JP2009178657A - Subcritical water treatment method for refinery wastewater organic sludge - Google Patents

Abstract

The present invention provides a stable and efficient method for treating organic waste containing a large amount of oil as generated in a petroleum refining process.
In a method for treating organic waste containing a large amount of oil as generated in a petroleum refining process, first, treatment is performed with subcritical water or supercritical water under predetermined conditions, and then methane is added to the reactant. A method of applying a fermentation treatment.
[Selection] Figure 2

Description

The present invention relates to a method for methane fermentation treatment of organic sludge by treating organic sludge by methane fermentation. In particular, the present invention relates to a method for methane fermentation treatment of organic sludge containing 50 mg to 10000 mg of petroleum per 1 kg of sludge as obtained in a treatment process of wastewater discarded from a petroleum refining process.

In a method for treating organic wastewater containing an organic matter containing an oil component generated from a petroleum refining process, treatment with activated sludge is generally known after separating the oil component in an oil / water separation tank or the like. Since sludge and organic waste generated in this process contain a lot of oil, there was no method other than final disposal mainly by incineration or landfill disposal. In recent years, in view of problems such as consumption of heavy oil accompanying incineration and a shortage of landfill disposal sites, there has been a demand for a processing method with less environmental impact. As such a treatment method, a method for methane fermentation treatment of organic waste has been developed. For example, after pulverizing organic waste into a slurry, it is supplied to a methane fermentation facility and subjected to anaerobic conditions. It has been known to convert organic waste into methane gas by fermentation with methane bacteria (for example, Patent Document 1). Here, the methane fermentation treatment method can decompose organic waste into biogas and water to significantly reduce the amount, and because it is fermentation under anaerobic conditions, it does not require aeration power and is a byproduct. There is an advantage that methane gas in the biogas produced as can be recovered as energy.
However, since the treatment by methane fermentation is a biological treatment, its treatment capacity is limited, and there is a risk that the treatment may not be sufficiently performed when the properties of the treatment target vary. Therefore, such a biological treatment alone has a limit in processing capacity.

Furthermore, in the methane fermentation treatment method, various pretreatments may be performed prior to supplying organic waste to the methane fermentation facility in order to efficiently perform methane fermentation in the methane fermentation facility and improve the processing capacity. is there. As an example of pretreatment, subcritical water treatment has been studied (for example, Patent Document 2 and Patent Document 3), and water-insoluble food-based organic waste such as waste yeast and wheat straw is treated under subcritical water conditions. Alternatively, such as waste yeast and wheat straw with a hydrothermal reaction treatment step that liquefies by a hydrothermal reaction under supercritical water conditions and a recovery step that recovers valuable materials from the liquefied hydrothermal reaction treatment product Methods for treating food-based organic waste have been reported. Moreover, in the methane fermentation processing method of the garbage or food residue which processes garbage or a food residue by methane fermentation, sub-critical water of 110-160 degreeC is supplied before supplying the said garbage or food residue to a methane fermentation installation. Also known is a method for methane fermentation treatment of raw garbage or food residue for treating the raw garbage or food residue at a treatment temperature for 2.5 to 10 minutes.
JP 2002-119937 A JP 2002-102897 A JP 2007-111673 A

As described above, in the method for treating organic waste generated in the oil refining process, the biological treatment alone has a limit in treatment capacity. In addition, prior to methane fermentation of organic waste treatment such as food waste, a method of treating with subcritical water has been known. The method of treating organic waste containing it with subcritical water or supercritical water and then treating it with methane fermentation has not been studied at all for many years, and its potential has not been known. .

The present invention has been made by paying attention to such conventional problems, and is capable of stably and efficiently reducing sludge (organic sludge) containing a certain amount or more of oil, particularly oil containing oil. It aims at providing the methane fermentation processing method which can be processed well.

As a result of intensive studies, the present inventor conducted a methane fermentation treatment after treating organic sludge containing a certain amount or more of oil with subcritical water at a specific temperature, pressure and time. The present inventors have experimentally found that the organic sludge can be efficiently fermented, whereby the organic sludge can be quickly treated at low cost.

