Fe-Mn binary oxides improve the methanogenic performance and reduce the environmental health risks associated with antibiotic resistance genes during anaerobic digestion

Unveiling molecular DOM reactomics and transformation coupled with multifunctional nanocomposites under anaerobic conditions: Tracking potential metabolomics and pathways

Anaerobic digestion (AD) offers great potential for pollutant removal and bioenergy recovery. However, it faces challenges when using livestock manure (LSM) as a feedstock given its high content of refractory materials (e.g., lignocellulose, long-chain carbohydrates, lipids, and crude protein). This would significantly inhibit AD-microbial activities, reduce organic transformation efficiency and limit gas production. To overcome this, multifunctional metal-doped hydrochars (HCs) were introduced here as AD supplements/accelerators, given that LSM degradation under AD results in complex dissolved organic matter (DOM). To assess this, the current study investigates the molecular interactions/transformations within DOM during LSM-AD coupled with metal-doped HCs, via batch-mode experiments. Expansive data mining techniques were employed to analyze DOM using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Substantial increments in peptide-like along with decrements in highly unsaturated-like molecules were observed in HC@MnCl2 containing-system. This indicates an increased capability for substrate hydrolysis and potential utilization of soluble microbial products (SMPs) (i.e., highly unsaturated-like molecules), leading to enhanced methane recovery (223.23 mL/g-VSadded, 1.77 times more than the control). However, accumulation of DOM-highly unsaturated molecules (i.e., a lack of SMPs' degradation) accompanied with low methane production (39.68 mL/g-VSadded) was noticed for HC@NiFe2O4. DOM reactivity during LSM-AD was validated via paired mass difference molecular network, indicating predominance of CHO and N-containing groups' transformations for HC@MnCl2 and HC@NiFe2O4, respectively. Potential metabolites and abundant pathways were verified via KEGG database. This study improves our understanding of LSM-AD-DOM complex transformation matrix, the fate of bioavailable/recalcitrant compounds, and identification of potential DOM regulators from thousands of molecules.

Comparison of the short- and long-term effects of zinc ions on the anaerobic mesophilic co-digestion of food waste and waste activated sludge: Digester performance, antibiotic resistance gene reduction and the microbial community

Heavy metals contained in waste activated sludge (WAS), especially zinc ions, have an inhibitory effect on the anaerobic digestion. However, the effects of zinc ions on digester performance, antibiotic resistance genes (ARGs) reduction, and the microbial community involved in the anaerobic mesophilic co-digestion (AcoD) of WAS and food waste (FW) have not been fully characterized. Therefore, batch trials and continuous stirred tank reactors were used under different zinc-ion concentrations. Findings showed that the AcoD system can tolerate a maximum zinc ion of 540 mg/L in a short-term batch and 470 mg/L in a long-term AcoD system, promoting methane production of approximately 1.0-17.0 %. Metagenomic analysis revealed that syntrophic H2 transfer occurred between Syntrophomonas and Methanoculleus and the aceticlastic and hydrogenotrophic methanogenic pathways were both enhanced by 1.18- and 1.16 times, respectively. Moreover, the relative abundance of Methanosarcina increased from 58.4 % to 72.5 % at 470 mg/L to adapt to the high zinc ion concentration during long-term continuous operation. These results revealed that AcoD with a low zinc ion concentration can effectively increase the removal percentage of ARGs. The results provide guidance for biogas recovery and use of mesophilic AcoD with FW and WAS containing high zinc ion concentrations without pretreatment process.

Seasonal dynamics of bacterial composition and functions in biological treatment of coking wastewater

Seasonal dynamics of bacterial composition and functions were demonstrated for the biological fluidized-bed bioreactors combined in the anoxic/aerobic1/aerobic2 (AOO) coking wastewater (CWW) treatment sequences. The bacterial composition and functions in the CWW activated sludge samples were revealed by 16S rRNA genes amplicon sequencing. Thiobacillus, Cloacibacterium, Alkaliphilus and Pseudomonas were determined as core genera with seasonal changes. Mutable microbial community composition fluctuated in different seasons in same bioreactor. Distributions of predicted KEGG pathways along four seasons consistently demonstrated enrichment in biodegradation of carbon- and nitrogen-containing compounds. The major contaminants were removed from CWW by biochemical pathway of xenobiotics biodegradation and metabolism. This Level 2 pathway mainly owned the Level 3 pathways of benzoate degradation, drug metabolism-other enzymes, drug metabolism-cytochrome P450, metabolism of xenobiotics by cytochrome P450, and aminobenzoate degradation. The RDA results showed that dissolved oxygen with seasonal fluctuation was the main parameter shaping the microbial community. The observed dynamics within the microbial community composition, coupled with the maintained stability of CWW treatment efficiencies and a consistent profile of microbial functional pathways, underscore the presence of functional redundancy in the AOO bioreactors. The study underscored stable and effective operational performances of bioreactors in the AOO sequences, contributing the knowledge of microbiological basics to the advancement of CWW biological treatment. KEY POINTS: • Seasonal fluctuations of bacterial composition described for the AOO system. • Seasonal distributions of metabolic functions focused on carbon and nitrogen removal. • Functional redundancy was revealed in the AOO microbial community.