Sludge population optimisation in biological nutrient removal wastewater treatment systems through on-line process control: A re/view

On-line process control may cause substantial changes to the microbial community in a biological wastewater treatment system. Recent studies have shown such effects can be exploited in control system design to achieve an optimised microbial community. Excellent progress has been made on the elimination of nitrite-oxidising bacteria (NOB) in biological nitrogen removal wastewater treatment systems using on-line aeration control, enabling nitrogen removal via the nitrite pathway. Control methods for eliminating NOB are now available for both continuous systems and sequencing batch reactors, and have been demonstrated with both domestic and various types of industrial wastewaters. The elimination or reduced growth of glycogen accumulating organisms (GAOs), a competitor of polyphosphate accumulating organisms (PAOs), in enhanced biological phosphorus removal (EBPR) systems via pH and carbon source control has been conceptually demonstrated through the use of enriched cultures. However, these strategies are not yet ready for the control of practical EBPR processes. Sludge population optimisation also involves selecting the most desirable organism or a consortium of organisms to perform a required function. This is particularly important for nitrification, one of the most important and delicate steps in modern wastewater treatment plants. Results from both experimental and simulation studies suggest that reactor operation could have a major impact on the nitrifier community structure, which should be further investigated in future studies. © 2008 Springer Science+Business Media B.V.