Assessment of the ammonia nitrogen removal efficiency from the liquid fraction of OFMSW digestate into a stripping-absorption combined pilot plant.

The envisaged population growth challenges the entire food production chain, which clings to the need for circular alternatives. The traditional Haber-Bosch industrial process for synthetic ammonia production significantly consumes energy and natural resources, affecting humans and the planet's health. Sewage sludge, food waste, and animal manure represent optimal sustainable substrates for ammonia extraction, paving the way to close-the-loop thinking. This thesis analyses the performances of a pilot plant combining stripping and absorption to assess the achievement of a 70% ammonia removal efficiency threshold, with successful results. Several tests are performed by changing the operating variables, thus evaluating different conditions. The inlet solution of around 50 l/h consists of the liquid fraction retrieved from the OFMSW digestate. The Minitab application provides a statistical interpretation of the experimental data and the definition of the significant variables. Among all, pH and HRT were found to be relevant. The Response Surface Methodology leads to the evaluation of the combined interactions of the factors, highlighting the possible scenarios for the plant up-scaling procedure, validated through the solution of an optimization problem. Finally, the full-scale stripping and absorption reactors are designed based on the future flowrate of 100 m3/d. Moreover, an evaluation of the heat requirements is reported for the stripping reactor, accounting for the seasonal variability of temperatures. Besides, the scrubber height and diameter design imply the McCabe-Thiele and Eckert graphical methods application, with the determination of the equilibrium and operating lines. Anyway, the outcomes outlined in this thesis should be corroborated by further studies, such as cost-benefit analysis, opening the discussion for future improvements.