JPH09295000A - Anaerobic digestion of sludge or raw excretion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently digest sludge generated in a sewage or excretion treatment plant without changing an apparatus or treatment operation and to enable the increase of treatment quantity and the miniaturization of a digestion tank. SOLUTION: In an anaerobic sludge digestion process, an extract containing 2% of quilaja saponin is added to sludge in an amt. of 2-30ppm within a medium temp. region and in an amt. of 1.5-17ppm in a high temp. region to increased the generation amt. of gas by 10% or more as compared with the case of non- addition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for promoting digestion of sludge generated in a sewage treatment plant, an excrement treatment plant, and the like, or a raw excrement carried into the excrement treatment plant. The present invention relates to the one to be treated by adding the extract of the tree.

[0002]

2. Description of the Related Art Wastewater and human waste that flow into a sewage treatment plant, a human waste treatment plant, etc. are finally separated into treated water and sludge, and the treated water is discharged into a river or the like. On the other hand, sludge may be incinerated or landfilled after dehydration, but since it still contains many organic substances, it is decomposed by anaerobic bacteria in a sludge digestion tank etc. in order to reduce the volume after dehydration. In many cases, BOD components are reduced and then dehydrated for incineration or landfill. On the other hand, in the case of human waste, the BOD component is 10,000
Since it contains more than ppm, anaerobically digest this and B
In some cases, the OD component is reduced and then sent to the aeration tank.

The digestion of sludge generated mainly in a sewage treatment plant will be described below. Anaerobic digestion, as described above, the organic matter in the sludge or raw human waste by the action of anaerobic bacteria and microorganisms, the enzyme as a catalyst, the acidic fermentation period,
Decomposes through three stages of acid decline and alkaline fermentation. This decomposition of organic matter is called digestion, which mainly decomposes sugars, soluble starch, fibrin, and soluble nitrogen compounds to produce organic acids, hydrogen sulfide, large amounts of carbon dioxide, nitrogen and bicarbonate, and the pH is 6 It decreases to about 0.8 to 5.1.
In the stage, the nitrogen compound is decomposed, the acidity is decreased, the ammonia nitrogen is increased, and the pH is increased to about 6.6 to 6.8. At the stage of, the insoluble matter such as proteins, amino acids, fats and oils is mainly decomposed, and the pH rises to 7.0.
Up to about 7.4, the methane content in the gas increases,
Sludge becomes stable coarse particles. The number of days required for digesting sludge until 90% of the final amount of gas produced is different depending on the digestion temperature. A digestion temperature of 40 ° C. or lower is called a medium temperature digestion zone, and a temperature of 40 ° C. or higher is called a high temperature digestion zone. The difference between the two is mainly due to the difference in anaerobic bacteria and microorganisms involved in digestion.

[0004]

However, unlike aerobic bacteria, anaerobic bacteria have a very slow organic matter decomposition rate, and digestion requires several tens of days (50 days by design, 35 days in reality). On the other hand, the amount of sludge generated is extremely large, and it is said that 10 to 20 m ³ / day is generated in a town of 10,000 people and 2000 to 4000 m ³ / day in a city of 1 million people in the case of sewerage. Therefore, in order to completely digest sludge, a large number of extremely large digestion tanks are required. At present, various improvements have been made, such as the development of an egg-type digestion tank with good digestion efficiency and the adoption of a high-temperature digestion method of heating to 40 ° C. or higher, but the improvement is at a level.

Therefore, the present inventor continued research by paying attention to improving the digestive efficiency by improving the activity of anaerobic bacteria and microorganisms by utilizing the existing digestive tank and digestion operation as they are, and completed the present invention. Let The extent of digestion is estimated by the amount of gas generated.

[0006]

SUMMARY OF THE INVENTION The present invention is characterized by adding soap tree extract, which was effective in activating aerobic bacteria and microorganisms, at a specific ratio in sludge. To do. That is, when the soap tree extract is added to the sludge, the gas generation amount increases according to the addition amount, but when the addition amount exceeds a certain amount, it decreases conversely, and finally, compared to the case of no addition. I found that it decreased. Further, the present invention has been completed by finding that the addition amount depends on the digestion temperature.

Quillaja saponin is a type of torpenoid saponin, and is contained in about 2% (about 4% as natural saponin) of soap tree extracted with alcohol. This extract contains about 20% saccharides and a little over 1% crude protein. Quillaja saponin, due to its physiological activity,
It has the effect of promoting the reaction of microorganisms and the effect of alleviating stress, and also has the effect of decomposing fats and oils and improving the efficiency of oxygen dissolution. In aerobic treatment, addition of soap tree extract to 0.5 to 4 ppm relative to the amount of wastewater and addition of about 10 ppm to wastewater containing a large amount of oil (normal hexane extract) produce a sufficient effect. On the other hand, in the anaerobic treatment, it is not necessary to dissolve oxygen, and the amount of oil and fat is small in the sludge. After all, the physiologically active action of Quillaja saponin seems to be important. However, saponin has an antibacterial effect. Therefore, if the concentration is too high, the activity of bacteria may be adversely affected.

On the other hand, the present inventor has learned from various experiences that not only quillaja saponin affects physiological activity of microorganisms but also other components contained in the extract of soap tree, especially sugars and crude proteins. It seems to have an influence. This is the result of treating two kinds of soap tree extract with a quillaja saponin concentration increased to 4.5% (about 10% as natural saponin) and measuring the effect on the microorganism. It turned out that the effect was inferior to the liquid. That is, one type of high-concentration saponin contains about 15 sugars.
%, 0.5% of crude protein was contained, and the other one contained about 30% of saccharide and about 1.5% of crude protein. Then, when these two kinds of liquids were diluted to 2% of quillaja saponin and subjected to wastewater treatment (activated sludge), the former was not so effective, and the latter was the same as or slightly more than the extract. If the physiological activity of Quillaja saponin was 100%, this result would not be obtained, and it is speculated that this may be due to the action of other ingredients. Other than the enzyme, it is unlikely that it exhibits a dramatic physiological activity at an extremely low concentration equivalent to that of saponin, and it is presumed that this enzyme or enzyme-like substance is contained in the crude protein.

