Effect of PCC crystallization and morphology on flocculation with microfibrillated cellulose, on sheet densification and liquid absorption behavior

Composite sheets consisting of elongated and aggregated cationically charged precipitated calcium carbonate (PCC) and native microfibrillated cellulose (MFC) were prepared with a wet laying method. The furnishes were prepared with and without an anionic flocculating agent (polyacrylamide) in order to adjust the structure of the sheet. The samples were compressed (densified) in order to determine the particle and microfibrillated cellulose-PCC structure coalescence and densification, as well as its subsequent influence on liquid absorption behavior. The densification affected both the vertical and lateral distribution of PCC, but the flocculating agent enhanced the compression stability and stabilized the sheets against PCC material flow. The differences between the sheets made with and without the flocculation aid affected the absorption of an anionic dye-based fluid ink, which was evident as a higher print density and less print bleeding. The absorption behavior was dependent on the sheet structure, especially on the PCC distribution within the sheets. Finally, the role of MFC on floc structure and floc formation is discussed. Graphic abstract

Denatured lysozyme-coated carbon nanotubes: a versatile biohybrid material

Carbon nanotubes (CNTs) are among the most versatile nanomaterials, but their exploitation is hindered by limited dispersibility, especially in aqueous solvents. Here, we show that AP-LYS, a highly cationic soluble derivative of denatured hen egg lysozyme, is a very effective tool for the unbundling and solubilisation of CNTs. AP-LYS proved to mediate the complete and stable dispersion of CNTs at protein: CNT ratios ≥1: 3 (w:w) in very mild conditions (10–20 minutes sonication in ammonium acetate buffer, pH 5.0). Electrophoretic mobility and ζ-potential measurements confirmed that dispersed CNTs were coated by the protein, whereas molecular docking was used to study the interactions between AP-LYS and CNTs. AP-LYS-coated CNTs proved to be a very effective microbial cell-flocculating agent with an efficiency similar to that of chitosan, one of the best available flocculating agents, thus suggesting that this hybrid could find industrial applications in the treatment of wastewaters contaminated by microbial cells, or to remove microbial cells after fermentation processes. Moreover, we exploited the low stability of AP-LYS-coated CNT dispersions in eukaryotic cell culture media to prepare scaffolds with an extracellular matrix-like rough surface for the cultivation of eukaryotic cells.

Volumetric modeling of two sludge piles from water treatment plants in a Brazilian reservoir

Water treatment plants are designed to continuously produce drinkable water, meeting defined criteria of potability. However, besides potable water, these plants produce sludges that are disposed of in the environment. The present work aimed to evaluate the sludges generated in two water treatment plants and disposed of in the margin of the Juturnaíba dam. Since alum has been used as a flocculating agent in these two plants, the concentrations of aluminum were measured in the sludges and in surface sediments. The generated piles are extremely soft to walk on and difficult to measure, so indirect modeling procedures had to be applied. The calculated mass of the sludge piles at each plant are similar and respectively 60,370 and 61,479 tons. The aluminum content of the residues, calculated according to its dosage, was 33.2 and 32.6 g kg−1 in the piles from the two plants. The amount of alum dosed to the water corresponds almost to the excess of aluminum in the sludge, compared to the sediments. It was concluded that regardless of the fact that residues are disposed of in very restricted areas, they are directly in contact with the water and may constitute a threat for the environment and humans’ health.