Liquid purification or separation – Processes – Treatment by living organism
Patent
1993-03-08
1994-12-13
Wyse, Thomas
Liquid purification or separation
Processes
Treatment by living organism
210614, 210617, 210903, 210906, C02F 306, C02F 330
Patent
active
053727207
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method of purification of waste water by treatment in a granular filter bed that has been activated by bacteria, preferably heterotrophic bacteria.
It is known in the art to remove nitrogen and phosphor simultaneously from wastewater with the use of an active sludge that contains aerobic bacteria. It is also known from the Swedish patent No 456 990 to add the sludge in anaerobic conditions, so that the aerobic bacteria are urged to liberate phosphor, which the anaerobic bacteria can then take up. The process takes place in treatment basins under heavy agitation.
It is known from the French patent No 2619 804 to denitrify drinking water using a granular filter bed, to which are added sources of phosphor and carbon. Here, the majority of the phosphor is taken up by anaerobic bacteria.
BRIEF SUMMARY OF THE INVENTION
It is an object of this invention to provide a method in contradistinction to the known art cited above, wherein wastewater is treated, in a granular filter bed that has been activated by bacteria, preferably heterotrophic bacteria. According to the invention, there then occurs simultaneous precipitation of phosphor and denitrification in the wastewater during the first part of its percolation through the filter bed, and later on in the bed an excess biological oxygen demand (BOD) is reduced, preferably close to zero.
It should be noted that before the mentioned inventive method is applied, the water has been first subjected to nitrification according to the known art, such that the nitrogen compounds in the wastewater have been converted to nitrates or to nitrites.
DETAILED DESCRIPTION
In a preferred method according to the invention, the BOD reduction takes place with the addition of oxygen, and, especially, in a simple and advantageous method, by blowing an oxygen-containing gas, preferably air.
A precipitation/flocking agent for precipitating phosphor is added to the wastewater immediately before the latter enters the filter bed.
The quantity of organic substances in wastewater that can function as sources of carbon for the bacterium strain is often not enough to provide sufficient denitrification. It may be necessary to add a further source of carbon, cheap hydrocarbons such as methanol, starch or molasses being selected for this purpose. These carbon sources may suitably be added to the wastewater immediately before it enters the filter bed. It is probable that the founding strain of bacteria adhere to the grains, usually sand, of the filter bed. Here they come into intimate contact with the carbon source, and nitrates present are reduced to nitrogen gas. A typical formula for such denitrification is: N+0.47N.sub.2 +0.76CO.sub.2 +2.44 H.sub.2 O bacteria.
If the amount of sludge is increased by relatively large and voluminous precipitates or floccules of phosphor, e.g. iron phosphate, then it is reasonable to assume that denitrification will be disturbed unfavorably by these precipitations. However, no negative effect at all by the phosphates on the denitrification process in different types of filter bed has been found. There thus exists the basic condition for enabling simultaneously the reduction of nitrogen, precipitation of phosphor, reduction of excessive BOD and filtration in a single process step, which requires two or three steps according to the known prior art.
Iron chloride is a suitable precipitation agent for phosphor. Other suitable precipitation/flocculation agents in use.. e.g. aluminum sulphate with or without polyeletrolyte additives, lime etc, have been found not to affect the denitrification process either.
A factor supposed to affect denitrification is washing the filter bed. Practically, it is quite possible to wash the bed so thoroughly that the bacterium strain is unfavorably reduced. Heavy counter-flushing of a stationary filter appears to be particularly injurious. However, it has been found that the washing sufficient for removing sludge and contaminants from the sand does not notably impoverish the bac
REFERENCES:
patent: 4167479 (1979-09-01), Besik
patent: 4279753 (1981-07-01), Nielson et al.
patent: 4353800 (1982-10-01), Besik
patent: 4917802 (1990-04-01), Fukaya et al.
Patent Abstracts of Japan, vol. 7, No. 100, 1983.
Research Journal WPCF, vol. 62, No. 3, 1990.
Nordic Water Products AB
Wyse Thomas
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