JP2009022825A - Judgment method of judging if final waste disposal site is sufficiently stabilized, using thermogravimetric analysis - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a judgment method of quickly, simply and properly judging whether or not a final waste disposal site satisfies required requirements for terminating its operation. <P>SOLUTION: The judgment method of judging whether a final waste disposal site wherein waste comprising incineration main ash or incineration residue of city garbage is dumped and disposed of has been sufficiently stabilized or not, uses thermogravimetric analysis in atmospheric air of the evaporation residue of the waste dumped therein from which water contained in the waste or seeping out therefrom has been removed by evaporation, and determines that the stabilization of the final waste disposal site is complete if the ratio of the weight reduction of the evaporation residue corresponding to an exothermic peak of not lower than 200°C and not higher than 400°C relative to the weight reduction thereof corresponding to an exothermic peak of not lower than 400°C and not higher than 500°C has reached 0.4 or below. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a method for diagnosing stabilization by thermogravimetric analysis of a waste final disposal site.

Conventionally, municipal waste incineration ash is mainly incinerated in a stoker-type incinerator or fluidized bed incinerator, and the incineration residue (main ash) of the incinerator is incinerated ash as a general waste final disposal site or industrial waste management type It is dumped directly from the incoming vehicle at the final disposal site and landfilled while being molded with heavy machinery. It is usually landfilled without any special pretreatment such as mixing or classification. The management-type final disposal site has a facility to collect water stored in the landfill due to natural rainfall, etc., while impeding the landfill. The collected water is purified to an appropriate quality and then released into the natural environment.

The final disposal site is fast and fills up in 5 years, usually 15 to 20 years. However, when landfilling is completed, the disposal site cannot be abolished. It is necessary to satisfy the abolition requirements.
1 The water quality of retained water, etc. shall satisfy the drainage standards for more than 2 years.
2 There is almost no generation of landfill gas, and no increase in the amount of gas generated is observed for more than two years.
3 The internal temperature of the landfill is not abnormally high compared to the surrounding underground temperature.

Non-patent document 1 created by the Ministry of the Environment includes landfill waste, leachate, source gas, internal temperature, landfill surface as an indicator of stabilization monitoring, analysis of microorganisms, There is a description that water distribution, hydraulic conductivity, and geophysical exploration can be adopted as supplementary indicators. However, a huge amount of work is required for the determination made based on the plurality of index diagnosis results. Therefore, development of a simpler and quicker diagnostic method is desired.

Waste Disposal Site Stabilization Monitoring Manual Environment Agency 1992

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a diagnostic method for determining whether a waste final disposal site satisfies abolition requirements promptly, simply and qualitatively.

A method for determining the stabilization of the final disposal site for waste containing municipal waste incineration main ash, and the thermogravimetric analysis of the evaporation residue of retained water or leachate collected in the collection pipe of the final disposal site in the air The weight loss corresponding to the exothermic peak of 200 ° C. or more and 400 ° C. or less is 0.4 or less with respect to the weight decrease corresponding to the exothermic peak of 400 ° C. or more and 500 ° C. or less. And a determination method that the stabilization is completed.

According to the final disposal site stabilization diagnosis method according to the present invention, municipal waste incineration main ash, such as determining whether a waste final disposal site satisfies the abolition requirements and estimating when to meet the abolition requirements Stabilization can be determined by thermogravimetric analysis at the final disposal site.

The main minerals that make up the main ash are calcium carbonate, quartz, feldspar, and gehlenite, but in addition to these, calcium silicate and calcium aluminate that hydrates upon contact with water are included. The main ash landfilled at the final disposal site generates hydrated minerals such as ettringite and Friedel's salt by reacting with precipitation that penetrates into the ground after filling. Since these hydrates grow while filling the particle gaps of the main ash, the main ash gradually changes into a dense solidified product. As this solidified material or solidified layer develops, precipitation gradually becomes difficult to penetrate.

Main ash is generated by incineration of municipal waste, but a small amount of organic matter remains 3% and a large amount of 12% remains unburned. These organic substances cause contamination of the quality of water retained in the disposal site and the leachate discharged from the disposal site.
If adequate water and oxygen supply is provided, the decomposition of organic matter in landfilled waste will proceed by aerobic microbial activity, so that it will take a relatively short period of time after the landfill. As the amount of generated gas decreases, the amount of pollutants in the leachate also decreases.

