This study aimed to develop and optimize a novel biochar-based fertilizer composed of rice husk biochar and urea–hydrogen peroxide (UHP), which can simultaneously slowly release nitrogen and immobilize cadmium (Cd). Response surface methodology (RSM) was adopted to optimize the fertilizer formulation with the lowest nitrogen release rate. Under the optimized conditions, the cumulative nitrogen release rate of the biochar-based fertilizer was 17.63%, which was significantly lower than that of ordinary fertilizer. Elementary analysis, scanning electron microscopy (SEM) images, and Fourier transform infrared (FTIR) spectroscopy proved that UHP attached to the porous structures of the biochar. The adsorption test showed that the adsorption of Cd onto biochar-based fertilizer quickly reached equilibrium with an equilibrium adsorbing quantity (Q_e) of 6.3279 mg·g⁻¹ with an initial concentration of 10 mg·L⁻¹. Compared to original biochar, the Cd immobilization ability of biochar-based fertilizer was significantly better. The adsorption of Cd on biochar-based fertilizer is mainly based on a monolayer adsorption behavior. Finally, improved crop growth was demonstrated by pot experiments, which showed a significant increase in the biomass of cabbage. The concept and findings presented in this study may be used as references in developing a novel biochar-based fertilizer for simultaneously enhancing crop yield and reducing environmental risk.

Calcium alginate (CA) beads as a green sorbent were easily fabricated in this study using sodium alginate crosslinking with CaCl₂, and the crosslinking pathway was the exchange between the sodium ion of α-L-guluronic acid and Ca(II). The experimental study was conducted on Cu(II), Cd(II), Ni(II) and Zn(II) as the model heavy metals and the concentration was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The characterization and sorption behavior of the CA beads were analyzed in detail via using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The adsorption experiments demonstrated that the CA beads exhibited a high removal efficiency for the selective adsorption of Cu(II) from the tetra metallic mixture solution and an excellent adsorption capacity of the heavy metals separately. According to the isotherm studies, the maximum uptake of Cu(II) could reach 107.53 mg/g, which was significantly higher than the other three heavy metal ions in the tetra metallic mixture solution. Additionally, after five cycles of adsorption and desorption, the uptake rate of Cu(II) on CA beads was maintained at 92%. According to the properties mentioned above, this material was assumed to be applied to reduce heavy metal pollution or recover valuable metals from waste water.

Biodegradation has been considered as an ideal technique for total petroleum hydrocarbon (TPH) contamination, but its efficiency is limited by its application in the field. Herein, an original TPH-degrading strain, SCYY-5, was isolated from contaminated oil sludge and identified as Acinetobacter sp. by 16S rDNA sequence analysis. The biological function of the isolate was investigated by heavy metal tolerance, carbon, and nitrogen source and degradation tests. To enhance its biodegradation efficiency, the response surface methodology (RSM) based on a function model was adopted to investigate and optimize the strategy of microbial and environmental variables for TPH removal. Furthermore, the performance of the system increased to 79.94% with the further addition of extra nutrients, suggesting that the RSM and added nutrients increased the activity of bacteria to meet the needs of the co-metabolism matrix during growth or degradation. These results verified that it is feasible to adopt the optimal strategy of combining bioremediation with RSM to improve the biodegradation efficiency, for contaminated oil sludge.