Liquid purification or separation – Processes – Treatment by living organism
Patent
1996-05-29
1998-06-02
Upton, Christopher
Liquid purification or separation
Processes
Treatment by living organism
210626, C02F 312
Patent
active
057594031
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a process for the purification of waste waters by biological means, of the so-called "activated sludge" type.
During the biological purification of waste waters by the activated sludge process, a process used in more than 60% of public purification stations in the developed world, waste waters that are often previously freed from sand and degreased are led (sometimes via a pre-separator) into the activation tank where biological degradation is carried out by bacteria. This activation tank is aerated at least during certain cycles in order to enable aerobic bacteria to develop, essentially with the aim of removing carbonaceous impurities. This tank can also be subjected to non-aerated cycles for the development of anaerobic bacteria also with the aim of degrading nitrates and it is also possible to provide a second non-aerated tank for the development of anaerobic bacteria. The bacteria or micro-organisms form flocs with a density close to that of water (called "activated sludges") and the purified waste waters are separated from these flocs by density difference, conventionally by gravity in a post-separator (generally called a "clarifier" or "secondary separator" which will from now on be called a "separator"). The purified water can then be directly discharged to the river.
Sludges collected at the base of the separator are partially led again to the activation tank so as to maintain a large number of purifying micro-organisms. Excess sludges are withdrawn and then treated separately so as to reduce their volume and mass, with a view to agricultural use or to be discharged as a sediment.
Operators of stations for the biological purification of waste waters by activated sludges are confronted with two main difficulties:
1) Maintenance of a sufficient concentration of purifying micro-organisms in the activation tank in contact with the water to be treated.
If, by the physico-chemical composition of the waters entering the station, the bacteria which develop in the medium associate in filamentous flocs which settle very little (40% of stations in Europe), the separation of water/purifying micro-organisms is very difficult to achieve. The separator can no longer play its part in the clarification of the treated water and the supernatant which is directed to the river contains many purifying micro-organisms. The activation tank is then regularly washed and gradually becomes empty of purifying micro-organisms, thus leading to a halt in the purification of used waters.
2) Nitrification of the ammonium ions of the effluent to be treated since, on the one hand, ammonium ions which constitute the greater part of the nitrogenous pollution are very toxic, and on the other hand, nitrification of ammonia is the limiting stage in the removal of nitrogenous nutrients responsible in part for the problems of eutrophication of large and small rivers and lakes.
When the quantities of waste waters to be purified are greater than the treatment capacity of the station (so-called "medium or heavy load" stations, signifying that the pollution to be treated is very large in relation to the quantity of purifying micro-organisms present in the activation tank), the operator can no longer recirculate the sludges coming from the separator tank through a lack of volume capacity in the installation. It is for example the case in stations purifying waste waters from towns with an increasing population. Activated sludges are then almost totally removed from the purifying system. It follows that the quantity of micro-organisms degrading the carbonaceous pollution in the activating tank is very low and that there is a total absence of micro-organisms degrading the nitrogenous pollution, the latter not being present in "young" sludges, that is to say in sludges which have not been held for a very long time in the station. The carbonaceous pollution entering the station is thus only slightly degraded while the nitrogenous pollution is not degraded at all.
Few solutions exist for maintaining a sufficient concentration o
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Capdeville, deceased Bernard
Clauss Frederic
Hangl Manfred
Trooper Harald
Wamser Norbert
Naintsch Mineralwerke Gessellschaft M.B.H.
Upton Christopher
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