Single-sludge nitrogen removal: modeling and experimental results

Abstract

basin which is maintained under anoxic conditions for denitri fication. The mixed liquor is then passed to the aerobic reactor for nitrification and residual organic carbon removal. Mixed liquor from the aerobic basin is recycled to the anoxic basin to provide nitrate for denitrification. Because of the interactions between various microbial species and substrates, and the recycle of mixed liquor, mathematical models that depict these systems can be rather complex. Several models with varying levels of complexity have been proposed in recent years.59 For design purposes, a highly sophisticated model, which accounts for every detail of the process, is hardly justified. The model should, however, be based on mechanistic principles so it can be extrapolated, and be capable of predicting performance with reasonable accuracy. The components of any mathematical model for the single sludge system consist of a set of equations that describe process kinetics, materials balance, and stoichiometry. Various equations have been used in the past for the individual processes of chem ical oxygen demand (COD) removal, nitrification, and denitri fication. The objective of this work is to examine the applicability of several of these alternative equations for the combined single sludge system. It also illustrates the derivation of some process parameters from experiments on continuous-flow single-sludge systems. The discussion here is limited to treatment systems for wastewater that contains carbonaceous organics (expressed as COD) and ammonia nitrogen. The concentrations of all nitrogen compounds are expressed in mg/L as N. Unless stated otherwise, nitrates or NO3 in this paper, mean total oxidized nitrogen or NOJ + NOJ.