PuriSoil®, Ecological Gain Without Economic Pain

By Dr. Ir. Nico Grootjen and Ir. Wim Steenbakkers
February 2003

The Authors are managing directors at Terreco BV in Geleen, the Netherlands. With their team of highly experienced specialists, they have developed a patented soil remediation technology whose effectiveness has been extensively proven over the last few years.

Introduction

PuriSoil® is an innovative, patented technology for treating contaminated soil. The PuriSoil® technology is marketed by Terreco, the Netherlands, and has been proven in a wide variety of polluted locations. In this paper a description of the technology is given as well as a comparison of the PuriSoil® technology with other soil remediation technologies. The paper is completed with two large scale examples of remediation projects with the PuriSoil® technology.

Technology

PuriSoil® is based on the principle of eco-friendly treatment of contaminated soil. In the area of the soil clean-up pipes are laid to a depth lower than the contaminated layer of soil. Air is injected into the soil from these pipes. A specially developed bio-active material (PuriSoil® starter) is mixed with the top layer of soil. As the air flows upwards through the soil it carries the contamination to the bioactive layer, where the contaminants are then completely and effectively broken down and converted to CO2 and water. The PuriSoil® technology is designed to clean the polluted soil naturally. Both soil and ground water are purified solely through biological activity. The result of the remediation is clean soil in which all life has been restored and from which no pollutants have been dispersed to the air or the environment. In the figure below an artists impression of the PuriSoil® technology is presented.

Technology

With PuriSoil® no major excavation is needed, and no heavy-duty equipment is used to treat the soil causing an obstruction above ground. Practical tests have shown that PuriSoil® can clean soil to a depth of more than 20 meters without any problems. Since no ground water is extracted in the process there is no risk of subsidence. PuriSoil® is particularly useful for complex pollution and in situations where it is important to avoid additional disruption of the local ecosystem.

The pipes can be laid in the ground quickly and with a minimum of disruption. The air can be injected in the ground with a compressor at high pressure. The use of high pressure means that large areas can be quickly treated. No additional equipment is required to treat the soil because the treatment and conversion of the contaminants to CO2 and water is an integral part of the remediation process, which takes place inside the soil. Soil remediation with PuriSoil® is ecologically friendly, works rapidly and causes scarcely any damage to the environment.

Applicability and Costs

PuriSoil® can be used anywhere, including polluted industrial sites and housing estates that have been built on polluted land. Because there is no need to demolish houses or other buildings with this technology there is no disruption to daily life. PuriSoil® can be used in saturated and unsaturated zones. Tests have proved that during the remediation process all volatile organic substances that are aerobically degradable, including many chemicals used in industry such as BTEX, hexane, styrene and acrylonitrile, are converted.

Soil remediation with PuriSoil® technology is efficient. For example, there are no costs for excavation or removal of contaminated soil. Large areas can be cleaned in a single operation, with significant results achieved quickly. This means that PuriSoil® is almost always cheaper than other remediation technologies.

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Real Life Experiences

PuriSoil® has been extensively tested in practice and has already proved itself in cleanup projects at a wide variety of contaminated sites.

Complete and fast

A number of projects have already been completed using PuriSoil®. These soil remediation operations have shown that PuriSoil® almost totally eliminates the contamination and does so very quickly compared with other in-situ remediation techniques. The speed of the remediation using PuriSoil® depends on a number of factors such as the level of the ground water, the type of soil, the nature and scale of the contamination and whether there are buildings on the site. Experiences on different sites are described in more detail in the examples below

Under existing infrastructure / houses

Soil can be cleaned with PuriSoil® under all sorts of buildings and infrastructure. A number of examples are:

Under houses and roads

In two housing estates soil was successfully cleaned without causing nuisance for the residents.

Little nuisance

One of the great advantages of PuriSoil® is that it causes little or no disruption for people in the vicinity, for instance in housing estates like Sprang Capelle in The Netherlands. Mr Dank, one of the residents of the area being cleaned in Sprang Capelle, was very impressed with the cooperation, the work methods and the final result. "You don't even notice it, apart from the fact that bubbles occasionally appear when it rains. This approach neatly solved all my objections and avoided a lot of inconvenience", according to Cees Dank.

