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Updated: Sep 13, 2025

Evaluation of Integrated Anaerobic Digestion and Hydrothermal Carbonization for Bioenergy Production
Published on: June 15, 2014
Effect of acidification on nitrogen transformation of solid digestate during thermal drying
1School of Agriculture and Biotechnology, Shenzhen Campus of Sun Yat-sen University, No. 66, Gongchang Road, Guangming District, Shenzhen, Guangdong 518107, PR China.
Abstract:
Strong acid pretreatment preserves ammonium nitrogen (NH4+-N) during thermal drying of solid digestate (SD), yet organic nitrogen dynamics are poorly understood despite its agronomic significance. This study investigated nitrogen transformations during SD drying (130 °C, 450 mL·min-1 airflow) at three pH levels (7.9, 6.5, 5.5) over five time points (150 min total). Unacidified SD (pH 7.9) suffered significant N loss: inorganic N decreased 49.5 % and organic N decreased 13.6 %. Crucially, the proportion of bioavailable organic nitrogen (BON) within total organic nitrogen fell from 51.1 % to 44.9 %, substantially diminishing the agronomic value of SD. Acidification (pH 6.5, 5.5) effectively inhibited ammonia volatilization, achieving 76.0 %-93.4 % NH4+-N retention. Although organic N loss still occurred with acidification, the BON/organic nitrogen proportion post-drying (55.6 %-57.6 %) remained significantly higher than in unacidified SD (44.9 %). These results collectively demonstrated that acidification enhanced the nitrogen supply potential of SD.
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