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AmmoniaAnaerobic DigestionBiogasCircular economyESTECHFORSUOFMSWVolatile Fatty Acids


The proposed invention is a method to optimizethe biological production of biohythane and volatile fatty acids (VFA) using an anaerobic digestion process in separate phases. This optimization is achieved by controlling the pH in the fermentation reactor, through the recirculation of the. The amount to be recirculated is controlled by a mathematical model based of pH reading and ammonia estimation.

Technical features

The proposed process of anaerobic digestion with separate phases includes a dynamic recirculation of the digestate. The recirculation ratio is managed by an algorithm that, through pH and electrical conductivity measurements from probes in the two reactors, estimates the ammonia concentration. The algorithm also automatically establishes the recirculation flow rate to maintain the pH in the fermentation reactor at a value close to optimal conditions while at the same time preventing an excessive accumulation of ammonia in the system. The system has a high resilience and a rapid and automatic ability to restore optimal settings, following stress conditions. The process can be fed by Organic Fraction of Municipal Solid Waste (OFMSW) or by sludge from wastewater treatment, as well as zootechnical and agro-industrial waste.

Possible Applications

  • Treatment of OFMSW or other fermentable organic waste;
  • Automation of anaerobic digestion processes;
  • VFA and biogas production.


  • Automatic process management;
  • Continuous pH and electrical conductivity measurements on line;
  • Ammonia concentration estimation with mathematical model;
  • Automatic control of the recycled portion;
  • Resilience and automatic system recovery in case of stress;
  • Minimal investment & operating costs.