JPH0490897A - Anaerobic treatment of high concentration organic waste water - Google Patents

Abstract

PURPOSE:To enhance treatment effect by providing a front stage effectively solubilizing org. suspended matter and a post-stage forming an org. acid and setting the environments matched with the treatment conditions of both stages. CONSTITUTION:Raw water is conditioned in a raw water tank 2 having a stirrer 1 and sent to reaction tanks 4, 4', 4'' by a raw water pump 3. The temps. of the reaction tanks are kept constant and raw water is uniformly stirred by the stirrers 5, 5', 5'' of the reaction tanks. Gas vent lines 6, 6', 6'' are provided to the reaction tanks and the inflow raw water is treated for a definite time to be discharged to a treated water tank 7 as treated water. In the methane fermentation of high concn. org. waste water treated in a conventional acid forming process, org. suspended matter is gradually accumulated in a reaction tank and can not be stably treated but, when high concn. org. waste water is subjected to acid forming treatment according to this method, high concn. waste water treatment wherein TOC is about 2700mg/l and a removal rate is about 81.3% can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an anaerobic treatment method for highly concentrated organic wastewater containing highly concentrated organic suspensions and turbid substances.

(Prior art) Organic wastewater containing a high concentration of organic suspended solids, such as wastewater mainly composed of wastewater, has a high concentration of organic matter, so if left as is, it will turn into activated sludge. It is difficult to apply aerobic treatment methods such as

Conventionally, this has been dealt with by reducing the amount of organic matter in the wastewater by removing suspended matter in the wastewater through pretreatment such as coagulation and sedimentation, or by lowering the concentration of organic matter through dilution.

However, the amount of wastewater generated continues to increase.
Various problems have been brought into focus, such as increases in processing equipment space and processing costs, and environmental problems related to industrial waste when processing pre-concentrates generated in pre-processing.

In response to these problems, in recent years, anaerobic treatment technology has been developed as a technology for treating high-concentration and high-load wastewater, and on the other hand from the standpoint of energy recovery, and methane fermentation technology for high-concentration organic wastewater has been developed. I started thinking about how it could be used.

Highly concentrated organic wastewater, especially wastewater containing highly concentrated organic suspended matter, cannot be used as a substrate for microorganisms to ferment methane if left as is. It is necessary to solubilize and reduce the molecular weight of substances, and convert them into volatile organic acids such as acetic acid, so that they can be easily attacked by microorganisms.

Among many anaerobic treatment methods, the two-phase anaerobic treatment method includes an acid generation step in which organic substances such as carbohydrates, proteins and lipids contained in wastewater are decomposed into intermediate products such as volatile organic acids; This process consists of two steps, including a methane fermentation process in which this intermediate product is gasified, and is thought to be used for anaerobic treatment of highly concentrated organic wastewater.

However, even if this two-phase anaerobic treatment method is applied directly to organic wastewater containing a high concentration of organic suspended matter, the conventional step-by-step acid generation process is unable to contain organic suspended matter. It is difficult to proceed with solubilization and molecular weight reduction, and it is necessary to take a sufficient amount of time to dissolve the suspended matter and convert it into a volatile organic acid.

If organic suspensions are insufficiently dissolved, especially in wastewater whose main component is waste milk, scum containing large amounts of fat and oil will build up and accumulate in the upper part of the reaction tank, causing the water supply line to the next process to be blocked. Problems such as blockage occur.

In this way, in high-concentration organic wastewater, especially in wastewater containing high-concentration organic suspended matter, the solubilization and low-molecularization of organic suspended matter in the acid generation process increases the overall treatment speed of anaerobic treatment. Since this is thought to be rate-limiting, several improvement proposals have been made to promote solubilization of organic suspensions and improve treatment efficiency in this acid production step.

For example, in the acid production process, there is a method in which microorganisms immobilized on a carrier are used for treatment, and as shown in Japanese Patent Application Laid-open No. 57-48396, the temperature in the acid production process is lowered to 20% in the subsequent methane fermentation process. There is a method of promoting acid production by increasing the temperature to 45 to 65°C, which is higher than ~40°C.

[Problem to be solved by the invention]

However, even if these conventionally proposed methods are used, wastewater containing a high concentration of organic suspended matter, such as a TOC of 25
00■/1 or more and 30% or more of which is solid suspension that does not pass through a filter medium with a pore size of 0.45 μm. The reduction in molecular weight did not proceed sufficiently, and the organic acid production reaction, which is the original process of the acid production process, was still not very active, and was not satisfactory.

Therefore, an object of the present invention is to provide an anaerobic treatment method that can simultaneously and efficiently promote the two functions of solubilizing and reducing the molecular weight of organic suspensions and generating organic acids in the acid generation process. And so.