Accordingly, the present invention has the following configuration.
[1] A method for treating organic sludge having the following steps.
(1) Process of treating organic sludge containing 50 mg to 10000 mg of oil per 1 kg of sludge with subcritical water (2) Process of fermenting treated organic sludge obtained in (1) with methane [2] Organic sludge Is obtained from the process of the wastewater treatment of a refinery, The processing method as described in said [1].
[3] The processing method according to [2], wherein the organic sludge is a surplus sludge obtained from an aeration tank in a refinery waste treatment step or a hydrous sludge obtained from a sludge preparation layer.
[4] The processing method according to any one of [1] to [3], wherein the organic sludge has a water content of 95% or more.
[5] The processing method according to any one of [1] to [4], wherein the subcritical water is treated at a temperature of 120 to 300 ° C. and a pressure of 0.2 to 10 MPa.
[6] The treatment method according to any one of [1] to [5], wherein the treatment time with subcritical water or supercritical water is 1.5 to 30 minutes.
[7] The processing method according to any one of [1] to [6], wherein the temperature of methane fermentation is in the range of 35 to 55 ° C.

According to the method of methane fermentation treatment of organic sludge containing a certain amount or more of the oil component of the present invention, organic sludge can be efficiently treated at low cost.

Examples of the organic sludge containing a certain amount or more of oil as used in the present invention include sludge obtained in a wastewater treatment process at a refinery. That is, wastewater treatment with wastewater containing petroleum components generated in the oil refining process is usually treated with activated sludge, and the activated sludge used here is treated. Therefore, it is obtained by mixing and concentrating activated sludge (hereinafter also referred to as surplus sludge) generated in an activated sludge treatment facility for processing with activated sludge, the sludge and waste generated in the wastewater treatment process. The sludge concentrate (hereinafter also referred to as hydrous sludge) corresponds to this.
FIG. 1 is a schematic diagram showing an example of a refinery wastewater treatment facility. Specific examples of the organic sludge used in the present invention include surplus sludge obtained from the activated sludge treatment facility in this schematic diagram or hydrous sludge obtained from a sludge blending tank.

The organic sludge treated in the present invention refers to sludge containing 50 mg to 10000 mg of oil per 1 kg of sludge (water-containing base). The oil content is preferably 90 mg to 6000 mg per kg of sludge, and more preferably 100 mg to 5000 mg of oil per kg of sludge. The oil content in the organic sludge includes oils and fats such as animal and plant oils and fats derived from domestic wastewater, but includes oils containing various hydrocarbons generated from the petroleum refining process. Petroleum is the main oil in organic sludge at refineries.

The treatment of subcritical water of the organic sludge of the present invention is desirably performed at a temperature of 120 to 300 ° C. and a pressure of 0.2 to 10 MPa. About temperature, Preferably it is 140-280 degreeC, More preferably, it is 170-260 degreeC. The pressure is preferably 0.2 to 9 MPa, more preferably 0.8 to 6 MPa. When the water enters the subcritical water region, the ionic product increases, so that the hydrolytic ability increases and becomes maximum at 250 ° C. For this reason, if the temperature is low, the hydrolysis capacity for reducing the molecular weight of organic sludge is not sufficient, and in the region above 260 ° C, the thermal decomposition reaction is dominant rather than hydrolysis, which is useful for methane fermentation. Production of organic acids is hindered.

The treatment time for the subcritical water of the organic sludge of the present invention is 1.5 to 30 minutes, preferably 2 to 10 minutes. The processing time is closely related to the processing temperature. Since the hydrolysis reaction proceeds in a short time when the treatment temperature is high, the treatment time may be short. However, when the treatment temperature is low, it is necessary to lengthen the treatment time. However, if the processing time is too short, it becomes difficult to control the process.

Moreover, it is preferable that the organic sludge which performs a subcritical water process by this invention performs a process in the state which made the moisture content 80% or more. Preferably, it is 90% or more, more preferably 95% or more. If the water content is too low, the fluidity is lowered and handling is difficult, and if the water content is too high, the energy required for the subcritical water treatment increases.

The methane fermentation referred to in the present invention refers to a series of processes organic matter is converted is assimilated into various microorganisms to methane (CH _4), sub-critical water treatment of organic sludge carbohydrates, amino acids, fatty acids, etc. The process is decomposed into water-soluble low-molecular substances (solubilization process), further decomposed to produce lower fatty acids such as acetic acid, propionic acid and butyric acid, the process decomposed into acetic acid and hydrogen gas, acetic acid and hydrogen It consists of a process of producing methane from gas, etc., and refers to the process of fermentation treatment by the action of methane bacteria in an anaerobic atmosphere. In the methane fermentation performed in the present invention, the temperature is preferably in the range of 35 to 60 ° C, more preferably 35 to 45 ° C. Methane fermentation includes medium temperature fermentation performed at 35 to 45 ° C. and high temperature fermentation performed at 50 to 60 ° C., but methane fermentation in the present invention is preferably medium temperature fermentation. In high-temperature fermentation, the temperature range where the activity of methane bacteria is high is narrow, and stricter temperature control is required. In addition, the amount of energy required to maintain a high temperature increases, resulting in lower economic efficiency. To do.

