FI64124B - ANORDER FOR THE RELEASE OF AVAILABLE MEDIA ANALYSIS - Google Patents

Description

64124

This invention relates to an apparatus for treating wastewater by anaerobic fermentation.

The present invention therefore relates to an apparatus for the treatment of wastewater containing biodegradable organic matter by anaerobic fermentation. In anaerobic fermentation, the decomposition of organic matter is performed by both facultative and completely anaerobic bacteria. First, carbohydrates, proteins, and lipids are hydrolyzed, and then these hydrolysis products continue to decompose primarily into acetic acid, hydrogen, and carbon dioxide. The final decomposition is performed by methane-generating bacteria. Thus, in order to obtain the best possible result, at least two types of bacteria must be used, with acid bacteria performing best in the low pH range, about 5.0-6.0, and methane bacteria performing best in the pH range of 7.0-7.5. Not only do acid bacteria work best in a lower pH range than methane bacteria, they are also not as sensitive to variations in fermentation conditions as methane bacteria.

Wastewater containing biodegradable organic matter has so far been treated e.g. the so-called. in fully stirred reactors where the acid and methane reactions take place in the same stirred state. Because methane bacteria are much more sensitive to variations in fermentation conditions than acid bacteria, the conditions in such full-blend reactors have had to be determined according to the requirements of the methane bacteria, so that acid reaction rates have obviously not been optimal in such full-blend reactors.

It is already known to digest sewage sludge 2 64124 containing anaerobically biodegradable organic matter in two stages in a digestion reactor in which both stages are arranged nested. Thus, for example, Finnish patent 57 579 discloses a device for digesting sewage sludge in two successively connected stages, which are arranged one after the other, whereby sludge water and digested sludge are removed from the second stage, part of which is returned to the first stage. In such a reactor, however, digestion cannot be carried out separately by means of two different types of bacteria, as these would automatically mix with each other when part of the second stage slurry is fed to the first stage as inoculum slurry. This device is thus in fact a full-stirred reactor, albeit divided into two nested stages.

It is clear that the disadvantages caused by fully stirred reactors can be overcome by using two separate reactors connected in series, the first of which would act as the acid stage and the second as the methane stage. However, such a device would be relatively expensive and complex compared to a full-stirred reactor and, in addition, would require more space.

It is therefore an object of the present invention to provide an apparatus for the treatment of waste water by anaerobic fermentation in which acid and methane reactions can be carried out under the conditions best suited to these reactions without substantially mixing the acid and methane bacteria and which is approximately as cheap and simple as a full mixing reactor. .

The main features of the invention appear from the appended claim 1.

The apparatus solution according to the present invention is very simple and economical, since both acid reactions and methane reactions are carried out in one and the same vessel.

In the apparatus solution of the present invention, both acid and methane reactions can be carried out under near-optimal conditions and without substantial mixing of acid bacteria and methane bacteria, since the vessel is divided into two overlapping parts by a biofilter of one or more methane bacteria. a filler layer, wherein each filler may be either inert or active, regardless of the properties of the other possible fillers. The acid reactions then take place in the mixing section below the filter, to which the wastewater to be purified is fed and from which the wastewater rises with the gas formed in the acid reactions after the acid reactions, reacting both with the filter filler surfaces and the methane bacteria above the filter.

A part of the sludge removed from the part below the filter can be returned to the reactor, but then to the same stage, in which case it is not mixed with the sludge in the second stage, as in the solution according to Finnish patent 57,579.

Immediately below the filter there is preferably a lamella separator known per se to distribute the water flowing through the filter from the bottom upwards evenly over the filter, to increase the size of the bubbles in the water and to separate and return the sludge particles to the vessel part below the filter.

Gravel, light gravel (Lecasora), plastic grit, and various porous materials such as coke, coal, slag and activated carbon can be used as the filler material for the anaerobic filter. Preferably, however, light gravel and slag are used, on the surface of which methane bacteria adhere. The possibility of attachment of methane bacteria is increased by the large total surface area of said substances.

Above the anaerobic filter, a relatively thick layer of fluid is maintained, consisting of a slurry and 4 64124 material which may act as a filter and / or fluid, such as activated carbon, ash, especially fly ash, sand and the like.

