Mixing strategies of high solids anaerobic co-digestion using food waste with sewage sludge for enhanced biogas production

• Published in: Journal of cleaner production Vol. 210; pp. 388 - 400
• Main Authors: Latha, K., Velraj, R., Shanmugam, P., Sivanesan, S.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 10.02.2019
• Subjects: Biogas; Co-digestion; Food waste; Microbial morphology; Mixing; Power dissipated; Food waste; Mixing; Biogas; Microbial morphology; Power dissipated; Co-digestion
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2018.10.219

Mixing strategies of high solids anaerobic digesters using food waste (FW), codigested with sewage treatment plant sludge (STP) was evaluated for green and clean biogas production. Improper anaerobic digestion (AD) mixing leads to poor biogas yield at high organic loading rate (OLR). The present study evaluated the novel method of biogas recirculation using new ‘O’ shaped diffuser design for the AD mixing and compared the performance with the conventional mode of impeller driven mixing and unmixed mode for the optimum FW to STP ratio of 3:1 at high OLR The biogas recirculation frequency of 15 min/h produced maximum biogas (0.28–0.86 L/gVSr). An enhanced biogas yield was observed at intermittant biogas recirculation intensity of 2000 mL/min (0.25–0.92 L/gVSr). This was attributed to the synergistic effect of CO2 acidification and high VFA production at OLR of 6 gVS/Ld. Consequently, led to benefit of reduced digester pH (from 8.3 to 6.6), NH3 control (2380 mg/L), in-situ CH4 enrichment (88%) and sheath protected microbial morphology than the other mixing intensities. It is constructed that an optimum intermittent biogas recirculation could be used as an alternative mixing method for the large scale AD, for enhanced biogas yield, reduced impeller power consumption, and improved energy efficiency. [Display omitted] •High R2 observed between stoichiometric and experimental methane potential.•The optimum mixing ratio for anaerobic co-digestion was 3:1.•Intense mixing depicted broken microbial morphology, with high power dissipation.•Intermittent biogas recirculation, feeding and waiting cycle produced high biogas.•Benefit of anaerobic process, pH, NH3 control and high CH4, at low gas mixing.