Liquid purification or separation – Processes – Treatment by living organism
Patent
1990-09-07
1993-05-04
Wyse, Thomas
Liquid purification or separation
Processes
Treatment by living organism
210613, 210622, 210631, C02F 328
Patent
active
052079112
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to a method for the break-down and recycling of solid urban waste by means of anaerobic fermentation.
The conventional technique for the break-down of solid urban waste provides for the recovery of re-usable raw materials, such as iron, paper and/or plastics, from the waste by sorting before the rest is left to ferment either spontaneously or after priming with suitable cultures.
In this case the materials recovered are contaminated with putrescible organic substances so that their transport and their working at re-processing plants cause foul-smelling emissions, atmospheric pollution and the risk of dermatosis to the personnel carrying out the re-processing.
In order to avoid these problems, the present invention provides a method characterised in that it comprises the steps of: transport on a fluidised bed, biological sludge from aerobic purification plants, inoculated with bacterial strains which can effect anaerobic break-down, fermentation cell, and until the emission of biogas has effectively ceased.
As a result of the fermentation, the method enables an inert material to be obtained which can be removed from the cell and used as an infill material for land reclamation, or which may be sorted to allow the recovery of raw materials which can be recycled or used as energy sources for the production of electrical energy by means of their gasification.
A further subject of the invention is constituted by the cell for the anaerobic fermentation of the aqueous suspension of urban solids and biological sludge in a fluidised bed, characterised in that it includes a closed containing structure provided with opening means for the discharge of the fermentation product, the bottom of the container and adapted to enable the liquid in the suspension to percolate along the walls of the container, and percolated through the filtration means.
A further subject of the invention is the whole installation for carrying out the method.
Further characteristics and advantages of the present invention will become clear from the detailed description which follows with reference to the appended drawings, provided by way of non-limiting example, in which:
FIG. 1 is a block-schematic diagram illustrating the method of the invention, and
FIG. 2 is a schematic view of a fermentation cell for carrying out the method.
With reference to the drawings, solid urban waste 1 is supplied, as it is, without prior sorting, to a grinding mill 2 where it is crushed to dimensions generally between 1 and 5 cm.
From the mill 2, the crushed solid waste is supplied to a mixer 5 constituted, for example, by a screw which mixes it with a flow 4 of an aqueous suspension of biological sludge 3 produced by the aerobic purification of aqueous effluent. The biological sludge used typically has a dry content of between 3 and 30% by weight.
According to a further innovative aspect, before mixing with the solid urban waste, the biological sludge is subjected to a heat-conditioning treatment in an autoclave 6 at a temperature of between 40.degree. and 100.degree. C. for a period of from 10 to 180 minutes and is inoculated with selected bacterial strains 7 in a quantity sufficient to effect the anaerobic break-down of the putrescible material contained in the mixture of solid urban waste and biological sludge.
The solid urban waste and the biological sludge are mixed typically in a ratio of from 10:1 to 10:10 and the mixing process is carried out at a temperature of between 20.degree. and 80.degree. C. over a period of between 1 and 30 minutes.
At the output of the mixer, a flow 8 is added to the mixture in a ratio such as to obtain a flow of a suspension which has a dry content preferably of between 15 and 30% by weight. The suspension 9 is then supplied by a centrifugal pump 10 with a backward rotor to a cell 11a where it undergoes anaerobic fermentation.
The cell 11a which is illustrated in greater detail in FIG. 2, is constituted by a reinforced concrete container provided with a door 12 which can be sealed and is
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patent: 4067801 (1978-01-01), Ishida et al.
patent: 4323367 (1982-04-01), Ghosh
patent: 4400195 (1983-08-01), Rijkens
patent: 4684468 (1987-08-01), De Baere
Pellegrin Roberto
Tasca Franco
Tasca Silvio
Rosewell Limited
Wyse Thomas
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