Coura, Renata D'arcRodrigues, Ana CristinaAlonso, Joaquim MamedeFerraz, Ana IsabelBrito, Luís MiguelAbrantes, João Carlos CastroBrito, Antonio Guerreiro De2021-05-272021-05-272021Coura, R.D.; Rodrigues, A.C.; Alonso, J.M.; Ferraz, A.I.; Brito, L.M.; Abrantes, J.C.C.; Brito, A.G. Combined Pretreatment by Ultrasound and Struvite Precipitation of Raw Substrates: A Strategy to Overcome C/N Ratio Unbalance in Nitrogen-Rich Anaerobic Co-Digestion Systems. Sustainability 2021, 13, 2175http://hdl.handle.net/10400.5/21366The present study aimed to optimize the struvite chemical precipitation process in nitrogenrich anaerobic co-digestion systems. Struvite precipitation experiments were carried out using a mixture of cattle slurry liquid fraction and sewage sludge, with and without ultrasound pretreatment. Marine salt or MgCl2 were used as magnesium source in NH4 +:Mg2+ stoichiometric proportions of 1:1.5 and 1:3. Under the tested conditions, ammonium nitrogen and orthophosphate were removed from the mixed liquor with a maximum observed efficiency of 43% and 92%, respectively, when the ultrasound treatment was applied prior to struvite precipitation, using MgCl2 as source of magnesium (NH4 +:Mg2+ of 1:3). The operating time was 40 min. Different pretreatments were tested prior to the biomethanization experiments, struvite precipitation, ultrasound and a combination of both pretreatments. The application of ultrasound (with an energy input of 218 kJ L􀀀1) and struvite precipitation (NH4 +:Mg2+ of 1:3) increased the methane content in the biogas by 82% and reduced hydraulic retention time by 28%, when compared to the anaerobic co-digestion assays without pretreatment. The hydrolytic pretreatment increased the bioavailability of nitrogen by 5%, thus enhancing the removal efficiency of ammonium nitrogen by 20%. Consequently, an increase in the carbon to nitrogen ratio was observed, favoring the methanogenesis processengultrasound pretreatmentstruvite precipitationnutrient recoverycircular economyanaerobic (co)digestionjournal articlehttps://doi.org/ 10.3390/su13042175