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The conventional disposal practices of rice stalks (RS) such as burning in situ or incorporating in the soil, contribute to climate change and endanger the long-term soil fertility. This study investigated the production of activated carbon (AC) using rice stalks as a sustainable recycling solution. The rice stalks (RS) were carbonized in a tube furnace at 500 °C and heating rate of 10 °C/min for 2 h. The rice stalks-based activated carbon (RSA) properties were analyzed based on Brunauer-Emmett-Teller (BET) technique to measure the surface area and transform infrared spectroscopy (FTIR) measurements to identify the surface functional groups. RSA was also characterized using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-Ray spectroscopy (SEM-EDX). Batch experiments were conducted to examine the efficiency of RSA in removing phenol, with varying operation parameters comprising pH (2–9), initial phenol concentration (IPC) (50–200 mg/L), reaction time (5–300 min), and RSA dose (0.2–2 g/100 ml). The surface area (SBET) of RSA was 488.26 m2/g with a total micropore volume of 0.165 cm³/g, and a pore diameter of 6.99 nm. The highest phenol uptake of RSA was 80.37 mg/g. The kinetics of phenol adsorption was found to be accurately described by the pseudo-second-order reaction, while the Langmuir model provided a better match for the isotherm process than the Freundlich model. The thermodynamic study indicated that the adsorption process was exothermic and spontaneous. These results confirm that the adsorption process occurred due to physical forces, rather than involving chemical bonding, providing further insight into the underlying mechanisms.

This study investigated the potential use of sewage sludge-based activated carbon in the removal of copper (Cu) and cadmium (Cd) ions from aqueous solutions. The activated carbon (AC) was prepared by chemical activation using potassium hydroxide KOH and heating in a tube furnace at 600 °C for 2 h. The produced activated carbon was further subject to a sulfurization process to enhance its removal efficiency. The study used Box-Behnken Design (BBD) in response surface methodology (RSM) to optimize several parameters, including initial metal concentration, activated carbon dose, pH, and contact time. Results showed that the sulfurization process introduced sulfur functional groups (SO) to the surface of the activated carbon and decreased its specific area from 190 to 173 m2/g. The quadratic model was suggested as the best model to describe the effect of the adsorption parameters on the removal percentage with high R2 values (≥0.9) and p-value less than 0.05. Second-order polynomial equations, analysis of variance (ANOVA), and three-dimensional surface plots were developed to assess the interaction between the parameters and the optimal conditions to remove copper and cadmium ions. The optimum removal parameters for copper ions were 300 min, 100 ppm initial concentration, 20 g/L activated carbon dose, and pH 6, with a removal efficiency of 83.9%. Cadmium removal of 87.5% was achieved at 11 ppm, 300 minutes contact time, pH 6, and 2.5 g/L adsorbent dose. The activated carbon capacity in removing copper and cadmium was 16 mg/g and 17.6 mg/g respectively. The sulfurization process increased the removal percentage for copper and cadmium ions by 14.5 and 18.7% respectively. Advanced analytical techniques such as FITR, SEM-EDX, BET surface area, and elemental analysis were used to characterize the materials.

The bond strength between the steel fiber and the ultra-high performance concrete (UHPC) matrix plays a significant role in improving the behavior of plain UHPC. This paper compiles the existing experimental research database on the pullout bond performance of steel fibers embedded in UHPC. The variations of key parameters in the database are the steel fiber type and geometry, fiber volume fractions, and fiber embedded length. The effects of these parameters are analyzed and discussed in detail. Based on the analysis of the results, it was found that the deformed steel fibers, i.e., the hooked-end, half-hooked-end, and twisted steel fibers clearly provided higher average bond strengths than that straight fibers. The average pullout bond strength was obtained by increasing of fiber volume fraction in the UHPC matrix up to 2% (11.21MPa) with an increment of 20.4%. When the steel fiber volume fractions increase beyond 2%, the average bond strength decreases. Additionally, it was also found that using smaller embedded lengths in deformed steel fibers could result in the improvement of bond strength. This could be due to the fact that the bond is controlled by the mechanical anchorage of the end-hook rather than the physio-chemical bond in the straight portion. Conversely, increasing the embedded length of steel fiber could greatly contribute to the enhancement of pullout resistance resulting in increased bond strength between the UHPC matrix and steel fibers.

Among the water-polluting substances, heavy metals stand out due to their carcinogenic and toxic effects on the creatures and environment. This study aimed to scrutinize the effectiveness of sewage sludge-based activated carbon in the removal of copper and cadmium from aqueous solutions in column study. Detection of breakthrough curves and related parameters was conducted by varying bed depths (3, 6, and 9 cm). The solution with an initial metal concentration (IMC) of 100 ppm was pumped to the column at a flow rate of 2 mL/min. In the process of copper removal, the breakthrough points for depths 3 cm, 6 cm, and 9 cm were achieved at 10 min, 15 min, and 60 min, respectively, whereas breakthrough points of similar depths in cadmium removal process were achieved at 5 min, 10 min, and 30 min, respectively. Adsorption kinetics were analyzed using the Adams–Bohart, Yoon–Nelson, and Thomas kinetics models. The Adams–Bohart model described only the initial part of breakthrough curves. The Thomas model represented the adsorption process with coefficients of determination (R2) ranging between 0.90–0.95 for cadmium removal and 0.89–0.96 for copper removal, while the coefficients of determination of Yoon–Nelson ranged between 0.89–0.94 for cadmium and 0.95–0.97 for copper. Yoon–Nelson was fitted well with copper removal data, while removal of cadmium data was best described by the Thomas model. This study demonstrated that using sewage sludge-based activated carbon to remove heavy metals is an alternative, more cost-effective option to reach the objectives of sustainable development.