TY - JOUR AU - Biasiolo, Marco AU - Ballarin, Marco AU - Tassinato, Graziano AU - Stoppato, Anna AU - Cavinato, Cristina PY - 2022/06/30 Y2 - 2024/03/28 TI - Semi-continuous Chlorella Vulgaris Cultivation Using Anaerobic Digestate Liquid Fraction Pre-treated by Ultrasonic Cavitation to Improve Carbon Dioxide Solubilization JF - Chemical Engineering Transactions VL - 92 SP - 151-156 SE - Research Articles DO - 10.3303/CET2292026 UR - https://www.cetjournal.it/index.php/cet/article/view/CET2292026 AB - Nutrients-enriched effluents such as digestate can represent a suitable and economically appealing substrate for microalgae growth since they combine the effluent treatment with biomass production. Then, microalgae biomass can be exploited to produce several bio-based compounds. However, the use of digestate for microalgae cultivation can be challenging due to its high levels of ammonia nitrogen and its low C/N ratio. For this reason, an ultrasonic cavitation (UC) process combined with carbon dioxide (CO2) insufflation was tested on digestate, in order to obtain a faster solubilization of the CO2 in the medium and thus an increase in the C/N ratio. The test was carried out growing Chlorella vulgaris on both digestate (mixotrophic condition) and BG-11 medium (autotrophic condition) in 1 L photobioreactors. For the first 14 days of the experiment the reactors were maintained in batch conditions to acclimatize microalgae. Then, they were switched to semi-continuous for 32 days. The reactors were fed three times a week, with an HRT (Hydraulic Retention Time) of 10.5 d as weekly average. Regarding the test on digestate, both UC pre-treated and untreated conditions reached the highest biomass production at the end of the batch (4.8 and 4.1 g L-1 respectively) and a complete ammonium (NH4+) removal after 9 days. The switch to semi-continuous caused an increase in NH4+ concentration and a consistent decrease in biomass concentration. Biomass production reached the steady-state, with a concentration of 1.9 and 1.2 g L-1 for the UC pre-treated and untreated digestate, respectively (+55.6 % biomass production obtained with UC pre-treated digestate). Moreover, an NH4+ removal of 93.5 % and 92.3 % was reached for UC pre treated and untreated conditions, respectively. ER -