Liquid purification or separation – Processes – Treatment by living organism
Patent
1997-04-03
1998-06-30
Wyse, Thomas G.
Liquid purification or separation
Processes
Treatment by living organism
210608, 210194, 210218, 210539, C12M 1113, C02F 1104
Patent
active
057735263
DESCRIPTION:
BRIEF SUMMARY
In the first instance, the invention relates to a method for the anaerobic fermentation of solid organic substances in a reactor tank in which there is a mixture of the solid organic substances and an anaerobic fluid, in which a layer of material floating on a methanegenerating fluid is moved from a supply end to a discharge end of said reactor tank and a methane-forming reaction is induced in the methane-generating fluid under the floating layer, and in which fluid is sprayed in and/or on the floating layer.
Such a method is described in U.S. Pat. No. 4334997.
Solid waste substances may consist, inter alia, of vegetable. fruit and garden waste, household waste and organic industrial waste.
Purification of sewage and the processing of manure has, for decades, employed fermentation processes. Fermentation leads to the production of biogas and to stabilization of waste or slurry. Increasingly, however, fermentation processes are also being used to process waste from the agro-industry and household waste (such as vegetable, fruit and garden waste).
When use is made of a completely mixed reactor or a plug-flow reactor, the residence times of the waste to be fermented and of the biomass (methane-generating sludge) are identical to each other. However, the growth rate of methane-generating bacteria is relatively low, which results in the residence time of the biomass and thus of the material to be fermented having to be relatively long (20 to 30 days). This results in relatively long reactor tanks. Although systems are known in which a separation is brought about between the residence times of fermenting material and methane-generating biomass, they usually make use of a plurality of reactors with complicated separation systems between them. This also leads to high production and operating costs.
In the method according to the abovementioned US patent specification, the floating layer is moved and discharged independent of the methane-generating fluid zone. In other words, the residence times of the floating layer and the methane-generating slurry do not have to be identical to each other. The fluid sprayed on the floating layer consists of deoxygenated water which fulfils only a transport function for the floating layer. The fluid will have to be vigorously squirted onto and in the floating layer, which will also have a mixing effect and, as a result of this, solid portions of the floating layer are squirted into the methane-generating fluid, to the detriment of the thickness of the floating layer. In each case, no attempt is made to ferment the components of the floating layer. The floating layer is regarded only as an inconvenience and is therefore kept as thin as possible. The floating layer is discharged from the reactor tank as quickly as possible.
The object of the invention is to generate a controlled fermentation reaction in the floating layer.
To this end, the method mentioned in the preamble is characterized in that the fluid sprayed in and/or on the floating layer is extracted from the methane-generating zone under the floating layer in order to induce fermentation in the floating layer and also, by means of percolation, to remove acid fermentation products from the floating layer and to drive them to the methane-generating zone under the floating layer, and in that the floating layer is moved in such a controlled manner that the said fermentation reaction can take place in the floating layer.
Solid waste and anaerobic slurry could be mixed outside the reactor, but it is preferable for this mixing to be carried out in a mixing section of the actual reactor.
During mixing, heavy material which has sunk has to be removed periodically.
The anaerobic slurry will have to be brought to the desired temperature in order to achieve adequate fermentation performance levels. In the case of the mesophilic bacteria, this means that the temperature has to be brought to between approximately 30.degree. and approximately 40.degree. C., whilst in the case of thermophilic bacteria, a temperature of between approximate
REFERENCES:
patent: 3981803 (1976-09-01), Coulthard
patent: 4334997 (1982-06-01), Peterson
patent: 4372856 (1983-02-01), Morrison
patent: 4735724 (1988-04-01), Chynoweth et al.
patent: 4826600 (1989-05-01), Ely et al.
patent: 5228995 (1993-07-01), Stover
patent: 5616241 (1997-04-01), Khudenko
Faber Jelle
Van Dijk Meine
Paques Solid Waste Systems B.V.
Wyse Thomas G.
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