The Impact of Temperature on the Removal of Nitrogen Compounds in Activated Sludge System

Introduction: The temperature, as one of the essential factors affecting the growth and survivability of all microorganisms, may have an impact on them in two opposite directions: the change in the temperature (its increase and decrease) may have a positive impact on the growth rate or may lead to the irreversible inactivation and degradation of the components. It influences on the efficiency of biological wastewater treatment carried out by microorganisms.

Aims: This paper presents the results of test performed in the model activated sludge system. The impact of temperature on the nitrogen compounds removal processes was investigated, within the temperature ranging between 10 and 37°C.

Methodology: The evaluation of the temperature impact on the processes of removal of nitrogen compounds was made on the basis of the laboratory tests conducted in the activated sludge system. The system was supplied with synthetic wastewater in the composition approximated that of the typical household wastewater. Each value of analyzed parameters (TKN, N-NH4, N-NO3, BOD5, COD, X) was determined as the average of the values measured in the following nine days. The formulations of ASM Models were used to calculate the kinetic parameters of transformations of the nitrogen compounds in the activated sludge process.

Results: The degree of removal of total nitrogen from the wastewater within the temperature range between 10 and 34°C was at the level of 75.5-90.6% (12.5-4.8 gN/m3), and at the temperature of 37°C, it amounted to 71.8% (14.4 gN/m3). The highest efficiency of overall nitrogen removal was observed within the temperature range from 10°C to 22°C and from 32°C to 35°C. Temperature coefficient values Q was different in various temperature ranges.

Conclusion: It was determined that the assumption of an exponential increase in the rate of biochemical reactions together with an increase in the temperature does not take into account the changes of the physiological condition of microorganisms. The activity of the bacteria does not change exponentially together with the increase in temperature, but rather demonstrates the minimum and maximum values. Temperature coefficient value Q can be regarded as a constant only within a strictly defined temperature range, characteristic for the respective groups of microorganisms.