Liquid purification or separation – Processes – Treatment by living organism
Patent
1990-12-20
1992-08-11
Wyse, Thomas
Liquid purification or separation
Processes
Treatment by living organism
210607, 210626, 210630, 210903, C02F 302, C02F 330
Patent
active
051376369
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the biological purification of waste water by the active sludge method, wherein the waste water is contacted with microorganisms in two treatment zones by being alternatingly introduced into said treatment zones and being treated under alternating anoxic and aerobic conditions and wherein the waste water thus treated is introduced into a clarification zone to separate sludge, at least a part of the separated sludge being recycled and mixed with non-treated waste water.
GB patent specification No. 1404565 discloses a process of the above-mentioned type. This prior art process permits an efficient removal of nitrogen at a relatively low energy consumption. The nitrogen removal is based on a nitrification followed by a denitrification.
The nitrification which is effected under aerobic conditions comprises the oxidation of nitrogen in the form of ammonia so as to form nitrate. The nitrification process can be represented as follows: ##STR1##
The denitrification which is effected under anoxic conditions involves the decomposition of organic matter using nitrate ions as oxidant. As a result of the decomposition nitrate ions are reduced to free nitrogen which is liberated in gaseous form.
The denitrification can be represented as follows: ##STR2##
Under aerobic conditions an oxidation of the organic matter contained in the waste water is also effected. This reaction can be represented as follows: ##STR3##
As mentioned above, nitrification in the presence of organic matter causes the organic matter to decompose. This is inconvenient as organic matter is a prerequisite for carrying out the denitrification.
As will appear from the above, the bacterial processes in question are processes wherein the bacteria use carbon for their reproduction which carbon is supplied by CO.sub.2 in the nitrification process and in the two other processes by the carbonaceous material contained in the crude waste water.
The above described biological purification process has been further developed as described in DE patent application No. 3427310.7. In this purification method the waste water is contacted with microorganisms in a first treatment zone under anaerobic conditions before it is subjected to alternating anoxic and aerobic conditions and the sludge from the clarification zone is recycled to the first treatment zone.
Apart from an efficient nitrogen removal such process affords satisfactory phosphorus removal.
The phosphorus removal is caused by the activity of two types of bacteria, viz:
During the anaerobic treatment of the waste water the phosphorus accumulating bacteria containing accumulated polyphosphate absorbs the low molecular organic matter which is stored, e.g. as polyhydroxy butyrate (PHB), the relatively energy rich polyphosphate being used as an energy source. This results in the formation of orthophosphate ions which are liberated to the aqueous medium in the anaerobic treatment zone.
During the subsequent aerobic treatment of waste water the accumulated and hydrolyzed suspended organic matter is oxidized and the energy thus liberated is used partly for the growth of the microorganisms and partly for the accumulation of orthophosphate ions from the aqueous medium in the phosphate accumulating bacteria in the form of polyphosphate. Thus, dissolved phosphate is removed from the waste water.
It applies to both the above known processes that the waste water introduced into the clarification zone should come from an aerobic treatment zone as an influx from an anoxic zone would result in a relatively high NH.sub.3 content in the effluent from the clarification tank.
The practical application of the above known processes requires that ratio of nitrification time to denitrification time is maintained at about 1,67:1 or higher in order to maintain the NH.sub.3 concentration in the purified waste water at a desirably low level.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 illustrate variations in the ammonia and nitrate concentrations in prior art processes.
FIGS. 3, 4, and 5 i
REFERENCES:
patent: 3964998 (1976-06-01), Barnard
patent: 3977965 (1976-08-01), Tholander et al.
patent: 4183809 (1980-01-01), Klapwijk et al.
patent: 4663044 (1987-05-01), Goronszy
patent: 4867883 (1989-09-01), Daigger et al.
Harold A. Nicholls, Prog. Wat. Tech. Vol. 8, Nos. 4/5, pp. 639-652, Pergamon Press 1977, Modification of Extended Aeration Plants in Johannesburg, South Africa, to Achieve Denitrification.
Gert Petersen, Kruger Publication, Nov. 16-18, 1987.
I. Kruger Systems A/S
Wyse Thomas
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