In the present study, oil in water emulsions (c = 100 ppm; d < 2 μm) was purified with ozonation followed by microfiltration using polyethersulfone (PES) membrane (d = 0.2 μm). The effects of pre-ozonation on membrane microfiltration were investigated in detail both in case of ultrapure and model groundwater matrices, applying different durations (0, 5, 10, and 20 min) of pre-ozonation. Simultaneously, the effects of added inorganic water components on the combined method were investigated. Size distribution of oil droplets, zeta potentials, fluxes, and purification efficiencies were measured and fouling mechanisms were described in all cases. It was found that the matrix significantly affected the size distribution and adherence ability of oil droplets onto the membrane surface, therefore fouling mechanisms also were strongly dependent on the matrix. In case of low salt concentration, the total resistance was caused mainly by reversible resistance, which could be significantly reduced (eliminated) by pre-ozonation. In case of model groundwater matrix, nearly twice higher total resistance was measured, and irreversible resistance was dominant, because of the higher adhesion ability of the oil droplets onto the membrane surface. In this case, pre-ozonation resulted in much lower irreversible, but higher reversible resistance. Increased duration of pre-ozonation raised the total resistance and reduced the elimination efficiency (due to fragmented oil droplets and water soluble oxidation by-products) in both cases, therefore short pre-ozonation can be recommended both from economic and performance aspects.

a b s t r a c tIn the present study membrane filtration was applied for the purification of crude oil containing stable oil in water emulsions (c oil = 100 ppm; d oil droplets < 1.5 µm) with and without pre-ozonation using polyethersulfone (PES) microfiltration membrane (d pore = 0.2 µm). The effect of ozonation on the size of oil droplets and on Zeta-potential was determined by dynamic light scattering measurements. The effects of applied transmembrane pressure, stirring speed and duration of ozonation were investigated in detail. Removal efficiency was determined by measuring turbidity, chemical oxygen demand (COD), total organic carbon content (TOC) and extractable oil content (TOG/TPH). Results pointed out, that short pre-ozonation (absorbed ozone was 30 ± 5 mg L -1 ) causes increased fluxes and decreased resistance without notable change in the purification efficiency in case of low transmembrane pressure (0.1 MPa). However longer pre-ozonation or higher transmembrane pressure results in increased irreversible resistance, lower permeate fluxes or even lower purification efficiency.

This study aimed to investigate the effect of ozone and Fenton-reaction as a pre-treatment before ultrafiltration of model dairy waste waters containing sodium caseinate. Filtration resistances and pollutant retentions were determined and compared. It was found, that both pre-treatment increased the retention, achieving almost 100 % pollutant elimination efficiency after short term pre-oxidation. The effect of Fe-ion concentration on Fenton pretreatment efficiency also was examined, and it was found that higher concentration resulted in decreased filtration resistances, revealing that coagulation-flocculation effect of reactants has dominant role in the protein separation efficiency. The presence of lactose also affects the pollutant removal efficiency, it promotes fouling in presence of Fenton reagents.

The dairy industry generates wastewater characterised by high levels of biological and chemical oxygen demands representative of their high degree of organic content; mainly carbohydrates, proteins and fats that originate from milk. Several investigations have been conducted into the reuse of dairy wastewater, e.g. membrane processes are a promising method to treat such wastewater. Earlier works have proven that with membrane filtration an appropriate degree of retention can be achieved and the permeate can be reused. However, membrane fouling is a limiting factor in these processes. Advanced oxidation processes (AOPs) are widely used in the fields of water and wastewater treatments and are known for their capability to mineralise a wide range of organic compounds. AOPs also exhibit some other effects on the filtration process, e.g. the microflocculation effect of ozone may play a significant role in increasing the elimination efficiency and causing a decreased level of irreversible fouling. By comparing ozone and Fenton pre-treatment (FPT) processes it can be shown that the fouling propensity of pre-treated pollutants does not depend on the pre-treatment method, while FPT was proven to be more efficient in improving the level of flux.

Membrane separation processes are space and cost-efficient, easy to scale-up operations, which have proved to treat food industrial wastewaters efficiently. Beside the advantages like high separation efficiency without any chemical changes and low energy-intensity, membrane filtration also has drawbacks, like decreased operational efficiency caused by flux decile resulting from fouling and concentration polarization. Combination of oxidation pre-treatment and membrane filtration is a promising method for decreasing fouling due to the physicochemical changes caused by pre-oxidation of the wastewater in structure of colloidal pollutants and in the interactions between the foulants and the membrane material. The aim of this work is to identify the parameters affecting the membrane fouling during treatment of dairy wastewaters, and present the current trends of research in this field.