Case specific: Addressing co-digestion of wastewater sludge, cheese whey and cow manure: Kinetic modeling

• Published in: Heliyon 2024-10, Vol.10 (19), p.e38773, Article e38773
• Main Authors: Stres, Blaž, Hatzikioseyian, Artin, Kousi, Pavlina, Remoundaki, Emmanouella, Deutsch, Leon, Vogel Mikuš, Katarina, Rak, Gašper, Kolbl Repinc, Sabina
• Format: Article
• Language: English
• ISSN: 2405-8440; 2405-8440
• DOI: 10.1016/j.heliyon.2024.e38773

The study investigated the methane production efficiency in a semi-continuous laboratory experiment with periodic feeding of wastewater sludge (WWS) as primary substrate and addition of whey (CW) and cow manure (CM). The short-term behavior of a real-scale anaerobic digester with WWS and the methane production improvements with different feeding mixtures of WWS, CW and CM were addressed. Gradual addition of CW to WWS (WWS:CW:CM = 70:20:0 to 70:55:0) increased the average daily methane production to 48.6 mL CH4/g COD/day and prevented reactor failure, but high VOA/TIC values showed that the reactors were conditionally stable evolution at an OLR of 8 g COD/L/day. Reactors that were additionally supplemented with CM (WWS:CW:CM = 70:55:10) achieved at least 12.3 % more methane than the reactors supplemented with WWS and CW alone. The highest methane production and process evolution in the reactors were achieved at OLRs between 7.5 and 8.7 g COD/L per day. After day 50, the addition of double the amount of CW further increased the methane production and VOA/TIC ratios. In this case, the OLR increased from 6.3 to 9.3 g COD/L/day. The concentration of propionic and acetic acid in all reactors increased above the recommended values and caused inhibition and instability. A strong positive Pearson correlation was found between the trace elements (Fe, Cu, Zn, Mn) detected by XRF. TE contributed to methane production, but to a lesser extent than TIC and NH4+-N. The simplified model successfully predicted methane production under a periodic feeding regime. [Display omitted] •Anaerobic co-digestion was stable with OLR up to 8.7 g COD/L/day.•Cow manure supplementation enabled methane production with high cheese whey loading.•Cow manure mitigated decrease in concentration of Fe, Zn, Mn and Cu.•Kinetic model successfully simulated the daily methane production.