Strength of wood-lath filters after 11 years of service in a waste-water treatment plant

Laths of Douglas-fir, western hemlock, southern pine, and redwood containing both sapwood and heartwood were compared with the redwood heartwood laths presently used in trickle filters in a continuously operated waste-water treatment plant at Forest Grove, Oreg. In addition to tests on untreated samples, all types of laths, except redwood heartwood, were treated with chromated copper arsenate or pentachlorophenol as a preservative. After 11 years of exposure to waste water, the strength of untreated and treated Douglas-fir and southern pine laths and CCA-C-treated redwood laths containing sapwood equaled or exceeded that of redwood heartwood and should perform at least as well over a 20-year period. Other woods tested are not likely to perform as well, but may provide 20 years of service. Only western hemlock and redwood heartwood laths weakened during 11 years of service. All laths remained in serviceable condition.

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