Pollution Control in the Wood-Preserving Industry. Part III: Chemical and Physical Methods of Treating Wastewater

Results of studies on wastewater from the wood-preserving industry show that significant reductions in the oxygen demand and phenolic content of this type of waste can be achieved by primary treatments involving flocculation and by secondary treatments that employ chlorination or activated-carbon filtration. Lime used in combination with polyelectrolytes was the most effective flocculating agent tested during the study in terms of initiating floc formation and total reduction in oxygen demand, but polyelectrolytes are now available which perform equally well alone. Dewatering and disposal of sludge resulting from primary treatments were most efficiently and economically accomplished by using sludge drying beds. Chlorination was effective in destroying most of the phenolic compounds in creosote and pentachlorophenol wastewaters, although occasional samples contained a residual concentration of 5 to 10 mg/liter of phenols that was resistant to oxidation. The completeness of oxidation of pentachlorophenol in wastewater was affected by the condition of the sample (flocculated or unflocculated), pH, and source of chlorine, either chlorine gas or calcium hypochlorite. Chlorination treatments reduced the oxygen demand of wastes by oxidizing part of the soluble organics. This effect was most pronounced at chlorine doses of 0.5 to 2.0 gm/liter. Very little additional benefit was derived from larger doses. Loading rates of 0.16 pounds of phenol and 1.2 pounds of COD per pound of carbon were obtained in carbon filtration studies of wastewater. For some samples the removal of phenols and COD from samples amounted to 96 and 80 percent, respectively. It was concluded that carbon-filtration of wood-preserving wastewater is not feasible on a commercial basis except for plants that produce small quantities of waste and those that have access to carbon regenerating equipment.

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