Autotrophic Nitrogen Removal From High Ammonium Containing Wastewater

The present thesis is framed within a wider project, promoted by the University of Cagliari and the Italian National Research Council, which pursued as its general objective the development of a novel integrated system for the biological combined anaerobic production of H2 and CH4 from the organic fraction of municipal solid waste (OFMSW), the valorization of solid residues by aerobic bio-oxidation (composting) and the biological treatment of ammonium-rich liquid by products by two-stage partial nitritation (PN)/anaerobic ammonium oxidation (anammox) process. According to the project plan, a biological combined anaerobic production of H2 and CH4 from the OFMSW took place in two different bioreactors, in a double-step configuration. The effluent from the second reactor underwent a liquid/solid separation. The assessment of feasibility of the treatment of the liquid fraction by means of two-stage autotrophic nitrogen removal was the research question that tracked the main investigation line of the work described in the present thesis. The application of the coupled PN/anammox process, also referred to as fully autotrophic nitrogen removal, would allow to increase the sustainability of the entire OFMSW treatment chain, since the need for carbon addition (and concomitant increased sludge production) is omitted, oxygen consumption (i.e., energy requirement) is reduced, and the emission of nitrous oxide (a significant factor in the greenhouse gas footprint of the total water chain) can be cut significantly. To date, few researches focused on the application of partial nitritation/anammox process for the treatment of the liquid fraction originated by the anaerobic digestion of organic substrates such as OFMSW. Moreover, the two-stage anaerobic digestion of such substrates is a relatively novel technology which has not deeply investigated yet in terms of its potential environmental impact, and few studies focused on characterization and management of the liquid residues. To the best of our knowledge, no previous study was performed concerning the application of the two-stage PN/anammox process for the treatment of the anaerobic supernatant of a two-stage anaerobic digestion of organic fraction of municipal solid waste and food waste.