DESIGN AND OPERATIONAL ASPECTS OF BIOFILM REACTORS (RBC)

Abstract

In recent years, the use of biofilm reactors (RBCs) has grown in developed countries. Certain studies have also expressed the potential application of RBCs in India. For better understanding of biofilm reactors, a significant amount of research work is also on the way for the past three decades. Thus, there is a need to strengthen the existing design and operation practices of biofilm reactors using the available knowledge. The present study is taken with this objective. Design of RBCs is currently based on certain available design curves for certain types of wastes. As these are based for a particular climatic conditions and waste, their general utility is restricted. To overcome this, the mechanistic models have been used in the literature. The design curves based on these mechanistic models are available. Unfortunately, the use of these curves results into severe interpolation errors because of the inappropriate parameterization of the design variables. In the present study, these design curves have been modified and presented in the form which makes their use free from interpolation errors. Thus, for a given waste these curves can be used to design the reactor by evaluating the kinetic parameters. An algorithm has been also developed using the mechanistic models to optimize the reactor volume requirements. The calibration aspects as well as selection of certain models have been considered in detail. This has also helped in removing some of the misconceptions about the superiority of certain models over each other. Also some of the models have been modified to yield unique solutions. ii Expressions have been developed to control the steady-state operation of biofilm reactors when the system state changes because of the alterations in the kinetic parameters. The applicability of these expressions have been demonstrated numerically. A new model for the variation of effluent quality during transient-state operation of RBCs is also developed. The model contains only two parameters which can be easily calibrated and used to predict efficiency on a short term basis. The most commonly used linear control of biofilm reactors has been given a theoretical basis. The conditions under which the linear control is valid, have been identified. Thus, different aspects related to design and operation of biofilm reactors have been considered in the study. It is hoped that the present work will be of interest to researchers, designers and operators associated with the biofilm reactors (RBCs). 111