Influence of temperature on biological phosphorus removal: process and molecular ecological studies

This paper describes the impact of long-term (weeks) temperature changes on stoichiometry and kinetics of the anaerobic and aerobic phases of the biological phosphorus removal process. Steady state conversion of relevant compounds for biological phosphorus removal was studied at 20, 30, 20, 10 and 5°C, following chronological order. Integrated in the process study, two methods (electron-microscopy and dry denaturing gradient gel electrophoresis) were applied to investigate the complexity of the bacterial community of biological phosphorus removing sludge cultivated at different temperatures. The coefficient for metabolic conversions obtained from long-term temperature tests was similar to the temperature coefficient observed in short-term (hours) tests (θ=1.085 versus θ=1.078, respectively).Temperature had a moderate impact on the aerobic P-uptake process rate (θ=1.031) during long-term tests. However, a strong temperature effect on other metabolic processes of the aerobic phase, such as polyhydroxyalkanoate consumption (θ=1.163), oxygen uptake (θ=1.090) and growth (θ>1.110), was observed. Different temperature coefficients were obtained for the aerobic phase from long-term and short-term tests, probably due to a change in population structure. This change was also visible from molecular ecological studies. The different temperature coefficient found for P-uptake compared to the other metabolic processes of the aerobic phase underlines that, in complex processes such as BPR, it is dangerous to draw conclusions from easily observable parameters (like phosphate) only. Such consideration can easily lead to underestimation of the temperature dependency of other metabolic processes of the aerobic phase of BPR.