Deep and large

PuriSoil® has proved to be capable of effectively cleaning soil to great depths (up to 20 metres) and across very large areas. Small areas can of course also be treated with PuriSoil®, but PuriSoil® really comes into its own with major (large area, deep contamination) remediation operations.

Under any conditions

PuriSoil® technology can be used under practically any conditions.

All aerobically biodegradable chemicals

PuriSoil® can remove all volatile, aerobically biodegradable chemicals. PuriSoil® has already been used to successfully clean soil contaminated with the following chemicals: Toluene, Benzene, Compounds of various BTEX (petrol and diesel), CAN, ACH, Acetone, Hexane, Styrene, MTBE, Methanol, Phenol, Mineral oil.

Comparison of Technologies

Many technologies have been developed for remediation of contaminated soil. Broadly speaking, they can be grouped in the following categories:

There are various options in each of these categories.

Ex-situ technologies In-situ technologies
IncinerationAir extraction
ExtractionWater extraction
LandfarmingBiorestoration

Ex-Situ Technologies

The major advantage of ex-situ technologies is that it takes relatively little time to remove the contaminated soil. The soil is excavated, treated or replaced and then filled in again. By comparison with PuriSoil® and other in-situ methods, however, this method of soil remediation has many drawbacks.

Table 1.   Comparison of in-situ soil remediation technologies
 Air extractionWater extractionPuriSoil®
ContaminationVolatile, aerobically degradable+o+
Hydrocarbons with more than 3 Cl atoms++-
Metals, easily soluble in water-+-
Type of SoilSand+++
Clay-o+
Loam--+
Soil/Ground WaterUnsaturated+-+
Saturated-++
Maximum DepthDepth >5m-o+
Depth >10m--+
Effective Range Injection/Extraction Point<5m+++
>5m-o+
Removal /Conversion of ContaminationIntegrated --+
Costs unrelated to volume--+

+ : suitable   o : less suitable   - : unsuitable

In-Situ Technologies

Increasingly, in-situ technologies are used for sustainable clean-up of contaminated sites. Air and water extraction have in practice proved to be reliable methods for various types of soil remediation. But compared with PuriSoil® air and water extraction have a number of constraints, as shown in table 1. Although biorestoration is also used, this technology works too slowly to be fully effective as a remediation technology.

Advantages

PuriSoil® has many distinct advantages compared with other technologies.

Conclusion

PuriSoil® is clearly technologically superior to and significantly cheaper than all other soil remediation technologies. For companies that take soil clean-up seriously and attach importance to reducing cost, nuisance and environmental impact and achieving the best possible results, PuriSoil® is really the only choice.

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Appendix 1: Project Rotterdam

At a site of DSM in the Netherlands, 150.000 m³ of contaminated soil (all in the saturated zone) was cleaned using PuriSoil®.

In 1999, DSM planned to build new facilities at their premises. The construction date for these facilities was January 2001. Remediation was a pre-requisite from the environmental authorities in that area to obtain the necessary permits before the end of 2000.

Within six months after the start of the remediation project, the soil was cleaned in such a way that the building permits were granted by the authorities.

Project Rotterdam

Data
LocationIndustrial. DSM, The Netherlands
Pollution and ConcentrationBenzene, toluene, phenol, thermex, diphenyl and diphenyloxide.
The concentration varied greatly with a maximum of 220 mg/l for both benzene en toluenes. On certain parts of the contaminated area, the toluene and benzene concentrations were of such magnitude as to categorize them as pure product. Also Diphenyl en diphenyloxide were present as pure product.
Contaminated AreaArea: 12.000 m². Contamination was present from the surface down to a depth of 13m below the surface. In total 150.000-m³ soil was contaminated. The groundwater level fluctuated between the surface and 1 meter under the surface. The soil consists of (starting from the surface) 5-meter sand, 1-meter loam and 7-meter sand.
StartedDecember 1999
FinishedNovember 2001 (for benzene, toluene and phenol). The remediation is continued to remove the thermex.