  However, when solidification of main ash occurs in the ground after landfill, and the supply of air and precipitation is obstructed or non-uniform, the decomposition of organic matter by microbial activity proceeds under anaerobic conditions with a very slow decomposition rate. As a result, the release of gas from the landfill will continue and the amount of pollutants in the leachate will not decrease.

The stabilization of the disposal site based on the decomposition of organic matter can be divided into the following five stages in time series.
1. Aerobic decomposition period: Oxygen is consumed and carbon dioxide begins to be produced. Nitrogen concentration is constant, and volatile organic substances are produced at some anaerobic sites.
2 Anaerobic acid fermentation period in which facultative anaerobes are dominant: Hydrolysis and acid fermentation of readily biodegradable organic substances consumes all oxygen and actively produces carbon dioxide. appear. The nitrogen concentration is relatively lowered.
3 Methane generation and development period in which absolute anaerobic bacteria are dominant: Volatile organic acids are converted into methane and carbon dioxide.

4. Steady phase of methane formation in which persistent organic substances are gradually solubilized and decomposed: When volatile organic acids are consumed, decomposition products of cellulose and lignin are used for methane production. The gas pressure in the bed rises due to the formation of methane.
5 Organic matter is reduced and the atmosphere is diffused and entered. End of methane fermentation: Nitrogen and oxygen concentrations are relatively increased.

Of the above-mentioned stabilization stages, the longest period is stage 4, and after this, the requirements for decommissioning the final disposal site are satisfied.

Further, even if the stage 4 is not completely passed, if the situation passing through this stage can be properly monitored, it is possible to determine when to satisfy the abolition requirement.

The first to third stages are characterized by the generation and reduction of hydrogen and volatile organic substances, and the rapid increase and decrease of gases such as carbon dioxide. On the other hand, the rate of decrease in the amount of cellulose is not great. The stage 4 is characterized in that the methane and carbon dioxide concentrations are constant, the amount of organic acid is small, and the amount of cellulose decreases relatively.

Therefore, the following examination revealed that the determination by the thermogravimetric analysis of the evaporation residue of the retained water or leachate collected in the water collection pipe etc. of the final disposal site as an index to grasp the status of the four stages did.

Collect the leachate from the waste disposal site and evaporate it to dryness to obtain a sample. From the final disposal site, there is often a mechanism for collecting retained water from the waste and leachate through the water collecting groove and water collecting pipe provided at the bottom, so the water collected in the water collecting pipe etc. Becomes a sample with good representativeness, and it is preferable to perform thermogravimetric analysis using the sample.
The thermogravimetric analyzer uses Thermo plus TG8210 manufactured by Rigaku Corporation, weighs about 10 mg of sample into a platinum pan, and changes the weight at a heating rate of 10 ° C./min from room temperature to 1000 ° C. in the air atmosphere (hereinafter referred to as “thermogravimetric analyzer”). TG) measurement and DTA measurement were performed. Α alumina was used as a standard sample. The rate of temperature increase is 10 ° C / min, and the temperature starts to increase from room temperature. As a result of temperature correction, 100 ° C after 10 minutes, 200 ° C after 20 minutes, and then continue temperature correction after 10 minutes. The temperature was adjusted to 1000 ° C. after 100 minutes.

FIG. 1 shows a TG-DTA curve of a sample collected from the disposal site in the first year where the stabilization has not progressed, and FIG. 2 shows a sample collected from the disposal site in the 10th year where the stabilization has progressed.

A broad exothermic peak at 260 ° C., 360 ° C., and 450 ° C. is observed in the DTA curve of the evaporated dry solid (A) from the leachate of the disposal site in the first year of FIG. Other endothermic peaks are thought to be due to dehydration of the hydrated mineral produced and melting of the complex chloride.

On the other hand, in the DTA curve of the evaporated dry solid (B) from the immersion liquid of the disposal site where the stabilization has progressed, a peak exothermic from 260 ° C. to 390 ° C. and an exothermic peak centered at 450 ° C. are observed, The exothermic peak of (A) and the temperature range substantially coincide. These correspond to peaks derived from organic matter dissolved in the immersion liquid at the disposal site.

