Plywood and Sawmill Liquid Waste Disposal

Improper road construction and inadequate slash disposal are two sources of water pollution in the logging industry. On the other hand reasonable precautions during logging activities can preserve water quality. Log handling and storage in water dislodges bark and permits organic materials to leach from the logs. Ponderosa pine bark deposits exerted an oxygen demand of 0.4 to 2.0 grams per square meter per day compared to 0.2 grams per square meter per day in a control area with no bark. One mill has installed a clarifier to treat hydraulic barker waste to permit recycling through the plant. The clarifier has a retention time of 2-1/4 hours and is preceded by chemical coagulation using 70 milligrams per liter (mg./1.) of alum and 1 mg./I. of polyelectrolyte. Suspended solids are reduced from 10 lbs. per 1000 gallons to less than 1/2 lb.per. 1000 gallons. The Pacific Northwest Water Laboratory is investigating the use of microscreens for removal of suspended solids. Early results indicate removals of 26 to 82 percent with screen cloth sizes of 100 to 10 microns. Plywood plants all produce wastes of high strength. Wastes from phenolic glues are toxic to aquatic organisms and cannot be treated by biological systems. Phenolic glues can be recirculated, however, and all waste discharge eliminated. Blood, and urea glues can be treated by conventional systems. Klamath Plywood Corporation received a Federal grant of $42,000 to demonstrate secondary treatment of wastes from a plywood plant using urea glue. Plant flows are reduced by recycling to 40 percent of the original volume and the treatment plant was designed to reduce waste strength by over 85 percent.

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