The increasing environmental burden of drilling wastewater calls for more efficient and mechanistically informed treatment strategies to support the sustainable development of oil and gas operations. This study systematically compares the performance of three flocculants—polyaluminum chloride (PAC), polyaluminum ferric silicate (PSAF), and aluminum sulfate (Al 2 (SO 4 ) 3 )—in the flocculation-flotation treatment of drilling wastewater, with an emphasis on elucidating floc–bubble interaction mechanisms. Flotation experiments demonstrated that PAC achieved the highest suspended solids (SS) removal efficiency (80.58 % at 1.0 g/L), followed by PSAF and Al 2 (SO 4 ) 3 . Comprehensive characterization, including FTIR, zeta potential, contact angle analysis, and floc size measurement, revealed that PAC formed large, moderately hydrophobic flocs with strong structural integrity and stable bubble adhesion. In contrast, Al 2 (SO 4 ) 3 generated smaller, highly hydrophobic flocs with low interfacial energy barriers, leading to poor aggregate stability. The EDLVO theory was applied to calculate interaction energy profiles, demonstrating that floc–bubble adhesion is governed by the combined effects of van der Waals, electrostatic, and hydrophobic interactions. PAC presented the most balanced profile, combining high adhesion potential with strong post-attachment stability. These findings provide novel mechanistic insights for optimizing flocculation-flotation processes in complex wastewater systems, offering a theoretical basis for practical engineering applications.
Huihui Zhang,Qiang Li,Futang Hu,Changkun Cheng,Nan Su,Zhiyong Zhang,Zhongzhi Zhang,Yijing Luo,Heming Wang
Drilling operations generate large volumes of wastewater; inadequate treatment poses a direct threat of groundwater and soil pollution. Biological treatment is environmentally friendly, yet it is constrained by prolonged treatment times. Coagulation offers the distinct advantages of rapid processing. Nevertheless, conventional organic polyacrylamide (PAM) flocculants increase the total nitrogen concentrations in wastewater, and traditional aluminum–iron salt coagulants exhibit limited efficiency and induce pipeline corrosion owing to their low degree of polymerization and the introduction of chloride ions. Therefore, developing a green and highly efficient coagulant has become a promising solution. In this study, an efficient polysilicate aluminum ferric (PSAF) was synthesized via copolymerization and applied to treat real drilling wastewater. In comparison to commonly used polyaluminum chloride (PAC), PSAF demonstrated a 14.3–21.4 % lower effective dose, a chloride ion release 1/17 that of PAC, and a reduced SV 30 value, indicating enhanced coagulation efficiency and sludge settling performance. In addition, the microscale coagulation mechanism was explored. It was found -OH and -COOH groups contributed to the coagulation process. Organics bearing these functional groups were effectively removed, while S 1 O x surfactants exhibited resistance to removal. This selective removal led to a substantial reduction in the organic molecular formula complexity of drilling wastewater. Notably, PSAF achieved a 2.8-fold greater reduction compared to PAC. Further analysis indicated that the formation of Si-O-Al/Fe-OOC or Si-O-Al/Fe-OH bonds enhanced adsorption and net trapping bridging capacities of PSAF, thereby improving overall coagulation performance. This study provides a technical reference for on-site treatment of drilling wastewater.
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