Bevattning av lagrat virke vid svensk skogsindustri : omfattning och miljökonsekvenser

University essay from SLU/Dept. of Crop Production Ecology

Abstract: Most of the saw and pulp industries have stored wood nearby their production, the main reason is to have a continuous wood flow to the production. Wet storage of wood is of great importance to keep the wood quality. Without water sprinkling the risk of drying outand decomposition through biological activity increases significantly and will result in a negative effect on future production and quality. One drawback of wet storage of wood is the leaching of chemical substances into the surrounding recipient. The log yard run-off contains phosphorus, nitrogen, phenols and organic substances. These substances can cause problems for the surrounding environment. The main objective of this project is to gain an understanding of the wet storage used by the Swedish wood industry and estimate the environmental consequences that run-off water will have on the recipient. To describe the leaching four different cases were constructed to show the risk of wet storage and run-off water. The cases reflect two different sprinkling systems. The first system is an open sprinkling system which sprinkles fresh water on the wood and the second system uses recycled water. The calculations for the leaching are based upon estimated argument association e.g. the leaching from a recycled sprinkling system is assumed to be an overflow of run-off water. The amount of water for an overflow can be equivalent to the precipitation during one storage season (5 months). Another estimate is the substance leaching from 1 m3 of wood which is based on storing 15000 m3 of wood on one hectare. The open system without sedimentation is calculated to leak 2.5g of phosphorus and 7.3g of nitrogen per m3 of wood during one storage season. For the recycled system the leaching per m3 of wood is 0.13g phosphorus and 1.6g nitrogen per m3 of wood. Expressed per hectare of storage area the leaching for the open system for phosphorus is 38,5kg per hectare and for nitrogen is 110kg per hectare. The corresponding value for a recycled system is 1,9kg of phosphorous and 23,5kg of nitrogen per hectare of storage area. The leaching of phenols and organic substances has not formed part of the analysis due to the lack of available information. However, estimates for levels of BOD7, COD and phenols present in leaching per hectare storage area are as follows. For a recycled system without sedimentation the leakage for BOD7 is 123 kg/season and 2950 kg/season for an open system. The value for COD in a recycled system is 654 kg/season and 14400 kg/season in an open system. For phenols the leaching is estimated at 0.17 kg/season in a open system and 22.0 kg/season in a closed system.

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