Sari Metsämuuronen

Critical flux in ultrafiltration of myoglobin and baker’s yeast

Abstract Critical fluxes were determined by constant flux ultrafiltration (UF) experiments under laminar flow conditions. The experiments were performed by using hydrophilic C30G and hydrophobic GR51 ultrafiltration membranes and dilute myoglobin solutions and baker’s yeast suspensions as model colloids. Solution concentration, pH and cross-flow were investigated. The critical flux increased with increasing flow velocity and decreasing solute concentration. The regenerated cellulose C30G membrane exhibited higher critical fluxes than the polysulphone GR51 membrane. The highest critical flux was obtained at pH 8 in the presence of repulsive electrostatic forces between the molecules and the surface of the membrane and the lowest at the isoelectric points of the colloids. In the case of baker’s yeast below the critical flux, the flux was about the same as the pure buffer solution flux showing a strong form of the critical flux. This also occurred with the C30G membrane at low concentrations of myoglobin except at pH 6 when a weak form of the critical flux was measured. With the GR51 membrane, the permeate flux deviated from the pure buffer solution flux even at the lowest fluxes.

Characterization and removal of humic substances in ultra- and nanofiltration

Abstract Sixty percent of the Finnish lakes can be described as humic waters. Humic-free water is required in industry; for instance, in the paper making process the brightness may decrease because ofhumic water. One aim of this investigation was to study the removal of humic substances from different waters with ultrafiltration (UF) and nanofiltration (NF) using salts and retention aids as pretreatments. The other aim was to characterize humic acids with different methods. In both UF and NF of moorland water, retention was good without any pretreatment, but a small positive effect was obtained with AlCl3, NaCl, KCl and FeCl3. Retention aids did not improve the retention, but the cationic ones were affected slightly positively. In NF a higher pressure evidently improved retention. In every case pH had a great influence because at a low pH the structure of humic acid is more compact and no fouling occurs. Humic acid was analyzed using COD, TOC, UV/VIS, SEM-EDAX, FTIR and zeta potential methods. Adsorption of humic acid was tested with polymer films using contact angle measurements and also with active carbon and carrot adsorbents. Adsorption was strongest at pH 3 in every trial and active carbon adsorbed humic acid much more than carrot adsorbents.

Natural Organic Matter Removal from Drinking Water by Membrane Technology

Aquatic natural organic matter (NOM) is a heterogeneous mixture of biopolymers and their degradation products that cause harmful by-products during drinking water production. The great variability in NOM composition makes it difficult to completely remove from drinking water by any single technique. The current article reviews the NOM removal by micro-, ultra- and nanofiltration and by hybrid processes combining membrane techniques with other unit processes: coagulation, adsorption, and oxidation, and by membrane bioreactors.

Effects of aquatic humic substances on a hydrophobic ultrafiltration membrane

Natural humic surface water (pH 5.9), ion exchanged samples of the same water (pH 5.5), and aqueous solutions of isolated humic substances at pH 4.5, 5.5 and 6.5, respectively, were ultrafiltered (15°C, 0.5 bar) using hydrophobic polysulfone membranes (GR51) in a cross-flow flat sheet module. The used membrane did not completely retain natural organic matter from the surface water and the addition of complexing metals did not affect the retention any further. The changes which were induced in the membranes during each filtration run were studied by simultaneous streaming potential and flux measurements in 0.01 M KCl solutions. Zeta potentials were calculated based on the streaming potentials and the results showed changes towards more negative values for all the samples due to adsorption of organic matter onto the surface of the membrane pores. Humic acid affected the membrane charges more than fulvic acid. High ionic strength and low pH enhanced flux reduction and fouling. Filtration of natural waters caused more pore plugging and flux reduction than filtration of solutions of the isolated humic substances.

Antibacterial Compounds in Predominant Trees in Finland: Review

The extracts of Scots pine, Norway spruce, silver and white birches stem, bark, roots, leaves and needles contain several useful bioactive compounds that exhibit antibacterial activity against pathogens. Both phenolic extracts and essential oils are bacteriostatic against several bacteria. The main individual antibacterial phenolic compounds in Scots pine are pinosylvins that effectively inhibit growth of pathogens such as Bacillus cereus, Staphylococcus aureus and Listeria monocytogenes. From other phenolic compounds lignans appeared to be the least bacteriostatic and flavonoids tend to occur as glycosylated forms which have lower antibacterial activity than their aglycones. Gram-positive bacteria are generally more susceptible to plants bioactive compounds than gram-negative bacteria.

Analysis of protein filtration data by PLS regression

Six different globular proteins were filtered with hydrophilic regenerated cellulose ultrafiltration membranes at their isoelectric points. The PLS regression was used to analyse the filtration data. The modelling of the relative flux failed, but that of the transmission of the proteins succeeded relatively well. As a conclusion of the data analysis the most important explanatory variables affecting the transmission of proteins are the permeate flux and the membrane cut-off value divided by the molar mass of the protein. They both have a positive linear relationship with the transmission.

Chapter 5 – Membranes

Aquatic natural organic matter (NOM) is a heterogeneous mixture of biopolymers and their degradation products that cause harmful by-products during drinking water production. The great variability in NOM composition makes it difficult to remove from drinking water completely by conventional coagulation or by any single technique. This chapter reviews NOM removal by membranes—namely, micro-, ultra-, and nanofiltration, and also reverse osmosis.

Chapter 9 – Integrated Methods

Integrating conventional coagulation with novel treatment methods is expected to enhance natural organic matter (NOM) removal in water treatment. The great variability in NOM composition makes it difficult to completely remove from drinking water by any single technique. This chapter discusses NOM removal by integrating coagulation with other treatment processes (ion exchange, oxidation, adsorption, and membrane technology) and hybrid processes combining membrane techniques with other unit processes (coagulation, adsorption, oxidation, and membrane bioreactors).