Production of highly efficient biomass-based microbial biopesticides significantly depends on downstream processing in terms of obtaining as high concentration of viable cells as possible. Microfiltration is one of the recommended operations for microbial biomass separation, but its main limitation is permeate flux decrease due to the membrane fouling. The effect of air sparging as a hydrodynamic technique for improvement of permeate flux during microfiltration of Bacillus velezensis cultivation broth was investigated. Modeling of the microfiltration was performed using the response surface methodology, while desirability function approach and genetic algorithm were applied for optimization, i.e., maximization of permeate flux and minimization of specific energy consumption. The results have revealed antagonistic relationship between the investigated dependent variables. The optimized values of superficial feed velocity and transmembrane pressure were close to the mean values of the investigated value ranges (0.68 bar and 0.96 m/s, respectively), while the optimized value of superficial air velocity had a more narrow distribution around 0.25 m/s. The results of this study have revealed a significant improvement of microfiltration performance by applying air sparging, thus this flux improvement method should be further investigated in downstream processing of different bacterial cultivation broths.

This paper investigates the separation possibilities of model emulsion oil-in-water using polypropylene fibre bed coalescence. Experiments were carried out over a wide range of physicochemical characteristics of mineral oils, bed permeability and operating fluid velocities. The aim of this study was to analyze the influence of the dispersed oil phase nature and of the bed geometry on the separation efficiency. From the obtained results, it can be concluded that polypropylene fibers in the broadest studied range of bed permeabilities and fluid velocities, effectively separate oil that is highly polar. On the contrary, for the other two investigated oils at low values of bed permeability a region was detected in which the coalescer is incapable to operate. It has to be emphasized that the polypropylene fibres efficiently separate all three investigated oils at the highest studied bed permeability.

Article Highlights • Separation of mineral oil droplets with stainless steel fibers bed different geometry was investigated • The separation efficiency for all operating conditions were higher than 90% • Low bed permeability is most favourable for the separation of mineral oil droplet from water • Separation of oil using stainless steel fibers is extremely sensitive to changes in oil properties Abstract This study is focused on the separation of oil droplets from water by applying a stainless steel fiber bed. The separation efficiency was followed by monitoring the oil concentration of three mineral oils that have a wide range of viscosity from 10 to 170 mP s, as well as neutralization number from 0.10 to 1.70 mg KOH/l. The bed properties were varied by altering the bulk density of the filter material, which resulted in a change of bed permeability from 0.7×10-9 to 5.389×10-9 m 2 and bed porosity from 91 to 98%. All experiments were conducted in a wide range of superficial velocity from 10 to 50 m/h. It can be concluded that high separation efficiency was achieved using stainless steel fibers, reaching values over 90%. Low bed permeability is most favorable for work at the selected conditions for the separation. The operation of stainless steel fiber bed is very sensitive to changes in the properties of oils. For lower viscosity of oily contaminants, the required efficiency of separation is achieved at lower superficial velocity through the fibrous bed. This phenomenon can be considered as a serious drawback since the bed coalescers often have to separate oils of different quality over time.

Bed coalescers are compact, easy to install, automate, and maintain with the ability to achieve high separation efficiencies. They have been increasingly applied in the industry even though their design often requires pilot plant experiments. In this paper, a new wetting property of polymer fibers regarding polar mineral oils was established. This property can be important for selection of filter media for liquid-liquid separation in many industrial applications. Medical oil was selected as the new reference liquid that does not wet the investigated polymers. The lipophilic/lyophobic ratio (LLR) reached values ranging from 3.28 to 18.81 and increased with the increase of the mineral oil polarity measured by the oil neutralization number. The LLR values were in an excellent agreement with the results obtained from the separation efficiency of a steady-state bed coalescer. Thus, simple, fast and inexpensive experiments can replace pilot plant or at least laboratory testing aiming at selecting a polymer for oil separation from wastewater.

The polypropylene fibers have been used in bed coalescers for separation of micro-sized oil droplets from water for a long time. Possibilities of applying different forms of polypropylene as filter beds are still being in the focus of many researches. The possibility of applying waste polypropylene bags used for packing vegetables (PPDJ) was investigated in this paper. The results are compared with results obtained by applying waste polypropylene fibers from carpet production (PP). It is well known that there are difficulties to separate the oils of low viscosity by polymer fiber beds. Due to the above mentioned, the presented research refers to separation of low viscosity mineral oil from water. The obtained experimental results confirm that the material PPDJ could be efficiently used as a bed material for coalescers. The critical velocity of 50 m h -1 could be reached at using both polypropylene forms that is from bags PPDJ and from the carpet industry PP, when the adequate bulk density of materials is used.