JPH02998B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves the treatment of solid organic matter derived from plants and/or animals in at least two stages, the first of which is carried out under anaerobic conditions to produce water-soluble products. The present invention relates to a process for the anaerobic conversion of solid organic substances as described above, in which methane is produced from the organic compounds under anaerobic conditions in the next step(s).

"Wiukler Prins Technische Encyclopedio"
(1) Page 119 (1975) states that so-called anaerobic digestion is a method of leaving solid organic waste for a long time in order to convert it into compost. The method of forming compost involves microbial digestion of easily attackable organic compounds under aerobic conditions. This composting method is usually an open air or land filling method in which waste is disposed of by forming stacks. During this process, the stacks are moistened and turned over several times with an excavator or gulag crane.

The latter method is labor-intensive, time-consuming and space-intensive, so its cost is significant. Another disadvantage of this method is that aerobic digestion requires conditions that, on the one hand, partially convert valuable organic matter into worthless carbon dioxide and water and, on the other hand, avoid contamination of groundwater.

“H ₂ O”Tijdschrift Voor Watervoorziening
en afvalwaterbehandeling (Periodical for Water Supply and Waste Water Treatment) (22) 531 (1977) uses anaerobic fermentation to aqueous suspensions and solutions of organic wastes and inorganic salts with low viscosity and low solids content. Describe what to do. According to this description, some of the polysaccharides present (e.g. cellulose) are hydrolyzed into soluble monomers in a previous step under the influence of anaerobic bacteria under non-strict anaerobic conditions, and subsequently this soluble monomer is Converts into fatty acids. Methane is then produced from the fatty acids in a reactor under anaerobic conditions. This method is not applicable for the digestion of organic waste to form compost.

Said anaerobic fermentation of aqueous suspensions and solutions with low viscosity and low solids content is obtained by carrying out the previous step in a tank under anaerobic conditions,
Even this method described in "H ₂ O" (10), 296 (1977) is not suitable for the digestion of solid organic wastes.

In these two embodiments of anaerobic fermentation of aqueous suspensions and solutions of organic matter with low viscosity and low solids content in a methane reactor, a bacteria-rich sludge, preferably a granular product, is separated from the effluent and gases. be done.

If it is desired to produce methane in a single step from a solid organic material instead of from an aqueous suspension or solution of the organic material with low viscosity and low solids content, the reaction rate is likely to be very low. Therefore, the reason why the medium has a strong transfer inhibiting effect on acid-producing microorganisms as well as methanogenic microorganisms is that high acidity is reached quickly. As a result, there is no further acid generation and no methane generation, but there is an odor evolution (H ₂ S, other sulfur compounds and
NH ₃ ) (Reference, Journal of the environmental
engineering division, June 1978, No. 415-422
page).

The percentage of dissolved COD and the curve of fermentation vs. time for this conversion are shown in FIG. 1, where the dotted line indicates the dissolved fatty acid-COD content.

From this figure the maximum solubility in this case is more than 25%
It is clear that the COD is already dissolved from the inoculated mixture of straw + beet pulp + dried cow dung after 3 days of pre-acidolysis. Next, this COD contains 14% fatty acids + COD.
After 30 days this increased to approximately 25%. No methane gas is generated at this stage.

A suspension or solution of organic matter having a low viscosity and low solids content is obtained by first grinding the dry material, then dispersing this ground material in water, and subsequently fermenting it anaerobically. On the other hand, attempts have also been made to carry out anaerobic fermentation of solid organic waste using the above-mentioned method. However, it was found that the dry solids content of this slurry could not exceed % by weight.

Additionally, US Department of Commerce PB-258499 dated August 1976.
On page 36 of the publication, a method is described for producing a slurry with a solids content of 12% by weight by using the effluent of a methane reactor for producing a slurry of solid waste. Wastes, such as fertilizers, municipal solid waste, raw sewage, primary sludge, activated sludge or biomass, which have likewise been subjected to a hydrolysis treatment if necessary, are added to the first stage of the reaction in amounts of 16 to 160 g/l. A method is described in US Pat. No. 4,022,665 in which low molecular weight fatty acids are formed under agitation and anaerobic conditions.

