Liquid purification or separation – Processes – Treatment by living organism
Patent
1993-06-25
1995-07-11
Wyse, Thomas S.
Liquid purification or separation
Processes
Treatment by living organism
210610, 210631, C02F 1104
Patent
active
054318190
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for the biological treatment of essentially solid organic material, wherein the material is successively subjected to a hydrolysis treatment and an anaerobic fermentation.
BACKGROUND OF THE INVENTION
Several types of treatment systems for solid biological waste are presently being developed. These systems should make it possible, firstly to obtain a stabilized and sanitarily reliable end product which can be used for example as compost or soil improver, and secondly to obtain a volume reduction, making dumping less expensive. The types of waste that can be treated using such treatment systems include: household refuse treatment plant;
The biological systems can be divided into aerobic and anaerobic systems. An aerobic system is concerned with conventional composting and improvements thereof. Anaerobic systems can be divided into anaerobic fermentation (30.degree.-40.degree. C.), thermophilic fermentation (55.degree.-65.degree. C.) and two-stage systems. Anaerobic fermentation and thermophilic fermentation are processes wherein the entire waste flow is treated, without differentiating between the residence time for liquids and the residence time for solids in the system. Such systems are mostly single-stage and they can be applied both as a completely mixed system or in a plug stream reactor. A disadvantage of these systems is the relatively long treatment time (residence time) and the resulting necessity of large and expensive equipment.
In a two-stage process as defined in the preamble, the selected residence time of the solid material can be longer than the residence time of the liquid and, moreover, different biological reactions can be carried out in different parts of a plant.
A process according to the preamble is known, for example from European patent applications 37612 and 142873. According to EP-A-37612 solid organic material is subjected to a two-stage anaerobic treatment, whereby the material is decomposed into mainly lower fatty acids and other water soluble substances, carbon dioxide, methane and a residual fraction in the first stage, and the water soluble substances and the fatty acids are treated in a second stage leading to formation of methane and carbon dioxide. According to EP-A-142873 the solid material resulting from the first stage (hydrolysis/acidification) is partly recycled and the liquid is treated in a methane reactor in the second stage.
An advantage of these known systems is the relative simplicity of the necessary equipment and of the execution of the process. A disadvantage, however, is that no advanced degree of degradation and thus no substantial volume reduction can be achieved for many types of waste, and thus the cost of dumping is not notably reduced.
A process for the production of methane from solid vegetable waste, wherein the vegetable material is treated with ciliates (microorganisms such as present in the rumen of ruminants) and methane bacteria in a liquid medium, is known from European patent application 159054. The liquid thus obtained can be treated in a separate anaerobic reactor wherein additional methane is produced. Such a method which is thus based on the use of the rumen flora of ruminants, is also known as the so-called RUDAD system (RUmen Derived Anaerobic Digestion).
The RUDAD system has the advantage that waste also containing components that are difficult to degrade can be degraded to a large extent and can thus be considerably reduced in volume. A disadvantage is however that the process should be carefully controlled and that fluctuations of the quantities and nature of the waste supply as occurring in practice disturb the process stability to the extent that an effective waste degradation is no longer achieved.
The problem of fluctations of the supply could in principle be solved by using a large equalizing buffering tank, but this does not solve the problem of rapid acidification of the easily degradable part of the waste (production of acetic and propionic acid). This acidi
REFERENCES:
patent: 4318993 (1982-03-01), Ghosh et al.
patent: 4384956 (1983-05-01), Mulder
patent: 4915840 (1990-04-01), Rozich
"High Rate Two-Phase for the Anaerobic Degradation of Cellulose, Employing Rumen Microorganisms for an Efficient Acidogenesis", Biotechnology and Bioengineering, vol. 31, 1988, By H. Gijzen et al., pp. 418-425.
Hack Petrus J. F. M.
Vellinga Sjoerd H. J.
Paques B.V.
Wyse Thomas S.
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