MicrobiologicalStudies on Enhanced Removal of Phosphates from Sewage

ReportNo WSAA 36

November 1991




Strainsof Acinetobacter were isolated frompilot- and laboratory-scale systems which were removing phosphate biologicallyfrom sewage. Several isolates accumulated phosphate as polyphosphate to levelsof 15-20% of the dry weight of the cells. Selected Acinetobacter isolates were studies to determine how changes ingrowth conditions affected their ability to accumulate polyphosphate. Mutantstrains which could not accumulate polyphosphate were obtained from some of thegood polyphosphate-accumulating Acinetobacterisolates. From studies on these mutant strains and their parent strains amodel has been proposed to explain how polyphosphate is accumulated by Acinetobacter.


Theproperties of the strains isolated has brought into question the acceptedhypothesis that release of phosphate from polyphosphate in the anaerobic zoneof plants is essential for removal of phosphate biologically.


Thesynthesis of poly--hydroxybutyrate, which has been regarded as an essentialprerequisite for phosphate removal, has also been studied in several Acinetobacter isolates.Not all isolates which synthesizepolyphosphate can form poly--hydroxybutyrate. This again raises some questionson the previous accepted hypotheses.


Theinformation obtained from this study should prove to be applicable to improvedoperation and design of enhanced phosphate removal treatment systems.


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