Search

The activated sludge process plays a crucial role in modern wastewater treatment plants. During the treatment of daily sewage, a large amount of residual sludge is generated, which, if improperly managed, can pose burdens on the environment and human health. Additionally, the highly hydrated colloidal structure of biopolymers limits the rate and degree of dewatering, making mechanical dewatering challenging. This study investigates the impact and mechanism of microwave irradiation (MW) in conjunction with peracetic acid (PAA) on the dewatering efficiency of sludge. Sludge dewatering effectiveness was assessed through capillary suction time (CST) and specific resistance to filtration (SRF). Examination of the impact of MW-PAA treatment on sludge dewatering performance involved assessing the levels of extracellular polymeric substances (EPS), employing three-dimensional excitation-emission matrix (3D-EEM), Fourier transform–infrared spectroscopy (FT-IR), and scanning electron microscopy. Findings reveal that optimal dewatering performance, with respective reductions of 91.22% for SRF and 84.22% for CST, was attained under the following conditions: microwave power of 600 W, reaction time of 120 s, and PAA dosage of 0.25 g/g MLSS. Additionally, alterations in both sludge EPS composition and floc morphology pre- and post-MW-PAA treatment underwent examination. The findings demonstrate that microwaves additionally boost the breakdown of PAA into •OH radicals, suggesting a synergistic effect upon combining MW-PAA treatment. These pertinent research findings offer insights into employing MW-PAA technology for residual sludge treatment. [ABSTRACT FROM AUTHOR]

Highlights: Fundamental principles for designing high-performance thermally conductive graphene-based polymer composites are reviewed in detail. The reasoning behind using the preconstructed graphene 3D networks for fabricating thermally conductive composites and recent progress are discussed in-depth. Insight into the existing bottlenecks and opportunities in developing preconstructed 3D networks of graphene and their thermally conductive composites is also presented.Electronic devices generate heat during operation and require efficient thermal management to extend the lifetime and prevent performance degradation. Featured by its exceptional thermal conductivity, graphene is an ideal functional filler for fabricating thermally conductive polymer composites to provide efficient thermal management. Extensive studies have been focusing on constructing graphene networks in polymer composites to achieve high thermal conductivities. Compared with conventional composite fabrications by directly mixing graphene with polymers, preconstruction of three-dimensional graphene networks followed by backfilling polymers represents a promising way to produce composites with higher performances, enabling high manufacturing flexibility and controllability. In this review, we first summarize the factors that affect thermal conductivity of graphene composites and strategies for fabricating highly thermally conductive graphene/polymer composites. Subsequently, we give the reasoning behind using preconstructed three-dimensional graphene networks for fabricating thermally conductive polymer composites and highlight their potential applications. Finally, our insight into the existing bottlenecks and opportunities is provided for developing preconstructed porous architectures of graphene and their thermally conductive composites. [ABSTRACT FROM AUTHOR]

To ensure the safe and effective application of deep geotechnical engineering, it is necessary to establish a suitable constitutive model of the rocks in thermal environment, including geothermal energy mining, and deep geological treatment of nuclear waste and tunnel fire. A strain-softening damage model of the rocks with defect growth is established based on damage evolution. According to the change in the tangent modulus from the compression phase to the elastic stage, we established a constitutive model reflecting the nonlinearity characteristics of the compression phase. According to the change in the energy conversion, the energy consumption coefficient is introduced to describe the deformation characteristics of the rocks when the residual stress is reached. The specific physical meaning and the calculation method of the energy consumption coefficient are given to correct the shortcomings of the evolution of the damage variable. We then analyzed the relationship between parameters in the constitutive model of the rocks at high temperature and normal temperature. Based on the constitutive model of the rocks at normal temperature, we established a constitutive model reflecting the influence of high temperature. Finally, the established model fit the stress-strain curves of several kinds of the rocks at different temperatures and generated desired results. The established model can be used to describe the stress-strain curve characteristics of the rocks at different temperatures. [ABSTRACT FROM AUTHOR]

The mechanical properties of rocks are greatly affected by water action. Many underground structures can be failed by changes in the water environment. To reveal the mechanical properties of the rocks after saturation, a series of saturated sandstones are prepared to study the changes in the mechanical properties during post-peak cyclic loading and unloading. The results show that the strength characteristics of the sandstones decrease after saturation. There is an exponential function between the peak strength and the damage degree and between the crack damage stress and the damage degree. A new method for calculating the elastic modulus is proposed. The results of both calculation methods show that the elastic modulus of the saturated sandstones decreases. The relationship between the elastic modulus obtained by the two methods and the damage degree is quite different. After saturation, the dilatancy of the sandstones increases in the post-peak stage. The volumetric strain, the plastic shear strain, and the peak dilatancy angle all increase with increasing damage degree. Because of the filling by water molecules, the P-wave velocity increases. There is an exponential function relationship between the P-wave velocity and the damage degree. Because of the softening after saturation, more macroscopic failure cracks and fracture surfaces will be formed in the saturated sandstones. The research results of this paper can provide some guidance for excavation and engineering design in water-rich rock. [ABSTRACT FROM AUTHOR]