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Characterization of forestry dry land sort runoff and treatment using a sand filtration process Doig, Peter Duncan James


Runoff generated from forestry dry land sort (DLS) operations contains materials from logs, chip piles, and industrial machinery and poses an environmental threat to receiving waters due to its high suspended particle loads, potentially high metals concentration, and frequent toxicity. Since there is currently no legislation or discharge regulations specific to DLS runoff (as for pulp and paper effluents), polluting DLS operations have largely gone unnoticed and as a result few treatment technologies have been tested. In this study, twelve samples of DLS runoff were taken from three dry land sorts located on the Sunshine Coast of British Columbia. Samples had chemical oxygen demand (COD) ranging from 346 mg/L to 3690 mg/L (of twelve samples tested), pH and metals (of two samples tested) that did not comply with British Columbia (BC) Approved Water Quality Guidelines and the BC Municipal Sewage Regulations. The particles of two samples were characterized chemically and morphologically and it was determined that fresh DLS runoff contains highly aggregated inorganic and organic colloidal particles ranging from 1 to 10 pm in size. Although some of these particles sedimented during storage at 4 °C or 25 °C, most particles remained relatively stable in suspension suggesting the requirement for filtration or a secondary treatment process. An oxide-coated sand filtration process performed well over three series of' column experiments, removing up to 86% of the COD and 92% of the turbidity, when operated as a re-circulating filter for 24 hours. Batch adsorption experiments using the oxide-coated sand removed averages of 17% and 26% DLS runoff COD over two series of experiments. The same sand, however with the oxide-coating stripped (oxidestripped sand), failed to remove COD from solution in batch adsorption experiments suggesting that the oxide-coating enhanced absorption of suspended particles. When oxide-stripped sand filters were run in parallel with oxide-coated sand filters treating successive batches of DLS runoff, the oxide-stripped sand treated on average 34% less COD and 32% less turbidity. Neither flocculation nor biological activity was determined to be an important mechanism to the sand filtration process over successive batch treatment runs.

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