MATHEMATICAL MODELING OF BIOFILM DEVELOPED IN ACTIVATED SLUDGE PROCESS (ASP)

Abstract

The activated sludge process system is a popular and versatile method of treating wastewater that uses biological reactions to convert waste into biological mass. It is a dynamic process and such systems must necessarily account for a large number of reactions among many components. The operational performance of the activated sludge process needs to be improved to achieve effective control. This can be done by a better understanding of the particle size distribution of the activated sludge floes. To realize this, a simple mathematical model has been developed which considers particle size distribution to calculate the area of the biomass and then substrate and nitrate removal efficiency is obtained for a steady state biof lm reactor. The proposed model uses Monod's expressions for growth kinetics and Ficks diffusion law for flux calculations. Flux equations were solved using Maple software using central finite technique without making any additional assumptions. Results showed that within the particle size range from 32p.m to 6001.tm, efficiency of the reactor increases with the size of particle the as the concentration profile is gets lowered with the increase in the particle size, moreover thickness of the biofilm is also increased. Through this, overall efficiency of the reactor was calculated for carbon and nitrogen substrate. Validation of the model was done with the results of experiments conducted by Arun Kumar, 2009 on the activated sludge biofilm reactor. The results were compared and found out to be very close to the experimental values, with Pearson's correlation coefficient (R) 0.83 for carbon substrate and 0.91 for nitrate and Root Mean Square Error (RMSE) 5.47 for substrate and 2.55 for nitrate. Thus, this modeling approach was found out to be very effective in calculating the removal efficiency for nitrate and substrate and can be performed for any substrate in future studies.