Phenylodigest

In the past decade anaerobic digestion has gained increasing importance in both, treating different (waste) substrates and generating energy from biomass in general. Hence, substrates spectra have been broadened and also the research on as well as the application of pre-treatment strategies have been progressively extended in order to better exploit the energy present in the respective substrates since still a rather high rate of carbon remains unused as it passes the processes. The increased use of protein-rich (co-)substrate and the pre-treatment of lignocellulosic material, of special importance as it encompasses a high energetic potential, also entail risks in view of undesired by-product formation including phenolic compounds known to possibly accumulate under unfavorable digestion conditions and to exert a negative effect on the anaerobic digestion processes. Generally speaking, there is a lack of information about the occurrence, fate, and the inhibitory effect of aromatic compounds phenylacetic-, phenylpropionic-, and phenylbutyric acid (PAA, PPA, PBA) representing (intermediate) degradation products of protein- and/or lignin-rich substrates. In particular, the microbial population dynamics during ana- and catabolism of aromatic compounds like PAA, PPA, and PBA has rather been neglected and data on the impact of phenyl acids on the microbial community engaged in the anaerobic decomposition process are missing completely. However, these data are of profound interest in order to improve the understanding of anaerobic digestion processes under unfavorable conditions, particularly regarding the recently increased application of protein-rich co-substrates and pre-treatment strategies. Therefore, the aims of the project comprise the clarification of the i. a) possible formation of PAA, PPA, PBA during mesophilic and thermophilic anaerobic digestion from defined substrates (protein rich, lignin derivatives) and b) the assessment of initial concentrations required to evoke an inhibition effect, ii. their impact on anaerobic digestion processes and its microbial consortium, iii. the ability of these consortia to adapt to different phenyl acid concentrations, and iv.the identification of organisms/communities capable of handling high phenyl acid concentrations while still maintaining high methane productivity. Concerning the methodology, a mixture of already well established chemical-analytical methods like HPLC, GC, etc., classical cultivation based methods as well as highly modern molecular biological methods will be applied. The project will allow insights into the formation, the degradation and/or the conversion of phenlyacids as well as possible inhibitory effects on the microbial community during anaerobic digestion.

FWF project Phenylodigest In the past decade anaerobic digestion has gained increasing importance in both, treating different (waste) substrates and generating energy from biomass in general. Hence, substrate spectra have been broadened and also the research on as well as the application of pre-treatment strategies have been progressively extended in order to better exploit the energy present in the respective substrates since still a part of carbon remains unused as it passes the digestion processes. The progressively improved exploitation of organic substrates for biogas production increased both, methane yields and the risk of undesired by-product formation. Especially the improved disintegration of lignocellulosic material leads not only to an effective degradation of these materials but also to an increased release of aromatic compounds like phenylacetate, phenylpropionate and/or phenylbutyrate (PAA, PPA, PBA). These compounds can inhibit methane formation and thus lead to severe and long-lasting process failures. The aims of the project Phenylodigest comprised the clarification of the i. possible formation of PAA, PPA, PBA during mesophilic and thermophilic anaerobic digestion from defined substrates (protein rich, lignin derivatives) ii. their impact on anaerobic digestion processes and its microbial consortia, iii. the ability of these consortia to adapt to different phenyl acid concentrations, and iv. the identification of organisms capable of handling high phenyl acid concentrations while still maintaining high methane productivity. In the course of this project, during which a mixture of already well-established chemical-analytical methods like HPLC, GC, etc., classical cultivation-based methods as well as highly modern molecular biological methods have been applied, it could be shown, that from protein-rich substrates and lignin derivatives notable concentrations of phenyl acids were originating. Particularly, at reactor overload conditions, when high concentrations of nutrients were available for the microbial community, an accumulation of phenyl acids was observed leading to a deterioration of reactor performance. It was found that the last step in the anaerobic digestion cascade, the methanogenesis, was not affected to an extent as previously hypothesized but rather upstream microbial groups. However, phenyl acid derived inhibition seemed to be reversible by a microbial redundancy within the present community able to adopt to unfavorable conditions after an adaptation period. Organisms identified to be involved in the generation of phenyl acids could be assigned to genera like Sedimentibacter, Tepidanaerobacter, Acetomicrobium, Sporanaerobacter, Syntrophomonas, Lactobacillus, Geobacillus, or Tissierella. In contrast, micorooganisms like Syntrophus sp. seemed to be engaged in the degradation process of phenyl acids and might be important players in maintain high reactor performance in the presence of phenyl acids.