Superiority of wet-milled over dry-milled superfine powdered activated carbon for adsorptive 2-methylisoborneol removal

Abstract

Superfine powdered activated carbon (SPAC), which is produced from conventionally sized powdered activated carbon (PAC) by wet milling in a bead mill, has attracted attention for its high adsorptive removal ability in both research and practice. In this study, the performance of dry-milled SPAC was investigated. 2-Methylisoborneol (MIB), an earthy-musty compound commonly targeted by water treatment systems, was used as the target adsorbate. Dry-milled SPAC exhibited lower adsorptive removal of MIB than wet-milled SPAC, even when both SPACs were produced from the same PAC and were composed of particles of the same size. One reason for the lower removal of MIB by the dry-milled SPAC was a higher degree of aggregation in the dry-milled SPAC after production; as a result the apparent particle size of dry-milled SPAC was larger than that of wet-milled SPAC. The dry-milled SPAC was also more negatively charged than the wet-milled SPAC, and, owing to its higher repulsion, it was more amenable to dispersion by ultrasonication. However, even after the dry-milled SPAC was ultrasonicated so that its apparent particle size was similar to or less than that of the wet-milled SPAC, the dry-milled SPAC was still inferior in adsorptive removal to the wet-milled SPAC. Therefore, another reason for the lower adsorptive removal of dry-milled SPAC was its lower equilibrium adsorption capacity due to the oxidation during the milling. The adsorption kinetics by SPACs with different degrees of particle aggregation were successfully simulated by a pore diffusion model and a fractal aggregation model.

Micro-milling of spent granular activated carbon for its possible reuse as an adsorbent: Remaining capacity and characteristics

“…There were clear increases of MIB removal rates with decreasing particle size when the GAC was milled to PAC and SPAC. The MIB removal rate was higher for SPAC than PAC, as reported elsewhere (Matsui et al, 2007;Matsui et al, 2013a;Pan et al, 2016). Improvements of MIB removal rates with decreasing carbon size were also observed for 1-to-3-year-old spent carbons (Fig.…”

Effects of decreasing activated carbon particle diameter from 30 μm to 140 nm on equilibrium adsorption capacity

“…On the basis of environmental relevancy, molecular size, and hydrophobicity, nine other adsorbates were tested in addition to MIB: geosmin (log Kow, 3.57; 182 Da), Except for PSS-210 and PSS-1100 (Sigma-Aldrich, St. Louis, MO, USA), all chemical reagents were purchased from Wako Pure Chemical Industries (Osaka, Japan). The working solution was organic-free water with the ion composition used in previous research (Table S3) (Matsui et al 2015, Pan et al 2016. The working solutions were adjusted to pH 7.0 ± 0.1 with HCl or NaOH as required.…”

Removal of trace organic contaminants from wastewater by superfine powdered activated carbon (SPAC) is neither affected by SPAC dispersal nor coagulation

“…Based on laboratory experiments, Bonvin et al (2016) showed that the use of SPAC would allow for a shorter contact time compared to PAC to achieve a similar TrOC removal from WW effluents. SPAC has also demonstrated greater removal capacities of taste and odor compounds compared to PAC in drinking water (DW) treatment (Matsui et al, 2013a;Pan et al, 2017Pan et al, , 2016, as well as an enhanced overall dissolved organic material removal (Ando et al, 2010;Matsui et al, 2012Matsui et al, , 2013b. Traditional coagulation/flocculation, sedimentation and sand filtration steps, as well as advanced filtration membranes can be implemented downstream to remove the SPAC particles from the water or WW stream (Kweon et al, 2009;Löwenberg et al, 2014;Nakazawa et al, 2018aNakazawa et al, , 2018b.…”

“…A potential limitation of the use of SPAC is the tendency of small particles to aggregate in solution, depending on particle concentration and solution conditions (temperature, pH, ionic strength and chemical composition) (Baalousha, 2009;Dempsey, 2006). In drinking water, Pan et al (2016) reported a slower sorption of MIB onto dry-milled compared to wet-milled SPAC, which they attributed to a combination of lower sorption capacity and aggregation state. These authors suggest that aggregated SPAC particles have interparticle spaces that act as pseudopores, which increase the total diffusive pass length, resulting in a lower sorption rate is lowered for aggregated SPAC compared to single particles (Pan et al, 2016).…”

“…In drinking water, Pan et al (2016) reported a slower sorption of MIB onto dry-milled compared to wet-milled SPAC, which they attributed to a combination of lower sorption capacity and aggregation state. These authors suggest that aggregated SPAC particles have interparticle spaces that act as pseudopores, which increase the total diffusive pass length, resulting in a lower sorption rate is lowered for aggregated SPAC compared to single particles (Pan et al, 2016). Based on their findings, they recommended to disperse SPAC particles by ultrasonication if the aggregated particle size is more than twice the dispersed particle size.…”