JPH0283098A - Treatment of sludge - Google Patents

Abstract

PURPOSE:To achieve the decomposition of an org. substance within a short time with high efficiency and to markedly reduce a sludge amount by further subject sludge treated with alkali to wet mill treatment and subsequently applying anaerobic digestion treatment to said sludge. CONSTITUTION:Alkali such as caustic soda is added to org. sludge such as sewage sludge until the pH of said sludge is 9-11 to solubilize bacterial cells in the sludge. Further, said sludge is subjected to wet mill treatment using a medium stirring type mill to crush the residual bacterial cells and anaerobic treatment is applied to the sludge after treatment so that the number of stagnation days is 2-5. Furthermore, aerobic digestion treatment due to a basophilic fine algae such as Spirulina is applied to the liquid phase part separated from the sludge after anaerobic digestion treatment. By this method, the treatment capacity of a digester can be enhanced to a large extent or the digester can be markedly miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for treating organic sludge such as sewage sludge and agricultural and fishery waste.

[Conventional technology]

In standard microbial treatment of municipal sewage in sewage treatment plants, sewage is first subjected to aerobic microbial treatment in an aeration tank and then sent to a settling tank. The supernatant discharged from the settling tank is sent to a secondary treatment process, while the large amount of settled sludge, or surplus sludge, may be incinerated or disposed of, but it cannot be dewatered or incinerated. Not only is it difficult to dispose of it, but there is also the problem of dispersing pathogenic microorganisms and deteriorating the environment, so it is necessary to reduce the amount as much as possible to make it easier to dispose of. A typical treatment method for this purpose is anaerobic digestion treatment,
Decomposes organic matter into organic acids, methane gas, carbon dioxide gas, etc. using the metabolism of anaerobic microorganisms.

However, excess sludge is like a mass of microorganisms and is extremely difficult to decompose, so the number of days required for anaerobic digestion is 2.
It is long, from 0 to 30 days. Moreover, even if such a number of days are spent, the decomposition rate of organic matter remains at about 40 to 50%, and therefore the effluent still contains a high concentration of organic matter, which becomes a heavy burden for subsequent water treatment.

[Problem to be solved by the invention]

As mentioned above, conventional sludge treatment methods are inefficient, require large anaerobic digestion tanks, and have unsatisfactory solids reduction effects. In addition, the discharged water has a high concentration of organic matter, so it cannot be discharged as is, and even if it were to be further treated, it would be a heavy burden.

Therefore, the present invention aims to solve the above-mentioned problems in conventional sludge treatment methods and to provide a sludge treatment method that can achieve a higher rate of weight loss and decomposition of organic matter in a shorter period of time.

[Means to solve the problem]

In the sludge treatment method provided by the present invention, organic sludge is
The microbial cells in the sludge are solubilized by adding alkali until the value reaches 9 to 11, and the remaining microbial cells are crushed by wet milling, and the remaining number of days in the sludge after treatment is 2.
The method is characterized in that an anaerobic digestion treatment is performed for ~5 days, and the water separated from the sludge after the anaerobic digestion treatment is subjected to an aerobic digestion treatment using alkaliphilic microalgae.

The sludge treatment method of the present invention will be explained in more detail below.

For alkaline treatment of sludge, add alkali such as sodium hydroxide or soda carbonate until the pH of the sludge reaches 9 to 11, and heat the sludge at a temperature of about 2.
This is carried out by holding at 0 to 30°C for 0.5 to 1 hour. This destroys the cell walls of microorganisms in the sludge and causes so-called solubilization, in which intracellular components such as proteins and sugars are eluted. Although making the pH strongly alkaline to 11 or more is effective in promoting solubilization, it may not allow a sufficient amount of methane bacteria that grow in such strongly alkaline sludge to accumulate in the digestion tank during the subsequent anaerobic digestion process. This is not desirable as it will be difficult.

The alkali-treated sludge is further subjected to wet mill treatment.

This wet milling process is a process in which the solids suspended in water are pulverized by mainly applying shearing frictional force to the solids. A high degree of grinding is performed using a type ball mill, a media stirring type mill, a colloid mill, etc. Among the wet milling methods, the media agitation mill is particularly preferred because it has the best processing effect.