In addition, it is desirable that biogas mainly composed of methane gas generated by methane fermentation can be effectively used. For example, it is supplied to a power generation device of an energy recovery facility and used effectively for power generation, heat supply, and the like. desirable. It is also desirable to use it for supplying heat for subcritical water treatment or for petroleum refining processes. On the other hand, digestive juice and digested sludge, which are residues obtained from methane fermentation, are sent to the digestive fluid treatment system and liquid fertilizer storage facility, and then returned to farmland as liquid fertilizer and compost, or discharged into rivers and transported to sewage treatment plants. Will be made.

According to the methane fermentation treatment method of the present invention, even organic sludge containing a certain amount or more of oil can be efficiently treated at low cost while recovering methane as an energy source. That is, in the present invention, prior to methane fermentation of organic sludge, the treatment of subcritical water at the specific temperature, pressure and time described above is performed as a pretreatment. Compared with the case where fermentation is performed, for example, a processing speed by methane fermentation of about 5 to 10 times and a generation amount of gas by methane fermentation of about 1.5 to 2.5 times can be obtained. In this way, organic sludge containing petroleum components can be efficiently processed at low cost.

EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example and a comparative example, this invention is not limited to these.

〔experimental method〕
The experimental methods of Example 1 and Example 2 below are shown below.
1. Collection of organic sludge Surplus sludge and hydrous sludge were used as the organic sludge to be treated with the subcritical water of the present invention. These were collected from the activated sludge treatment facility and the sludge blending tank, respectively, in the schematic diagram of the wastewater treatment facility generated in the oil refining process shown in FIG. The sludge properties are analyzed under the following conditions, and the analysis results are shown in Table 1.
<Analysis conditions>
Oil content (IR): In accordance with “TPH test method”, analysis was performed by an IR method oil concentration meter (Horiba Seisakusho, OCMA-350 oil concentration meter) using chlorotrifluoroethylene telomer as a solvent.
Water content: The test was conducted under the conditions of 105 ° C. × 2 hours in accordance with “Sediment Survey Method”.
Ignition loss: Performed under conditions of 600 ° C. × 2 hours in accordance with “Sediment Survey Method”.

2. Treatment method of organic sludge with subcritical water Reaction tube (with Swagelok caps on both ends of stainless steel (SUS304) pipe with inner diameter 6.4mm, outer diameter 9.5mm, wall thickness 1.6mm, length 150mm) 4 g of each organic sludge was charged and sealed, and then subcritical water treatment was performed under predetermined conditions described later.

3. Method of treatment by methane fermentation 4 ml of methanogen (digestion fermentation sludge from Yagi Bioecology Center) was charged into 1 ml of the reaction product treated with subcritical water in a mini vial (22 ml) with aluminum seal. After replacing the gas with a mixed gas (80% nitrogen, 20% carbon dioxide), the cells were cultured in an incubator maintained at 37 ° C. and treated by methane fermentation. The amount of methane produced in the gas phase of the vial after the lapse of a predetermined time after the start of culture (after the start of methane fermentation) was measured by gas chromatography.

[Example 1]
Using surplus sludge as organic sludge, treatment with subcritical water at temperatures of 140 ° C., 170 ° C., 200 ° C., 230 ° C., and 260 ° C. for 2 minutes, or 10 Went for a minute. After the treatment with subcritical water, the treated product was subjected to methane fermentation treatment according to the treatment method using methane fermentation, and the amount of methane gas generated was measured over time. Further, as a comparative example, the amount of methane generated was measured by performing methane fermentation in the same manner without performing treatment with subcritical water (represented as “untreated”). The measurement result of the amount of methane generated when methane fermentation is performed after the subcritical water treatment of each condition is shown in FIG. In the figure, the amount of methane generated is shown as the amount generated per vial (absolute amount).
Moreover, what showed the methane generation amount at the time of performing methane fermentation treatment for 170 hours about each subcritical processing condition by the relative value which set the methane generation amount in the case of un-processing to 1 is shown in FIG.

