Liquid purification or separation – Processes – Treatment by living organism
Patent
1989-10-04
1992-01-07
Wyse, Thomas
Liquid purification or separation
Processes
Treatment by living organism
210903, C02F 334
Patent
active
050788841
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for biological denitrification combined with the oxidation of ammonium ions.
The denitrification process is based on the reduction of nitrate or nitrite ions into nitrogen gas, via the intermediate nitrogen oxides NO and N.sub.2 O, by, in essence, aerobic bacteria, see for example R. Knowles, Denitrification, Microbiol. Rev., 46, 43 (1982). The above mentioned nitrogen oxides often act as terminal electron acceptors in the absence of oxygen. Under anoxic conditions, the overall reaction will be (R. K. Thauer et al., Energy conservation in chemotrophic anaerobic bacteria, Bacteriol. Rev. 41, 100 (1977)): ##STR1##
In respect of the electron donor, distinction can be made between heterotrophic denitrification, with organic compounds used as electron donor, and autotrophic denitrification with sulphide used as electron donor (see U.S. Pat. No. 4,384,956).
E. Broda (Two kinds of lithotrophs missing in nature, Z. Allg. Microbiol. 17, 491 (1977)) suggested that, in theory, ammonium ion can be used as inorganic electron donor as well: ##STR2##
The overall denitrification reaction (reaction scheme 3) is then rather exergonic. ##STR3## Therefore E. Broda suggested that denitrifying microorganisms which use ammonium ion as electron donor, theoretically may exist. However, the existence of these microorganisms has never been demonstrated, as is indicated in the title of the article by E. Broda "lithotrophs missing in nature".
As a result of extensive research and experimentation we have now surprisingly found a process for biological denitrification in which ammonium ion is used as electron donor in the denitrification.
The advantages of the process are enormous, much less oxygen is required for the ammonium ion oxidation and no extra carbon-source is necessary to achieve denitrification.
The process may advantageously be applied under conditions of high ammonium ion concentrations in waste water or in cases in which conventional nitrification will result in high concentrations of nitrate ion in the effluent. For example the process may be applied in the purification of fish ponds, swimming pools or manure.
Generally, the denitrification process is preferably carried out at pH of 5-9, more preferably 6-8 and preferably at a temperature of 5.degree. to 60.degree. C., more preferably 15.degree. to 40.degree. C. The process is preferably used under conditions resulting in 5-5000 mg/l NH.sub.4.sup.+ -N and 0-5000 mg/l NO.sub.3.sup.- -N. This gives an overall efficiency of at least 80-90% nitrate removal according to reaction scheme 3.
According to another advantageous aspect of the invention a process is carried out in which the combination of reactions 3 and 4 takes place resulting in the overall reaction scheme 5 ##STR4##
In this process part of the ammonium ion is oxidized into nitrate ion by nitrifying bacteria. This nitrate ion will be treated further with the remaining ammonium ion, according to reaction scheme 3. This process may be applied where substantially no nitrate is present or when the ratio of nitrate and ammonia is not in proportion to reaction scheme 3.
A person skilled in the art will easily find optimal microbiological conditions or will be able to design appropriate reactor(s) in which the process of the invention is to be carried out. For example, when using the process in a waste water purification plant, in which reaction 5 will take place, it is possible to denitrify in more than one reactor, in each part of this the process occurs. One reactor in which the whole process takes place is also possible, for example, by using zones having different reaction conditions or by immobilising all necessary microorganisms on a particulate solid phase e.g. on solid particles.
The process of the invention is advantageously carried out, for example when treating waste water in an activated sludge reactor, fluidized-bed reactor or fixed film reactor.
The ammonium ion oxidation into nitrogen gas using nitrate ion (according to reaction scheme 3) appears from the differen
REFERENCES:
patent: 4552663 (1985-11-01), Spector et al.
Gist-Brocades N.V.
Wyse Thomas
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