Plant husbandry – Process
Patent
1999-05-06
2000-09-05
Poon, Peter M.
Plant husbandry
Process
71 9, 210602, A01B 7902, C05F 1108, C02F 332
Patent
active
061124583
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND ART
The invention concerns a process for the conversion of sewage sludge to humus as well as a polder for the carrying out of the process.
Large parts of the population have reservations concerning the use of sewage sludge as a fertilizer and for the improvement of the ground. Although legislation attempts to ensure the general public that there are ordinances for indirect polluters of public sewage sludge, parts of the public fear an accumulation of harmful substances in the ground.
Furthermore, the surplus sludge of the waste water treatment plant is of very liquid consistency (99% water). In order to keep the transportation costs within limits it is necessary to carry out expensive dehydration processes.
One known process for the conversion of sludge to humus applies reeds (Phragmatis). These plants, however, are very expensive as they must be cultivated in bales. Furthermore, the strong stalks and roots of the reed require increased working before the converted sludge can be processed. Due to the regular filling with sludge in the known process the degree of complete drying of the converted sludge is relatively low. As the reed plants are used over the entire filling period of 10-15 years the percentage of decomposed plants is relatively low.
German Patent No. DE 43 23 610 describes a bio-polder (interim storage) for the biological clarification and/or mineralization of soil and sludge and for the biological clarification of waste water that is polluted by organic and inorganic substances. The bio-polder usually contains at least one aerobic and one anaerobic layer that lie on top of each other. The harmful substances that have not been eliminated in the aerobic layer are drawn into the anaerobic layer by gravity and are subjected to successive oxidative and reducing processes.
The invention is the result of the task to find a process for the conversion of sewage sludge to humus avoiding chemicals. This task is met for the process for the conversion of sludge to humus by the characteristics as stated in the describing part of claim 1.
Further development and advantageous arrangement of the invention arise from the further claims, the description, and the drawings.
SUMMARY OF INVENTION
The invented process for the conversion of sludge to humus is characterized by the following steps: filling height; and/or discharge of the impounding water; and
The invented process is a low-cost process for the dehydration of sludge that in comparison to mechanical processes reduces the quantity of the sludge. The invented use of fast-growing plants with fine roots results in a fine and even root penetration, an accumulation of micro-organisms, and a reduction of harmful substances (a PCB--polycyclic biphenol, AOX, PAK).
In addition, the sludge that is covered with grass decompose in a shorter period of time than can be achieved by the known process with reed. Furthermore, the use of fast-growing plants with fine roots has the advantage that the low height of the plants favors ultraviolet radiation. This results in a remarkable reduction of salmonella or phatalates (softening agents) that are contained in the sludge. The degree of hyginisation is considerable.
The final product is dry, crumbly, dark-brown soil that is completely free of waste water odors and is characterized by good physical features for the improvement of soil. Furthermore, a remarkable reduction of the volume can be achieved.
Due to the use of fast-growing plants with fine roots cycles of the conversion can be achieved that are clearly shorter than by the known process with reed. In addition, the invented process is cost-saving compared to the known process.
Furthermore, the low depth of the filling layers and the long resting periods of the sludge result in a better aeration of the soil in the invented process.
In a further arrangement of the invented process, the single steps of the process are carried out in parallel in further polders. Thus, interruption of the filling process can be avoided. It is preferred to use three polders: Th
REFERENCES:
patent: 4317671 (1982-03-01), Willisch
patent: 5174897 (1992-12-01), Wengrzynek
Bencsik et al., Acclerated Degradation of Toxic Compounds . . . Grass Cultivation, Abstract, Sep. 1996.
Palo Francis T.
Poon Peter M.
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