DE4001558C1 - Decontaminating soil contg. mineral oil hydrocarbon - by three-stage biological degradation of contaminants under non-aerobic and aerobic conditions - Google Patents

Abstract

Process for decontaminating soil contg. small amts. of mineral oil hydrocarbons, polycyclic aromatic hydrocarbons, halogenated hydrocarbons and other biodegradable contaminants under non-aerobic and then aerobic conditions. Firstly, the initial feed is aerated with a stream of air, displacing most of the volatile contaminants; the soil is then treated with an anaerobic microorganism, in the presence of nutrients and a methane atmosphere, displacing residual chlorocarbons in a stream of methane; and then further biodegradation with an aerobic microorganism in the presence of suitable nutrients and a stream of air. USE - The process facilitates the desorption of soils for recycling.

Description

The invention relates to a method for decontaminating especially with mineral oil hydrocarbons (MKW), polycyclic aromatic hydrocarbons (PAHs) and halogenated Hydrocarbons (HKW) such as chlorinated hydrocarbon (CKW) and other biodegradable pollutants Soil through biodegradation.

The disposal of various hydrocarbons Decontaminated floors are extremely problematic. Warehousing on landfills does not lead to sustainable and complete environmental relief such as burning the contaminated Products in high temperature furnaces.  

According to Karstedt et al (TIS; civil engineering, civil engineering, Straßenbau, 1986, pp. 514 to 521) volatile CHC Drilling of several suction wells in loose soil Remove soil air extraction and then the exhaust air from one Undergo cleaning treatment or ex-situ the floor in the developed state by means of bacteria with nutrient supply each by type of bacteria under aerobic or under anerobic conditions to treat. Biological decontamination in Bioreactors through bacterial degradation of the hydrocarbons with the addition of oxygen, nutrients and other biological Active ingredients to support the degradation performance of Bacteria z. B. according to Frantzius (Tiefbau BG, 9/1989, p. 603 to 604) in special disposal centers can, because there are the different cleaning techniques as Have the process combination carried out better. Here you can also gas supply and distribution facilities such. B. according to DE OS 36 34 377 or biofilter devices according to DE-OS 34 14 007 be used.

However, the previously known methods are not sufficient versatile; this also applies to biobedding processes that are essentially based on an aerobic method of working for complete decontamination  of contaminated with various pollutants Soil is not enough.

The invention has set itself the task of being economical Propose procedures to decontaminate soil enable which with the most diverse products is contaminated, such as mineral oil hydrocarbons (MKW), polycyclic aromatic hydrocarbons (PAHs) and halogenated hydrocarbons (HKW) and in particular Chlorinated hydrocarbons (CHC) and other biodegradable Pollutants, especially the bacteria in the bioreactor are not their effectiveness may be impaired prematurely.

To solve this problem, an essentially three-stage Proposed method as characterized in the main claim is, preferred embodiments in the subclaims are mentioned.

Furthermore, it is an object of the invention to implement a Propose a suitable device as described in Claim 5 is marked.

Surprisingly, it has been shown that one with the invention three-stage process in an economical way almost complete breakdown of various contaminants can reach.

The principles of the method according to the invention are both suitable for decontamination on site, for example a container with the appropriate connections for additional devices brought to the site, as well as for use in a bio bed, namely a plant where the contaminated Soil is delivered and decontaminated in this organic bed.

In the three process steps according to the invention first stage of the process by supplying air to the soil  Most of the halogenated hydrocarbons HKW and a lower proportion of mineral oil hydrocarbons MKW as well PAK exempt.

In the second stage of the process, an anaerobic purification carried out and the essential residual content of HKW reduced.

This has the advantage that the load or damage the later aerobic process section bacteria used is switched off by HKW.

In the third stage of the process it becomes aerobic by means of a bioreactor the rest of the impurities on MKW, PAK and HKW on the tolerable end values reduced.

In the second stage of the process, namely anaerobic decontamination there are two variants available, namely one the saturation of the soil with methane gas and preferably one Circulation of the same and further by flooding with water, both variants can be combined, especially if you work with sieve tray containers. Even when processing in A bio-bed is the second process step, namely treatment with methane gas or water flooding, possible.

In the following, the invention will be explained in more detail with reference to drawings are explained; show it:

Figure 1 is a diagram of the first stage of the process with a sieve tray.

FIG. 2 shows the second process step with a sieve tray container;

Fig. 3 shows the third process stage with a sieve tray.

The container or container 2 shown is about 2 to 3 m wide and 6 to 10 m long and about 2 m high and has a capacity of 10 to 60 m³. Provided in the lower region is a sieve plate 4 which is arranged at a distance from the bottom surface of the container and extends as far as the container walls, the passage openings of which are, for example, 0.5 to 2 mm in size. Below the sieve bottom is a feed line 6 through which air, water or methane can be introduced. Furthermore, there is a discharge line 8 below the sieve bottom in order to be able to supply the contaminated water to the bioreactor 18 .