[Means to solve the problem]

In the present invention, when wastewater containing a high concentration of organic matter is treated by an anaerobic fermentation method consisting of an acid generation step and a subsequent methane fermentation step, the acid generation step is performed using a plurality of reaction tanks to reduce the pH to 5. The first reaction stage mainly promotes the solubilization of suspended organic matter, and the pH was adjusted to 5.5 to 7.5 and the temperature was set to a high temperature fermentation range. This is an anaerobic treatment method for high-concentration organic wastewater, which is characterized in that it is carried out separately with a subsequent reaction stage that mainly promotes the production of organic acids.

Furthermore, in the present invention, when carrying out the acid production step separately into two stages, as described above, a reaction tank filled with a filler is used for the first stage reaction, and a reaction tank filled with a filler is used for the second stage reaction. The reaction efficiency can be further increased by using a reaction tank without the above. At this time, the filler to be filled into the reaction tank is one commonly used in biological treatment of wastewater, such as PVC chips, anthracite, activated carbon,
Zeolites, filter media, nets, bricks, natural porous materials, etc. may be mentioned.

In addition, in the arrangement of the plurality of reaction tanks used in the acid generation step in the present invention, all the tanks may be connected in series, or at least one tank may be connected in parallel, and both may contain organic suspensions. An intermediate tank may be provided between the reaction tank in the step of promoting solubilization and the reaction tank in the step of promoting the production of organic acid, for transferring the treatment conditions of the present invention.

In addition, wastewater mainly composed of waste milk refers to wastewater mainly composed of unsold product waste and highly concentrated organic wastewater discharged during product manufacturing related to the production of dairy products such as milk, yogurt, and ice cream. It refers to something that does.

[For production]

For organic wastewater containing a high concentration of organic suspensions, the acid generation process of the two-phase anaerobic treatment method, which is a conventional method, uses a single reaction tank, the temperature is in the meso-temperature fermentation range, and the pH is not adjusted. When carried out, the solubilization of the suspension does not proceed rapidly and at the same time the formation of organic acids is slow. And the reaction tank is 1
In the case of a tank, for example, the temperature is set in the high temperature fermentation range and the pH is adjusted, or the pH is not adjusted in the medium temperature fermentation range and a filler is filled in the reaction tank to process water temperature, pH, etc. No matter how the conditions are changed, the solubilization of the suspension and the production of the organic acid cannot proceed simultaneously and sufficiently.

On the other hand, in the acid generation process using multiple reaction vessels, according to the present invention, the process is divided into a pre-stage to effectively solubilize the organic suspended matter and a post-stage to generate the organic acid. By setting the environment to suit the environment, processing effects can be improved.

The appropriate number of reaction tanks used in the present invention is 2 to 4, considering the initial cost of equipment relative to treatment performance.

Regarding the solubilization of organic suspensions in the first reaction stage of the acid production process in which the number of reaction vessels is multiple, if the temperature conditions are below the high temperature fermentation range, that is, 45 to 60°C, the organic suspensions are not effective. If the temperature exceeds the high temperature fermentation range, the cost for heating becomes high and it is not economical.

If the reaction tank is not filled with a filler in the first reaction stage, the dissolution of the organic suspension will not proceed efficiently. Therefore, in order to further promote solubilization under conditions where the temperature of the reaction tank in the first reaction stage is in the high temperature fermentation range, it is effective to fill the tank with a filler.

In the latter reaction stage of the acid production process, if the reaction proceeds without neutralizing the pH, it will not be possible to produce a high concentration of organic acid no matter how other conditions are changed, and the amount of organic acid produced will decrease. low. In order to actively generate organic acids, the pH should be set to 5.
．． It is necessary to maintain it within the range of 5 to 7.5. Furthermore, if the reaction temperature is in the high temperature fermentation range, the production of @acid will be lower than in the conventional method, and the processing cost will also be higher.

Further, in the mesotemperature fermentation range, that is, below 25 to 45°C, the amount of acid produced generally decreases. Note that the absence of filler is more efficient in producing organic acids.

As described above, in the method of the present invention, the treatment conditions of the acid generation step are set to conditions effective for solubilizing the organic suspension in the first stage and conditions suitable for the generation of volatile organic acids in the second stage. Therefore, if the conditions of the first stage and the second stage are reversed, there is no effect at all.

〔Example〕

The present invention will be described in detail below with reference to the drawings.

Figures 1 and 2 show the outlines of the double-tank and single-tank acid production process experimental equipment, respectively.

Raw water is adjusted in a raw water tank 2 equipped with a stirring device 1, and sent to reaction tanks 4, 4' and 4'' by a raw water pump 3.The temperature of the reaction tank is kept constant, and the reaction tank stirrer 5.5' and 5" are used to uniformly stir the mixture. The reaction tank is provided with degassing lines 6.6', 6'', and the inflowing raw water flows out into the treated water tank 7 as treated water after a certain period of time due to the extrusion flow.

