The role of environmental effects and Acinetobacter spp in enhanced biological phosphate removal

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).