The biological treatment of wastewater has evolved significantly from simple single sludge systems practicing organic carbon removal to ones which now include either nitrification/denitrification (N/DN) and / or phosphorus (P) removal. The inclusion of more biological processes have increased the complexity of current wastewater systems which has subsequently led to the development of more complex mathematical models. The operation of plants can be assessed and improved by the use of mathematical modelling tools which require
accurate input data. Thus, knowledge of the wastewater characteristics is an important step towards the optimum modelling, design and operation of present and future plants. However, for these tools to be effective, the input data needs to be accurate which is dependent on the current methods used to determine them.

Wastewater is a complex substrate consisting of compounds of differing biodegradability. The organic matter is discussed in terms of chemical oxygen demand (COD). Biokinetically, these compounds have been divided into readily biodegradable (RBCOD), slowly biodegradable (SBCOD) and unbiodegradable substrate groups. Compounds with intermediate biodegradability i.e. compounds which fall between the RBCOD and SBCOD groups, have been termed readily hydrolyzable organic substrates (RHCOD). The readily biodegradable and readily hydrolyzable COD fractions of wastewater can be determined by respirometric tests such as the oxygen utilization rate (OUR) and nitrate-N utilization rate (NUR) tests.

Project Objectives
The primary aims of this project were as follows :

• Study the protocol of NUR batch tests and apply it to a range of wastewater and sludge samples with the aim to : (1) assess, (2) understand, and (3) make recommendations which could improve the procedure and make it easily applicable on-site.
• Characterize a variety of municipal wastewater samples by the nitrate-N utilization rate test – biological respirometry, physico-chemical methods (settling, centrifugation, filtration and coagulation)
• Study the utilization of an experimental readily biodegradable COD substrate, acetate, under anoxic conditions.
• Perform exploratory investigations to clarify the impact of enhanced biological phosphorus removal (EBPR) sludge (biomass) samples on wastewater characterization, Determine the influence of storage on wastewater characteristics; Assess the influence of sludge acclimatization on wastewater characterization