Subsequently, said liquid mixture containing fatty acids and other decomposition products is passed into at least one second (methane-forming) stage from the first (acidifying) stage of the reaction in an amount of 1.6 to 8 g/day of organic matter. The acidic liquid mixture is stirred and reacted with carbon dioxide and methane under anaerobic conditions. After optional hydrolysis treatment, the remaining portion of said liquid mixture of liquid and/or solid substances is recycled to the first stage of the reaction and undergoes the entire process again.

Currently in the reaction space, the water-soluble fatty acids and other water-soluble organic and inorganic substances generated in the first stage of the reaction are substantially completely removed, washed with an aqueous liquid and the resulting solution is washed with at least one auxiliary liquid. is fed to a reactor, where the water-insoluble substances still present in the reaction space are left in said reaction space, while in said auxiliary reactor the organic matter of said aqueous solution is converted into a mixture of carbon dioxide and methane. It has been found that an effective anaerobic conversion of the solid organic matter can be obtained by subsequently removing from said reaction space the substances left in the reaction space which have the properties of a stabilized compost.

The important differences between the method of the present invention and the method of U.S. Pat. No. 4,022,665 are as follows: (1) The method of the present invention does not continuously feed waste to the reaction space; (2) The method of the present invention In the first step, the water-soluble fatty acids and other water-soluble organic substances produced under anaerobic conditions, as well as the inorganic substances present therein, are substantially completely removed from the reaction mass by washing with an aqueous liquid. As a result, water-insoluble substances remain in the reaction space. This condition results in the PH becoming too low in the reaction space and/or the concentration of other inhibitory products becoming so high that the growth of the microbial flora is inhibited by too high a concentration of inhibitory substances or by a medium with a PH value that is too low. can be avoided. Furthermore, it is avoided that substances that have not been decomposed into liquid products, such as cellulose-containing substances, are fed to an auxiliary reactor, in which they are decomposed and converted, and that they affect the production of methane; (3) According to a preferred embodiment of the process according to the invention, the aqueous phase is used just after the separation of water and gas in the auxiliary reactor to wash the mass present in the reaction space; A converted compost is formed in the reaction space, and the compost is removed from the reaction space when the conversion is complete. No stabilized mass could be obtained in the reaction space with the known method.

U.S. Department of Commerce PB-258499 and U.S. Patent No.
The disadvantages of the process known from No. 4,022,665 are that the grinding of the solid material consumes energy and that the presence of a large amount of colloidal material in the slurry requires the use of very expensive reactors.

When applying the method according to the invention, water washing is effective to reduce the concentration of inhibitors in the reactor and avoid a decrease in the PH value. In this way, it is avoided that the propagation of the microbial flora is inhibited by too high concentrations of inhibitors or by too low PH values of the medium.

The rinsing can be carried out with freshly supplied water, which can be used after conversion of the fatty acids present by recycling the effluent from the auxiliary reactor as a rinsing liquid for the reactor. preferable.

The above anaerobic fermentation was carried out in the mesophilic temperature range (5-45
C) and in the high temperature range (25-70 C).

Examples of solid organic matter to be decomposed are household waste, straw, fruit waste, leaves, peels of rinsed fruits, etc.
Mention may be made of rinds, potato skins, grasses and organic materials generally having a water content of 10 to 60% by weight. Furthermore, this method is used especially for wet, perishable and malodorous animal and/or plant wastes which have to be stored in closed spaces.

In the process according to the invention it is also possible to use so-called "energy-farming plants", such as kelp, as organic starting material.

It has been found that in the case of semi-stagnant operation, ie when the reaction space is drained and renewed once a day, a COD-solution curve such as that shown in FIG. 2 is obtained, for example. In this case, the dissolved COD is 2
About 30% fatty acids after days - COD and about 35% after 7 days
of fatty acids - including COD.

When applying continuous water washing, a COD-curve in the reactor effluent versus time as shown in FIG. 3 is obtained.

In this case, the effluent from the auxiliary reactor is used as a rinsing agent for the (primary) reaction space.

Therefore, it can be seen from the solid line that after 10 days very little COD has dissolved from the reaction space, and the dotted line shows the fatty acid-COD content, which indicates that this soluble COD consists mostly of fatty acids.

Methane evolution in this conversion within the mesophilic temperature range is shown in Figure 4. The solid line relates to gas evolution in the (primary) reaction space. The dotted line indicates gas evolution in the auxiliary reactor.

