Pollution Prevention Guidelines to provide technical advice and guidance to staff and consultants involved in pollution-related projects. The guidelines represent state-of-the-art thinking on how to reduce pollution emissions from the production process. In many cases, the guidelines provide numerical targets for reducing pollution, as well as maximum emissions levels that are normally achievable through a combination of cleaner production and end-of-pipe treatment. The guidelines are designed to protect human health; reduce mass loadings to the environment; draw on commercially proven technologies; be cost-effective; follow current regulatory trends; and promote good industrial practices, which offer greater productivity and increased energy efficiency.
Table of Contents
- Industry Description and Practices
- Waste Characteristics
- Pollution Prevention and Control
- Target Pollution Loads
- Treatment Technologies
- Emissions Guidelines
- Monitoring and Reporting
- Key Issues
Industry Description and Practices
Wood preserving involves imparting protective properties to wood to guard against weathering and attack by pests. Three main types of preservatives are used: water based (for example, sodium phenylphenoxide, benzalconium chloride, guazatin, and copper chrome arsenate); organic solvent based (for example, pentachlorophenol and such substitutes as propiconazol, tebuconazol, lindane, permethrin, triazoles, tributyltin compounds, and copper and zinc naphthenates); borates; and tar oils (such as creosote). Note that some of the preservatives mentioned here (for example, lindane, tributyltin, and pentachlorophenol) are banned in some countries and are not to be used.
The preservatives are applied to the surface of wood by pressure impregnation, with a pressure range of 800 kilopascals (kPa) to 1,400 kPa; by deluging (mechanical application by flooding or spraying), by dipping or immersion; and by thermal processing (immersion in a hot bath of preservative). Application of vacuum helps to improve the effectiveness of the process and to recover some of the chemicals used. Pesticides are applied using appropriate protective clothing, including gloves, aprons, overalls, and inhalation protection.
Any or all of the substances used in wood preserving, such as preservatives and solvents, can be found in the drips and the surface runoff streams. Air emissions of solvents and other volatile organics result from the surface treatment steps, drying of the treated wood, and storage and transfer of chemicals. Soil contamination may result from the drippage and surface runoff, and this may happen near the process areas and the treated wood storage areas. Some of the major pollutants present in drips, surface runoff, and contaminated soil include polynuclear aromatic hydrocarbons, pentachlorophenol, pesticides, dioxins, chrome, copper, and arsenic.
Pollution Prevention and Control
Wood preserving involves different combinations of a wide variety of processes, and there are many opportunities to improve on the traditional practices in the industry. The following improvements should be implemented where feasible.
- Do not use pentachlorophenol, lindane, tributyltin, or copper chrome arsenate (or its derivatives).
- Give preference to pressurized treatment processes to minimize both wastage of raw materials and the release of toxics that may be present.
- Minimize drippage by effective removal of extra preservative from the wood surface by mechanical shaking until no drippage is noticeable. Provide sufficient holding time after preservative application to minimize free liquid.
- Recycle collected drips after treatment, if necessary.
- Heat treated wood when water-based preservatives are used.
- Use concrete pads for the wood treatment area and intermediate storage areas to ensure proper collection of drippage. Treated wood should be sent for storage only after drippage has completely stopped.
- Minimize surface runon by diversion of stormwater away from the process areas.
- Cover process areas and collect surface runoff for recycling and treatment. Where waterbased preservatives are used, prevent freshly treated wood from coming into contact with rainwater.
- Sites should be selected that are not prone to flooding or adjacent to water intake points or valuable groundwater resources.
- Preservatives and other hazardous substances should be stored safely, preferably under a roof with a spill collection system.
- Proper labels should be applied, and used packaging should be returned to the supplier for reuse or sent for other acceptable uses or destruction.