[Example 2]
Using hydrous sludge as organic sludge, treatment with subcritical water and methane fermentation treatment were performed in the same manner as in Example 1, and the amount of methane gas generated was measured. As a comparative example, methane fermentation was performed in the same manner without performing treatment with subcritical water, and the amount of methane generated was measured over time (represented as “untreated”).
The measurement result of the amount of methane generated when methane fermentation is performed after the subcritical water treatment of each condition is shown in FIG. Moreover, what showed the methane generation amount at the time of performing a methane fermentation process for 170 hours by the relative value which set the methane generation amount in the case of un-processing to 1 is shown in FIG. From these results, the example (subcritical water treatment) according to the present invention using the organic sludge containing oil is approximately 1.2 to 2.5 times as large as the comparative example (subcritical water treatment untreated). About methane was generated, and it was found that the effect of the present invention was remarkable.

[Test Example 1]
Change in properties of organic sludge by subcritical water treatment Test method After treating the organic sludge with subcritical water at 170 ° C, 200 ° C, and 230 ° C for 10 minutes, the reaction product was transferred to a test tube, added with n-hexane, and stirred into a centrifuge. The n-hexane phase (n-C6 phase), the aqueous phase and the solid phase were separated, and the upper n-hexane phase was recovered to obtain the n-hexane dissolved phase. The n-hexane phase was measured after evaporating n-hexane, and the solid phase was weighed after drying. The solid phase was subjected to elemental analysis of C, H, N, and S, and the measurement results are shown in Table 2. . In the table, all wt% were measured based on the charged amount.

2. Test results From the analysis results of the solid phase of Table 2 and Table 3, the surplus sludge is reduced to 1/2 to 1/3 by performing the subcritical water treatment of the present invention. Also decreased to 4/5 to 2/3. These are considered to be the organic substances contained in the sludge decomposed and solubilized by the subcritical water treatment. In addition, since the oil extracted into the n-hexane phase is reduced by carrying out the subcritical water treatment, the oil contained in the organic sludge is hydrolyzed by the subcritical water treatment and converted into water. It is considered to be a soluble substance.
The aqueous phase was analyzed for amino acids and organic acids by liquid chromatography. As for amino acids, formation of various amino acids including aspartic acid was observed. For organic acids, acetic acid, Formation of organic acids including formic acid was observed. Sub-critical water treatment of organic wastewater sludge reduces the molecular weight of organic matter contained in organic sludge and generates various amino acids and organic acids to efficiently perform subsequent methane fermentation It can be seen that energy can be recovered efficiently.

According to the methane fermentation treatment method of the present invention, organic sludge containing petroleum components can be efficiently treated at low cost.

It is a schematic diagram of an example of the waste water treatment equipment generated in the oil refining process for showing the collection place of the organic sludge used for this invention. It is a graph which shows the measurement result of the amount of methane generation at the time of performing methane fermentation for 170 hours after performing subcritical water treatment of each condition (in the case of surplus sludge) It is a graph which shows the measurement result of the amount of methane generation at the time of performing methane fermentation for 170 hours after performing subcritical water treatment of each condition (in the case of hydrous sludge). It is a graph which shows the measurement result of the amount of methane generation at the time of performing methane fermentation after performing subcritical water treatment of each condition (in the case of surplus sludge). It is a graph which shows the measurement result of the amount of methane generation at the time of performing methane fermentation after performing subcritical water treatment of each condition (in the case of hydrous sludge).

Claims (7)

The processing method of the organic sludge which has the following processes.
(1) Process of treating organic sludge containing 50 mg to 10000 mg of oil per 1 kg of sludge with subcritical water (2) Process of subjecting the treated organic sludge obtained in (1) to methane fermentation The processing method according to claim 1, wherein the organic sludge is obtained from a refinery wastewater treatment step. 3. The treatment method according to claim 2, wherein the organic sludge is an excess sludge obtained from an aeration tank in a refinery waste treatment step or a hydrous sludge obtained from a sludge preparation layer. The processing method according to any one of claims 1 to 3, wherein the organic sludge has a water content of 95% or more. The treatment method according to any one of claims 1 to 4, wherein the subcritical water is treated at a temperature of 120 to 300 ° C and a pressure of 0.2 to 10 MPa. The treatment method according to any one of claims 1 to 5, wherein the treatment time with subcritical water is 1 to 30 minutes. The processing method in any one of Claims 1-6 whose temperature of methane fermentation is the range of 35-55 degreeC.