Liquid purification or separation – Processes – Treatment by living organism
Patent
1987-05-04
1989-11-28
Wyse, Tom
Liquid purification or separation
Processes
Treatment by living organism
210617, 210622, C02F 306
Patent
active
048835943
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for biological and/or physical elimination of unwished water components from water by means of flooded biofilm reactors and a plant for application of the process.
More particularly, the process and the plant is for purification of water contaminated with unwished inorganic compounds like ammonium, nitrate and nitrite, and toxic volatile hydrocarbons like halogenated hydrocarbons or for example ammonia containing compounds respectively. It is known that biofilm reactors have advantages compared with thoroughly mixed reactors concerning slow growing microorganisms like nitrifying bacteria. For example, microorganisms grown on the support material remain in the system and are enriched additionally. The problem of biofilm reactors is to supply oxygen or other gases like hydrogen to biofilm microorganisms and to eliminate the metabolic end products carbon dioxide and nitrogen in case of denitrification. Further, concentration gradients are formed in biofilm reactors from the reactor inlet towards the reactor outlet, decreasing performance. The enlargement of inner surface of a biofilm reactor by means of a support material with large specific surface (for example O.sub.s .gtoreq.250 m.sup.2 /m.sup.3) can increase the biomass production and the turnover essentially. With fixed bed reactors the hydraulic flow, indeed, can be affected. This problem does not exist using fluidized bed reactors. Therefore they were tried for a long time for water purification. The realization of a 15 to 20% bed expansion in a technical scale has turned out, indeed, as problematic, because the fluidized bed got uncontrolled after direct aeration of the reactor for support of microbial growth. The air injection at the bottom of the fluidized bed reactor for covering the oxygen requirement has also turned out as disadvantage, because bubbling up gas is continuosly expelling support material and therefore complicating continuous operation. For this reason the external enrichment with oxygen became important. The oxygen concentration of supplied water is increased to values of approximately 50 g O.sub.2 /m.sup.3 before introduced into fluidized bed, using pure oxygen at overpressure in an oxygen generator. A characteristic feature of this process is a significant decrease of oxygen concentration, corresponding to the height of fluidized bed. Possible impairments of biological turnover process can only be prevented by high recirculation rates, what also is thought to be disadventageous.
The problem of the invention is to provide a process and a plant for application of the process, where gases for water purification are introduced into the biofilm reactor in such a way that no obstruction of the reactor or inhibition of microbial growth does occur.
According to the invention this problem is solved in that the reactor support material all over the height of the reactor's bed is constantly admitted with a gas for gas supply or gas removal. A fluidized bed reactor is used as a biofilm reactor where a substance exchanger made of non-porous synthetics is inserted. A bubble free gas introduction into the biofilm reactor is achieved by this substance exchanger, so that e.g. oxygen supply for the entire microbial population is achieved to fluidized bed support material. If required, the gases in recirculated water stream can be concentrated by means of a further gas exchanger of non-porous synthetics. Unwished flotations, caused by metabolic end products carbon dioxide and respectively nitrogen from denitrification are prevented by simultaneous removal by means of a substance exchanger, deviating a partial gas stream or placing an appropriate absorber unit into the gas cycle. Other volatile substances like e.g. low molecular halogenated hydrocarbon compounds or other organic compounds are eliminated continuously from the gaseous phase and thus from the water by activated carbon in the absorber. Therefore the substance exchanger(s) simultaneously are for gas supply and gas removal. The special and uniform gas sup
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Braeutigam Hans-Juergen
Sekoulov Ivan
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