K. Akhter
Research Officer
Wood Preservation Division, Forest Research Institute, Chittagong, Bangladesh.
Environmental pollution, Legislation, Fixation, Wood preservative chemicals.
Wood Preservation Division, Forest Research Institute, Chittagong, Bangladesh.
Postharvest and Agro-processing
To know the present status of the wood preservation and pollution due to wood preservative chemicals, more survey is needed. From the present survey it is seen that treatment plants are installed near the agricultural land, near the pond or no the edge of densely populated towns. So that there is a possibility to pollute the soil and washed away by rains and finally ended in municipal and natural drains and adjacent ponds. These ponds are generally used by local people for the domestic purposes.
Preservation Techniques :
All of the three treatment plants are using full cell and empty cell pressure processes for the treatment of Anchor Log, Meter Board and Cross arm. Retention is measured from boring by ASOMA S-ray Analyzer. Difference of retention between inner and outer surface can be measured from the first half and second half of the boring. Sometimes retention is calculated on the basis of amount of preservative solution absorbed. At that time no allowances are made for bleeding or dripping of excess preservatives when the timber is removed from the treatment vessel. Penetration is measured by colour test, using chrome azurol solution and tarmeric solution.To improve penetration, methods of incising, steaming or pressure cycles have not been applied. Preservation techniques influences the service life of treated timber due to the insufficient penetration and retention.
Conditioning and Fixation :
When the material is treated with CCA preservative, the copper, Chromium and arsenic in the mixture become insoluble. As chemical reactions proceeds and the chemicals are fixed in the material. This fixation process take time to complete. But the techniques of conditioning to allow fixation of CCA at the treatment plant are rather unusual. As a result timber removed from the treatment vessel, stacked in the open place. During the rainy season, the process of leaching starts even before the timber is in service. Higher concentration of leached CCA elements causes pollution around the storage areas. Freshly treated timber must be as potentially dangerous to human beings, animals, plants and the environment.
Health and safety at plants :
Preservative chemicals are highly toxic. So if there is any escape of the chemicals from the treating plants there is a danger of polluting the surrounding air, soil and stream. The escape of the chemicals can occur through leakage of the treating tanks and pipe.
Waste management :
Problems concerning the disposal of treated timbers removed from service is a major issue in many countries. Once the timber has been treated and sold, the industry is not concerned about the disposal after use. Burning of the treated material containing arsenic and chromium is very dangerous. Arsenic will evaporate at high temperature and contaminate the air. Some of it will remain in the ash rendering the ash very poisonous. The waste of the treated materials must never be burnt in an enclosed space and it never be used for fuel in cooking stoves. It should be buried under the ground.
The International Research Group on Wood Preservation (IRG), Section 4 (Processes), IRG Document No. IRG/WP 2000 – 50148. 7pp.
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