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Kemisk oxidation af sediment- og grundvandsforureningen på depotet ved Høfde 42 - fase 1: Projektbeskrivelse og forundersøgelser
Summary and Conclusions
This report is an assessment of the possibility of cleaning up the sediment and groundwater contamination at Høfde 42 using chemical oxidation - phase 1. The report comprises the following parts:
- Gathering knowledge of the use of in situ chemical oxidation
- Limited laboratory tests to illustrate the effect of chemical oxidation
- Proposal for a full scale clean up using chemical oxidation
- Proposal for a pilot study using chemical oxidation
In situ chemical oxidation (ISCO) is an aggressive remediation technology for soil and groundwater contamination. This report will go through the most relevant methods in the area of in situ soil and groundwater contamination clean up, which are:
- Fenton's reagent
- Ozone and ozone/hydrogen peroxide (advanced oxidation - AOP)
- Permanganate
- Persulphate
Gathering knowledge
A study of the literature shows that no experience with chemical oxidation for the specific contamination composition at Høfde 42 is available, neither in Denmark nor abroad. However, individual studies of especially parathion and malathion exist, but not in the area of in situ soil and groundwater clean up. On the basis of the literature study, it was assessed that Fenton's reagent and advanced oxidation with ozone and hydrogen peroxide seem to be the most effective methods. As permanganate is very stable in the groundwater zone, this substance has practical advantages during field clean up compared to the other oxidants. On the basis of the knowledge gathered, it was recommended to carry out a preliminary laboratory test using Fenton's reagent, ozone/hydrogen peroxide and permanganate.
Laboratory tests
Limited laboratory tests have been carried out with groundwater samples form Høfde 42 using Fenton's reagent, ozone/hydrogen peroxide and permanganate. The laboratory tests showed that all the methods used result in a fast breakdown of the pesticides, but using oxidation with ozone (only) and permanganate creates hazardous oxones as degradation products. From the tests carried out, oxidation with ozone and hydrogen peroxide (AOP) is assessed to be the most effective. Fenton oxidation also shows good results, but with a single problem; during the process, MP2 acid is generated, which might be due to a too large dosage of phosphate in the added iron catalyst. However, MP2 acid is not particularly hazardous.
On the basis of the laboratory analyses, it was assessed that chemical oxidation is a very relevant in situ remediation method for Høfde 42. Fenton seems to be the most attractive method for a full scale solution from an economical, environmental and practical point of view. Fenton oxidation is in practice simple to carry out without major risks and environmental problems. It has a large range, dosing is simple and it can degrade pesticides, substance contamination and degradation products. It is expected to be possible to avoid the production of MP2 acid by using another iron compound than in the laboratory tests. It is assessed that advanced oxidation and possibly permanganate are also potential methods. This must depend on an overall assessment of advantages and disadvantage in the use of the two methods on the specific site.
Proposal for a full scale clean up
A conceptual design of a full scale clean up in the upper aquifer has been set up. It is assessed that the total expenses for this constitute approximately DKK 67 million excl. VAT, and that a project can be carried out within a period of three to five years. It is expected that a full scale clean up will reduce the environmental risk from the depot substantially.
The method can also be used in the lower aquifer, but it is assessed to be more difficult to use the method in the low permeable separating stratum of clay.
Proposal for a pilot study
A proposal for a pilot study using Fenton's reagent in the upper aquifer has been prepared. The primary objective of the pilot study using Fenton's reagent is to assess whether the method is a cost effective method for cleaning up the contamination at Høfde 42. The proposal for a test area comprises a 100 m² area with four injection points and approx. five monitoring borings. The test cell is placed in an area with relatively heavy soil and groundwater contamination and minor volume free phase. Fenton's reagent is injected three to five times with an injection volume of 1.9 m³ liquid in each injection point per round of injection. Using a 15 % solution is proposed as starting point. The period between every injection is approx. six to eight weeks. The cost of the pilot project is in the order of DKK 1.1 - 1.75 million.
It is proposed that prior to the pilot project, a supplementary laboratory test is carried out in order to prepare the design basis for the pilot project. The following tests are proposed: (1) determination of the oxidation requirement of the soil, (2) tests with traditional Fenton's reagent, (3) test to reduce the production of MP2 acid, (4) tests to optimise the dosing of Fenton's reagent, and (5) test for treating free phase.
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Version 1.0 Oktober 2007, © Miljøstyrelsen.
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