Integrated magnetic flocculation-horizontal tube sedimentation process for treating dredging residual water: environmental restoration of Wolong Lake

Abstract

Residual water from dredging contains high concentrations of heavy metals, causing severe environmental pollution in lakes. The present study develops integrated magnetic flocculation-horizontal tube sedimentation equipment. In the Wolong Lake region of China, the impact of treatment with the device on the residual water from dredged sludge under various inlet water flows was investigated. In a single-factor experiment, flocculants such as polyaluminum chloride (PAC), polymeric ferric sulfate (PFS), ferric chloride (FeCl₃), and aluminum sulphate (Al₂(SO₄)₃) were used at doses of 20–120 mg L⁻¹ to treat the residual water from dredged sludge. The residual wastewater from dredged sludge was best treated with PAC at 60 mg L; the removal efficiency of suspended solids (SS), chemical oxygen demand (COD), total phosphorous (TP), and ammonia nitrogen (NH₃-N) were (81.37 ± 1.66)%, (44.65 ± 2.31)%, (76.48 ± 1.08)%, and (17.64 ± 0.85)%, respectively. The pollutants in the water were further removed using magnetic flocculation (single-factor test and orthogonal analysis). The response surface method was used to optimize the PAC, magnetic powder, and polyacrylamide (PAM) doses to achieve 93.1% SS, 91.2% TP, and 71.2% COD removal. The device was operated for 30 consecutive days at various water intake volumes (4, 6, and 8 m³ h⁻¹). The residual water's COD, SS, TP, and NH₃-N levels effectively meet the environmental quality standards for surface water. With SpaceClaim as the pre-processing software and Fluent as the solver, a computational fluid dynamics (CFD) simulation analysis of the test device was conducted. CFD validations confirmed the design reliability. The reliability and rationality of the test device's operation were verified through simulation and analysis using the dual Euler model. The circular treatment design has significant environmental implications in restoring the ecological balance of the Wolong Lake Wetland.