DE3015239A1 - Bio-gas generation from household refuse and clarifying sludge - by mixing and grinding, swelling, flotation, water-extn., anaerobic putrefaction and composting - Google Patents

Abstract

Bio-gas generation comprises comminuting and mixing untreated household refuse with non-dehydrated clarifying sludge by a 2- or multi-step grinding process, pref using a 2- or multi- compartment ball mill. The sludge obtd is swelled for several hrs. All sludge components incapable of rotting, including plastics, are sepd by one or more flotation processes. The solids content of the remaining sludge is increased to 40% by mechanical water-extn. The dehydrated sludge mixt is made to undergo a controlled anaerobic putrefaction at 30-35 deg C. Anaerobic putrefaction is broken off on reaching max combustible bio-gas yield. A controlled aerobic composting process is then applied to increase hygiene and form humus. The heat required for anaerobic putrefaction is abstracted from the composting process. The compost can be used as soil-improver. The sludge can be used without processing and the refuse requires no preliminary sorting.

Description

Process for the production of bio-gas

from household waste and sewage sludge The invention relates to a method for the generation of bio-gas from household waste and municipal sewage sludge.

It is known to digester gas from sewage sludge in digestion towers and from this To obtain methane (CH4). For the rotten energy is required, which is generated separately and must be fed to the digestion process. The sludge produced during the digestion process is dried and sent to separate landfills, as it is not hygienically perfect and is not stabilized.

It is also known to extract bio-gas from landfills, their organic Parts of bio-gas as metabolites producing bacteria serve as food. The bio-gas produced there under anaerobic conditions is drained through drainage pipes sucked off. Finally, it is known to produce bio-gas from agricultural waste Digestion of manure, straw, vegetable or fruit waste in a container to win; See Umschau 73 (1973), Issue 12, pp. 364 to 369, Bild der Wissenschaft, 10-1977, pages 87 to 102.

All these methods have in common that the processing of household waste is extremely expensive, as this one due to its heterogeneous composition The putrefaction process is not readily available, and that the putrefaction is carried out so far is until the sludge resulting from the digestion is storable, or he must For example, they can be post-treated in rents, i.e. composted or disposed of in an orderly manner.

As a result of the costly pre- and post-treatment of the initial and Such bio-gas generation is therefore only carried out in isolated cases and has so far not been able to establish itself on a large scale.

On the other hand, the household garbage, sewage and sludge treatment always comes greater importance, as both the population density and thus the amount of waste always increases, as well as energy recovery and the return of incurred Waste in the ecological cycle is becoming more and more necessary. So far the orderly one Landfill of household waste is still the most common method of waste disposal. Another method is to burn garbage, which creates high environmental impacts leads. It is also known to sort household garbage into rotting and rot-proof ones Parts, the partial removal of paper parts and subsequent shredding to be mixed and composted together with drained sewage sludge, see US-PS 3,533,775. The effort for this process is also very high, the sludge dewatering requires expensive chemical flocculants. It has also been shown that on this ~ Not a uniform intermediate product that is well suited for subsequent composting is achievable.

From DE-PS 6148 705 it is known to garbage, which also includes ash, wood and bone meal can contain, to sift out larger pieces of iron and then with greasy sewage from urban slaughterhouses and pottery shops mix. The mixing process is at the same time a flotation process, since it is here the ashes and other fine Components of the garbage from the heavier minerals and metals are divorced. The mixture produced is kept in pits and then made with bituminous liquids refineries and after slight heating to about 40 to 50 0C to compressed coal pressed and fed to a combustion process. But experience shows that Such mixtures do not dewater or only with great effort and become compressed coal let press.

According to the so-called Brikollare method - communal management, booklet 9/1965 - digested sludge from digester tanks is used in a sludge road about 12% solids content flocculated with the help of flocculants and through suction cell filters dehydrated to about 70% water content before being treated with shredded garbage mixed with the help of a two-shaft mixer and then by blow compression is deformed into compacts. These compacts can be stored for any length of time before they for example, be fed to a rotting process.

This process is also time-consuming and expensive, as both sewage sludge and to pretreat waste separately from one another in different processes before they are fed into the manufacturing process for the intermediate product. Furthermore, the uniformity and homogeneity of the material to be fed further allows for further processing Intermediate product leaves much to be desired.

In all known processes for the disposal of municipal waste and / or their partial conversion into bio-gas is therefore already pretreated shredded garbage, already pretreated, at least partially dewatered sewage sludge are added and beMe components are only then mixed before they are added to the following Process steps are supplied.

The invention is based on the task of eliminating communal Waste, especially the transfer of household waste and municipal sewage sludge into To simplify bio-gas as much as possible and under Using a To optimize the digestion process by making the digestion process a simple and cost-saving one Wise, more even and more homogeneous intermediate product than previously available is, the digestion process is simplified and at the same time the digested sludge by a biological one To convert the rotting process into a valuable, biologically sound compost.

