Organochlorines Bulletin 5
July 1997, Ref. INFO 6
Bulletin 5 reports on pilot-scale technology trials:
- to clean up soil contaminated by organochlorines
- to destroy organochlorine pesticides
Clean Up Technology Report
Introduction
The Ministry for the Environment has recently received a research report on the performance of a new procedure to treat soil contaminated by organochlorines. The report presents the work carried out in the development of a thermal desorption treatment of soil and materials contaminated by pentachlorophenol (PCP), dioxins, and several organochlorines pesticides.
These pilot scale trials demonstrated, perhaps for the first time internationally, the potential for a single stage soil heating process (i.e. thermal desorption) to clean up organochlorine and dioxin-contaminated soils. The main findings of this report are outlined in this bulletin.
Background
The thermal desorption technology had previously been successfully demonstrated at the laboratory scale. This was reported in Bulletin 3, June 1996 and is referred to in this article as the Phase 1 Study.
The purpose of the second series of trials, Phase 2 Study, was to further assess the effectiveness and feasibility of the technology. This pilot scale assessment is an intermediate step in the research and development of the technology prior to a full-scale clean up. The technology report will be of interest to the owners of sites contaminated by residues of PCP and dioxin arising from historic wood treatment operations in New Zealand. This technology potentially could also assist to clean up the Mapua pesticides site near Nelson which is contaminated by DDT.
About the technology
The thermal desorption process involves the heating of a mixture of contaminated soil and lime. The process renders the organochlorine contaminants in the soil into harmless constituents, namely water, carbon and inorganic chloride. All gaseous emissions from the process are washed and filtered, and any particulate material entrained in the movement of gases is captured and recycled back through the process. The treated soil is sterile and safe to return to the site and if desired may be amended with compost to restore its viability as a plant growing medium.
About the trials
The assessment of this pilot-scale technology was jointly commissioned and partially funded by Fletcher Challenge Forests, Carter Holt Harvey Timber Group, Forestry Corporation of New Zealand Limited, and the Ministry for the Environment, in conjunction with ADI Limited and ESR Limited.
The technology assessment used a pilot-scale experimental thermal desorption unit owned by ADI Limited, Australia, and jointly operated with ESR Limited. The trials were carried out at the Gracefield campus of ESR Limited with all analytical work undertaken in the ESR laboratory.
Phase 1 Study
Phase 1 of this study was commissioned in April 1995 and was reported to the Ministry for the Environment in December 1995. It confirmed, at a laboratory scale, the effectiveness of the ADI thermal desorption process and suggested operating conditions and additives necessary to remediate soils contaminated with PCP and dioxins.
ADI's ADOX-BCD process for destroying organochlorine substances, was also verified at the laboratory scale as being capable of destroying any organochlorine condensates produced from the thermal desorption process.
As a result, pilot scale trials were recommended to further develop the technology and to build confidence in the process at a semi-commercial scale.
Phase 2 Study
In this pilot scale study, PCP and dioxin contaminated soil samples were treated in a continuous, indirectly heated, thermal desorption pilot plant in the presence of lime. Several residence times were investigated at the process temperatures chosen.
One important technical objective was to establish the feasibility of achieving residual concentrations in the soil less than 50 parts per billion (ppb) of PCP, and less than 1 ppb (TEQ) dioxins. These levels are less than the target clean up criteria judged suitable for residential land use.
First trial series
In the first series of trials, PCP levels in contaminated soils (range 561 -1440 parts per million [ppm]) were reduced to less than 20 ppb (the limit of detection of the analytical method used). Dioxin levels (TEQ) were reduced from around 17 ppb to less than the target level of 1 ppb.
Second trial series
A second series of trials were conducted using 10% and 25% contaminated sawdust/sand mixtures. Clean river sand rather than soil was used as a carrier medium for the contaminated sawdust. PCP levels (range 2020 - 3110 ppm) were reduced to below 0.02 ppm after treatment. Dioxin levels (range 190 - 245 ppb TEQ) were reduced to below 3.2 ppb after treatment; this suggested that with further process optimisation it would be possible to treat contaminated sawdust to residual dioxin levels less than 1 ppb TEQ.
Third trial series
A third series of trials were conducted on contaminated soil samples containing the organochlorine pesticides DDT (482 ppm), lindane (-HCH, 241 ppm), and chlorothalonil (587 ppm). This trial was carried out to determine how effectively the technology treated soil contaminated by organochlorine pesticides.
The levels of the DDT and lindane pesticides (and any chlorinated organic compounds of decomposition) were less than 1 ppb after treatment. No chlorothalonil was detected in the treated soil using analytical techniques sensitive to levels above 0.1 ppm.
