No abstract

In this study, FeCl 3 was added to improve methane production from aluminum waste-activated sludge (Al-WAS) during anaerobic digestion. The results showed that the addition of 160 mg/L FeCl 3 resulted in the maximum methane yield of 169 mL/g volatile solids (VS), exceeding the methane yield of the control group by 31.33%. The fractal dimension (D f ) decreased after adding FeCl 3 , suggesting an alteration of the sludge's physical structure. The Lewis acid−base interaction free energy (ΔG SL AB ) was significantly affected by the FeCl 3 addition, and the maximum absolute value was obtained at the dosage of 160 mg/L (10.7 mJ/m 2 ). ΔG SL AB contributed the most to the interfacial free energy, suggesting the dominant force between the digested sludge and water was an AB interaction. Further, the value of ΔG SL AB changed from positive to negative after the FeCl 3 addition, suggesting the interfacial interaction of the digested sludge changed from hydrophilic to hydrophobic. The hydrophobic surface of the digested sludge improved the contact with enzymes via hydrophobic attraction, thus improving sludge biodegradability. The sludge hydrophobicity enhanced floc aggregation through hydrophobic interactions, improving the dewatering ability. This work provides a new method for the large-scale utilization of Al-WAS via anaerobic digestion.

The iron-containing chemically enhanced primary sedimentation (Fe-CEPS) sludge, as an alternative low-cost iron source, can be used to promote methane production of aluminum-waste activated sludge (Al-WAS) during anaerobic digestion (AD). Generally, the aging time would induce changes in iron species and compounds in the Fe-CEPS sludge and subsequently affect the methane production process. Here, the effects of Fe-CEPS sludge aging on methane production of Al-WAS were investigated. After a 10-day aging treatment, the iron compounds showed a high crystallinity, and the structure of the CEPS sludge became compacted. The aging treatments always increased the methane yield, with the maximum value (143.3 mL/g VS) occurring after 3 days of aging. Following an addition of short-term (0–3 days) aged Fe-CEPS sludge, the physical structure of Al-WAS obviously collapsed during AD. Meanwhile, the surface of the digested sludge became hydrophobic, which benefited the contact between enzymes and sludge flocs, thereby enhancing the biodegradability of the sludge. The results suggest that the addition of short-term aged Fe-CEPS sludge is an effective approach for Al-WAS digestion, which reflects a “treat the wastes with wastes” concept.

Efforts are being dedicated to refining agricultural management practices and policies regarding ecosystem restoration. Agricultural management practices, such as reduced soil tillage, rational fertilization, crop rotation, and crop residue or livestock excreta management, enhance the sustainability and resilience of agroecosystems in Mollisol regions.This special section of the Soil Science Society of America Journal includes eight peer-reviewed papers, with six field studies and two laboratory incubation experiments. Those papers address the biogeographic distribution of N-related microbes, and the current research on the effect of agricultural management practices on soil hydraulic properties, nutrient cycling, and biotic and abiotic mechanisms in Mollisol-based agroecosystems. Collectively, these articles provide a systematic understanding of the ecosystem characteristics and resilience, and C and N cycling patterns in Mollisol agroecosystems. They also identify controlling factors that will shed light on the optimization of sustainable management and utilization of Mollisols.A brief summary of the studies in this special section is provided below:• Denitrifiers control the stepwise reduction processes of NO 3 − to N 2 in global N cycles. Among these, the reduction

No abstract