This object is achieved according to the invention in that untreated Household waste and undewatered sewage sludge together with the help of a two- or multi-stage Grinding process are crushed and mixed that the resulting slurry is subjected to a swelling time of several hours, after which all of them are not rotting parts of the Schlemme excreted by one or more flotation processes and that the solids content of the remaining slurry by mechanical Dehydration is increased to about 40%, and that the so dehydrated slurry one controlled anaerobic digestion process at temperatures from approx. t300 to +35 0C and when the maximum emission of flammable bio-gas is reached and aborted is then sanitized and humidified by a controlled rotting process, where the heat required for the anaerobic digestion process is downstream The rotting process is withdrawn.

Further features of the invention emerge from the subclaims.

According to the method according to the invention, there is thus a moisture content from approx. 35 to 45 ## domestic waste in the delivered untreated structure for example fed to a two- or multi-chamber mill. At the same time is in this Ball mill feeds the resulting, untreated and undewatered sewage sludge. This sewage sludge has a moisture content of approx. 95%, so it is aqueous Broth. The mixing ratio is approx. 80 percent by volume of undewatered sludge and approx. 20 percent by volume household waste. This mixture is now in the liquid-grinding process crushed in the ball mill, which has a slotted or perforated wall at the discharge. Of the The desired degree of fineness of the ground mixture can thus be achieved by appropriate Hole sizes be set and there will be a favorable grain fraction distribution in the ground product achieved. The grain fractionation can be carried out using appropriately large or small grinding media (Balls) can be set.

The liquid grist - i.e. the garbage and sludge mixture - leaves the mill is completely homogeneous, which is of great importance for further processing is.

The liquid regrind is removed from inorganic by flotation processes Shares such as glass, stones, metals, etc. and freed from plastic materials and after a swelling time directly or with the interposition of a thickener Gas generation process initiated in a digestion tower. The use of a thickener is only necessary if the solid content in the slurry is less than 40% is. This depends on the type of waste generated.

A big advantage is that the garbage is not sorted before grinding and also does not have to be freed from metal. Metal parts, e.g. food cans, remain in the grinding chamber of the ball mill until they are ground so small that that they can leave the ball mill through the hole openings. during the stay In the mill chambers they are by no means annoying, but act there as a grinding aid. Another advantage is to be seen in the fact that in liquid grinding, soft components, such as paper, textiles and food waste has already been dissolved by the liquid and thus no longer burden the grinding process.

Should for some reason no or insufficiently liquid sewage sludge exist, so sewage water from the sewage treatment plant can be used to irrigate the garbage be taken. Since the grinding process generates heat through friction between the grinding media, the ground mixture leaves the mill warmed up, which is ready for further processing is very beneficial.

Because there is a lot of fiber in the mixture, due to the garbage content are contained, it can then, if necessary, aflch without flocculants drain well and achieve a relatively high solids content. This is another one Advantage, as the otherwise required for drainage all or part of the infectious agents can be omitted or saved.

If the liquid regrind is pumped into a silo or a thickener, so the solids can settle. The remaining ones swim Plastic parts on the surface so that they can be fished off there. Will the ground liquid before being fed into the thickener via a ventilated from the bottom Conveyor channel passed, the amount of air to be supplied is adjusted so that through Turbulence the organic parts remain in the liquid and only heavy parts, such as metals, stones, glass, etc. drop. Here, the conveyor trough be technically equipped so that it is provided with a porous bottom by that the air will carry. Between the porous floor and the one above it Liquid mass automatically forms an air cushion, which results in a sorting of Heavy proportions is also possible. Regardless of the type of flotation separation chosen it must be ensured that all organic substances with the liquid through a sieve go and all solids remain as sieve residue.

The swelling time of the mixture, for example in the thickener, is approx.

8 hours. Here the solids can settle down, so that the excess water can be drained off.

Heavy metals can also be used in the thickener by means of an ion exchange process be removed in order to avoid any water-soluble contamination in the later compost To have heavy metals or their compounds.

The slurry produced in this way is now subjected to a controlled gas generation process in a bio-gas generation stream # 9 as described, for example, in DE-OS 28 14 795 is, supplied The bio-gas production proceeds with complete exclusion of air, So it is a completely anaerobic process, with the purpose of optimizing the function of the container is heated at the sole. The heating is done with waste heat from the exhaust air Bio-reactor made in which the further processing of digested sludge to compost he follows. Since the starting product for the digestion process is completely homogeneous and without inorganic Shares is and is fed to a controlled digestion process is the first time optimal bio-gas generation possible, for the starting products in any quantity be available.

