Asphalt overlays have been widely employed in airport runway maintenance in recent years due to their ability to minimize traffic disruption. However, they continue to face the challenge of reflective cracks originating from the expansion joints of the underlying cement concrete runway. To better understand the cracking behavior of asphalt overlays under the combined temperature variations and aircraft loads, this study developed a finite element (FE) model. with the model incorporate two types of landing methods and typical temperature conditions. Simulation results indicate that critical loading positions are located at the edges of original cement concrete slabs, where shear stress is identified as the primary driver of crack evolution, with the peak stress coinciding with the arrival of aircraft load. Furthermore, findings suggest that the use of asphalt overlays significantly reduces the stress intensity in crack-prone areas, particularly under rough landing conditions. Reflective cracks predominantly manifest as type II shear cracks, While aircraft loading and initial crack length exert a relatively limited impact on crack propagation compared to temperature effects, the horizontal location of the initial crack substantially influences both the direction and speed of crack propagation. To mitigate crack propagation, increasing the linear shrinkage coefficient of the overlay material and the thickness of the asphalt overlay are effective strategies for enhancing the cracking resistance of airport runways with asphalt overlays. The methodologies and findings of this study provide valuable insights for engineering practices involving similar structural configurations and materials.

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Anaerobic fermentation for volatile fatty acids (VFAs) production is a promising technology for sewage sludge treatment and reutilization. The fundamental aspects and actual developments of VFA production from sewage sludge by anaerobic fermentation are critically reviewed. Based on fermentation mechanisms and microbiological analysis, controlling strategies for VFA production from sewage sludge were concluded into three aspects, namely methanogenesis inhibition, hydrolysis acceleration, and product optimization. At present, the preliminary process for VFA production has been determined, but research in this field is still full of challenges, as, for instance, the concentration and purity of VFAs are too low for further commercial applications. Though current attempts of pretreatment, cofermentation, high-solid fermentation, and liquid fermentation have shown great potentials in overcoming those bottlenecks, including low conversion rate of sludge organics, inappropriate compositions of substrates, low concentration of VFAs, and high cost of operation, there are still some possible difficulties for full-scale applications in both economic benefits and technical feasibility. Therefore, the application of VFAs from sewage sludge on externally added carbon for nitrogen and phosphorus removals in wastewater plants seems more practical recently. Finally, based on the difficult situations, most important perspectives need to be seriously considered before extensively preceding large-scale application of this technology.@en

A novel strategy of liquid fermentation using anaerobic dynamic membrane reactor (AnDMBR) was proposed to enhance volatile fatty acids (VFAs) production from sewage sludge. Results indicated that liquid sludge fermentation in AnDMBR had the potential in commercial VFAs production. VFAs productivity and concentration as well as substrate conversion rate could reach as high as 7.8 kg VFA−COD/m³ d, 60 g/L and 0.38 kg VFA−COD/kg VS, respectively. Moreover, dynamic membrane was stably operated for approximately 70 days. During the operational period, membrane flux was increased from 6.25 to 25 L/m² d and only once online membrane cleaning was implemented. Results of microbial analyses showed bacterial richness and evenness in AnDMBR were increased by membrane separation and organic loading rate (OLR) increase, but reduced by excessive OLR, which should led the variations in the performances of AnDMBR. Furthermore, the necessity of liquid sludge fermentation for VFAs production was further confirmed by economic assessment and the bioavailability analysis of the residual solids in pretreated sludge. The residual solid was proved to be not conducive to enhance VFAs yield. Conversely, the energy consumption for VFAs production could be reduced from over 100 to below 20 kwh/kg VFAs by avoiding the “useless” residual solids entering into fermenters.

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