Above the sieve bottom there is a spray unit 10 in order to supply the decontaminated soil with water or with bacteria and nutrients, this spray unit 10 being connected via a line 19 to the bioreactor 18 or to a follow-up tank 20 of the same. Furthermore, there is a gas discharge line 12 above the sieve plate 4 or above the spray unit 10 , which is connected to a biofilter 14 and a carbon filter 16 and is also connected to the supply line 6 , which also serves for the circulation of methane gas.

Ultimately, the bioreactor 18 is still connected via a line 15 to the biofilter 14 and the carbon filter 16 connected thereto, in order to ensure that any pollutants that may escape are cleaned.

When carrying out the method according to the invention, the contaminated soil in the container is supplied by air from below the sieve tray in the first stage and guided through the soil by means of the suction device. The HKW absorbed by the air is partially broken down in the biofilter 14 and the remaining HKW are absorbed in the carbon filter 16 ; ( Fig. 1).

In the second stage of the process, anaerobic conditions are created by supplying methane via the feed line 6 and displacing the oxygen, whereby in the present case an anaerobic state is achieved in the contaminated soil by means of a cycle of the methane and, if appropriate, after addition of microorganisms, nutrients and biochemical active substances a further dismantling of the HKW is achieved; ( Fig. 2).

In the third stage of the process, water, possibly enriched with bacteria, and air / oxygen, nutrients and other biochemically active substances, such as e.g. B. bioemulsifiers, for the bacteria a further MKW, PAK and HKW degradation in the soil and a washing out of water-soluble MKW, PAK and HKW is achieved, with the further biodegradation taking place in the bioreactor, together with a stripping of volatile impurities with subsequent air purification the biofilter and the carbon filter with residual adsorption by supplying air through the supply line 6 and the water laden with nutrients in the circuit through the soil via the line 8 into the bioreactor 18 and via the secondary tank 20 and line 19 to the spray unit 10 again. The air is discharged from the bioreactor 18 via the line 15 through the filters 14 and 16 .

The method according to the invention proceeds during the treatment Analogous polluted soils in organic beds, but that Contaminated soil in the organic bed is loosened beforehand must be and the flow of air in the first step or with methane gas and / or water and microorganisms, Nutrients and biochemical agents in the second process step depending on the design of the organic bed in different ways can be done, for example, that the entire cycle the treatment media from top to bottom or vice versa will, if for a corresponding cover with a vacuum carpet is taken care of.  

In the following, the invention will be described in more detail by means of examples are explained.

Example 1

One with 15,000 mg / kg TS mineral oil hydrocarbons (MKW) and 100 mg / kg TS chlorinated hydrocarbons (CHC) contaminated heterogeneous structured soil was in an amount of 10 m³ in one Dumping height of 1 m applied to the sieve bottom of a container and by repeatedly adding water to a soil moisture of 15% set.

In the first stage of the process, 6,300 m³ / h of air were introduced via the supply line, which air was drawn off through the poured soil at the suction port of the container lid via the gas discharge line 12 . The CHCs released by the air were sucked off by the biofilter 14 and then by the carbon filter 16 .

After 10 days of operation of 24 hours, about 90% of the CKW and about 15% MKW sucked off and fed to the air purification. The The efficiency of the biofilter for cleaning on CHCs was around 40% and about 97% in terms of MKW, while the rest of the other discharged pollutants in the carbon filter completely was absorbed.

In the second stage of the process, 10 microorganisms, nutrients and biochemical additives were first supplied via the spray unit. Subsequently, methane gas was introduced via the supply line 6 in an amount of approximately 10 m 3 in order to completely displace the air contained in the container. This air / methane mixture was first drawn off via the gas discharge line 12 and then introduced into the filter system. After the air was completely displaced by methane, the filter system was closed and methane was recirculated via a vacuum pump. No further methane was added during this anaerobic treatment step. The methane circulation was maintained for six working days, 24 hours a day.

The proportion of CHC was reduced from 10 mg / kg to 0.8 mg / kg TS.

In the third stage of the process, air was returned to break down the remaining MKW and small residues of CHC by first displacing the methane from the pores of the soil with the filter system open. The air extraction and the soil air supply were then switched off and the sprinkling with water via the bioreactor 18 was started . With the sprinkler system, up to 10 m³ of water including nutrients and bacterial preparations were brought into the soil and continuously circulated through the bioreactor to break down the dissolved pollutants. The total treatment time at this stage was 55 working days.

The remaining HKW washed out were the bioreactor in Water flow also supplied and there via forced ventilation fed to the filter system in which it is completely broken down or were absorbed.

The dismantling performance of the third stage resulted in a residual load in the Bottom of

MKW: 400 mg / kg TS
CHC: 0.2 mg / kg TS.

Example 2

The procedure was analogous to Example 1, but in the second stage of the process instead of adding methane to the soil Water was flooded until the pore space was saturated. 5.5 m³ of water were used for this. Then was through Foreclosure of the container created an anaerobic situation.  Here, the water was during the entire treatment period of Not exchanged for 8 days.

The efficiency for MKW and CKW dismantling was the same Range as for gas treatment according to example 1.

Example 3

The reprocessing was used instead of the mobile container polluted soils carried out in organic beds. In one Bio beds of 1000 m² were 1000 m² contaminated Soil introduced. A bioreactor was available a capacity of 20 m³ with a storage tank and appropriate compressors, pumps and subsoilers with double nozzle units for the supply of liquid or Air or gas as well as a biofilter and an activated carbon filter.