After 10 days about 75% of the fermentable solid organic matter had decomposed and this was discharged in the form of a solution.

It takes 30 days to break down the remaining 25% of the fermentable organic matter.

When carrying out the process according to the invention, it seems appropriate to use one or more (primary) reaction spaces for each auxiliary reactor. When applying this method of operation, an influent of homogeneous composition can be fed to the auxiliary reactor in order to obtain optimal performance of the auxiliary reactor.

Auxiliary substances can be added to accelerate the decomposition of certain substances in the primary reaction space.

Thus, in order to accelerate the hydrolysis of cellulose, cellulase or microbial, ie bacterial or fungal, cellulase generation medium can be added to the cellulose-containing material to be degraded.

Other hydrolysis-promoting additives are diastase or amylase for the hydrolysis of starch, pectinase for the hydrolysis of pectin and inulase for the hydrolysis of inulin.

The primary reaction space can be used as an odor-free storage yard. If the waste is transferred intermittently into the reaction space, this reaction space is completely sealed so that no foul odors begin to develop, while the acid present and the acid produced have a preservative effect.

Place the reaction space into operation by flushing with an aqueous liquid at any time desired. This method of using this reaction space offers significant advantages compared to older methods that require preparation on weekends to work with accumulated waste in efficient succession.

In this combination of (primary) reaction space and auxiliary reactor, little explanation is needed to show that the (primary) reaction space is operated in batch mode and the auxiliary reactor is operated in series. do not. In the system according to the invention, the auxiliary reactor operates faster than in normal applications of upflow reactors, because unlike the known methods for dispersions with low viscosity and a small percentage of solids (primary) This is because the effluent from the reaction space does not contain colloidal particles of slowly decomposable substances.

The compost obtained as a sludge from the reaction space has a C:N ratio such that it is substantially free of malodor and contains food salts present in the solid organic starting material.

EXAMPLE Large parts such as wood, shoes, tires, etc. were removed from domestic waste with a Flakt device.

Additionally, metal waste, paper and major plastic parts were removed from this household waste.

The remaining part was a moist, fluffy mass that quantitatively passed through a sieve with a mesh size of 100 mm. Analysis revealed the following composition: Water 47.6% by weight Ether extract 1.6% by weight Water extract 7.4% by weight Water-soluble protein 1.6% by weight Pectin 0.3% by weight Hemicellulose 1.9% by weight Cellulose 7.1% by weight Lignin 4.2% by weight Ash content 28.1% by weight 99.8% by weight From the above analysis, 1 kg of the above household waste is 359%
It can be calculated to have a COD of g/Kg.

100 kg of the pretreated waste described above was mixed with 5 kg of anaerobically decayed domestic waste having a water content of 48% by weight. This mixture was fed into a primary reaction space equipped with a sieve bottom. Water at 35° C. was then fed into the reaction space until the water level in the reaction space was about 10 cm above the domestic waste level. The effluent was collected under the sieve bottom of the reaction space in a vessel with a capacity of 50 mL. This effluent had a COD of 32g/day on the first day.
and in subsequent days this COD value had the course shown in FIG.

The liquid was pumped from the 50 vessel into the lower side of the auxiliary reactor (methane reactor) at a rate of 71/day.

The methane reactor had a capacity of 200.
The contents of the auxiliary reactor were maintained at a temperature of 35° C. by heating the jacket.

A separator was provided at the top of the auxiliary reactor to separate the bacterial sludge effluent (water) and biomass.

The separated bacterial sludge was returned to the auxiliary reactor in the usual manner. Biomass was fed into the gas holder. If an auxiliary reactor (methane reactor) is used sufficiently high, the effluent can be fed under the influence of gravity to the primary reactor (71/
(in percentage of days).

By feeding 71 effluents from the primary reaction space to the auxiliary reactor, a total of 825 methane quantities of biomass were produced on the first day. The total amount of biomass produced in the auxiliary reactor during 10 days was
Contained 6417 methane. The methane production described above had the course shown in FIG. After 10 days, the supply of liquid to the auxiliary reactor was completed.

After 3 days, biomass production started in the primary reaction space. The total amount of methane produced had the course shown in FIG. The biomass produced within 30 days in the primary reaction space contained a total of 2140 methane.

