Emil Dražević

Wastewater from wood and pulp industry treated by combination of coagulation, adsorption on modified clinoptilolite tuff and membrane processes

Wastewater from the wood and pulp industry is of environmental concern. It contains high concentrations of organic and inorganic matter. In this work a combined method of coagulation, adsorption and nanofiltration/reverse osmosis (NF/RO) was investigated in the purification of biologically treated wastewater from wood processing. Coagulation with 0.8 g dm−3 AlCl3·6H2O and adsorption on 2.5 g m−3 modified clinoptilolite tuff resulted in removal efficiencies of total carbon (TC), total organic carbon (TOC) and inorganic carbon (IC) up to 67.1%, 77.4% and 49.5%, respectively. Almost complete removal of solutes was achieved after NF/RO treatment. The TOC removal efficiency with RO membrane (CPA-3, LFC-1, XLE) and tight NF membrane (NF90) was 98% and with highly porous NF membrane (DK), 88%. After the proposed treatment the purified water stream can be recycled into the process or safely disposed to the river.

Interactions of Organics within Hydrated Selective Layer of Reverse Osmosis Desalination Membrane: a Combined Experimental and Computational Study

In this work we have examined a computational approach in predicting the interactions between uncharged organic solutes and polyamide membranes. We used three model organic molecules with identical molecular weights (100.1 g/mol), 4-aminopiperidine, 3,3-dimethyl-2-butanone (pinacolone) and methylisobutyl ketone for which we obtained experimental data on partitioning, diffusion and separation on a typical seawater reverse osmosis (RO) membrane. The interaction energy between the solutes and the membrane phase (fully aromatic polyamide) was computed from molecular dynamics (MD) simulations and the resulting sequence was found to correlate well with the experimental rejections and sorption data. Sorption of the different organic solutes within the membrane skin layer determined from attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) nicely agreed with interaction energies computed from molecular simulations. Qualitative information about solute diffusivity inside the membrane was also extracted from MD simulations while ATR-FTIR experiments indicated strongly hindered diffusion with diffusion coefficients in the membrane about 10-15 m2/s. The computational approach presented here could be a first step toward predicting rejections trends of, for example, hormones and pharmaceuticals by RO dense membranes.

Microfiltration of cutting-oil emulsions enhanced by electrocoagulation

Electrocoagulation (EC) was examined as a pre-treatment to the microfiltration (MF) of oily emulsions within the metalworking industry. The aim of this pre-treatment was to improve the MF performance in terms of flux decline and removal of oil by applying the minimum time of EC pre-treatment. Aluminium electrodes were used in EC, and flat sheetregenerated cellulose membrane in MF. The experiments were carried out using cutting-oil emulsions at different concentrations (0.1, 0.5 and 1.0% (v/v)) and conductivity of about 700 μ Sc m −1 . Drop size and zeta potential distributions were carried out to evaluate the impacts of EC time on zeta potential and average particle size. We found that in all emulsions, 10 min of EC made the average size of oil particles bigger than the average size of the pores in MF and substantially reduced pore clogging and irreversible fouling. Reduced flux decline was related to the continuous formation of Al(OH)3 in EC that interconnected the colloidal oil particles into porous and irregularly shaped flocs which formed highly porous cake layer on the membrane surface.