Abstract:
One aim of this work was to define the role of Ac/nefojbacfer spp. in enhanced
biological phosphate removal (EBPR). A culture enrichment and selective
medium technique was developed to isolate Acinetobacter spp. from both
conventional and EBPR activated sludges. The methodology proved to be
successful and Acinetobacter spp. thus isolated were investigated for their
enhanced phosphate removing abilities alongside reference cultures. The
cultures were studied in shake flask batch investigations and in sequencing
batch reactors (SBRs). None of the Acinetobacter spp. isolates studied
exhibited EBPR.
A study of the effect of several environmental parameters; temperature, pH
and influence of electron acceptors was the other aim of the work.
Acclimatised EBPR sludges were used in these investigations which were
studied in shake flask batch investigations and in SBRs. Temperature was
shown to be an important variable; optimal wastewater temperature for
anaerobic release and aerobic uptake of phosphate was found to be around
30°C. EBPR was still observed at extremes of 5 and 40°C and activation
energies were also determined. pH levels also influenced EBPR. Batch studies
showed different pH optima for anaerobic phosphate release and aerobic
phosphate uptake. The presence of nitrates and nitrites in the anaerobic
phase, thereby establishing anoxic as opposed to truly anaerobic conditions
was evaluated. Under the operating conditions of the study, nitrate and nitrite
concentrations up to 100 mgN I'1 still showed ~ 70 % phosphate removal.
During comparison of nitrate, nitrite and air as electron acceptors, aeration
removed over 90% phosphate, nitrate addition 51-64% and nitrite addition
<10%. Acetate was shown to be the preferred carbon substrate as opposed
to glucose and methanol. Nitrate had less inhibitory effect on EBPR at the
higher substrate concentration of 400 mg I'1 (as COD).