After 30 days, the household waste had decayed to the point that it could be used as compost. 77.8 kg of compost was obtained. This has a moisture percentage of 49.2% by weight, 39% by weight
It had a percentage of ash and a percentage of organic matter of 10.9% by weight.

EXAMPLE The walls and bottom of a reaction space with a surface of 10 x 5 m and a height of 1 m were internally covered with plastic foil. A system of drainage pipes was applied on the bottom foil of this reaction space. Next, a 60cm thick layer is placed on top of this drainage system.
A sand layer with a sand layer was applied. 100 m ³ of failed tomato seedlings were stacked on top of this sand layer.

The plant had the following average composition: Water 84.8% Teter extract 0.43% Water extract 2.17% Insoluble protein 1.26% Pectin 1.07% Hemicellulose 0.70% Cellulose 3.31% Lignin 1.27% Ash 4.54% Total 99.55% Composition as above. The above plants have a COD of 130g/Kg.
It can be calculated that

A system of spirinkle tubes was applied on top of the formed pile of tomato seedlings. A plastic tilt was then applied on top of the deposit, which formed an airtight connection with the foil covering the bottom and walls of the reaction space. 1500
The effluent of the methane reactor having a temperature of 35° C. was sprinkled through the sprinkle tube onto the pile at a volume of 1/h.

The permeate was withdrawn from the reaction space through a drainage system. This permeate has a COD of 3.7 g/day after the first day.
It had value. The liquid described above was fed into a container with a capacity of 10.000. The heated liquid was transferred to the lower part of the methane reactor with a capacity of 10 ^m3/ 1500 m3.
Supplied at the rate of time.

The organic matter was converted into biomass in the conventional manner by anaerobic bacteria in the reactor at a temperature of 35°C.

Biomass and purified water were removed separately in the upper side of the reactor. This water was pumped into a sprinkle tube in the reaction space. The liquid flow from this reaction space to the methane reactor was maintained for 30 days.
After said 30 days in the reaction space, an amount of organic matter having a COD value of 1240 Kg was dissolved in the permeate and thus removed. A total of 750 m ³ of biomass with a methane percentage of 60% was formed and removed from the above amount of organic matter. After 30 days, the Thomas seedlings were sufficiently rotten to be used as compost. 15% by weight
13 m ³ of compost were obtained with a solids percentage of .

[Brief explanation of drawings]

Figure 1 shows the curves of percent dissolved COD and acid generation versus time for conversion, Figure 2 shows the curves of dissolved COD versus time when the reaction space is washed with water, and Figure 3 shows the curves of dissolved COD versus time for continuous shows the curve of COD in the reactor effluent versus time when washing with water is carried out.
and FIG. 4 shows the curves of methane production versus time at conversion for each reactor.

Claims (1)

[Scope of Claims] 1. Solid organic matter derived from plants or animals, or both, is subjected to at least two stages of treatment, the first of which is carried out under anaerobic conditions to decompose it into water-soluble products. In the anaerobic conversion process of solid organic matter, in which low molecular weight fatty acids are produced, while in the next stage(s) methane is evolved from said organic matter under anaerobic conditions, in the reaction space, the methane produced in the first stage of the reaction is The water-soluble fatty acids and other water-soluble organic and inorganic substances are removed by washing with an aqueous liquid and the resulting liquid is fed to at least one auxiliary reactor, where the water-insoluble substances still present in the reaction space are removed. left in said reaction space, while in said auxiliary reactor the organic matter of said aqueous solution is converted into a mixture of carbon dioxide and methane, and subsequently left in said reaction space with the properties of stabilized compost. 2. A method according to claim 1, characterized in that said substances are removed from said reaction space. 2 One or more primary reaction spaces are used to feed each auxiliary reactor, and the said auxiliary reactions are controlled by pipes provided with valves for intermittently loading and shutting off said primary reaction space. A method as defined in claim 1, characterized in that the method is connected to a device. 3. Claim 1, characterized in that the effluent from at least one auxiliary reactor is used for washing at least one primary reaction space.
or the method defined in paragraph 2. 4. A method as defined in claim 1, characterized in that the water washing process is inhibited as soon as methane generation in the reaction space occurs spontaneously.