GPS-X Technical Reference

217 Suspended Growth Models
CHAPTER 7
Attached-Growth Models
INTRODUCTION
This chapter describes the aerobic attached-growth models available in GPS-X. These models are
associated with the trickling filter, rotating biological contactor (RBC), submerged biological
contactor (SBC), simple/advanced biological aerated filter (BAF) and hybrid (IFAS or MBBR)
objects. The biofilm model is also used in the anoxic denitrification filter object in the Tertiary
Treatment process model group.
The major difference between these models and the suspended-growth models described in
Chapter 6 (page 94) is the inclusion of the diffusion process in the biofilm. Although diffusion
occurs in suspended-growth systems (substrate and oxygen must diffuse into the activated
sludge floc), it is usually neglected since the rate limiting steps are the biological reactions;
however, in attached-growth processes, the diffusion and biological reactions must be considered,
increasing the complexity of the models.
The trickling filter, RBC, SBC and hybrid processes are similar. They provide biofilm biological
treatment, with excess biofilm sloughing separated in a clarifier object. The SBC and BAFs are
flooded processes, with mechanical supplemental aeration.
The BAFs differ from the other processes in that it:
is a combined biological and solids separation process, and
has a mechanical process for controlling excess biomass growth and captured solids
(i.e. backwash)
The advanced BAF model is a combination of an attached-growth model, and a filtration model.
The filtration model is described in the One-Dimensional Models section of Chapter 8.
GPS-X Technical Reference