Influence of Temperature and Reaction Time on the Efficiency of Alkaline Pretreatment of Hay Biomass

Low biodegradability caused by polymeric structure is the main barrier in the use of lignocellulosic materials in biofuels production by using biological methods. Pretreatment of the biomass is the way to improve the suitability of hardly biodegradable biomass for biogas or bioethanol production. Evaluation of the influence of thermal and thermochemical alkaline pretreatment on the efficiency of hydrolysis of hay (mixture of various grass species) was the aim of the study. The batch scale experiment was carried out with the use of NaOH and distilled water as solvents, and the changes in pretreatment time (2, 4 and 8 hours) and temperature (22 and 80°C) were also considered. The efficiency of biomass solubilisation was assessed based on the results obtained from the measurements of chemical oxygen demand (COD) and volatile fatty acids (VFA) concentration in the hydrolysates. The solubility of the biomass, expressed as a percentage of soluble COD in total COD, was calculated. The experiment showed that the highest solubilisation of hay biomass was observed at 80°C under alkaline conditions. In this case, the solubility of the COD was 3-times higher, and the VFA concentration in hydrolysates was 4-times higher in comparison to the distilled water-based test at 22°C. It was noted that time of the process significantly influenced the efficiency of biomass solubilisation only during the experiment carried out at 22°C. Extension of hydrolysis time from 2 to 8 hours increased the value of soluble COD of 70% and 55% for water and alkaline solvent, respectively. The process conducted at 80°C was not time-dependent over the considered period

Fouling behavior during microfiltration of silica nanoparticles and polymeric stabilizers

Nanotechnology applications give rise to new forms of water pollution, resulting in a need for reliable technologies that can remove nanoparticles from water. Membrane filtration is an obvious candidate. The tendency of nanoparticles to become instable in suspension and form aggregates strongly influences their filtration behavior. This experimental study investigated fouling and rejection during dead-end microfiltration of sterically stabilized nanoparticles. Polyvinylpyrrolidone (PVP) with different molecular weights at different concentrations was used as model steric stabilizer. The large difference between membrane pore size (~200 nm) and the size of the silica nanoparticles (25 nm) allowed a detailed investigation of the filtration process and fouling development. We characterized the feed solution with optical reflectometry, dynamic light scattering, zeta potential measurements and asymmetric flow field flow fractionation (AF4) combined with static light scattering. Subsequently, we looked at the influence of the steric stabilizer (PVP) on nanoparticle fouling development during pore blocking and cake filtration stages. Our work demonstrates that molecular mass, concentration of the steric stabilizer (PVP) and filtration pressure significantly influence pore blockage and cake filtration. Using a stabilizer with a lower molecular mass generally led to better stabilization of the nanoparticles and the stabilizer contributed less to the fouling. While higher concentrations of the stabilizer enhanced the stability of the nanoparticles, they also caused faster fouling development due to the higher total solute load. Stabilizer with a higher molecular mass was found to contribute more to pore blockage and lead to faster fouling development. Use of a higher transmembrane pressure resulted in compression of the filtration cake, resulting in improved nanoparticle rejection at the expense of permeability