title: Effect of humic acid on anaerobic digestion of cellulose and xylan in completely stirred tank reactors: inhibitory effect, mitigation of the inhibition and the dynamics of the microbial communities.
abstract: Inhibition effect of humic acid (HA) on anaerobic digestion of cellulose and xylan and the mitigation potential of the inhibition were evaluated in controlled fed batch reactors at 30 °C and a hydraulic retention time (HRT) of 20 days. Reactor performances were evaluated by biogas production and metabolite measurements for 220 days. Microbial population dynamics of the reactors were monitored with next-generation 16S rRNA gene sequencing at nine different sampling times. Our results showed that increasing levels of HA inhibited the hydrolysis efficiency of the digestion by 40% and concomitantly reduced the methane yield. Addition of hydrolytic enzymes helped to reverse the negative effects of HA, whereas calcium addition did not reverse HA inhibition. Microbiological analyses showed that the relative abundance of hydrolytic/fermentative bacterial groups such as Clostridiales, Bacteroidales and Anaerolineales was significantly lowered by the presence of HA. HA also affected the archaeal populations. Mostly hydrogenotrophic methanogens were negatively affected by HA. The relative abundance of Methanobacteriaceae, Methanomicrobiales-WCHA208 and Unassigned Thermoplasmata WCHA1-57 were negatively affected by the presence of HA, whereas Methanosaetacea was not affected.
authors.affiliation: Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands. samet.azman@wur.nl.|Sub-department of Environmental Technology, Wageningen University, Bornse Weilanden 9, 6708, WG, Wageningen, The Netherlands. samet.azman@wur.nl.
authors.forename: Samet
authors.identifier: http://orcid.org/0000-0003-2564-0488
authors.initials: S
authors.lastname: Azman
authors.affiliation: Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands.|Faculty of Civil Engineering and Geosciences, Department of Water Management, Section Sanitary Engineering, Delft University of Technology, Stevinweg 1, 2628, CN, Delft, The Netherlands.
authors.forename: Ahmad F
authors.initials: AF
authors.lastname: Khadem
authors.affiliation: Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands.
authors.forename: Caroline M
authors.initials: CM
authors.lastname: Plugge
authors.affiliation: Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands.
authors.forename: Alfons J M
authors.initials: AJ
authors.lastname: Stams
authors.affiliation: Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands.
authors.forename: Sabina
authors.initials: S
authors.lastname: Bec
authors.affiliation: Sub-department of Environmental Technology, Wageningen University, Bornse Weilanden 9, 6708, WG, Wageningen, The Netherlands.
authors.forename: Grietje
authors.initials: G
authors.lastname: Zeeman
mesh_terms: D000693:Anaerobiosis; D019149:Bioreactors / Q000382:microbiology*; D058448:Biota / Q000187:drug effects*; D002482:Cellulose / Q000378:metabolism*; D019641:DNA, Archaeal / Q000737:chemistry / Q000235:genetics; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D059014:High-Throughput Nucleotide Sequencing; D006812:Humic Substances / Q000633:toxicity*; D006868:Hydrolysis; D008697:Methane / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013696:Temperature; D014990:Xylans / Q000378:metabolism*
chemical_list: D019641:DNA, Archaeal; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D006812:Humic Substances; D012336:RNA, Ribosomal, 16S; D014990:Xylans; D002482:Cellulose; D008697:Methane
keywords: Calcium; Hydrolysis; Hydrolytic enzymes; Inhibition; Microbial community analyses; Mitigation