Pollution Control in the Wood-Preserving Industry Part II. In-Plant Process Changes and Sanitation

Reductions in the quantity and oxygen content of wastewater from wood preserving plants resulting from changes in steam conditioning, improvement in efficiency of oil recovery, and plant sanitation practices were studied. Closed steaming, a practice in which steam for conditioning green stock preparatory to preservative treatment is generated within the report, was the most important process change studied in terms of the reduction in quantity and improvement in quality of wastewater obtained. Daily flow rates from plants employing closed steaming were only a fraction of those from plants using conventional open steaming, and COD of the wastewater was reduced by 50 to 65 percent by this practice. The latter result was due primarily to reductions in the oil content of the wastewater. Inefficient recovery of oil from the waste stream was the most serious cause of pollution at most of the plants visited. For plants employing closed steaming, the installation of efficient oil separators was usually sufficient to solve that problem. Primary treatments of the wastewater involving flocculation and sedimentation, in addition to separators, were generally required for effluents from plants using conventional open steaming. Barometric condensers were responsible for most of the volume of wastewater released by plants employing a single-pass system. Although not as heavily contaminated as steam condensate from the treating cylinders, the volume was too large to be treated economically. Plant sanitation practices that affect the quantity and quality of wastewater that must be tested to meet applicable standards are discussed.

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