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Enhancement of Volatile Fatty Acid Production from Dairy Wastewater

Time: Thu 2020-09-10 10.00

Location:, Stockholm (English)

Subject area: Chemical Engineering

Doctoral student: PhD Candidate Merve Atasoy , Resursåtervinning

Opponent: Professor Juan Lema, University of Santiago de Compostela

Supervisor: Docent Zeynep Cetecioglu, Resursåtervinning, KTH Royal Institute of Technology

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Resource recovery from waste-streams is a highly promising approach to meet with urbanization and modernization consequences. Rapid human population growth, expanding industrialization and excessive consumption of resources lead to increasing demand for raw materials and energy sources, and an escalation of greenhouse gas emission. The recovery of valuable raw materials from waste-streams is a vital step towards environmentally friendly and sustainable bio-based production. One of the most promising resource recovery approaches from waste-streams is based on anaerobic digestion. In recent years, anaerobic digestion technology has started to go beyond energy recovery with the carboxylate platform. Volatile fatty acids (VFA) are intermediate products of anaerobic digestion and possess great potential for bio-based production from waste streams. Because of its wide range of applications, high market demand and low greenhouse gas emissions, bio-based VFA production has gained attention in recent years. Nevertheless, the current bio-based VFA production is economically non-competitive compared to petroleum-based production because of high substrate cost and production inefficiency. In this thesis, the bioaugmentation strategy was applied in the mixed culture fermentation to produce one-type dominant VFA from dairy industry wastewater. After the optimization of inoculum and dairy industry wastewater for maximal VFA production in the batch reactors, the bioaugmentation strategy was applied by selected pure cultures (Clostridium aceticum, Clostridium butyricum and Propionibacterium acidipropionici) in the anaerobic sequencing batch reactors. Bioaugmentation is a well-known method to enhance the microbial community for different purposes by adding external microbial cultures. The mixed culture was bioaugmented by C. aceticum for acetic acid dominant VFA production, C. butyricum for butyric acid dominant VFA production and P. acidipropionici for propionic acid dominant VFA production, respectively. Simultaneously, a non-bioaugmented control reactor is operated for comparison. The bioaugmented mixed culture by C. aceticum increased acetic acid production as ten-fold; C. butyricum improved butyric acid production more than ten times; P. acidipropionici IV increased propionic production more than four times. The quantity of the selected pure cultures strongly correlated with the acid composition confirming the efficiency of the bioaugmentation strategy. This thesis proves the powerful applicability of bioaugmentation strategies to increase the concentration of the desired VFA type in mixtures. Our approach has the potential to push resource recovery from waste-streams a significant step forward to achieve the United Nations Sustainable Development targets 12. Responsible Consumption and Production and 13. Climate Action by controlling global warming and reducing GHG emissions.