This media stirring type mill rotates a stirring disk inserted into a cylindrical container at high speed to violently stir the screws in the container, creating a shearing friction force between the beads and grinding them. Beads of various sizes are used depending on the purpose, but the beads preferred for solubilizing sludge have a particle size of O.
, OS ~ 1 mm. In that case, the rotation speed of the stirring disk is 1000 to 3000 rpm+n (peripheral speed 10 to
30 m/5ee), and the residence time of the sludge to be treated is approximately 5 to 60 minutes when ordinary sludge is treated.

Microbial cells and fibrous organic matter that were not solubilized by alkaline treatment are also solubilized by this wet mill treatment.
Alternatively, it is crushed into a form that is more amenable to anaerobic digestion. Although solubilization and crushing can be achieved by wet milling alone, the effects of wet milling are more pronounced and appear in a shorter time on sludge constituents that have swelled and been partially solubilized by alkali treatment.

Anaerobic digestion of sludge after wet milling is carried out in a single anaerobic digestion tank as follows.

The sludge is strongly alkaline due to the alkali treatment, but if necessary, alkali is further added to the sludge and the sludge is supplied to the anaerobic digestion tank at a pH of 9 to 11.

Alternatively, alkali is continuously injected into the digestion tank to maintain the inside of the tank at the above 9H. Normally, the pH suitable for the growth of methane bacteria in sewage sludge is considered to be weakly alkaline, less than 8. In particular, in the case of single-tank digestion in which acid-producing bacteria and methane bacteria coexist, the pH has traditionally been adjusted. Since it is around 7 in both cases and without adjustment, 9H is set to a much higher value in the digestion method of the present invention than in the past. In the digestion method of the present invention, due to such a high value of 9H, firstly, the solubilization of the sludge components further progresses, making the sludge components more susceptible to digestion by anaerobic microorganisms. Secondly,.

The pathogenic microorganisms die before they can be detected at all.

As mentioned above, alkaliphilic methane bacteria, which proliferate vigorously in sludge with a high pH, are rare in normal sewage sludge and digested sludge from conventional anaerobic digestion tanks, but when operating an anaerobic digestion tank, By providing an acclimatization period in which the tank PAL is maintained at 9 to 11 at the start, the anaerobic bacterial flora in the tank can occupy most of the flora.

Once the alkaliphilic anaerobic bacteria group is prepared by acclimatization, the sludge to be treated is supplied to the digestion tank and anaerobic digestion is started as normal operation. In this treatment, the temperature inside the tank is not particularly limited, but 30 to 40°C is appropriate, and the residence time is 2 to 5 days. If the retention period is longer than this, the proportion of alkaliphilic methane bacteria among the methane bacteria in the tank will decrease, leading to a decrease in digestibility.

The sludge discharged from the anaerobic digestion tank can be appropriately disposed of as it is after separating the solid and liquid, but in the treatment method of the present invention, the liquid phase portion is further subjected to aerobic digestion treatment using alkaliphilic microalgae. I do. The treatment requires a residence time of 4 to 10 days. This treatment reduces the organic matter content in wastewater by allowing the organic matter solubilized by alkali treatment and wet milling that is not decomposed by anaerobic microorganisms to be used as a nutrient source for the algae. Suitable algae to be used include macroscopic microalgae that can be easily separated later, such as Spirulina and Anabaena. The reason why alkaliphilic algae is particularly used in this treatment is that it can treat wastewater from an anaerobic digestion tank that has been subjected to strong alkalinity without neutralizing it, there is little fear of bacterial growth, and culture management is easy. .

The present invention has been described above for the case of treating surplus sludge, but the treatment method of the present invention is of course suitable for treating other sludge generated in sewage treatment plants, as well as in agricultural and fishery processing plants such as mills. It can also be applied to the disposal of waste from animals, livestock manure, livestock processing waste, fish iliac bones, etc.

〔Example〕

Excess sludge and mixed sludge collected from urban sewage treatment plants (
A treatment according to the present invention and a comparative experiment were conducted on a 1:1 mixture of excess sludge and initial settling sludge. The composition of the sludge and the experimental conditions are as follows.

