Enhanced dewatering of dredging slurry by Fenton preoxidation and composite coagulants: optimization experiments and dewatering mechanisms.

In this work, the Fenton preoxidation and composite coagulant method was used to carry out the rapid dewatering experiment of Chaohu Lake (China) dredging slurry. The changes in extracellular polymeric substances (EPS), particle size distribution, zeta potential, specific resistance to filtration (SRF), and capillary suction time (CST) of the dredging slurry were characterized. The results showed that the molar ratio of H2O2 and Fe2+ had the greatest effect on the dewatering of dredging slurry by Fenton preoxidation. The coagulant selected through the coagulation test was polyaluminum ferric chloride. The model simulated by the response surface method exhibited significant adaptability and high accuracy (p < 0.01, R2 = 0.9461, accuracy is 12.115). Fenton preoxidation resulted in the transformation of tightly bound EPS to soluble EPS. After preoxidation-coagulation treatment, the dewatering performance of the slurry improved significantly. The EPS quantity rose by 20.3%, while the SRF (3.65 × 109 s2/g), CST (71.25 s), and zeta potential (- 28.0 mV) shifted to 0.33 × 109 s2/g, 27.60 s, and - 14.9 mV, respectively. The disintegration of EPS by Fenton peroxidation and the subsequent adsorption bridging and charge neutralization through coagulation were the key mechanism for improving the dewatering performance of the dredging slurry.

Purification of dredged water by magnetic coagulation: Response surface optimization and dissolved organic matter removal characteristics.

In the present study, magnetic coagulation was used to treat dredged water and the response surface method was used to optimize process parameters. The dissolved organic matter (DOM) removal characteristics were characterized by three-dimensional fluorescence spectrometry and ultra-high resolution mass spectrometry. During the magnetic coagulation process, the suspended solids (SS) removal rate increased initially and then decreased under conditions of increasing magnetic powder dosage and stirring rate. After magnetic coagulation and precipitation for 20 min, the contents of SS, ammonia nitrogen, chemical oxygen demand, and total phosphorus in the treated dredged water met the requirements of the discharge standard (GB8978-1996, China). Three-dimensional fluorescence results showed that magnetic coagulation selectively removed fulvic acids and humic acid substances. After magnetic coagulation with precipitation for 10 min and 20 min, the total relative content of lignins, tannins, proteins, lipids, aminosugars, unsaturated hydrocarbons, condensed aromatic structures, and carbohydrates decreased by 26.3% and 39.4%, respectively. After magnetic coagulation, the distribution range of small molecule DOM shifted to the low H/C and high O/C regions. This study provides a novel perspective for studies on the removal of DOM in dredged water by magnetic coagulation. PRACTITIONER POINTS: SS and DOM removal were significantly enhanced by the use of magnetic coagulation. SS removal efficiency was affected by stirring rate and magnetic powder dosage. Magnetic coagulation selectively removed fulvic acids and humic acid substances. DOM molecule shifted to low H/C and high O/C regions after magnetic coagulation.

Life cycle assessment of a wastewater treatment plant focused on material and energy flows.

Life cycle assessment (LCA) was applied to analyze a food-processing wastewater treatment plant and investigate the economic and environmental effects of the plant. With the long-term operational data of this plant, an inventory of relative inputs, e.g., flow rate, chemical oxygen demand (COD), and suspended solids, etc., and outputs of the plant, e.g., effluent COD and suspended solids, methane production, etc., was compiled. The potential environmental effects associated with those inputs and outputs were evaluated, and the results of the inventory analysis and impact assessment phases of the plant were interpreted. One feature of this study was the assessment of the treatment plant based on both energy and material flows. Another feature was the establishment of an assessment model with an integration of plant operating parameters, system recognition and grey relation. The analytical results are helpful for the design and operation of wastewater treatment plants.