First, the biofilm has strong adaptability to the change of sewage quality and quantity, convenient management and no sludge bulking.
Second, microorganisms fixed on the surface of the carrier with longer generations can also proliferate, and the organisms are relatively richer and more stable, with less residual sludge. Third, it can treat low-concentration sewage.
The disadvantage of biofilm process in sewage treatment is that biofilm carrier increases the investment of the system; The specific surface area of carrier material is small, the volume of reaction device is limited and the space efficiency is low, so the treatment efficiency of municipal sewage is lower than that of activated sludge method. The number of microorganisms attached to the solid surface is difficult to control and the operation flexibility is poor; Natural ventilation is not as sufficient as activated sludge, and it is easy to produce anaerobic.
Biofilm method is to attach microorganisms to the surface of carrier. When sewage flows through the carrier surface, it decomposes pollutants through adsorption of organic nutrients, diffusion of oxygen to biofilm and biological oxidation in the membrane. In the biofilm reactor, pollutants, dissolved oxygen and various necessary nutrients first spread to the surface of biofilm through liquid phase, and then spread to the inside of biofilm; Only the pollutants diffused to the surface or inside of biofilm can be decomposed and transformed by biofilm microorganisms, and finally various metabolites (CO2, water, etc.) are formed. ) can be formed. With the extension of time (about 30 days), the distribution of biofilm along the direction of water flow, microbial composition and organic matter degradation function reached a balanced and stable state, and the biofilm matured, forming a composite ecosystem of organic matter, bacteria, protozoa and metazoa.
In the outermost layer of the biofilm, a biofilm layer with aerobic microorganisms as the main body is formed, while in the deep part of the aerobic layer, diffusion limits the penetration of dissolved oxygen and often forms an anaerobic zone. Here, due to the role of anaerobic bacteria, hydrogen sulfide, ammonia, organic acids and other substances are easy to accumulate. However, if the oxygen supply in the system is sufficient, the thickness of the anaerobic layer will be compressed to a certain limit, and the formed organic acids will be transformed into CO2 and water under the action of heterotrophic bacteria, while ammonia and hydrogen sulfide will be oxidized into various stable salts under the action of autotrophic bacteria. With the increase of anaerobic metabolites, the immobilization is weakened and the biofilm ages and falls off.
Chapter 1 Biofilm and Biofilm Reactor in Sewage Treatment; Chapter two: immobilization mechanism of microorganisms on the surface of carriers; The third chapter is the selection of biofilm carrier and cell fixation technology; Chapter 4: Kinetics of biofilm growth and substrate removal; The fifth chapter is the energy metabolism theory of biofilm microorganisms; Chapter VI Biofilm Analysis Technology; Chapter seven: the main factors affecting the operation of biofilm reactor; Chapter 8 Typical Biofilm Reactor Process; Chapter 9: Practical novel biofilm reactor technology; Chapter 10 Combined Biofilm/Suspended Growth Treatment Process.