Magnetite particles were applied to excess sludge anaerobic digestion. The methane production and sludge reduction were related to magnetite particle dosage, and the Methanosaeta and Methanoregula involved in the electron transfer were enriched.

Dewatered municipal sludge was used as raw material to prepare activated carbon (SAC), and the SAC was modified by walnut shell and nano-titanium dioxide (MSAC). The results showed that the MSAC had a higher specific surface area (SBET) (279.147 m2/g) and total pore volume (VT) (0.324 cm3/g) than the SAC. Simultaneously, the functional groups such as C-O, C = O, and Ti-O-Ti on the surface of MSAC were enhanced due to modification. These physicochemical properties provided prerequisites for the diffusion and degradation of pollutants in MSAC. Furthermore, the MSAC was applied to adsorb amoxicillin (AMX) from aqueous solution, in batch experiments, the maximum removal rate (88.19%) was observed at an initial AMX concentration of 30 mg/L, MSAC dosage of 5.0 g/L, pH of 8, contact time of 180 min, and temperature of 25 °C. In addition, the adsorption process was well described by the Freundlich isotherm model and pseudo-second-order kinetic model, indicating that the adsorption of AMX onto MSAC was dominated by multilayer chemisorption. Also, the adsorption thermodynamics suggested that the adsorption process of AMX onto MSAC was endothermic, feasible and spontaneous.

Batch tests were carried out to study the effect of simultaneous addition of ethylenediaminetetraacetic acid and Ni²⁺ (EDTA-Ni) on anaerobic digestion (AD) performances of kitchen wastes (KWs). The results indicated that the cumulative biogas yield and methane content were enhanced to 563.82 mL/gVS and 63.7% by adding EDTA-Ni, respectively, which were almost 1.15 and 1.07-fold of that in the R2 with Ni²⁺ addition alone. At the same time, an obvious decrease of propionic acid was observed after EDTA-Ni addition. The speciation analysis of Ni showed that the percentages of water-soluble and exchangeable Ni were increased to 38.8% and 36.3% due to EDTA-Ni addition, respectively. Also, the high-throughput sequencing analysis revealed that the EDTA-Ni promoted the growth and metabolism of Methanosarcina and Methanobacterium, which might be the major reason for propionic acid degradation and methane production.

In the present work, porous carbon was made from sewage sludge and hybrid liriodendron leaves, and modified with iron ions (Fe@LS-BC) carried out on Cr(VI) in aqueous solution from a single-component system and in competitive biosorption with methyl orange (MO) from a binary-component system. The iron ion-modified porous carbon (Fe@LS-BC) showed higher efficiency in the removal of Cr(VI) compared to porous carbon prepared by the co-pyrolysis of sludge and hybrid liriodendron leaves. The incorporation of the Fe element improved the ability of the material to redox Cr(VI), while imparting magnetic characteristics to the porous carbon and improving the reusability of the porous carbon. On the other hand, Fe@LS-BC exhibited a better pore volume, facilitating the contact of the material with Cr(VI) ions. The highest adsorption capacity was 0.33 mmol g⁻¹, and the adsorption experimental results for the single-component and binary-component systems of Cr(VI) matched well with the Langmuir–Freundlich models. When the concentration of MO was 0.2 and 0.8 mmol L⁻¹, respectively, the highest adsorption capacity of Cr(VI) was 0.35 and 0.46 mmol g⁻¹ in the binary system. The positively charged N–CH₃ ⁺ on the MO molecule promoted the electrostatic adsorption between HCrO₄ ⁻, CrO₄ ²⁻, and Fe@LS-BC, and increased the adsorption potential of Cr(VI).