Ahydraulic debarker is a machine removingbark fromwooden logs by the use of water under a pressure of 700kilopascals (100pounds per square inch) or greater.[1] Hydraulic debarking can reduce soil and rock content of bark, but may increase the water content. Debarking water may be recycled after effective settling, but suspended solids may increase wear on high-pressure pumps. Hydraulic debarking has declined where water quality problems have arisen.[2]
Bark on matureredwood trees of coastalCalifornia can vary from 10 to 46 centimetres (4 to 18 in) in thickness. Redwood bark is thick, stringy and tough; and can causesawmill machinery to malfunction. Men called peelers removed bark from fallen trees in the woods through the early 20th century, but the process was dangerous andlabor intensive.[3] In the mid-20th century hydraulic barkers were built at several large sawmills including the Union Lumber Company atFort Bragg, California, the Northern Redwood Company atKorbel, and thePacific Lumber Company atScotia, California.[4] The last was featured in a popular sawmill tour.[citation needed]
Although less expensivemechanical debarkers were adequate for smaller logs harvested from young trees on redwood tree farms, hydraulic barkers remained in operation until allold growth trees had been harvested from company timberlands. TheUnited States Environmental Protection Agency published hydraulic barking category effluent limitations in the 1970s. Wastewater discharged from debarking could average no more than 2.5 pounds ofbiochemical oxygen demand (BOD) and 12 pounds oftotal suspended solids (TSS) perthousand board feet of lumber produced (0.5 kg BOD and 2.3 kg TSS per cubic meter of lumber). Daily waste discharge rates could be three times as high as 30-day averages, but pH was required to remain between 6 and 9.[5]
