Advanced bioprocesses for N removal from the liquid fraction of co-digestated piggery/poultry manure and agro-wastes

The liquid fraction of the digested material is rich in ammonium and its disposal on agricultural soil is regulated by the European directive on nitrates (91/676/CEE). In this paper, results of a two-years project funded by the Italian Ministry for Agriculture and Forestry will be discussed. The aim of this research was to evaluate the applicability of two treatment options, namely nitritation-denitritation process (DENO2) and partial-nitritation/anammox for biological N removal from a supernatant coming from the anaerobic digestion of a mixture of piggery manure, poultry manure, and of agro-wastes. The DENO2 process in SBR configuration (650L, 300d experimentation) confirmed to be a technically feasible option to treat liquid fraction of agricultural digestate despite the high influent variability. N2O emission is a relevant issue and accounted for 3-24% of total N removed. Results obtained by operating two lab-scale reactors (an SBR and MBR) at increasing percentage of real wastewater suggest that both reactor types allowed to support a stable anammox process and could efficiently remove the N load as long as the % of real wastewater in the feed was up to 70%. Stable partial nitritation (in a 650 L SBR) was achieved at pilot-scale, obtaining a suitable influent for the anammox SBR reactor (150 L). The undiluted realwastewater was finally fed to the anammox reactor for 3 months obtaining N removal higher than 90%