the process of immobilizing microbial sludge with metabolic activity on the filler of a biological treatment system is called membrane hanging. biofilm is also the process of culture and domestication of membrane sludge in biofilm treatment system.
when the biofilm process is first put into operation, it needs a film-hanging stage. there are two purposes: one is to make microorganisms grow and propagate until the surface of the filler is covered with biofilm, and the quantity of microorganisms can meet the requirements of sewage treatment; the other is to make microorganisms gradually adapt to the quality of the sewage treatment, that is, to domesticate microorganisms. during the process of membrane deposition, the effluent from the reflux sedimentation tank and the sludge at the bottom of the tank can facilitate the early completion of the membrane.
generally, there are two ways to use the membrane hanging method and indirect hanging method.
among all kinds of biofilm treatment facilities, bio-contact oxidation tank and tower biofilter can be used by direct membrane-hanging method because of their aeration system and large filler volume and filler void, while conventional biofilter and bio-turntable facilities need to use indirect membrane-hanging method.
1. direct film hanging method.
the method is to make the treatment system run normally under suitable water temperature, dissolved oxygen and ph, bod5, c/n and other environmental conditions. for domestic sewage, municipal sewage or industrial wastewater mixed with a large proportion of domestic sewage, the direct membrane method can be used, generally after 7 to 10 days to complete the membrane process.
2. indirect film hanging method.
for industrial wastewater which is not easy to be degraded, especially when ordinary biofilter and biological rotary table are used, in order to ensure the smooth operation of membrane hanging, the corresponding activated sludge can be pre-cultured and domesticated, and then added to the biofilm treatment system for membrane hanging, that is, distributed membrane hanging. the usual practice is to cultivate activated sludge from domestic sewage or its mixed sewage with industrial wastewater, then put the sludge or other similar sewage treatment plant together with industrial wastewater into a circulating tank, and then pump into the biofilm treatment facility, the effluent and sedimentary sludge are returned to the circulating tank. after circulatory operation, biofilm is formed, which runs through water and joins industrial waste water to be treated. 20% of the industrial wastewater can be allocated first. after analyzing the water quality of the influent and effluent, the biofilm has a certain treatment effect, and then gradually increase the proportion of industrial wastewater until all of them are industrial wastewater. biofilm can also be directly cultured with domestic sewage mixed with a small amount (20%) of industrial wastewater, and then the proportion of industrial wastewater can be gradually increased after the success of membrane hanging until all of them are industrial wastewater.
in the process of cultivating and taming biofilms, we should pay attention to the following matters:
1. when the membrane is started, the influent flow should be less than the design value, and it can start running at 20% to 40% of the design flow. it can be seen from the appearance that when the existing biofilm is formed, the flow rate can be increased to 60%-80%. when the effluent effect meets the design requirements, the flow rate can be increased to the design standard.
2. in the biological rotating table method, the time of membrane hanging should be increased by 2-3 weeks, and the bod of influent should be less than 30 mg/l. because of the long generations of autotrophic nitrifying bacteria, the growth of autotrophic nitrifying bacteria is slow. if the organic matter in influent is too high, heterotrophic bacteria in the membrane will be dominant, thus inhibiting the growth of autotrophic bacteria.
3. when nitrite appeared in the water, it indicated that the nitrification process on the biofilm had begun; when nitrite in the effluent decreased and a large amount of nitrate appeared, it indicated that the nitrifying bacteria had predominated on the biofilm, and the work of hanging the biofilm was over.
4. the environmental conditions required for the membrane hanging are the same as those for the bacteria cultivation with activated sludge. it is required that the influent should have proper nutrients, temperature and ph, especially the amount of nutrient elements such as nitrogen and phosphorus, and the large amount of toxic substances should be avoided.
5, because the initial membrane volume is small, the oxygen content in the reactor can be slightly less. at the same time, the method of small load water intake is adopted to reduce the scouring effect on biofilm and increase the film hanging speed of filler or filler.
6. when the film was suspended at 13 degrees in winter, the whole period was 2~3 times longer than that in the warm season.
7. during the period of biofilm cultivation, because of the poor adaptability of the newly formed biofilm, a large number of membrane sludge will fall off, which can be said to be normal, especially when industrial wastewater is used for domestication, the phenomenon of membrane removal will be more serious.
8. we should pay attention to controlling the thickness of biofilm, keep it at about 2 mm, avoid excessive growth of anaerobic layer, and make the biofilm fall off balance by adjusting the hydraulic load (changing the amount of reflux water). at the same time, microscopic examination was carried out at any time to observe the changes of biofilm biophase and pay attention to the variety and quantity of characteristic microorganisms.
source: polaris water treatment network
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