Synergistic Co-Digestion of Microalgae and Primary Sludge to Enhance Methane Yield from Temperature-Phased Anaerobic Digestion

Abstract

A two-stage temperature-phased mesophilic anaerobic digestion assay was carried out to study the interaction between various biological pretreatment conditions and the possible synergistic co-digestion of microalgae and primary sludge. The study of growth kinetics of the biochemical methane potential test revealed that a maximum of 36% increase in methane yield was observed from co-digestion of a substrate pretreated by thermophilic aerobic conditions (55 °C and HRT = 2 days) and an 8.3% increase was obtained from the anaerobic pretreated substrate (55 °C and HRT = 3 days). Moreover, no synergistic effects on methane yields were observed in co-digesting the substrate pretreated with high temperature (85 °C). The study also identified specific conditions in which interaction between biological pretreatment and co-digestion might substantially reduce methane yield. Careful optimization of operating conditions, both aerobic and anaerobic pretreatment at moderate thermophilic conditions, can be used as a biological pretreatment to enhance methane yield from the co-digestion of microalgae and primary sludge.

Integrated anaerobic digestion and algae cultivation

“…In WWTPs, an AcoD option exists between sludge and microalgae or microalgae with other residues. Damtie et al (2020) obtained a 36% increase in CH 4 production when studying AcoD from biologically pre-treated algal biomass and primary sludge. Solé-Bundó et al (2019b) obtained a 65% increase in CH 4 production in the AcoD of microalgae with primary sludge and a generation of 4.5 times the energy consumed, whereas the microalgae mono-digestion AD generated 2.7 times the energy consumed.…”

Anaerobic co-digestion of sewage sludge with other organic wastes: A comprehensive review focusing on selection criteria, operational conditions, and microbiology

“…Vassalle et al [179] and Beltran et al [178] concluded that mixing 30 w/w% and 25 w/w% of microalgae with SS increased the methane production by 25% and 22%, respectively. However, many studies reported that ACoD of SS and microalgae reduces the process performance and efficiency [175,177,180]. According to Goncalves et al [181] and Olsson et al [182], adding 20 w/w% and 40 w/w% microalgae as co-substrate decreased specific methane production by 5% and 26% compared to SS mono-digestion.…”

Anaerobic Co-Digestion of Microalgae and Industrial Wastes: A Critical and Bibliometric Review

“…From Table 3 it can be seen that low thermal pretreatments (60-55°C; 1−2d) have none or very little effect on AcoD [19,86], however, when the temperature increased to 120°C, the biomethane production improve greatly (up to 43%) [18,49]. Other successfully tested pretreatments are ultrasonication, hot water, and a combination of thermal and alkaline pretreatments [57,71].…”