Recovery of organic carbon from municipal waste streams
Time: Wed 2020-08-19 13.00
Subject area: Chemical Engineering
Doctoral student: Isaac Owusu-Agyeman , Kemiteknik, Resource Recovery Division
Opponent: Professor Irini Angelidaki, Technical University of Denmark
Supervisor: Professor Elzbieta Plaza, Hållbar utveckling, miljövetenskap och teknik; Associate Professor Zeynep Cetecioglu, Resursåtervinning
The focus of the current study was on the recovery of carbon from municipal bio-waste streams. Firstly, the relationship between methanogenic pathways and the properties of anaerobic granules was studied using two pilot-scale upflow anaerobic sludge blanket (UASB) reactors with different granule size distribution. UASB1 granules were larger (3-4 mm) with multi-layered internal structure and the archaeal community was dominated by acetoclastic methanogens, while the UASB2 granules were smaller (1-2 mm) without a layered internal structure and the archaeal community was predominated by hydrogenotrophic methanogens. The acetoclastic methanogenic activities of UASB1 (250-437 mL CH4/g VS·d) than UASB2 (150-260 mL CH4/g VS·d), confirming that acetoclastic methanogenesis was more dominant in UASB1. Temperature increase from 20oC to 28oC did not change the microbial community but resulted in increased and stable biogas production for both reactors. There was an increase in chemical oxygen demand (COD) with hydraulic retention time due to increased contact time.
The second part of the study focused on anaerobic co-digestion to produce volatile fatty acid (VFA) due to its higher value. The impact of substrate ratio of primary sludge (PS) and external organic waste (OW) and the robustness of the VFA system in the long term were assessed. Lab-scale batch study with different proportions of PS and OW; 0%, 25%, 50%, 75%, 100% of OW in terms of COD and scaled up in a semi-continuous pilot reactor with substrate ratio of 50% OW based on the results of the lab-scale study were performed. There was an increase in VFA production with an increase in OW proportion due to the availability of biodegradable organics. Acetic acid was the most dominant VFA in the batch reactors while in the semi-continuous experiment, caproic acid was dominated (50%). As carbon sources, the VFA-rich liquid attained the highest specific denitrification rate when compared with acetate and methanol.