魯雨環(huán)

【Abstract】Biological filter bed as a new type of sewage treatment biological treatment technology， in the practical application has made rapid development， the most important role in the process of microbial water pollutants attached to this article describes the attachment of its working principle include： the formation of surface membrane， cell transport to surface， adhesion， surface colonization and detachment，

【Key words】biological filter bed technology； the formation of surface membrane； cell transport to surface； adhesion； surface colonization and detachment

Biodegradation through porous geological media and biodegradation in soil systems is a natural phenomenon that affects water quality in groundwater recharge and is used in natural treatment systems such as drinking water treatment and wastewater treatment. And the resulting water treatment technology that is biological （diafiltration） filtration， derived from the biological filter bed （pool） technology. Initially used filter material is mainly stone， sand， clay and other natural materials.

The biological filter bed is composed of a solid carrier and an activated biofilm wrapped with its biological process. The biological process involves the transformation or mineralization of organic matter and the transformation of some non-organic matter （such as nitrogen and phosphorus）. The physical drive includes Suspended particles （or colloidal particles） and microbial barrier effect.

In the biological filter bed treatment， the microbial attachment to the surface of the filter to form a mature biofilm is a complex process. The adhesion of microbial adherence on the surface of the filter material is mainly affected by environmental conditions， microbial species， surface properties and fluid characteristics. The attachment process involves the formation of surface membrane， cell transport to surface， adhesion， surface colonization and detachment，

Surface state membrane： clean filter through the water body of organic matter and some microbial cell transport will be obtained nutrients， which is a chaotic dynamic process. The surface state membrane components include glycoproteins， proteins and humus， with a thickness of 30-80 nm， which can interact with the structure of certain bacteria at the next stage of biofilm formation. In the process of biosorption， the role of the surface state membrane includes changing the physicochemical properties of the matrix， as a concentrated nutrient source， inhibiting the release of toxic metal ions， the adsorption of dissolved inhibitory substances and the supply of metal trace elements.

The cells are transported to the surface： the microorganisms in the fluid reach and adhere to the surface of the filter by mass transport， thermal effects （Brownian motion， molecular diffusion） and gravity effects （sedimentation）. The convective action in the flowing liquid， which is of great significance to the bacteria that are inactive in the absence of gravity， may be transported to the surface of the filter at random or at a certain concentration gradient. Mass transport is severely affected by fluid state （laminar or turbulent flow） and flow rate. The laminar flow is slow and steady. Random and chaotic turbulence increases the microbial adhesion to the surface of the filter， and the risk of falling off when the biofilm is thick high.

Adhesion： The initial adhesion is the physical and chemical process， depending on the different ionic strength of the double electrostatic force and van der Waals force balance， van der Waals force and the effective size of bacteria. Van der Waals force， static electricity and specific interactions will form irreversible bonds and produce extracellular polysaccharides. In the process of adhesion， the formation of extracellular polysaccharides on the biofilm is very critical. The physical and chemical properties of the filter have a significant effect on the adhesion of microorganisms. Generally， the hydrophobicity and roughness， and the filter media with divalent cations （such as Ca2 +， Mg2 +） promote the adhesion of bacteria.

Surface colonization： Adhesive bacteria on the surface of the filter material begin to consume nutrients from the water and form a community. If the bacteria and bacteria on the surface of the filter material are interconnected， the adherent microorganisms can be exchanged with the suspended microorganisms， and the irreversible adherent microorganisms in the biofilm thus formed are strongly associated with the filter surface and other bacteria contact.

Shedding： falling off is a common phenomenon in the whole process of biofilm formation. When the shear stress， nutrient and oxygen are absent in the filter bed， the shedding process has a significant damage to the distribution of the microorganisms in the biofilm and its structure， but on the other hand， the shedding will transfer the dead microorganisms into new microbes Adhesion provides a point. so microbes can be quickly replaced while ensuring the stability and activity of microbial communities.

Because of its low cost， low energy consumption， simple operation and maintenance， strong impact resistance， high unit biomass， high capacity reaction rate and environment friendly， it is widely used in different areas of sewage treatment， become the current sewage treatment technology A research hotspot.

References：

[1]Gimbel R，Collins MR.Recent progress in slow sand and alternative biofiltration processes.Iwa Publishing 2006.

[2]Om elia CR.Particles，pretreatm ent and performance in direct filtration.J EED，ASCE.1985，114（6）：874-890.