Preparation of a coarse flocculant from concentrated organic matter: Regulation by hydrothermal pretreatment

The process of preparing a flocculant using concentrated organic matter has demonstrated effective results in enriching organic matter in municipal wastewater. The basic preparation process involves a combination of hydrothermal treatment and chemical modification. To enhance the enrichment effect of organic matter, the optimal hydrothermal conditions and their influence on the characteristics of liquid products and coarse flocculant were investigated. The results indicated that liquid products obtained at 140 °C for 30 min yielded a high concentration of active groups and exhibited a significantly higher molecular weight, making them suitable as precursors for the coarse flocculant. When the dosage of the coarse flocculant was set at 10 mg/L, the turbidity removal rate of the kaolin suspension reached 93 %. In the treatment of municipal domestic sewage, a COD removal rate of approximately 62 % was achieved at a dosage of 10 mg/L. Within the experimental range, a decrease in hydrothermal time and temperature favored the production of more reactive groups from the dissolved polymeric substances (DPS), thereby enhancing the charge density of the coarse flocculant. The intrinsic viscosity of the coarse flocculant was influenced by both the number of reactive groups and the molecular weight of DPS. Specifically, obtaining a molecular weight distribution of 8-9.5 kDa favored the production of a coarse flocculant with high characteristic viscosities.