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UBC Theses and Dissertations

Flocculation of Fraser River sediments due to pulp mill effluents Evans, Wayne John


Recently, researchers noted an aggregation phenomenon downstream of a pulp mill effluent discharge. A large quantity of the sediment in the Athabasca River deposited downstream of the discharge of the pulp mill effluent (Krishnappan et al., 1994). This effect may be significant on the Fraser River, where a number of pulp mills along its length discharge effluent. This aggregation phenomenon could not be explained by existing coagulation / flocculation theories, and an experimental investigation was undertaken. Experiments involved simple jar testing and settling tests in settling columns. The jar tests were completed in Prince George using pulp mill effluent, and Fraser River water. Throughout these tests, turbidity measurements were made which resulted in some ambiguity surrounding interpretation of the results. Nonetheless, on addition of pulp mill effluent to river water, it was noted that a reduction in turbidity occurred with respect to expected values immediately after mixing. The magnitude of this turbidity reduction was also shown to be greatest when effluent and river water were mixed in equal proportions. The turbidity reduction was thought to indicate aggregation of solids in the effluent - river water mixture. Settling experiments were completed in a settling column, and measurements of total suspended solids were made. This enabled information regarding settling velocities to be obtained, which are related to aggregate size. It was found that on mixing effluent with a suspension of illite, the settleability of the suspended solids was greatly improved. The same results were not achieved when a suspension of Fraser River sediment and effluent were mixed, and it appeared that the settleability of suspended solids was actually impeded due to the addition of effluent in this instance. An analysis of the field data collected by field researchers (Krishnappan, 1994; Droppo, 1994) was also completed. The analysis completed was more detailed than any previously completed, and indicated that there may be aggregation of particles within the effluent plume of the Northwood mill at Prince George. The degree of aggregation appeared to be slight, and hence not likely to affect the overall transport of suspended solids within the Fraser River.

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