Evaluation of Factors Affecting Stream Self-Purification

摘要

Four identical parallel-flow models were constructed to simulate certain characteristics of flowing streams in order to evaluate self-purification processes. The models were maintained at nearly constant temperatures and housed to prevent photosynthesis. Each model consisted of 28 sequentially connected, rectangular, plastic basins equipped with paddle agitators. The relationships of residence age of water at any point in the model to flow rates was determined both theoretically and empirically. The relationships agreed quite closely. The longitudinal dispersion of a tracer through the models is high but quite predictable using derived equations. The ratio of liquid volume to wetted surface area (i. e. effective stream depth) was very low. This resulted in a predominance of metabolic activity by attached organisms and a high degree of self-purification in the first few basins of any model. Substrate biodegradability, as indicated by k values for BOD exertion, changed significantly and rapidly as flow progressed through the models. Self-purification response to copper sulfate fed as a possible toxicant indicated a retardant effect that persisted beyond the wash-out period for the toxicant. (Author)