Critical review of process control strategies in anammox-mediated nitrogen removal systems

Anaerobic ammonium oxidation (ANAMMOX) is an efficient nitrogen removal process that is increasingly gaining traction within the wastewater treatment sector. However, slow growth rate of ANAMMOX bacteria (AMX) and their sensitivity to operating and environmental conditions hamper its widespread application. Although different control strategies have been developed, several challenges affecting process stability are still frequently reported and there is need for further improvements. This paper therefore critically reviews process control strategies applied in ANAMMOX-mediated systems, focusing on low- and high-strength treatment systems. The influence of different control strategies including those based on aeration regime, nitrogen (ammonium (NH4+), nitrite (NO2-) and nitrate (NO3-)) concentrations, ORP (oxidation-reduction potential), alkalinity, conductivity and pH on system performance was analysed and discussed. Factors such as NO2- inhibition, NO3- accumulation/reduction, SRT control, alkalinity depletion and maximisation of nitrogen removal were considered. In sum: (I) inclusion of supervisory layers in cascaded control structures enhance performance compared to regulatory structures that individually maintain parameter values within certain set limits, (II) Conductivity-, pH- and ORP-based controllers can prevent alkalinity depletion, (III) DEAMOX (DEnitrifying AMonium OXidation) requires less stringent conditions compared to partial nitrification-denitrification (PN/A), (IV) swing zones mitigate against limitation of active biomass population in mainstream systems, and (V) Regulatory pH- and DObased strategies are prone to cause NO2- -inhibition.

Automated summary

This paper critically reviews the process control strategies applied in ANAMMOX-mediated systems and analyzes their impact on system performance. The study finds that the inclusion of supervisory layers in control structures enhances performance and conductivity-, pH-, and ORP-based controllers can prevent alkalinity depletion.