Performance evaluation of chitosan-based flocculants with good pH resistance and high heavy metals removal capacity

Combination of Coagulation and Ozone Catalytic Oxidation for Pretreating Coking Wastewater

In this study, coagulation, ozone (O₃) catalytic oxidation, and their combined process were used to pretreat actual coking wastewater. The effects on the removal of chemical oxygen demand (COD) and phenol in coking wastewater were investigated. Results showed that the optimum reaction conditions were an O₃ mass flow rate of 4.1 mg min⁻¹, a reaction temperature of 35 °C, a catalyst dosage ratio of 5:1, and a O₃ dosage of 500 mg·L⁻¹. The phenol removal ratio was 36.8% for the coagulation and sedimentation of coking wastewater under optimal conditions of 25 °C of reaction temperature, 7.5 reaction pH, 150 reaction gradient (G) value, and 500 mg·L⁻¹ coagulant dosage. The removal ratios of COD and phenol reached 24.06% and 2.18%, respectively. After the O₃-catalyzed oxidation treatment, the phenols, polycyclic aromatic hydrocarbons, and heterocyclic compounds were degraded to varying degrees. Coagulation and O₃ catalytic oxidation contributed to the removal of phenol and COD. The optimum reaction conditions for the combined process were as follows: O₃ dosage of 500 mg·L⁻¹, O₃ mass flow of 4.1 mg·min⁻¹, catalyst dosage ratio of 5:1, and reaction temperature of 35 °C. The removal ratios of phenol and COD reached 47.3% and 30.7%, respectively.

Preparation of a selective flocculant for treatment of oily wastewater produced from polymer flooding and its flocculant mechanism

There are residual polymers in the oily wastewater produced from polymer flooding (OWPF); keeping the residual polymer in the water during the flocculation is meaningful and challenging. In this paper, a selective flocculant (denoted as PDC10) which can remove the oil while keeping partially hydrolyzed polyacrylamide (HPAM) in water was prepared by copolymerization of decyl two methyl vinylbenzyl ammonium chloride (C10MVBA) and dimethyl aminopropyl methacryamide (DMAPMA). By using oil removal and HPAM retention as evaluation indexes, the synthesis condition of PDC10 was optimized. The optimum PDC10 exhibited oil removal of 98.0% and HPAM retention of 80.5%. Its HPAM retention is much higher than that of a regular cationic flocculant. Measurements of zeta potential, interfacial tension, interfacial dilational modulus and a dual polarization interferometry (DPI) test were carried out for investigating the flocculation mechanism of PDC10. The mechanism of PDC10 was that it can bridge and flocculate oil droplets by electrostatic interaction and hydrophobic interaction. It also preferred to distribute at the interface, and its interaction with HPAM in bulk water was weak, which confirms its selective flocculation properties.