Liquid purification or separation – Processes – Treatment by living organism
Patent
1992-08-28
1995-10-17
Wyse, Thomas
Liquid purification or separation
Processes
Treatment by living organism
210150, C02F 306
Patent
active
054587794
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for purification of water and to a reactor for use in the method.
There are known various different methods for purification of waste water, for instance mechanically by sedimentation or sieving, chemical purification by addition of chemicals and gas treatment, for instance with ozone or chlorine. Further, it is known to treat the water biologically, i.e. by exposing the water to a culture of bacteria that will cause the desired conversion of the pollutants. To a great extent all the above mentioned method are combined.
The present invention is connected with problems in biological purification with bacterial cultures.
Biofilm, as discussed below, should be understood to be a layer of a bacterial culture, in which the bacteria may be of aerobic, anoxic or anaerobic type, depending on what kind of purification is desired.
Biological purification methods are primarily used for waste water, but may also be used for purification of water in aquacultures and for drinking water. The present invention may be exploited in all the fields where biological methods may be used for water and sewage purification, particularly in aerobic, biological processes where the reactor content is oxygenated and stirred by means of aeration, but also in anaerobic processes where the reactor content is not aerated, but is kept under stirring mechanically or hydrodynamically.
Biological methods are extensively used for purification of polluted water. Traditionally, biological methods have been used to reduce the content of organic material in the water, but particularly in the later years biotechnological methods have also been taken into use for removal of ammonium (nitrification), removal of nitrogen by denitrification and removal of phosphorus.
A distinction is made between aerobic and anaerobic processes. In aerobic processes the microorganisms need oxygen, while the microorganisms which live in anaerobic processes must have an oxygen free environment. Most of the purification plants around the world are based on aerobic processes, but there is a growing interest for anaerobic processes, particularly in connection with removal of nitrogen and purification in connection with nitrogen removal and purification of concentrated organic industry sewage.
A distinction is also made between bioslurry systems and biofilm systems. In bioslurry systems the microorganisms are floating in the water aggregated together in sludge particles in a bioreactor. In aerobic slurry systems, active slurry systems, the slurry particles are separated from the water and then returned to the bioreactor, thereby to maintain the amount of biomass as high as possible.
In biofilm systems the microorganism grow on fixed surfaces in the bioreactor. The biofilm grows in thickness as the microorganisms propagate, and parts of the biofilm will eventually peel off and new biofilm will be formed. Because the biofilm is fixed and the water moves by, the biomass does not have to be returned for the microorganisms to be exploited as much as possible.
Lately, there has been a considerable tendency to replace slurry systems by biofilm systems. The main reasons for this are: result that the bioreactor will be smaller in volume. also in the composition of the raw water, which make the biofilm methods more robust than the active slurry methods. dramatic consequences in the biofilm methods as in the active sludge methods, because the sludge concentration out of the bioreactor is much lower. biorotors (rotating biological contactors), trickling filters and fluidized bed reactors. Examples of trickling filters are given in British patent 2197308, EP-A2 301.237 and French patent 73.17859, in which the reactor is packed with elements that are immobile. There are also biofilters in which the carrier medium for the biofilm is immersed and where the water volume is aerated, but these systems are based on a solid carrier which is stationary in the reactor, or on foam rubber like elements which are allowed to float in an active sludge reactor.
REFERENCES:
patent: 4067936 (1978-01-01), Ellis et al.
patent: 4122011 (1978-10-01), Strigle, Jr.
patent: 4391703 (1983-07-01), Crosby
Abstracts of Japan, vol. 5, No. 145, C287, Abstract of JP60-28888 publ. 1985, Feb. 14.
Database WPIL Week 8721, Derwent Publications Ltd., London, GB; AN 87-146447 & JP-A-62 083 097, 16 Apr. 1987.
Kaldnes Miljoteknologi A/S
Wyse Thomas
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