Fourth trial series
The ADI Thermal Desorption process produces a variable amount of dust (usually less than 5% of the original soil feed) and condensates, both containing dioxins. While these are captured and contained within the system, they must be able to be safely decomposed for the total process to be considered effective.
The initial intent was to chemically destroy any residual organochlorine substances in the collected dusts and the condensates in a small but separate ADI ADOX-BCD plant designed for that purpose. However, as results obtained early in the desorption study suggested strongly that significant destruction of PCP and dioxins was occurring during the thermal treatment process, the possibility of completing their destruction by recycling them in the plant was proposed.
To test this approach, a trial was undertaken where the contaminated dust collected during the project was mixed with clean sand and lime, and then treated by thermal desorption.
From an initial level of 1280 ppb (TEQ), residual dioxin levels in the treated material of below 0.1 ppb (TEQ) were achieved, demonstrating an almost total destruction of dioxins under the treatment conditions employed.
From these results it is concluded that a single stage thermal desorption treatment process could be employed in the treatment of organochlorine contaminated soils and materials. In other words, a second stage separate facility or method to destroy the organochlorine substances associated with the dusts and condensates may not be necessary.
Conclusions
The trials of the thermal desorption process demonstrated that :
- A range of soils contaminated with various levels of PCP, dioxins and organochlorine based pesticides can be effectively treated using the ADI indirectly heated thermal desorption process.
- The target performance criteria of less than 50 ppb PCP and 1 ppb dioxin (TEQ) in treated soils can be safely achieved.
- Sawdust contaminated with PCP and dioxins, when mixed with sand, can also be effectively treated.
- The levels of the organochlorine pesticides DDT and lindane in soils can be reduced to below 1 ppb, and chlorothalonil can be reduced to below 0.1 ppm, after treatment.
- It is feasible to implement a single stage treatment technique based on the recycling of dusts and condensates from the process vapour streams back through the desorber. This could be provided for in the design of a full scale plant.
ADOX-BCD Trial on Organochlorine Pesticides
A study into the effectiveness of the ADOX-BCD technology to destroy waste organochlorine pesticides has been commissioned by the Ministry for the Environment. The study is also being undertaken to identify the Resource Management Act consent and conditions that would be needed for use of this technology in New Zealand.
The BCD process was first developed and patented by researchers working for the USEPA. This technology has to date mainly been used to treat PCBs in transformer oils. It offers a viable alternative to the high temperature incineration of contaminated oils. ADI Limited is one of several companies to acquire the rights to the BCD process.
The BCD process uses an hydrocarbon oil to dissolve the organochlorine substances. Following the addition of common alkalis, such as caustic soda, and proprietary catalysts, decomposition and dehalogenation of the organochlorines occur at temperatures between 280 and 340 C.
As a result of extensive research and development by both ADI Limited and the USA-based BCD Group, a more cost-effective ADOX-BCD liquids process has been developed for the destruction of organochlorine compounds. The reaction is faster and yields non toxic residues including carbon and sodium chloride. The diluent oil used in the reaction is recovered and can be reused. The ADOX-BCD process is being applied in the New Zealand trials.
The pilot scale trial is being carried out at the Gracefield campus of ESR Limited using a BCD unit owned by ADI Limited, Australia, and jointly operated with ESR Limited. Test quantities of a range of organochlorine pesticides (including DDT, lindane, dieldrin, PCP) for the trial have been supplied by regional councils. Bench scale reactions are being carried out prior to the commissioning of the pilot scale unit.
An update on the trials will be reported in the next Bulletin.
Do you want to be kept informed ?
The purpose of the Bulletin is to provide the interested public with updated information about the Organochlorines Programme.
If you would you like to be placed on the mailing list to receive future issues of the Bulletin, or if your address label needs updating, please contact:
Organochlorines Programme
Ministry for the Environment
PO Box 10362
WELLINGTON
Phone (04) 498 7400
Fax (04) 471 0195
Organochlorines Consultative Group
- Howard Ellis, Ministry for the Environment (Chair)
- Simon Buckland, Ministry for the Environment
- Paul Dell, Local Authorities
- Jim Waters, Ministry of Health
- Dr Bill Jolly, MAF Regulatory Authority
NGOs
- Dr Jim Barnett, Agricultural sector
- Mark de Bazin, Timber industry
- John Hohapata, Adviser on iwi
- Jocelyn Keith, nominee of Ministry of Women's Affairs
- Tony Petley, AGCARM, NZCIC, Waste Disposal industry
- Peter Sligh, Pulp and paper industry
- Michael Szabo, ECO
- Norm Thom, CAE, IPENZ, NZIC, WMINZ
- Simon Towle, ECO
Technical Specialists
- Dr Michael Bates, ESR Communicable Diseases Centre
- Dr Donald Hannah, ESR Wellington Science Centre