When activated carbon was used as a filter and fluid, according to the present invention, it was surprisingly found that the activated carbon regenerated on its own. Activated carbon has previously been used as a filler in an anaerobic filter according to German application 25 31 598. In this method, the wastewater is first purified by an anaerobic filter using activated carbon as a filler, and then also by an aerobic treatment. This method has been tried under different conditions and has been able to treat wastewater and sludge, but gas production has been relatively low and, in addition, activated carbon has had to be replaced from time to time, which has complicated processing and caused production interruptions. The activated carbon used as a fluid in the device according to the present invention does not need to be replaced, which was a very surprising finding and the reason for this effect is not known. Thus, the activated carbon used as a fluidizing agent in the apparatus of the present invention does not need to be replaced due to the deterioration of its filtration capacity. Detoxifying agents such as activated carbon can also be used in the acid phase.

The invention will be described in more detail below with reference to the accompanying drawing, in which: Figure 1 schematically shows a cross-sectional elevational view of a preferred embodiment of the invention and Figure 2 shows a similar elevational view of an alternative embodiment of the invention.

In the drawing, a vertical cylindrical reactor is generally indicated by reference numeral 1. In the embodiment shown in Figure 1, a centrally vertical cylinder 10 is arranged inside the reactor 1, which is open at both its upper and lower ends. At the top of this vertical cylinder 10, its inner I! Also arranged on the side 64124 is a vertical pipe 12 open at both ends, into which a mixer 11 extends from the top of the reactor 1 and into which the waste water supply line 2 to be treated leads from outside the reactor 1.

The reactor 1 is further divided into two overlapping parts by a filter 8, through which the vertical cylinder 10 extends so that the wastewater to be purified fed to the cylinder 10 via the feed pipe 2, mixed by the mixer 11, settles to the part below the filter 8, where it is further mixed by the mixer. to prevent settling to the bottom of reactor 1. The lower part of the reactor 1 further has an outlet pipe 3 for reducing the amount of acid stage sludge, from which a branch 13 has a pump 14 for feeding a part of the sludge removed from the reactor 1 acid stage together with the wastewater to be treated from the feed pipe 2 to the mixing pipe 12 in the vertical cylinder 10. in the part of the vessel below the filter 8, the acid-forming bacteria react with the organic substances contained in the wastewater to form a sludge as well as a gas.

Immediately below the filter 8 is a lamella separator 15 in which water from the acid stage is made to flow from bottom to top between the diagonally arranged lamellae to distribute water evenly over the entire cross-sectional area of the filter 8, increase the size of gas bubbles in the water and separate and return sludge particles.

The anaerobic filter 8 contains an inert filler, such as light gravel and / or slag, which acts as a support medium for methane bacteria and has a large adhesive surface to prevent the leaching of slow-growing methane bacteria. There is a relatively thick layer of fluid and sludge 9 on top of the filter 8 to enhance the actual methane fermentation, resulting in a larger and more evenly distributed microbial base in this reaction space. Activated carbon is used as the fluidizing agent, which at the same time acts as a filter medium. In the part above the filter 8, methane gas is further formed and the gases are separated from the mixture of water and slurry on the sloping surfaces of the bubble separator 7 arranged in the top of the reaction vessel 1. Finally, the purified wastewater and the slurry therein are discharged from the reaction vessel 1 by means of an outlet line 5 above the bubble separator 7 and the gases separated in the bubble separator 7 are removed through an outlet line 6 at the upper end of the reaction vessel 1.

Figure 2 shows a slightly simpler embodiment of the device according to the invention, in which the wastewater to be treated is led directly by means of a pipe 2 to the lower part of the reactor 1, which is separated from the upper part by means of a biofilter 8. Excess sludge is removed from the lower part of the reactor 1 by means of an outlet pipe 3. At the top of the reactor 1, on the other hand, there are means 7 for separating the gas from the mixture of purified wastewater and sludge before it is discharged by means of an outlet pipe 5. Especially in wastewater that is difficult to purify, the separation of gas bubbles can be improved by means of a stirrer 12 mounted on the top of the reactor.

The gases, on the other hand, are removed through a pipe 6 centrally arranged in the upper part of the reactor 1.

The device according to the present invention provides a better cleaning result and a higher resistance to toxic substances when activated carbon is used as a filter and fluid, as this surprisingly retains its normal filtration capacity, i.e. it regenerates on its own, so that it does not have to be replaced. Furthermore, the device according to the invention is very simple and inexpensive, because the construction, installation and other side costs are low and the operating costs are low.

