pH and Phosphate Induced Shifts in Carbon Flow and Microbial Community during Thermophilic Anaerobic Digestion

Inhibition of anaerobic digestion by various ammonia sources resulted in subtle differences in metabolite dynamics

The impact of ammonia on anaerobic digestion performance and microbial dynamics has been extensively studied, but the concurrent effect of anions brought by ammonium salt should not be neglected. This paper studied this effect using metabolomics and a time-course statistical framework. Metabolomics provides novel perspectives to study microbial processes and facilitates a more profound understanding at the metabolic level. The advanced statistical framework enables deciphering the complexity of large metabolomics data sets. More specifically, a series of lab-scale batch reactors were set up with different ammonia sources added. Samples of nine time points over the degradation were analyzed with liquid chromatography-mass spectrometry. A filtering procedure was applied to select the promising metabolomic peaks from 1262 peaks, followed by modeling their intensities across time. The metabolomic peaks with similar time profiles were clustered, evidencing the correlation of different biological processes. Differential analysis was performed to seek the differences in metabolite dynamics caused by different anions. Finally, tandem mass spectrometry and metabolite annotation provided further information on the molecular structure and possible metabolic pathways. For example, the consumption of 5-aminovaleric acid, a short-chain fatty acid obtained from l-lysine degradation, was slowed down by phosphates. Overall, by investigating the effect of anions on anaerobic digestion, our study demonstrated the effectiveness of metabolomics in providing detailed information in a set of samples from different experimental conditions. With the statistical framework, the approach enables capturing subtle differences in metabolite dynamics between samples while accounting for the differences caused by time variations.

Mechanisms of anaerobic treatment of sulfate-containing organic wastewater mediated by Fe0 under different initial pH values

The anaerobic treatment of sulfide-containing organic wastewater (SCOW) is significantly affected by pH, causing dramatic decrease of treatment efficiency when pH deviates from its appropriate range. Fe0 has proved as an effective strategy on mitigating the impact of pH. However, systematic analysis of the influence mechanism is still lacking. To fill this gap, the impact of different initial pH values on anaerobic treatment efficiency of SCOW with Fe0 addition, the change of fermentation type and methanogens, and intra-extracellular electron transfer were explored in this study. The results showed that Fe0 addition enhanced the efficacy of anaerobic treatment of SCOW at adjusted initial pH values, especially at pH 6. Mechanism analysis showed that respiratory chain-related enzymes and electron shuttle secretion and resistance reduction were stimulated by soluble iron ions generated by Fe0 at pH 6, which accelerated intra-extracellular electron transfer of microorganisms, and ultimately alleviated the impact of acidic pH on the system. While at pH 8, Fe0 addition increased the acetogenic bacteria abundance, as well as optimized the fermentation type and improved the F420 coenzyme activity, resulting in the enhancement of treatment efficiency in the anaerobic system and remission of the effect of alkaline pH on the system. At the neutral pH, Fe0 addition had both advantages as stimulating the secretion of respiratory chain and electron transfer-related enzymes at pH 6 and optimizing the fermentation type pH 8, and thus enhanced the treatment efficacy. This study provides important insights and scientific basis for the application of new SCOW treatment technologies.

Efficient hydrogen production in single-chamber microbial electrolysis cell with a fermentable substrate under hyperalkaline conditions

Hydrogen production from food waste is of great significance for energy conversion and pollution control. The aim of this study was to investigate the glucose fermentation from food waste and hydrogen (H2) production in the single-chamber microbial electrolysis cell (MEC) under hyperalkaline conditions. Single-chamber MECs were tested with 1 g/L glucose as substrate under different pH values (i.e., 7.0, 9.5, and 11.2) and applied voltages (i.e., 0.8, 1.2, and 1.6 V). With pH increase from 7.0 to 11.2, H2 production with methanogenesis inhibition was significantly improved in the MEC. At pH of 11.2, the maximum current density reached 180 ± 9 A/m3 with the H2 purity of 93.3 ± 1.2% and average H2 yield of 7.72 ± 0.23 mol H2/ mol glucose under 1.6 V. Acetate from glucose fermentation was the largest electron sink within 12 h. Methanobacterium alcaliphilum dominated the archaeal communities with the relative abundance of > 99.0% in the cathodic biofilms. The microbial communities and mcr A gene copy numbers analyses showed that high pH enhanced the acetate production from glucose fermentation, inhibited syntrophic acetate-oxidizing with hydrogenotrophic methanogenesis in the anodic biofilms, and inhibited hydrogenotrophic methanogenesis in the cathodic biofilms. Our results of hyperalkaline conditions provide a feasible way to harvest H2 efficiently from fermentable substrates in the single-chamber MEC.

Aerobic granular sludge for efficient biotransformation of chalcogen SeIV and TeIV oxyanions: Biological nutrient removal and biogenesis of Se0 and Te0 nanostructures

Simultaneous removal of selenite (Se^IV), tellurite (Te^IV) and nutrients by aerobic granular sludge (AGS) was investigated. A sequencing batch reactor (SBR) was operated with increasing Se^IV and Te^IV (up to 500 µM each) for 205 days to evaluate metalloid oxyanion and nutrient removal. AGS efficiently removed Se^IV and Te^IV by readily converting them to biomass associated forms. The total Se and Te removal efficiencies were higher at 98% and 99%, respectively. Formation of biomass-associated Se⁰ and Te⁰ was confirmed by XRD, Raman spectroscopy and SEM-EDX. Feeding of Se^IV and Te^IV elicited inhibitory action on ammonium removal initially, nonetheless removal performance was recovered during the subsequent cycles. Ammonium, total nitrogen and phosphorus removals were stabilized at 85%, 80% and 75%, respectively, at 500 µM of Se^IV and Te^IV. Sequencing of 16S rRNA gene confirmed enrichment of known Se^IV and Te^IV reducing bacteria in the granules. qPCR and removal kinetics supported ammonia removal via nitritation-denitritation. This work demonstrates functional capabilities of AGS for effectively removing toxic Se^IV and Te^IV oxyanions apart from performing simultaneous COD, nitrogen and phosphorus removal. Efficient biological nutrient removal in the presence of toxic Se^IV and Te^IV concentrations, suggests robustness of AGS and its resilience to toxic contaminants.

Methanogenic performance and microbial community during thermophilic digestion of food waste and sewage sludge in a high-solid anaerobic membrane bioreactor

The methanogenic performance and microbial community of the thermophilic anaerobic mono-digestion and co-digestion of food waste and sewage sludge in a high-solid membrane bioreactor were investigated by a continuous experiment. The methane recovery rate of the system reached 98.0% and 89.0% when the substrate was pure food waste and 25% sewage sludge substitution, respectively. Kinetics characterization showed that hydrolysis was the rate-limiting step in both mono-digestion and co-digestion while methanogenic performance and microbial community were significantly affected by feed condition. The dominant archaea for methane generation shifted from Methanothermobacter thermophilus (72.82%) to Methanosarcina thermophila (96.25%) with sewage sludge gradually added from 0% to 100% in the substrate. The relationships between digestion performance, such as the accumulation of soluble proteins in the reactor, and functional microbial groups were also carefully analyzed. Finally, reasonable metabolic pathways for mono-digestion and co-digestion were summarized.