Sludge composition: TS (%) VS (%) Surplus sludge 4.0 3.0 mixed sludge
3.8 3.1 Alkaline treatment conditions: Add 25% aqueous soda solution until the sludge pH reaches 10, and stir at room temperature for 30 minutes.

Wet mill processing conditions: Equipment used: Media agitation mill/pearl mill (Ashizawa Co., Ltd., model PMISTS, bead diameter 0.2 mm).

Disc rotation speed: 1300, per-circumference speed: 6 m/see Residence time: 5 minutes Anaerobic digestion conditions: Use a 5Q capacity fermenter, continuously stir at 300 rpm, and maintain pH at 10 with a pH controller.

Digestion temperature = 37°C Residence days: 2 days Acclimatization at the start of the experiment: Medium-temperature digested sludge collected from a sewage treatment plant was used as the initial seed sludge and carried out as follows: First 2 weeks: Retention days: 10 days 2 weeks: Retention days: 5 days Last 2 weeks: Retention days: 2 days Treatment with alkaliphilic algae: Algae used: Spirulina sp.
Residence time: 4 days Culture tank: Capacity 25Q1 Liquid depth 5 cm, pH 10500
Illuminate the liquid level with a W flat lamp.

For lighting comparison, Klnx was subjected to the same anaerobic digestion and alkaliphilic algae digestion without any alkali treatment or wet mill treatment (Comparative Example 1), and an experiment with only wet mill treatment and no alkali treatment. An experiment (Comparative Example 2) was conducted in the same manner as described above.

For 10 days after the acclimatization of the anaerobic digester, the digestibility (VS removal rate), amount of gas generated, methane content of gas, and amount of volatile organic acids in the anaerobic digester were measured. Digestibility, volatile organic acid content, and nitrogen content (centrifugation supernatant) were measured.

The average values of the measured values are shown in Tables 1 and 2.

Table 1 Comparative example 1 of sludge and surplus sludge Comparative example 2 Example Anaerobic digestion Digestion tank pH 9.8 Digestibility (%) 14 Gas generation amount (A/VS-M) 113 Methane in gas (%) 43 Volatilization Organic acid (mg#) 830 Contains nitrogen! (%) 4.0 Digestion rate of alkaliphilic algae (%) 25 Volatile organic acids (mg/D l 2 Nitrogen content i (%) o, og 9.9 10.1 4B30 1100 3.9 3. 9 0.08 0.07 Table 2 Sludge: Mixed sludge Comparative Example 1 Comparative Example 2 Example Anaerobic Digestion Digestion tank pH 9,910,1 Digestion efficiency (%) 18 34 Gas generation amount (
Q/VS-kg) 120 290 Methane in gas (
%) 5258 Volatile organic acids (mg/Q) 750 4700 Nitrogen content (%) 4.1 3.8 Digestion treatment with alkaliphilic algae Digestion rate (%) 32 Volatile organic acids (mg #I) l.

Nitrogen content (%) 0.04 [Effects of the invention] According to the sludge treatment method of the present invention, as mentioned above, a high digestibility equal to or higher than the highest level of conventional methods can be achieved in an extremely short time using the anaerobic digestion process. The amount of sludge can be significantly reduced, and the quality of the discharged water can also be improved. Therefore, it is possible to significantly improve the throughput per unit volume of the digester, or to significantly reduce the size of the digester, compared to the conventional method.
The remarkable effect is that the amount of digested sludge generated is reduced and subsequent treatment becomes easier. In addition, because the sludge is treated with strong alkalinity, the digested sludge discharged from the anaerobic digestion tank not only does not contain pathogenic microorganisms, but also contains the remaining anaerobic microorganisms that have grown in the strong alkalinity. Since most of the digested sludge will die if it is released into the natural world, it has the advantage that there is little risk of contaminating the environment when it is disposed of.

Claims (1)

[Claims] Alkali is added to the organic sludge until the pH becomes 9 to 11 to solubilize the microorganisms in the sludge, and the remaining microorganisms are crushed by wet milling, and the treated sludge is Perform anaerobic digestion treatment for 2 to 5 days of residence,
A method for treating sludge, characterized in that water separated from the sludge after the anaerobic digestion treatment is subjected to aerobic digestion treatment using alkaliphilic microalgae.