Natural Communities of Microalgae and Cyanobacteria from Eutrophicated Waters as Potential Co-substrates for Small-scale

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Natural Communities of Microalgae and Cyanobacteria from Eutrophicated Waters as Potential Co-substrates for Small-scale Biogas Production Denis Deže 1 & Melita Mihaljević 2 & Đurđica Kovačić 1 & Daria Jovičić 1 & Davor Kralik 1 Received: 19 February 2020 / Accepted: 23 June 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020

Abstract

The purpose of this study was to determine the biogas potential of biomass produced by microbiotic communities developed under natural conditions in freshwater systems such as ponds incorporated into agricultural landscapes. Natural communities of microalgae were collected from a small eutrophicated pond where dominant species were euglenoids (Lepocinclis species). Cyanobacterial communities dominated by Lyngbya species were taken from a domestic aquarium and cultivated under makeshift conditions. Experiments were done using dairy cow manure (DCM) for codigestion with natural communities of microalgae (MDM) and cyanobacteria (CDM) and conducted during 42 days in thermophilic regime. The total biogas yields were 421.40 and 383.34 mL/g volatile solids (VS), while the average methane contents were 63.97 and 64.06% for MDM and CDM, respectively. Our results indicate that the natural communities of microalgae and cyanobacteria used in this study possess the potential for biogas production, which is, in comparison with particular algal and cyanobacterial strains cultivated under strictly controlled cultivation conditions, more promising. Therefore, this study aims to motivate further investigations into the diverse natural communities of microalgae and cyanobacteria and pretreatments that are environmentally friendly and cost-effective and will eventually enhance small-scale biogas production on agricultural farms. Keywords Biogas . Anaerobic fermentation . Natural microbiotic communities . Microalgae . Cyanobacteria

* Melita Mihaljević [email protected]

1

Faculty of Agrobiotechnical Sciences, Osijek, Josip Juraj Strossmayer University of Osijek, Vladimira Preloga 1, HR-31000 Osijek, Croatia

2

Department of Biology, Osijek, Josip Juraj Strossmayer University of Osijek, Cara Hadrijana 8/a, HR-31000 Osijek, Croatia

Applied Biochemistry and Biotechnology

Abbreviations DCM Dairy cow manure MDM Microalgae and DCM mixture CDM Cyanobacteria and DCM mixture TS Total solids VS Volatile solids TOC Total organic carbon TN Total extractable nitrogen GC Gas chromatograph SD Standard deviation

Introduction During the last decade, algae have drawn attention as anaerobic digestion co-substrates for biogas production due to the high potential biomass yield per unit area which is often higher than that of terrestrial plants or cultivation systems that do not compete with crops for land or freshwater. However, despite their considerable potential, we are yet to see economically viable commercial-scale fuel production from algae [1–3]. Today, micro-scale biogas plants which mainly rely on farm biomass sources are becoming more attractive [4]. These production unit