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 nextgeneration 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.

A New Approach to Assess the Effect of Various Humic Compounds on the Metabolic Activity of Cells Participating in Methanogenesis

“…In another investigation, in the process of anaerobic cellulose and xylan digestion with crushed anaerobic granular sludge that was realized with the introduction of HCs (Sigma-Aldrich; CAS number 68131-04-4) at concentrations of up to 0.4 g/L, microbiological analysis showed that the concentrations of bacterial cells of the genera Clostridiales, Bacteroidales, and Anaerolineales, as well as hydrogenotrophic methanogens, were significantly reduced in the presence of HCs [29]. It was found that the relative number of bacteria of Methanobacteriaceae and Methanomicrobiales-WCHA208 was greatly reduced in the presence of HCs, whereas the number of Methanosaetacea bacteria did not change.…”

Inhibition of anaerobic digestion processes: Applications of molecular tools

“…Y.M. Amha et al Bioresource Technology 247 (2018) decrease in relative abundance of hydrolytic/fermentative bacterial populations including Clostridiales, Bacteroidales, and Anaerolineales (Azman et al, 2017). Inhibition due to LCFA has also been reported, with inhibition of hydrolytic bacteria occurring at 2.6-9.4 kg COD m −3 and acidogenic bacteria at a similar concentration range, 2.1-7.9 kg COD m −3 .…”

“…Hydrolytic bacteria are inhibited by elevated levels of VFAs, LCFAs, hydrogen partial pressure, and humic acids (Azman et al, 2017;Azman et al, 2015;Cazier et al, 2015) (Tables 1-4). Inhibition occurs via activity loss, reversible reduction of hydrolases (e.g., when inhibitors bind to enzyme active sites or substrate-enzyme complexes), or irreversible impacts resulting from changes in enzyme chemical structure (Azman et al, 2015).…”

Ecophysiology of Acetoclastic Methanogens

“…However, there are examples where Methanothrix seems to be more resistant. Methanothrix is more resistant to longchain fatty acids (Silva et al 2016) and humic substances (Azman et al 2017) than Methanosarcina. The higher tolerance in these cases was thought to be related to the different cell wall structure.…”