ACINETOBACTER CELL BIOMASS, GROWTH STAGE AND PHOSPHORUS UPTAKE FROM ACTIVATED-SLUDGE MIXED LIQUOR

Enhanced biological phosphorus removal activated sludge plants often d o not remove phosphorus adequately in order to meet legal demands. Cur rently FeSO4 is being added to almost all South African nutrient remov al activated sludge systems discharging effluents to the sensitive cat chments to prevent phosphorus from entering fresh water systems. In or der to understand biological phosphorus removal mechanisms in order to optimise the process, the role of growth rate and phosphorus removal in Acinectobacter was investigated. Phosphorus was accumulated in the lag phase of the normal growth cycle. Little or no phosphorus was accu mulated in the logarithmic growth phase, instead phosphorus was releas ed at the beginning of logarithmic growth. Further phosphorus accumula tion took place in the stationary phase, once active growth had ceased . Cells bad a limit to the amount of phosphorus that could be accumula ted per cell irrespective of substrate availability. It was therefore concluded, that the number of cells (biomass) in a system and their gr owth stage were crucial factors governing biological phosphorus remove d. Maximum cell numbers should therefore be obtained and logarithmic g rowth should be prevented in the aerobic zone, in order to optimize bi ological phosphorus removal from activated sludge.