Liquid purification or separation – Processes – Treatment by living organism
Patent
1998-01-16
1999-03-02
Upton, Christopher
Liquid purification or separation
Processes
Treatment by living organism
210752, 210764, C02F 1114
Patent
active
058766138
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the treatment of sludge with a high content of fermentable organic matter, in particular sludge derived from processes for urban and industrial waste water treatment, drinking water treatments using surface or ground water, or sludge derived from network cleaning operations. The invention also applies to the treatment of other waste from treatment facilities such as screen debris, fats and sand.
More precisely, the invention relates to a process for stabilizing such sludge or waste, that is to say in particular for its deodorization or sanitization.
In France, the quantity of sludge produced by wastewater and drinking water plants is over one million tonnes of dry matter per year. Approximately, one half of this sludge is put to agricultural use while 35% is stored in waste tips. As the production of this sludge is on the increase, it should not cause a hazard for the environment or human health. This sludge contains germs of which some are pathogenic (Coliform bacteria, salmonellae, helminth eggs. . . ). In addition, it is highly fermentable and is a source of gas generation (amines, hydrogen sulphide, mercaptans) giving rise to olfactory nuisances.
These considerations account for the necessity, for the above-mentioned treatment sectors, to make provision for at least one stage of sludge stabilization intended to obtain sludge that is no longer undergoing change, or at least undergoing very slow change, both at biological level and at physico-chemical level.
This sludge is made up of a soluble part and a dry matter part. The dry matter comprises approximately 30% mineral compounds and approximately 70% of so-called "volatile" organic matter. Traditionally, the main objective of sludge stabilization treatments is in particular to reduce its fermentable ability by oxidizing the organic matter for its improved bio-assimilation or by eliminating the reducing germs which are the cause of fermentation.
As specified above, sludge stabilization treatments are also intended to meet two main objectives: by reducing the number of reducing bacteria (in particular sulphato-reducing germs) and/or by reducing organic matter concentration.
Also, the stabilization stage must, for reasons relating to operating costs, cause the least possible deterioration to sludge dehydrating capacity This parameter has a direct effect on polymer consumption required by treatment processes to convert sludge to other uses or to store as waste.
2. Description of the Prior Art
There are numerous stabilization processes in the state of the art for such sludge. They are essentially classified as follows:
More recently, two new processes were examined but have not yet, as at the date of filing of this present application, been properly developed at industrial level.
All these processes can be applied to sludge having a relatively high concentration of dry matter, frequently between 50 and 100 g/l. This therefore requires that this sludge is submitted to preliminary thickening treatment generally by settling or flotation. Treatment facilities must therefore be designed so that they are of sufficient size to allow a minimum contact time of 24 hours.
Aerobic digestion reduces organic matter concentration and consists of extended aeration of sludge so that the development of the aerobic microorganisms it contains can be continued until elimination of the organic matter substrate, achieving self-oxidation of these microorganisms.
Aerobic stabilization can be conducted at 30.degree.-40.degree. C. (mesophil stabilization) or at 45.degree.-60.degree. C. (thermophil stabilization). In the latter case, the temperature increase leads to partial sanitization of the sludge.
The stay length of the sludge in aerobic stabilization reactors is generally 10 to 15 days which achieves 30 to 40% elimination of organic matter, 90-96% elimination of sulphurated matter emission, and a reduction of over 2 log in faecal germs. If the facilities in which this aerobic stabilization is carried
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27 Feb. 1985, Database WPI/Derwent Publications Ltd., 85-089562, London, Great Britain, JP A 60,038,100, 1 Page.
Bonnin Christophe
Coriton Gabriel
Omnium De Traitements et de Valorisation
Upton Christopher
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