilm layer is thick, and the part near the carrier is often in anaerobic state. Biofilm method

The depth of the filter bed is related to the filtering speed and filtering material. For a long time, the depth of gravel filter layer is about1.8 ~ 2m. If the depth is increased, the surface of the filter bed is easy to block the accumulated water. The filtration rate is about 1 ~ 4 m3/(m2/ day). If it is improved, the bed surface is easy to accumulate water. The first breakthrough is the improvement of filtration speed. When the hydraulic loading rate (i.e. filtration rate) is increased to above 8 ~ 10 m3/(m3/ day), the biofilm will not block the filter bed due to the scouring action of water flow, and the loading rate of organic matter (calculated by BOD5) can be increased from about 0.2kg/(m3/ day) to 1kg/(m3/ day). In order to meet the requirements of hydraulic load rate, incoming water is often diluted by reflux. In order to stabilize the processing efficiency, two stages can be connected in series. This kind of biofilter with innovative process, improved load rate and unchanged structure is called high load rate biofilter. Then, it was found that when the depth of the filter bed increased from about 2 meters to more than 8 meters, the ventilation was improved. Even if the hydraulic load rate is increased, the filter bed is no longer blocked and the filter works well. At the same time, the organic loading rate can be increased to about 65,438+0 kg/(m3 day). Because the plane diameter of this filter is generally about 1/6 ~ 1/8 of the height of the pool, it looks like a tower, so it is called a tower filter. Since the appearance of plastic blocks, ventilation and blockage are no longer problems, and the depth and filtration speed of the filter bed can be designed according to needs.

Rotating biological disk

It appeared with the popularization of plastics. Dozens or hundreds of plastic or glass fiber reinforced plastic discs pass through the shaft and are laid flat on the groove surface of a strip groove with a semicircular cross section. The diameter of the disc is generally less than 4 meters, and the diameter of the groove is about several centimeters. There is a motor and deceleration device to rotate the disc shaft, and the rotation speed is about 1.5 ~ 3 rpm, depending on the disc diameter, and the circumferential linear speed of the disc is about 15 m/min. Waste water flows from one end of the water tank to the other. The axis of the disk is higher than the water surface, and about 40% of the disk is submerged in water, and about 60% is exposed to the air. When the disk shaft rotates, the disk surface alternately contacts with waste water and air. The disk surface is covered by a membrane formed by the growth of microorganisms, and the biofilm alternately contacts with wastewater and air to continuously obtain pollutants and oxygen and purify wastewater. The shear stress between the film and the disk surface caused by rotation increases with the increase of the film thickness. To a certain extent, the film falls off the disk surface and goes with the water. Compared with biofilter, the contact time between wastewater and biofilm is longer in biological turntable method. But also has certain controllability. The pool is often segmented and the turntable is often grouped, which can not only prevent short flow, but also help to improve the load rate and effluent quality, because the load rate is gradually reduced. If the biological turntable smells, it can be stamped. When the amount of water is not large, the biological turntable is generally used.

Biological aerated filter

Aeration tank with plastic blocks. According to its process, it is also called biological contact oxidation. Its work is similar to the aeration tank in the activated sludge process, except that the sludge does not flow back and aeration cannot be used. Generally, bubble aeration is used in the whole pond, and the biomass in the pond is much higher than that in the activated sludge method, which can shorten the aeration time. The operation is stable, and the problem of sludge bulking will not occur. There are also granular materials (such as sand and activated carbon). At this time, the water flows upward, and the filter bed expands and will not be blocked. Because of its large surface area, large biomass and sufficient contact, it can shorten aeration time and improve treatment efficiency, and it is still in the research stage.

Anaerobic biofilter

The structure is similar to that of biological aerated filter, except that no aeration system is needed. Because of the high biomass, compared with sludge digester, the treatment time can be greatly shortened (the residence time of sludge digester is generally more than 10 day), and it is possible to treat low-concentration wastewater such as urban sewage.