For identification of each peak, TG-DTA curves of humic substances extracted from humic acid as a reagent and natural humic soil are shown in FIGS. In both cases, a two-stage exothermic peak ranging from 200 ° C. to 600 ° C. is obtained, the middle of each step is about 400 ° C., and each peak is about 360 ° C. and about 470-490 ° C. As the humus progresses, the peak at the front stage tends to decrease and the peak at the rear stage increases.

Accordingly, when the exothermic peaks in FIGS. 1 and 2 are examined again, the first stage peak from 200 ° C. to 400 ° C. is due to the exothermic heat of the organic matter in the initial disposal site, and the exothermic peak exceeding 400 ° C. is the age of the organic matter. It can be considered as an organic substance modified by decomposition.

The weight loss corresponding to the sample weight corresponding to the peak in the first stage assigned to the organic matter in the initial disposal site is taken as the content rate. Moreover, the ratio of the weight loss corresponding to the peak of the second stage at a higher temperature can be the content of the organic substance modified by aging decomposition.

Referring to FIG. 1, the weight loss due to the combustion of the first stage peak attributed to the organic matter that is abundant in the initial disposal site of the evaporated dry matter (A) from the leachate of the disposal site in the first year is represented by the DTA curve. Since the weight loss corresponding to the peak in the exothermic temperature from 200 ° C to 400 ° C rising rapidly from the baseline is specified, the amount of decrease is 9 on the scale of the vertical axis, and the peak of the second stage at a higher temperature Since the corresponding weight loss is specified from 400 ° C. to 500 ° C., the weight loss is 1.5 on the vertical scale. Therefore, the ratio of the weight loss due to combustion corresponding to the first peak in the sample (A) to the weight loss due to combustion corresponding to the second peak is 6.

On the other hand, as shown in FIG. 2, the weight loss due to the combustion in the first step of the evaporated dry solid (B) from the immersion liquid in the disposal site where the stabilization has progressed is the exothermic temperature 250 at which the DTA curve departs from the baseline. Since the weight loss from ℃ to 400 ℃ is specified, the weight reduction amount is 8 on the vertical scale, and the weight loss due to the combustion in the second step is similarly specified from 400 ℃ to 500 ℃. The weight reduction amount is 16 on the vertical scale. Therefore, the ratio of the weight loss due to combustion corresponding to the first peak in the sample (B) to the weight loss due to combustion corresponding to the second peak is 0.5.

Furthermore, the ratio of the weight loss due to combustion corresponding to the first peak of the samples collected from several aging disposal sites to the weight loss due to combustion corresponding to the second peak, and the elimination of the waste final disposal site The relationship between requirements 1 to 3 is as shown in Table 1.

Therefore, when the ratio of the weight loss due to combustion corresponding to the first peak to the weight loss due to combustion corresponding to the second peak is 0.4 or less, it is determined that the waste disposal site is stable, and the abolition requirement Turned out to be satisfied.

  By the determination method according to the present invention, it is possible to obtain a guide for the progress of stabilization of the final waste disposal site more easily and quickly, and it is easy to determine whether the abolition requirement is satisfied.

The figure which shows the TG-DTA curve of the evaporation dry matter (A) from the leachate of the disposal site of the first year. The figure which shows the TG-DTA curve of the evaporative dry matter (B) from the leachate of the disposal site which stabilization advanced. The figure which shows the TG-DTA curve of humic acid. The figure which shows the TG-DTA curve of humus extracted from natural humus soil.

Explanation of symbols

Claims (1)

A method for determining the stability of a final disposal site for waste containing municipal waste incineration main ash, wherein the evaporation residue of retained water or leachate from the final disposal site is subjected to thermogravimetric analysis in air, and 200 ° C. As described above, the weight reduction amount corresponding to the exothermic peak of 400 ° C. or lower is less than 0.4 with respect to the weight reduction amount corresponding to the exothermic peak of 400 ° C. or higher and 500 ° C. or lower. Judgment method to be completed.

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