The inventive preparation of the garbage-sewage sludge mixture and its conversion into bio-gas has the great advantage that undewatered te communal Sewage sludge, including animal excrement waste and industrial sludge, if none require special treatment, as well as sewage water used as waste products so far none ge.

profitable recycling could be supplied. Particularly beneficial is also that a garbage sorting is not necessary before the shredding and that a complete homogenization of the mixture is guaranteed, one favorable Kornfraktionsvertei development in the grist is available. A sort of the Garbage is special after it has been shredded by known flotation processes easily possible. Heavy metals are also removed using ion exchange processes also particularly easy and the liquid ground product can be drained easily, and largely without the use of expensive flocculants. Finally enable the applied process steps an optimization of the bio-gas generation.

One embodiment of the invention is based on a flow chart described below.

About 20 to 50 percent by volume of untreated household waste with a damp activity of approx. 45 to 55% is untreated with approx. 80 to 50 percent by volume Sewage sludge with a humidity of approx. 95 to 98% of a two-chamber ball mill fed and ground there. The holes the perforated wall of the first Chambers have a diameter of about 40 mm; the perforated wall at the outlet of the ball mill has holes with a diameter of about 10 mm. The slurry becomes a thickener forwarded. After a swelling time of approx. 1 to 2 hours, ferrous parts become magnetically removes and flotation plastic parts from the surface and others Heavy parts removed from the body. The remaining mixture is then added an energy generation tower, i.e. a digester of a known type, which is heated by the warm exhaust air of a bioreactor. In this bio-reactor the digested sludge coming from the digester is composted.

The controlled anaerobic treatment takes place in the power generation tower the gluttony through putrefaction at temperatures of approx. c300 to +35 0C, which when reaching for example, the maximum methane release is canceled. Sensors are used for this in exhaust pipes, not shown, of the power generation tower, which have a Control device, not shown, when a predetermined maximum value is reached interrupt the putrefaction. The methane release is measured continuously and then the energy generation process is controlled. The digested sludge then gets there into the bio-reactor via a drainage device. The C / N ratio of the digested sludge is brought into a rotable condition by means of suitable aggregates.

In the bio-reactor, the essentially aerobic treatment takes place in Form of a controlled rotting process through which the rotten and with aggregates provided sludge is sanitized and humidified.

Such controlled biological rotting processes within aeration reactors are for example described and shown in detail in DE-AS 25 41 070.

The heat generated during the biological rotting process becomes The digestion of the fresh sludge is exploited.

As supplements for the Schlemme serve a strong with microorganisms occupied intermediate product from the downstream rotting process or * the thickener a anaerobic material in the form of liquid mass from the digestion process.

The digested sludge can be dewatered on a belt filter press, namely to about 30 to 40% solids content, optionally with the addition of anaerobic inoculum from the power generation tower.

The compost taken from the bio-reactor is particularly useful as a soil improver can still be used.

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Claims (8)

PATENT CLAIMS 1. Method for producing bio-gas using of household waste and municipal sewage sludge, therefore not marked, that untreated household waste and undewatered sewage sludge together with the help of one two- or multi-stage grinding process are crushed and mixed that the thereby the resulting slumber is subjected to a swelling time of several hours that it then all of the non-rotting portion of the sluggishness through one or more Flotation processes are eliminated and that the solids content of the remaining Schlemme is increased to approx. 40% by mechanical drainage, and that the so dehydrated Schlemme a controlled anaerobic digestion process at temperatures of Subject to approx. +300 to +350 # and upon reaching the maximum emission of combustible Bio-gas broken off and then sanitized by a controlled rotting process and is humified, where: the heat required for the anaerobic digestion process the downstream rotting process is withdrawn. 2. The method according to claim 1, characterized in that g e k e n n z e i c h -n e t that the grinding and mixing process with the help of a two- or multi-chamber Kugelmu.hle is carried out. 3. The method according to claim 1 and 2, characterized in that g e k e n n -z e i c h n e t that the flotation is carried out with the help of a conveyor trough, which from sieve-like floor is ventilated ago in such a way that the resulting turbulence there are only parts that cannot rot, such as metals, stones, glass and the like. ?occupy. 4. The method according to claim 3, characterized in that g e k e n n z e i c h -n e t that the plastic parts of the slurry floating up during flotation from the Surface can be peeled off. 5. The method according to claim 1, characterized in that g e k e n n z e i c h -n e t that the Schlemme after the putrefaction process an inoculating material, preferably a strong one Intermediate product contaminated with microorganisms from the downstream rotting process, is added. 6. The method according to claim 5, characterized in that g e k e n n z e i c h -n e t that the Schlemme as inoculum is an anaerobic material in the form of liquid Mass from the putrefaction process is added. 7. The method according to claims 1 to 4, characterized g e k e n n -z e i c h n e t that the sluggish heavy metals with the help of an ion exchange process be withdrawn. 8. The method according to claim 1, characterized in that g e k e n n z e ~ i c h. <En n e t that the rotten slurry before being fed to the rotting to a maximum of 75 percent by volume Water content is dehydrated.