Microalgae Cultivation in Electrochemically Oxidized Anaerobic Digestate from Coffee Waste Biomass

Abstract

Anaerobic digestate contains rich nutrients, such as nitrogen and phosphorus, which could be reused in microalgae cultivation. However, a clear growth medium is required for the cultivation to facilitate light permeable condition. The aim of this work was to investigate microalgae cultivation in electrochemically oxidized liquid digestate from coffee waste biomass. After removing the solid fraction of the digestate through microfiltration, the liquid digestate was treated by electrochemical oxidation using a boron-doped diamond anode. The liquid digestate (LD) and electrochemically oxidized liquid digestate (ELD) were used as media for microalgae cultivation.The effects of dilution from 5 to 20 times of the LD and reaction time from 1 to 5 h of the ELD on microalgae growth were also investigated. The results showed that the electrochemical oxidation had little influence on ammonium concentration in the digestate, whereas a color removal of up to 85% was observed. The ELD showed better microalgal growth performances than diluted LD, based on the data from optical density at 680 nm and cell density. The 10 times diluted, 2 h ELD achieved the best growth performance (additional optical density of 1.5 (-)) in all conditions. Our experiments proved that the ELD as a highly light permeable medium, better improved the growth performance of C. sorokiniana cultivation when compared with the LD medium.