Using these experimental devices, we conducted a continuous water flow test of highly concentrated organic wastewater (hereinafter referred to as raw water) whose main component is waste milk.
The state of dissolution of suspended solids and the state of organic acid production were investigated under the following treatment conditions.

pH in the reaction tank: Adjusted using 30% sodium hydroxide solution if necessary.

Temperature inside the reaction tank: 35°C or 55°C Presence or absence of filler: Pieces of silicone rubber sponge were filled to an extent of 20% of the volume of the reaction tank (if indicated as present).

Number of reaction vessels: When there is no distinction between the two stages and the second stage, the total number is shown, and when the reactor is divided into the first stage and the second stage, the number of each is shown.

Table 1 shows the raw water quality.

3.4 15000 16000 56.7S
S: Suspended substances TOC: Total organic carbon TOC dissolution rate: Ratio of TOC before dissolution to TOC Raw water is passed through at a rate of 0.64 kg/'/day with a TOC loading amount, and the residence time in the reaction tank is It was set as the 25th.

The TOC load amount here is the reaction tank capacity in? 1 hit
This is the amount of raw water TOC flowing into the water per day.

Table 2 shows the suspension solubilization state and the organic acid production state as a result of operating these devices by adjusting the residence time in each reaction tank to be equal. In the same table, the SS removal rate is the ratio of removed SS to the inflowing SS, the organic matter dissolution rate is the ratio of decreased insoluble TOC to the inflowing insoluble TOC, and the organic acid concentration is the ratio of acetic acid and propionic acid. , the total amount of butyric acid, isobutyric acid, valeric acid, isovaleric acid, and caproic acid converted into equimolar amounts of acetic acid, and the organic acid conversion rate means the ratio of organic alcoholic carbon to TOC, respectively. ing.

These results show that it is not possible to efficiently convert organic suspensions to organic acids simply by connecting multiple tanks in series.
Furthermore, it can be seen that particularly excellent results are obtained when the reaction conditions of the first and second stages each match the conditions of the present invention (Test 6).

(Example 2) Using an anaerobic treatment equipment having the acid production process experimental equipment shown in Figures 1 and 2 above, high concentration organic wastewater (raw water of Example) containing waste pores as its main component was treated. An anaerobic treatment test was conducted to compare the conventional two-phase anaerobic treatment method C (which has the acid generation step shown in Figure 2) and the method of the present invention (which has the acid generation step shown in Figure 1). The processing performance was compared.

Methane fermentation was carried out using a floating sludge method at a liquid temperature of 35°C, and the resulting treated water was allowed to stand for 2 hours, and its supernatant water was collected and the water quality was compared. The results are shown in Table-3.

Conventional method 16000 0.0 method 81.3 TOC removal rate: T removed relative to influent TOC.

In contrast, in methane fermentation of highly concentrated organic wastewater treated with conventional acid production processes, organic suspended matter gradually accumulated in the reaction tank and could not be treated stably. Therefore, when highly concentrated organic wastewater was subjected to acid production treatment according to its nature, it was possible to treat highly concentrated wastewater with a TOC of 2700/1 and a removal rate of 81.3%.

〔Effect of the invention〕

As is clear from the above experiments, according to the present invention, organic suspended matter is effectively solubilized and reduced in molecular weight in the first stage of the acid generation process, and active volatile organic acids are actively generated in the second stage. It will be done. Therefore, by increasing the processing efficiency of the acid generation process, it is possible to downsize the anaerobic treatment equipment and reduce running costs.

[Brief explanation of drawings]

FIG. 1 shows an apparatus for carrying out the acid generation process of the present invention, and FIG. 2 shows an example of a conventionally known acid generation process treatment apparatus. 1... Stirring device, 2... Raw water tank, 3... Raw water pump, 4.4', 4'... Reaction tank, 5.5', 5'''.
... Stirrer, 6... Gas venting line, 7... Treated water tank.

Claims (4)

[Claims] (1) When treating wastewater containing a high concentration of organic matter by an anaerobic fermentation method consisting of an acid generation step followed by a methane fermentation step, the acid generation step is performed using multiple reaction vessels to reduce the pH to 5. A first reaction stage that mainly promotes solubilization of suspended organic matter in a high temperature fermentation region adjusted to .5 to 7.5;
Anaerobic treatment of high-concentration organic wastewater, characterized in that the pH is adjusted to 5.5 to 7.5 and the reaction is carried out in a meso-temperature fermentation region, with a subsequent reaction stage mainly focused on promoting the production of organic acids. Processing method. (2) The anaerobic treatment method according to claim (1), wherein a reaction tank charged with a filler is used in the first reaction stage, and a reaction tank without a filler is used in the second reaction stage. (3) The anaerobic treatment method according to claim (1) or (2), wherein the high temperature fermentation range is 45 to 60°C, and the medium temperature fermentation range is 25 to 45°C. (4) The anaerobic treatment method according to any one of claims (1) to (3), wherein the highly concentrated organic wastewater is mainly composed of waste milk from the production of dairy products.