Characteristics of digested sludge-derived biochar for promoting methane production during anaerobic digestion of waste activated sludge.

This study investigated a novel method for enhancing methane production during anaerobic digestion of waste activated sludge with digested sludge-derived biochar (DSBC). Using response surface methodology, the following process conditions for DSBC synthesis were optimized: heating rate = 13.23 °C/min, pyrolysis temperature = 516 °C, and heating time = 192 min. DSBC significantly enhanced the methane production by 48 % and improved key coenzyme activity that accelerated the bioconversion of organic matter while promoting the decomposition and transformation of volatile fatty acids. Consequently, the lag period of methane production was shortened to 4.89 days, while the average proportion of methane greatly increased to 73.22%. Thus, DSBC could facilitate efficient methanogenesis in the anaerobic system by promoting electron transfer between syntrophic partners through the charge-discharge cycle of surface oxygen-containing functional groups. The study provides a reference for the resource utilization of anaerobic sludge residues and efficient anaerobic methanogenesis from sludge.

Application of Iron Tailings-Based Composite Supplementary Cementitious Materials (SCMs) in Green Concrete.

How to treat the iron tailings of mining solid waste with high value is an urgent problem on a global scale. In recent years, the application of iron tailings in the building materials industry has attracted the attention of many scholars. The conversion of iron tailings into green building materials helps achieve carbon neutrality and high-value utilization of solid waste, and promotes sustainable development. Although iron tailings have been extensively studied as supplementary cementitious materials, the performance of concrete is not ideal due to its low activity. In this study, the hybrid supplementary cementitious materials system was prepared by iron tailings, phosphorus slag, and steel slag, and the effects of supplementary cementitious materials type, iron tailings content, iron tailings grinding time, and supplementary cementitious materials content on concrete performance were studied. The compressive properties, iron tailings properties, pore structure, interfacial transition zone, and element distribution of hydration products of concrete were tested by compressive strength tests, X-ray Diffractometer (XRD), X-ray Photoelectron Spectroscopy (XPS), Mercury Intrusion Porosimetry (MIP), Backscattering Electron Tests (BSE), and Energy Dispersive Spectrometer (EDS). The results show that further grinding improves the iron tailings activity. There is a synergistic mechanism between steel slag and phosphorus slag in the composite supplementary cementitious materials, which overcomes the low activity defect of iron tailings and produces concrete with a compressive strength exceeding 40 MPa. The composite supplementary cementitious materials can optimize the interfacial transition zone of the concrete interface and reduce the calcium-silicon ratio of the hydration products. However, it will deteriorate the pore structure of the concrete matrix, cause part of the concrete matrix to be damaged and lead to a loss of compressive strength, and the loss is acceptable. This work broadens the methods of comprehensive utilization of iron tailings and also provides a reference for a more detailed understanding of the properties of iron tailings-based concrete.