Chemical and biological phosphorus removal in the activated sludge process

Master Thesis


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University of Cape Town

This investigation set out to establish in what degree the phosphorus removal characteristics of the Modified Activated Sludge Process could be enhanced by the in-plant addition of iron salts. The motivation for the investigation was: 1. Due to the lack of understanding of the exact pre-requisites for inducing excess biological phosphorus removal (luxury uptake), such removal could not always be guaranteed in many activated sludge plants, even in those designed in accordance with the best available knowledge for inducing this removal mechanism. 2. There was evidence to suggest that even where excess biological phosphorus removal took place, the removal was limited by the process and the sewage characteristics. As a result, in plants where the specified phosphorus removal exceeded the possible biological removal, additional or alternative methods of removal had to be sought. In view of these factors it was concluded that only by chemical addition to the process, could a specified effluent quality be guaranteed. A laboratory scale Modified Activated Sludge (or Phoredox) Process, similar to that proposed by McLaren and Wood ( 1976), but without a secondary anoxic zone was set up and the process was evaluated with and without in-plant iron salt addition. Problems were encountered in predicting the biological removal as the removal tended to differ from one sewage batch to another, making it difficult to determine accurately the efficiency of the iron salt addition.

Bibliography: leaves 86-88.