Example

The multi-stage reactor of the present invention has been compared to a previously known full-stirred reactor in terms of purification yield. The multi-stage reactor according to the invention with an acid fermentation stage, a lamellar clarifier and above it a filtration and fluidized bed stage in the methane fermentation stage has given a much more uniform purification result than a full stirred reactor in which both acid and methane fermentation take place in the same reaction stage.

In the multistage reactor according to the invention, Lecasora and activated carbon crumb were used as filler. The liquid volume of the reactor was 30.8 liters and the temperature during the experiments was 34 + 1 ° C. The pH of the wastewater to be treated was adjusted to neutral, i.e. pH 7.

A full agitation reactor of the same size was used, and the same experimental setup as in the above-mentioned multistage reactor was used.

The table below shows the results obtained with the above reactor types. It can be seen from the table that the multi-stage reactor has a significantly better BOD 2 reduction (average 80%) than the full-stirred reactor (average 50%). Similarly, CODCr reduction and gas production were better in the multi-stage reactor.

Table

Quantities used as reference parameters between multi-stage and full-stirred reactors.

Multi-stage reactor Fully stirred reactor B0D7-red. X * 80 50

Drainage water B0D_-pit.

mg / 1150 300-600 C0DCr-red. % * 60 45

Gas yields m3 / kg B0D? add 0.20 0.15 Running time, days 150 135 xBOD_ reduction: reduction in biological 7-day oxygen consumption (mg 02 / l) 1st reduction.

C0D_ reduction: reduction in the amount of chemical oxygen demand Cr (mg 02 / l).

8,641 24

Gas production and BOD 2 reduction levels have varied in both reactors according to wastewater properties.

When studying the effect of toxic wastewater, the BOD ^ reductions were higher than average because the quality of the wastewater used was uniform during the study. The effect of the toxic water on the operation of the reactor was then clearly different from the normal variations in the operation of the reactor. The BOD 2 reduction in the multi-stage reactor, which was about 90% at the beginning of this experimental phase, decreased to about 70% of this toxic wastewater treatment and returned to a reduction level of about 90% when the toxic wastewater ceased. The reduction of the BOD7 in the full-stirred reactor decreased from the corresponding 80% starting level to about 30% and only returned to a reduction level of only about 70%. It can be seen from this that the operation of the full mixing reactor was very strongly affected by the toxic effluents. The operation of the multi-stage reactor according to the invention, on the other hand, was considerably smoother all the time and the variations were smaller. This shows a much better resistance of the multi-stage reactor to toxic wastewater.

Despite the long operation of the multi-stage reactor (150 days), the cleaning result did not change, although the hydraulic delay was shortened all the time. Activated carbon has not had to be replaced to improve cleaning efficiency, as previously described and has also been common practice.

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Claims (8)

An apparatus for purifying wastewater by anaerobic fermentation comprising an acid and a methane fermentation step, comprising a closed vessel (1) and therein (2, 10) for feeding the wastewater to be purified in the vessel, means ( 5, 6, 3) for removing purified water, gas and sludge from the vessel, means (4) for stirring the contents of the vessel and means (7) for separating gas in the upper part of the vessel, characterized in that the vessel (1), in order to keep the acid and methane fermentation steps substantially separated from each other, have been divided into two superimposed parts by means of a filter (8) comprising a filler layer containing at least one filler, which acts as an attachment base for the methane bacteria, and on this a sludge and flow material layer, such that in the lower part of the vessel below the filter is the first part, in which the stirring means (4) are located and in which the feed water (2, 10) to be purified, opens, whereby acid fermentation the step takes place substantially in the first part and in the upper part of the vessel is the second part, in which the drainage means (5, 6) for purified water and gas open, and to which the filter (8) belongs, the methane fermentation step taking place substantially in the the second part. Device according to claim 1, characterized in that beneath the filter (8) there is a lamellar separator (15) for dividing flowing water through the filter evenly over the filter and for enlargement of bubbles present in water as well as for removal and removal. -circulation of sludge particles to the first vessel part under the filter. 3. Device according to claim 1 or 2, characterized in that the means for supplying wastewater to be purified comprises a receptacle (1) presumably centrally fitted and at its upper and lower ends.