Results

Over 90% of the pollution was removed within half a year (mid 2000), the authorities were confident that the remainder of the contamination would be adequately removed. The building permit was given, and the intended time schedule for building the plant was met.

With respect to Benzene and Toluene, the remediation could be stopped 2 years after the start, as the agreed value (T-value) was realized. For detailed information, see table 2 and table 3.

For the removal of thermex, a component with a low solubility in water, the remediation will be continued. It is expected that within 5 years after the start, Thermex will be fully removed.

Conclusions

PuriSoil® has been proven to be a very fast in-situ remediation technology in saturated soil, for volatile organic materials such as Benzene and Toluene. Furthermore, PuriSoil® does not influence the daily operations on the site, including construction activities. This makes PuriSoil® a unique and unmatchable remediation method for industrial areas.

Table 2.   Benzene content (g/l) as measured in December 1999 and November 2001.
Place19992001Removal
1160.550.9656
2423<0.20.9995
316<0.20.9875
4457<0.20.9996
575<0.20.9973
6220000<0.21.0000
71400002.51.0000
8780.890.9886
984<0.20.9976
10110<0.20.9982
11160<0.20.9988
1228<0.20.9929
1340<0.20.9950
1429<0.20.9931
Table 3.   Toluene content (g/l) as measured in December 1999 and November 2001.
Place19992001Removal
212.1<0.20.9048
22170000<0.21.0000
232800002.51.0000
24900<0.20.9998
251200<0.20.9998
264700<0.21.0000

Appendix 2: Remediation Leakage Pygas Pipe

At the location of Chemelot/DSM in Geleen 500 m³ soil (all in the unsaturated zone), contaminated with 579 kg BTEX was cleaned using PuriSoil®. The contamination was caused due to leakage of a pygas pipe. The contamination was spread in an area of 64 m² and a depth of 8m.

The remediation started 1995 and finished in 1997.

Via frequent measurement it was determined that during the remediation there was no emission of BTEX. The remediation was steered via measurement of VOC and oxygen in several monitoring boxes, placed under and in the bioactive layer.

After 1.5 year the required value of the Dutch environmental authorities (T-value) was realized in most parts of the site. After 3 years the T-value was realized everywhere.

Data
LocationIndustrial. DSM, The Netherlands
Pollution and ConcentrationIn total 579 kg BTEX was present in 500-m³ soil. The maximum start concentration of BTEX was 4900 mg/kg.
Contaminated AreaArea: 64 m². Contamination was present from the surface down to a depth of 8m below the surface. The soil consists of loess (clay). The groundwater was below the contaminated area.
StartedIn April 1995 the remediation started.
FinishedIn October 1997 only 0.8 kg BTEX was still present with a maximum concentration of 2.8 mg/kg. In total over 99.9 % BTEX was removed.

Results

In table 4 the concentration BTEX as a function of time en depth is given. In table 5 the total amount of BTEX per meter soil is presented. From the tables it is clear that from the 579 kg BTEX present in the soil during the start only 12 kg was present after 1.5 year and 0.8 kg after 3 years. These figures represent an efficiency of 97.9 and 99.9 %, respectively.

Table 4.   Concentration BTEX in mg/kg per m depth, measured at the start and after 1.5 and 3 years.
Deptht=0t=1.5 yrst=3 yrs
0-12246.342.78
1-249001.730.32
2-37400.590.32
3-42300.840.34
4-52301.000.38
5-62201.831.52
6-7457.510.94
7-829077.161.43
Table 5.   Amount of BTEX in kg per m depth, measured at the start and after 1.5 and 3 years.
Deptht=0t=1.5 yrst=3 yrs
0-1230.650.29
1-23920.140.03
2-3590.050.03
3-4280.100.04
4-5280.120.05
5-6260.220.18
6-704.600.08
7-8236.170.11
Total57912.050.80
Rendement 0.9790.999

Conclusion

In this project, PuriSoil® has been used for the first time. PuriSoil® has been proven itself as a fast remediation technology, which combines a very high environmental efficiency with a low price. Furthermore, PuriSoil® didn't cause any nuisance for DSM.

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