Phosphate uptake by immobilized Acinetobacter calcoaceticus cells in a full scale activated sludge plant

An in situ study of the P-uptake ability of Acinetobacter calcoaceticus was carried out using the alginate immobilization technique. Immobilized A. calcoaceticus cells displayed a high P-uptake ability (> 97% P-accumulating cells) when immersed in the aerobic zone of an activated sludge system for 30-240 min. The overall P-accumulation pattern of the anaerobic zone depicted a typical P-release mechanism. However, limited P-accumulation was also observed at this stage. Growth and anaerobiosis were not prerequisites for P-uptake. The immobilized cell retention time in the anaerobic zone did not affect remarkably the inherent P-uptake ability of immobilized A. calcoaceticus when exposed to the aerobic stage. P-uptake and release were reversible and depended on the environmental conditions to which immobilized cells were exposed. Immobilization of A. calcoaceticus using alginate can be regarded as a reliable method of studying pure cultures in the activated sludge process.