Redirection of organic matter and nitrogen with the PRONOX process

The PRONOX project, carried out by GS INIMA in collaboration with the University of Girona (UdG) and funded by the Centre for the Development of Industrial Technology (CDTI), has developed the PRONOX process. The project was undertaken with a clear vocation to address the challenges identified in the Spanish Strategy and the European Union, as reflected in the HORIZON 2020 programme.

J.Canals , O.Carbó, A. Ordóñez, B. Gutiérrez, M. Baldi , F.Huertas, H. Monclús, M.Martin, M.Poch*
*GS Inima, Madrid Spain.
** LEQUIA. Ud G, Girona Spain


The PRONOX process is a variant of the HRAS (High Rate Activated Sludge) process and proposes the redirection of organic matter and nitrogen to Anaerobic Digestion prior to the Conventional Activated Sludge stage, as an alternative to the Primary Settling Tank. The aim is to redirect the maximum possible organic load to Anaerobic Digestion. This achieves the dual objective of increasing biogas production and reducing the organic load in the downstream Activated Sludge Unit, which is highly energy intensive.

What is innovative about the PRONOX Process is that it works with two reactors, a stratified anoxic reactor and an aerobic reactor, to promote bio-flocculation processes, with the dual objective of increasing biogas production and reducing organic load. Unlike the Conventional Activated Sludge process, the PRONOX Process operates with a low Hydraulic Retention Time (HRT) of less than one hour and a low Solids Retention Time (SRT) of less than one day.


The main objective of the process is to maximise Carbon and Nitrogen Capture and Redirection with minimal carbon oxidation. Until now, the minimum organic matter demand at the inlet of the Activated Sludge Unit in order to carry out Denitrification

• Evaluation of COD consumption in the PRONOX Process.
• Evaluation of energy savings results obtained with the Pilot and Simulation Plants.
• Evaluation of the reduction in the volume of Activated Sludge Reactors after the PRONOX Process.

Published in #81 FuturENVIRO June – July 2021