THE SPECIFIC ROLE OF MICROBIAL BIOFILMS IN THE DETERIORATION OF CONCRETE TANKS FOR ANAEROBIC DIGESTION PLANTS

Author(s): Cedric Perez, Christine Lors and Benjamin Erable
Paper category: Proceedings
Book title: Proceedings of the Final Conference of RILEM 253-MCI Microorganisms-Cementitious Materials Interactions Volume II
Editor(s): Alexandra Bertron and Henk Jonkers
ISBN: 978-2-35158-207-7 (Set)
ISBN: 978-2-35158-210-7 (Volume 2)
e-ISBN: 978-2-35158-206-0
Publisher: RILEM Publications SARL
Publication year: 2018
Pages: 565-566
Total Pages: 308
Language : English

Abstract: Anaerobic digestion is a fermentation process of biodegradable biomass (food, agriculture and green waste), leading to biogas production. The biogas produced is mainly made of CO2 and CH4. It can be valued to produce heat, electricity or biofuel. CH4 can also be purified to be directly injected into the natural gas networks. The European projections to the horizon 2030 predict the production of 12-20 billion m3 of biogas, which represents about 3% of the current natural gas consumption [1] . In industrial anaerobic digestion plants, digesters are usually made of cementitious materials. But the microbial activity in the digester produces aggressive metabolites responsible for severe deterioration of concrete structures. The biogenic molecules, already identified as particularly aggressive in anaerobic digestion, are CO2, NH4 + and volatile fatty acids[2] . Usually for the concrete deterioration the chemical attacks by biogenic molecules are even more intense when the microorganisms are directly present on the cement, certainly because the production of aggressive metabolites is more localized and particularly sustained on the concrete surface [3] . In short, biofilms formed on the concrete surface are suspected to catalyze deterioration [4] . The goal of our study is to evaluate the specific role played by the biofilm formation on the biodeterioration of cementitious materials during the anaerobic digestion process. Firstly, we want to give more insight into the biofilm heterogeneity and his development on cementitious materials in anaerobic digestion. For that, lab scale anaerobic bioreactors mimicking industrial anaerobic digestion media experiments are planned. As the interactions of NH4 + and volatile fatty acids with cementitious materials implies an acid/ base reaction [2], monitoring pH inside the biofilm could lead to a better understanding of the effects of these compounds on the biodeterioration of cementitious materials. Fluorescent dyes sensitive to pH or pH micro-electrode are used to monitor local pH and gradients in the microscopic scale of a biofilm. As the microbial diversity in anaerobic digestion media is complex, the determination of the key microbial populations involved in the microbial biofouling of concrete surface could help in finding a way to limit colonization and microbial proliferation. For that, accessing the microbial heterogeneous repartition within the biofilm at a microscopic scale is necessary by separately extracting the different layers of the biofilm using physical biofilm removal techniques. The different layers can then be analyzed through molecular biology techniques such as 16s rRNA gene sequencing analysis and qPCR. The use of fluorescent dye specific to a microbial population, using the FISH approach, could also clarify the microbial spatial repartition. SEM observations can be used to confirm the efficacy of the layer extraction technique and to study the structure of the biofilm at a smaller scale.
Secondly, single strain biofilms producing only one of the aggressive compounds will be studied individually, in order to determine the effect of each aggressive compound on cementitious materials. The possible interactions existing between those single strains will be also explored by combining strains in the form of bacterial cocktails. The selected strains must respond to a few criteria: being relatively easily cultivable at conditions representative of anaerobic digestion media, being characterized, known to form biofilms and also available in bacterial resource centers. For practical reasons, we wanted to avoid strict anaerobes as much as possible. For the volatile fatty acid production, a strain producing either butyric, acetic or propionic acid was looked for. A strain producing propionic acid, Propionibacterium acidipropionici, was chosen because this strain adheres to all the criteria listed above: Concerning the CO2 producing strains a bacteria realizing anaerobic respiration was selected with nitrate as the final electron acceptor. The strain chosen is Paracoccus denitrificans known in the denitrification field. About only producing NH4 + , after some unsuccessful researches, the idea of finding a strain producing NH4 + and not consuming or not producing either CO2 or volatile fatty acids was given up. We decided to search a strain producing NH4 + and another aggressive compound. As in anaerobic digestion NH4 + is originating from amino acid fermentation, we decided to choose: Clostridium Sticklandii which is a specialized bacteria in this fermentation. Since it is a strain commonly found in anaerobic digestion media, it responds to the criteria listed above. However, this strain present a lower tolerance toward oxidative stress than P denitrificans and P acidipropionici but this strain is supposed to be able to grow in microaerobic conditions [5] . P denitrificans might be able to produce both NH4 + and CO2 [6] and could be as well used. Finally, a specific experimental set-up of anaerobic bioreactor allowing to discriminate between the chemical and biological actions involved in the biodeterioration will be designed. By combining the pure strain culture using this device with the techniques developed to study the biofilm heterogeneity, we hope to be able to explain and find a model of the impact of biological aggressive components on the biodeterioration of cementitious materials.

Online publication : 2018
Publication type : full_text
Public price (Euros) : 0.00