The organic bed was loaded with 1000 m³ of contaminated soil, which contained 15,000 mg / kg TS MKW and 100 mg / kg TS CKW. The Dumping height on the organic bed was 1 m. The water moisture was adjusted to 15% by repeated addition of water.

The soil was loosened up using a subsoiler and the penetrating as well as that already in the previous system existing air at the same time via the floor surface drainage by means of a vacuum pump with a capacity of up to 30,000 m³ / h aspirated. The polluted exhaust air was then a Biofilter and an activated carbon filter passed. Here were about achieves the same cleaning performance as that according to Example 1 were obtained with the container method. After 7 Operating days were 80% CKW and 20% MKW via the exhaust system removed or degraded or absorbed in the filter system.

In the second stage of the process, 200 m³ of methane and Microorganisms and biochemical additives using the deep loosening machine  within 12 days at intervals of each 3 days injected into the pore spaces of the floor, at the same time by maintaining a slight negative pressure in the Drainage system a possible stripping of the methane for Bed surface was prevented. The extracted little Methane gas mixture was cleaned through the filters. In contrast however, the methane was not used to operate according to Example 1 circulated.

The expiration performance after 12 days of treatment resulted in a Reduction in terms

MKW: from 12,000 mg / kg to 10,500 mg / kg TS
CHC: from 20 mg / kg to 3.5 mg / kg TS.

In the third process step, the soil was again covered with the Loosening machine loosened and a total of 200 m³ of air while maintaining the vacuum through the vacuum pump Drainage system entered. The recycled methane / air mixture was again fed to the bio bed and the carbon filter. Then 100 m³ of water were injected and then that Sprinkling water via the drainage system and a booster pump fed to the bioreactor to break down the pollutants. The water purified in this way was enriched with microorganisms and nutrients via a buffer tank to the Sprinkler system fed and then continued in the cycle guided. In some cases, when the water was introduced Soil air extraction set.

The breakdown performance after 40 days of treatment was as follows:

MKW: from 10 500 mg / kg to 350 mg / kg TS
CHC: from 3.5 mg / kg to 0.2 mg / kg TS.

Example 4

The procedure was analogous to Example 3, but with the air extraction in the opposite direction, d. that is, the organic bed covered with a vacuum carpet and the extraction nozzle of the Vacuum carpet was connected to a vacuum pump. Thereby the air wasn’t sucked from top to bottom as before, but from bottom to top, with the gas supply and the gas discharge took place accordingly.

Example 5:

The procedure was analogous to Example 3, but now instead of the methane addition a complete flooding of the pore volume of the introduced soil was carried out, namely 350 m³ of water are used, which over a treatment time of 8 Days remained in the organic bed and was not replaced. Here too showed that through the set in this way anaerobic conditions a dismantling for MKW and CKW similar to that previous example was achieved.

Claims (5)

1. Process for the decontamination of soil contaminated in particular with mineral oil hydrocarbons (MKW), polycyclic aromatic hydrocarbons (PAK) and halogenated hydrocarbons (HKW) such as chlorinated hydrocarbons (CKW) and other biodegradable pollutants by biological degradation processes, characterized in that

• a) in a first stage of the process, the contaminated soil placed in a container with a sieve bottom or in a bio bed is flushed with air and the air laden with extracted CHC and MKW is fed to a biofilter and then to a carbon filter until at least 70% CHC and 10% MKW are removed on what
• b) in a second stage of the process, after the air has been displaced, the contaminated soil is supplied with methane gas and / or water, is supplied with microorganisms, nutrients and biochemical active ingredients under anaerobic conditions until the residual content of CHC is reduced to at least 20% thereof, wherein the methane gas used, after being loaded with essentially CHC, is passed through the biofilter and the carbon filter, after which
• c) in a third stage of the process, the contaminated soil is fed with air and water after displacement of the methane gas and the water laden with residual pollutants is passed through a bioreactor, with bacteria and nutrients for the latter and other biochemical active substances being fed to this and / or the circulating water will.

2. The method according to claim 1, characterized in that at the first stage of the process each 10 m³ contaminated soil about 200 to 350 m³ / h air in a period of 7 to 10 Operating days are flushed out. 3. The method according to claim 1, characterized in that at the second stage of the process and when treating the contaminated Soil in the sieve tray container Methane is circulated. 4. The method according to claim 1, characterized in that during the second stage in the treatment of contaminated Soil in the organic bed at intervals of two to three Days more methane gas is injected. 5. Transportable closed container for performing the method according to claim 1 to 3, characterized by

• a) a sieve bottom (4) extending at a distance from the bottom surface of the container ( 2 ) and reaching as far as the container walls,
• b) a feed line ( 6 ) located below the sieve bottom ( 4 ) and a discharge line ( 8 ) leading to a bioreactor ( 18 ),
• c) a spray unit ( 10 ) located above the sieve plate ( 4 ) and
• d) a gas discharge line ( 12 ) located in the top wall of the container ( 2 ).