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The nitrogen and phosphorus requirements of microorganisms in activated sludge Hattingh, Willem Hendrik Jacobus


A synthetic substrate of highly reproducible composition was used to study the nitrogen and phosphorus requirements of the microorganisms and settling characteristics of activated sludge. The study showed that the production of biological growth or activated sludge with maximum nitrogen and phosphorus contents, required a substrate with BOD:N and BOD:P ratios not wider than 19:1 and 81:1, respectively. To produce an activated sludge with optimum nitrogen and phosphorus contents, the BOD:N and BOD:P ratios of the substrate should not be wider than 23:1 and 168:1. A highly significant interaction existed between the quantities of nitrogen and phosphorus required by the activated sludge microorganisms. The phosphorus requirements increased logarithmically with the quantity of nitrogen consumed. Bulking of activated sludge was caused by wide BOD:N and BOD:P ratios of the substrate and the presence of a filamentous bacterium, Sphaerotilus sp., in the sludge. Bulking was most severe when the substrate had BOD:N and BOD:P ratios wider than 37:1 and 420:1, respectively. Sphaerotilus organisms were present in all sludges, but their growth was favoured by wide BOD:N and BOD:P ratios of the substrate.

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