This work developed an environmentally-friendly soil remediation method based on BC and g-C₃N₄, and demonstrated the technical feasibility of remediating petroleum-contaminated soil with biochar/graphite carbon nitride (BC/g-C₃N₄). The synthesis of BC/g-C₃N₄ composites was used for the removal of TPH in soil via adsorption and photocatalysis. BC, g-C₃N₄, and BC/g-C₃N₄ have been characterized by scanning electron microscopy (SEM), Brunauer–Emmett–Teller surface area analyzer (BET), FT-IR, and X-ray diffraction (XRD). BC/g-C₃N₄ facilitates the degradation due to reducing recombination and better electron-hole pair separation. BC, g-C₃N₄, and BC/g-C₃N₄ were tested for their adsorption and photocatalytic degradation capacities. Excellent and promising results are brought out by an apparent synergism between adsorption and photocatalysis. The optimum doping ratio of 1:3 between BC and g-C₃N₄ was determined by single-factor experiments. The removal rate of total petroleum hydrocarbons (TPH) by BC/g-C₃N₄ reached 54.5% by adding BC/g-C₃N₄ at a dosing rate of 0.08 g/g in a neutral soil with 10% moisture content, which was 2.12 and 1.95 times of BC and g-C₃N₄, respectively. The removal process of TPH by BC/g-C₃N₄ conformed to the pseudo-second-order kinetic model. In addition, the removal rates of different petroleum components in soil were analyzed in terms of gas chromatography–mass spectrometry (GC-MS), and the removal rates of nC₁₃-nC₃₅ were above 90% with the contaminated soil treated by BC/g-C₃N₄. The radical scavenger experiments indicated that superoxide radical played the major role in the photocatalytic degradation of TPH. This work definitely demonstrates that the BC/g-C₃N₄ composites have great potential for application in the remediation of organic pollutant contaminated soil.

Oily sludge (OS) contains a large number of hazardous materials, and froth flotation can achieve oil recovery and non-hazardous disposal of OS simultaneously. The influence of flotation parameters on OS treatment and the flotation mechanism were studied. OS samples were taken from Shengli Oilfield in May 2017 (OSS) and May 2020 (OST), respectively. Results showed that Na₂SiO₃ was the suitable flotation reagent treating OSS and OST, which could reduce the viscosity between oil and solids. Increasing flotation time, impeller speed and the ratio of liquid to OS could enhance the pulp shear effect, facilitate the formation of bubble and reduce pulp viscosity, respectively. Under the optimized parameters, the oil content of OST residue could be reduced to 1.2%, and that of OSS could be reduced to 0.6% because of OSS with low heavy oil components and wide solid particle size distribution. Orthogonal experimental results showed that the impeller speed was the most significant factor of all parameters for OSS and OST, and it could produce shear force to decrease the intensity of C-H bonds and destabilize the OS. The oil content of residue could be reduced effectively in the temperature range of 24–45 °C under the action of high impeller speed.

The solid phase composition in oily sludge (OS) is a key factor affecting the oil–solid separation of OS. In this paper, the effects and mechanisms of solid-phase particle factors on the oil content of residue phase were investigated in order to improve the oil–solid separation efficiency. Flotation experiments were carried out on single-size sand and mixed-size sand OS consisting of three particle sizes at room temperature without adding flotation reagents. The effects of different-size particles as solid phase composition of OS and flotation parameter settings such as flotation temperature (Tp), flotation time (Tt), impeller speed (Rs) and liquid-solid ratio (L/OS) on the oil–solid separation efficiency were investigated. The experimental results showed that the oil content of residue phase decreased with the increasing of solid-phase particle size for single-size sand OS, and the optimal flotation conditions were Tp of 50 °C, Tt of 25 min, Rs of 1450 r/min and L/OS of 12:1. The oil–solid separation was more pronounced for mixed-size sand OS with a complex particle composition, while different particle compositions of the solid phase in OS promoted oil–solid separation. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FT-IR) characterisation of OS before and after flotation confirmed the relative advantage of coarse particle OS in the oil–solid separation process. The classical first-order model was well fitted to the flotation kinetic process of single-size sand and mixed-size sand OS. The response surface methodology (RSM) method was used to determine the Rs as the main control factor of the flotation process, and the oil content of residue phase in mixed-size sand OS was optimised to 2.63%. This study provides important process parameters and theoretical basis for the efficient treatment of OS.

In this study, micron-sized monodisperse SiO₂ microspheres were used as sacrificial templates, and chitosan/polylactic acid (CTS/PLA) bio-microcapsules were produced using the layer-by-layer (LBL) assembly method. Microcapsules isolate bacteria from their surroundings, forming a separate microenvironment and greatly improving microorganisms’ ability to adapt to adverse environmental conditions. Morphology observation indicated that the pie-shaped bio-microcapsules with a certain thickness could be successfully prepared through LBL assembly method. Surface analysis showed that the LBL bio-microcapsules (LBMs) had large fractions of mesoporous. The biodegradation experiments of toluene and the determination of toluene degrading enzyme activity were also carried out under external adverse environmental conditions (i.e., unsuitable initial concentrations of toluene, pH, temperature, and salinity). The results showed that the removal rate of toluene by LBMs can basically reach more than 90% in 2 days under adverse environmental conditions, which is significantly higher than that of free bacteria. In particular, the removal rate of toluene by LBMs can reach four times that of free bacteria at pH 3, which indicates that LBMs maintain a high level of operational stability for toluene degradation. Flow cytometry analysis showed that LBL microcapsules could effectively reduce the death rate of the bacteria. The results of the enzyme activity assay showed that the enzyme activity was significantly stronger in the LBMs system than in the free bacteria system under the same unfavorable external environmental conditions. In conclusion, the LBMs were more adaptable to the uncertain external environment, which provided a feasible bioremediation strategy for the treatment of organic contaminants in actual groundwater.