[0009] It is unknown which of Quillaja saponin and crude protein is more effective, but in any case, the soap tree extract containing them is used to digest sludge. On the other hand, in both the middle temperature range and the high temperature range, a large increase was observed in the amount of gas (methane gas) generated compared to the case without addition. The ultimate total gas generation amount is determined by the organic matter content in the sludge, and an increase in the gas generation amount means that the digestion period is shortened. Therefore, the rotation rate of the sludge in the digestion apparatus is increased, which makes it possible to downsize the apparatus. In addition, the existing device can process a larger amount of sludge.

By the way, the gas generation amount by the addition of the soap tree extract increased by about 30% only by adding 5 ppm in the middle temperature range, and increased by 60% at 10 ppm. However, after that, the rate of increase decreased, and at 20 ppm, it increased to only about 40%. It is speculated that this is because methane fermentation was inhibited because the number of acid-producing bacteria increased with the increase in the amount of saponin added and produced lower fatty acids more than necessary. Alternatively, it may be caused by the antibacterial action of saponin. The rate of inhibition of methane fermentation due to the addition of a high concentration of soap tree extract becomes more pronounced as the temperature of sludge increases. That is, in the high temperature range, 5pp
The gas generation amount increased by about 36% with the addition of m, and increased by 90% at 10 ppm, but conversely with the addition of 20 ppm, it decreased by about 25% as compared with the case without addition. Considering the cost of adding soap tree extract, it is said that there is a sufficient reason for adoption if the amount of gas generated increases by 30% compared to the case where no gas is added, but it will only increase. Considering the cost of increasing the equipment for sludge treatment, even if the increase is about 10%, the effect will be great.

Therefore, from the above results, the gas generation amount is 10
%, It is sufficient to add about 2 ppm to 30 ppm in the case of the soap tree extract in the medium temperature range. To increase the amount by 30%, it is sufficient to add 5 ppm to 25 ppm. In the high temperature range, 1.5ppm to 17ppm, 30 to increase the gas generation rate by 10%.
%, It is sufficient to add 4 ppm to 14 ppm. In any case, if cost is taken into consideration,
The addition of 10 ppm can increase the gas generation amount by 10 to 60% (90% in the high temperature range). Although these are batch-type test results, since the sludge is continuously fed in an actual device, the total production amount is worse than this, but it still increases by about 40% when 10 ppm is added.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples. Four sets of experimental anaerobic digestion tanks each having a capacity of 5 L (liter, the same applies hereinafter) were prepared, and 2 L of raw sludge and 2 L of digested sludge collected from a sewage treatment plant were put into each of them. Nothing was added to one anaerobic digester, and soap tree extract (Quillaja saponin 1.9% (about 4% as natural saponin)) was added to each of the other three anaerobic digesters. Sugar (total sugar)
21.6%, including crude protein 1.1%) 5m against sludge amount
g / L (5ppm), 10mg / L (10ppm), 20m
g / L (20 ppm) was added. The four sludge mixtures were slowly stirred for 30 days while maintaining the temperature at 38 ° C (medium temperature digestion). The amount of gas generated (mL / day) was measured daily for each digester. The total amount is shown in Table 1. Table 1 Addition amount of extract solution No addition 5ppm 10ppm 20ppm Medium digestion 8,980ml 11,730ml 14,420ml 12,520ml High temperature digestion 8,830ml 11,985ml 16,810ml 6,670ml

From Table 1, it can be seen that the amount of gas generated is increased in the case where the soap tree extract is added. However, in the case of high-temperature digestion, it decreased at 20 ppm. This is probably due to the lower pH in this anaerobic digester than in other cases. That is, it is generally said that methane fermentation is inhibited and gas generation is stopped when lower fatty acids are accumulated at 2000 ppm or more. Therefore, when the amount of saponin added is large, the acid-producing bacteria are activated regardless of the medium temperature range and the high temperature range, and since lower fatty acids are produced more than necessary, the dynamic parallelism between acidic fermentation and methane fermentation cannot be obtained, It is presumed that the fatty acid accumulates in a high concentration and causes an obstacle to gas generation. This is more remarkable in the high temperature region. This is presumably because even in the same methane-fermenting bacterium, the mesophilic bacterium has a large ability to decompose an acid, whereas the thermophilic bacterium has a poor ability to decompose an acid.

[0014]

As described above in detail, the anaerobic digestion method of sludge or human waste according to the present invention is performed by adding a soap tree extract during the anaerobic digestion step. . And, especially for sludge amount, 2ppm in the middle temperature range
-30 ppm, and 1.5 ppm-17 ppm in the high temperature range for digestion.

Therefore, it is understood that the amount of methane gas generated during digestion increased by about 40% or more as compared with the case of no addition, and digestion was greatly promoted. Moreover, the digestion tank and other devices and processing operations are exactly the same as the conventional ones, and the cost is only the additive, and the total processing cost is greatly reduced.

Claims (2)

[Claims] 1. A method for anaerobic digestion of sludge or raw human sewage, which comprises adding an extract of a soap tree during the anaerobic digestion step of sludge or raw human sewage. 2. A soap tree extract containing 2% of quillaja saponin is used in the range of 2 to 30 ppm in the medium temperature range and in the high temperature range.
The method for anaerobic digestion of sludge or raw sewage according to claim 1, which is added in an amount of 1.5 ppm to 17 ppm.