Author(s): Coura, Renata D'arc ; Rodrigues, Ana Cristina Costa ; Alonso, Joaquim Mamede ; Ferraz, Ana Isabel ; Brito, Luis Miguel ; Abrantes, João Carlos de Castro ; Guerreiro Brito, António
Date: 2021
Persistent ID: https://hdl.handle.net/1822/70363
Origin: RepositóriUM - Universidade do Minho
Subject(s): Ultrasound pretreatment; Struvite precipitation; Nutrient recovery; Circular economy; Anaerobic (co)digestion
The present study aimed to optimize the struvite chemical precipitation process in nitrogen-rich 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, or 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 process.
