Effects of charge density and molecular weight of papermaking sludge-based flocculant on its decolorization efficiencies

Kangying Guo; Baoyu Gao; Jingwen Pan; Xue Shen; Caiyu Liu; Qinyan Yue; Xing Xu

doi:10.1016/j.scitotenv.2020.138136

Effects of charge density and molecular weight of papermaking sludge-based flocculant on its decolorization efficiencies

Sci Total Environ. 2020 Jun 25:723:138136. doi: 10.1016/j.scitotenv.2020.138136. Epub 2020 Mar 23.

Authors

Kangying Guo¹, Baoyu Gao², Jingwen Pan¹, Xue Shen¹, Caiyu Liu¹, Qinyan Yue¹, Xing Xu¹

Affiliations

¹ Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Qingdao 266000, PR China.
² Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Qingdao 266000, PR China. Electronic address: bygao@sdu.edu.cn.

PMID: 32224406
DOI: 10.1016/j.scitotenv.2020.138136

Abstract

The charge densities (CD) and molecular weights (MW) of the flocculants are closely related to their application performances, but seldom researches focus on the effects of flocculant CD and MW on decolorization efficiencies. Herein, a series of flocculants with various CD and MW levels, named as PBF₁_-₉, were designed and synthesized from papermaking sludge. The physicochemical characteristics of the PBF₁_-₉ were measured by fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS) and particle charge density analyzer (PCD). The efficiencies of PBF₁_-₉ were studied in the reactive blue (RB) dye removals by flocculation under different process conditions. The operation costs of the flocculants were evaluated at their optimal dosages. Also, the pH-independences and ion-tolerances of the aforementioned flocculants were studied in terms of the molecular levels. The experimental results exhibited that the flocculants CD or MW values were relevant to their flocculation behaviors and operation costs. CD values played a dominant role in color removal efficiencies and the costs, whereas MW values were critical to the floc structure. The pH or ion-independences of the flocculants were significantly dependent on the CD and MW values. However, some conclusions, conflicted with prior studies, were observed in this work. For instance, flocculant with the highest CD and MW levels was not the most effective one in enduring pH variation and the coexisting ions. The floc properties, including floc size, resistance and recovery ability, were relatively insensitive to flocculant intrinsic CD and MW levels when the flocculants were used at their optimal dosages. Furthermore, the possible relevance between CD or MW levels and the flocculation mechanisms have been proposed in this work. Exploring the effects of flocculants CD and MW levels could precisely control the flocculant characteristics to achieve satisfactory decontamination efficiencies with low costs.

Keywords: Biomass-based flocculant; Flocculation mechanism; Ion-insensitivity; Structure-activity relationship; pH-insensitivity.