Sponge iron enriches autotrophic/aerobic denitrifying bacteria to enhance denitrification in sequencing batch reactor.

Sponge iron (SFe) coupled with a sludge system has great potential for improving biological denitrification; however, the underlying mechanism is not yet fully understood. In this study, the denitrification performance and microbial characteristics of ordinary sludge and SFe-sludge systems were investigated. Overall, the SFe-sludge reactor had faster ammonium degradation rate (94.0 %) and less nitrate accumulation (1.5-53.3 times lower) than ordinary reactor during the complete operation cycle of sequencing batch reactors. The addition of SFe increased the activities of nitrate and nitrite reductases. The total relative abundance of autotrophic denitrifying bacteria (Acidovorax, Arenimonas, etc.) in the SFe-sludge system after 38 days of operation was found to be 10.6 % higher than that in the ordinary sludge reactor. The aerobic denitrifying bacteria (Dokdonella, Phaeodactylibacter, etc.) was 5.3 % higher than ordinary sludge. The SFe-sludge system improved denitrification by enriching autotrophic/aerobic denitrifying bacteria in low carbon-to-nitrogen ratio wastewater treatment.

Bacillus licheniformis inoculation promoted humification process for kitchen waste composting: Organic components transformation and bacterial metabolic mechanism.

Kitchen waste (KW) composting always has trouble with slow humification process and low humification degree. The objective of this study was to develop potentially efficient solutions to improve the humification of KW composting, accelerate the humus synthesis and produce HS with a high polymerization degree. The impact of Bacillus licheniformis inoculation on the transformation of organic components, humus synthesis, and bacterial metabolic pathways in kitchen waste composting, was investigated. Results revealed that microbial inoculation promoted the degradation of organic constituents, especially readily degradable carbohydrates during the heating phase and lignocellulose fractions during the cooling phase. Inoculation facilitated the production and conversion of polyphenol, reducing sugar, and amino acids, leading to an increase of 20% in the content of humic acid compared to the control. High-throughput sequencing and network analysis indicated inoculation enriched the presence of Bacillus, Lactobacillus, and Streptomyces during the heating phase, while suppressing the abundance of Pseudomonas and Oceanobacillus, enhancing positive microbial interactions. PICRUSt2 analysis suggested inoculation enhanced the metabolism of carbohydrates and amino acids, promoting the polyphenol humification pathway and facilitating the formation of humus. These findings provide insights for optimizing the humification process of kitchen waste composting by microbial inoculation.

Effect of biochar derived from biogas residue on methane production during dry anaerobic fermentation of kitchen waste.

Kitchen wastes (KW) dramatically increasing with population and economy enhancing, and dry anaerobic fermentation was used to treat it. However, the large amount of biogas residue severely restricted the application of dry anaerobic fermentation, because the high total solid might lead to the system failure. Therefore, it is urgent to find appropriate way to improve the efficiency of dry anaerobic fermentation and reduce the great amount of biogas residue. In this study, a tentative experiment was conducted to investigate the effect of biochar prepared from biogas residue on the performance of dry anaerobic fermentation system. The results showed that almost half of the biogas residue was reduced and converted into biochar. At the presence of biochar, methane yield was 308.6 mL/gVS, which was 10.5% higher than that of control. Compared to the system without biochar, the highest volatile fatty acid (VFA) concentration was 19.3% higher and the percentage of acetate and valerate was 25.3％ and 12.8％, while it was 16.3% and 22.0% in the control, suggesting that biochar accelerated the degradation of VFA. Bacteria community diversity increased, Fastidiosipila and Proteiniphilum enriched at the presence of biochar, which might accelerate the hydrolysis and acidification of KW. Hydrogenotrophic methanogens was dominated and syntrophic acetate oxidation was the primary pathway to produce methane. This study developed a new recycle route for improving the efficiency of dry anaerobic fermentation while reducing the large amount of biogas residue generated from dry anaerobic fermentation.

A novel preparation process of straw-based iron material for enhanced persulfate activation of reactive black 5 degradation.

In this study, a new straw-iron composite material (ST@Fe) was synthesized through impregnation and freeze-drying process for persulfate (PS) activation to degrade reactive black 5 (RB5). Scanning electron microscope, Brunauer-Emmett-Teller, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy confirmed that straw owns huge pore structure and varieties of organic functional groups, including hydroxyl carboxyl groups, which could effectively adsorb and complex iron ions. The interaction between the active iron particles in ST@Fe and straw generated Fe2+ for PS activation, effectively degrading over 94.80% of RB5 at an initial concentration of 20 ppm in 100 min with a specific degradation capacity of 18.97 min-1 per unit of iron ions. ST@Fe/PS system demonstrated high tolerance in a wide initial pH range, which could gradually attack the RB5 molecular structure and significantly reduce the mineralization of water. Quenching experiments and electron paramagnetic resonance demonstrated the efficient generation of ROS including sulfate radicals, hydroxyl radicals, and singlet oxygen, and confirmed the dominance of sulfate radicals in the degradation process. The continuous degradation capacity and reusability of ST@Fe were also evaluated, which proved that the contaminant could be effectively degraded even after multiple cycles in the simulated textile wastewater, indicating its potential for use in practical remediation. This work provided a new method for the preparation of modified functional materials for the degradation of organic pollutants in textile wastewater and posed a novel strategy for the utilization of waste biomass.

Characteristics of Cadmium Sorption by Heat-Activated Red Mud in Aqueous Solution.

Red mud as a waste material is produced in large quantities by the aluminum industry. Heat activation has been used to enhance sorption capacity of red mud for its beneficial reuse as an effective sorbent. In this study, heat-activated red mud (HARM) was investigated for its Cd(II) sorption capacity under various process conditions (Cd concentration, pH and contact time) using response surface methodology (RSM). Analysis with RSM identified pH as the most important process parameter. The positive correlation between higher pH and greater Cd(II) sorption was likely due to: (i) decreased proton competition with Cd(II) for sorption sites at higher pH; (ii) enhanced sorption via ion exchange by monovalent Cd species from hydrolysis at higher pH; and (iii) improved thermodynamics of sorption at higher pH as protons are being released as products. Further analysis indicated the sorption process was thermodynamically favorable with a negative change in Gibbs free energy. Additionally, the sorption process exhibited a positive change in enthalpy, indicative of endothermic nature of sorption; this is consistent with sorption increase at higher temperature. These findings provide needed insight into the mechanisms underlying Cd(II) sorption by HARM for more effective applications of heat-activated red mud as sorbents for Cd(II) removal.

Effect of precursors combined with bacteria communities on the formation of humic substances during different materials composting.

The aim of this work was to put forward a method to improve HS amount by studying the formation regularity of HS. Five precursors have been detected and few researches combined them with bacteria to study HS formation. During composting, the polyphenols, carboxyl and amino acids concentration decreased by 75.8%, 63.2% and 68.3% on average, respectively. However, the polysaccharides, reducing sugars and HS concentration increased by 61.2%, 47.1% and 37.33% on average. Relationships between precursors and HS concentration showed that the HS formation were significantly affected (p<0.05). The key bacteria community and physical-chemical parameters which affected HS formation have also been identified by redundancy analysis. Twelve key bacteria communities have been selected, which were significantly affected by physical-chemical parameters (p<0.05). Accordingly, we proposed an adjusting method to promote HS amount during composting based on the relationship between the key bacteria communities and the precursors as well as physical-chemical parameters.