Biological waste treatment plant

Details Biological waste treatment plant Biological waste treatment plant

1999-06-08

2001-09-04

Redding, David A. (Department: 1744)

Chemistry: molecular biology and microbiology

Apparatus

Bioreactor

C435S290200

Reexamination Certificate

active

06284529

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a biological waste treatment plant.
BACKGROUND OF THE INVENTION
An enormous amount of organic waste is produced daily, by the human food chain, in agriculture and by the agro-industrial sector. This organic waste accounts for a large part of solid urban waste, it is one of the main components of sewage and constitutes the residue of the agro-industry and other industries.
The problem is how to treat this waste, so as to prevent its entering the sewerage, and to reutilize it.
Aerobic decomposition by means of micro-organism (composting) is undoubtedly a very efficient and economic technique. The biological treatment plants currently known generally operate by feeding the organic matter, either continuously or discontinuously, into treatment tanks of various shapes, where it is stirred by mechanical means, so as to achieve a state of homogenization, and moved forward, so as to make room for the inflowing waste matter; furthermore, the treated matter is kept well aerated, so as to ensure that the micro-organism which perform the biological process, are kept well supplied with the necessary amount of oxygen.
Various waste treatment plants are known which operate according to the above mentioned technique, however, they all feature drawbacks which limit their efficiency. For instance, Swedish patent 7306001-4, deposited on Apr. 27, 1974 by Johnson Construction Company AB, provides for a treatment tank with a sloping base, above which are suspended one or more sets of screw propellers, pivoted around a horizontal axis attached to a roller bridge, which are dipped inside the mass and move across the entire length of the treatment tank, from the inflow will to the outflow wall, thus mixing and pushing the mass forward to make space for new waste matter. When the screw propellers reach the outflow wall they are turned around their hinges, pulled out of the mass and then moved back to the inflow wall, where they are once again dipped into the mass and begin a new cycle. The air for the micro-organisms performing the biological process is pumped through the screw propellers themselves, which are hollow inside. This kind of system features various serious drawbacks, such as a loss of about 50% of the working time for the idle return of the screw propellers across the treatment tank after each process cycle, the non-uniform progress of the mass from the inflow side of the treatment tank to the outflow, due to the necessary extraction and re-immersion of the screw propellers inside the mass, and the prerequisite of a treatment tank with a heavily sloping base, to help the mass in its progress, since otherwise it would exercise too strong a resistance against the screw propellers, jeopardising the correct operation of the system's mechanical parts. This loss of time translates into a reduction of the treating capacity, while the non-uniform progress of the mass, as well as the variation, in the order of 50%, of the time required by the waste matter to achieve a sufficient degree of maturation, may completely alter the outcome, which is measured as the degree of maturation and is closely linked to the time spent in the treatment tank by the totality of particles composing the mass, and other parameters, such as mixing and aeration.
Italian patent 23342 of Oct. 18, 1983, deposited by Secit SpA, provides for a technique similar to the one described in the Swedish patent, whereby the screw propellers advance in the same direction as the mass, while in this case the screw propellers are removed from the mass by means of translation along their axis, perpendicularly to the base of the tank, and the aeration of the mass takes place through protected pipes laid on the bottom of the treatment tank.
With the exception of the non-uniform advance of the mass, which defect is remedied by the extraction and re-immersion of the screw propellers, which translate along their axes, no remedy is found for the other drawbacks of the Swedish patent, on the contrary, to these one must add the further disadvantage of having to provide for a building large enough to house the entire plant, which is quite tall, so as to enable the lifting of the screw propellers.
Since all plants of this kind must be adequately sealed from the outside, for obvious reasons of environmental impact, a higher building, besides entailing higher construction costs, also requires higher operating costs, due to the larger amounts of air to be circulated within the building and then deodorized, since the number of change of air per hour must remain equal.
Italian patent of Aug. 7, 1987 in the name of Sorain Cecchini SpA describes a technique whereby the organic matter is contained inside a preferably sloped treatment tank and one or more sets of slanted screw propellers, suspended from a sliding bridge parallel to the tank base, stir and move the mass, not by pushing it but by pulling it toward the outflow, in order to reduce the stress exercised by the mass on the screw propellers.
In this case, the screw propellers move in an opposite direction compared to the mass, but this plant too features the drawback of their idle return run, as well as the overturning of the screw propellers at the end of the cycle and their re-immersion into the mass, thus featuring the same drawbacks as the previous invention.
DISCLOSURE OF INVENTION
The present invention relates to a biological waste treatment plant aimed to remedy the drawbacks affecting the above mentioned inventions and to allow economies, with regard to both the initial investment and operating costs.
The main objects of the present invention are:
to eliminate of the dead time due to the idle return of the screw propellers;
to use horizontal treatment tanks and industrial pavings, without having to incorporate any channels of pipes;
to guarantee a regular and uniform progress of the treated mass, thanks to the use of a simple and easily adjustable system;
to ensure the continuous and proportioned outflow of the mass from the tank, without the need of any effluent clearing pockets;
to guarantee the self-cleaning of the screw propellers, with the continuous elimination, while operating, of the threads and rags which inevitably get wrapped round the screws;
to maintain a constant height of the mass in the tank, so as to compensate the reduction of volume due to evaporation and to other chemical processes, by adopting simple measures;
to continuously remove the dense and hardened layers of matter, which may accumulate on the bottom of the tank, if they are not stirred by the screw propellers for a long time;
to ensure the forced aeration of the organic mass, so as to minimize condensation inside the building housing the biological treatment tank;
to recover the heat produced by the biological processing cycle and use it to heat the ventilated air circulating inside the building, in the colder and damper season, thus reducing humidity, with considerable benefits from the point of view of the enviromental impact.
The present invention is based on the principle that the waste matter to be treated is stirred and moved exactly as if it were done manually, thus creating a close succession of heaps, by means of mechanical tools such as screw propellers.
According to the present invention, the treatment tank is a horizontal rectangular tank into which the organic solid waste is fed, either continuously or discontinuously, along one of the longer walls, by means of conveyor belts or any other mechanical means, the processed matter outflowing on the opposite side.
According to the preferred embodiment of this invention, above the tank there is a bridge with a trolley to which two screw propellers are attached, in a slightly slanted position, with the tips pointing towards the inflowing side. The screw propellers are lowered into the mass near the inflowing side of the treatment tank and are then moved longitudinally across the entire length of the tank by the bridge. Due to their inclination, the screw propellers plough through the mass forming longitu

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