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Olive mill wastewater (OMW) produced from small units scattered in rural areas of Southern Europe is a major source of pollution of surface and subsurface water. In the present work, a treatment scheme based on physical separation methods is presented. The investigation was carried out using a pilot‐plant unit equipped with ultrafiltration, nanofiltration, and reverse osmosis membranes. Approximately 80% of the total volume of wastewater treated by the membrane units was sufficiently cleaned to meet the standards for irrigation water. The concentrated fractions collected in the treatment concentrates were characterized by high organic load and high content of phenolic compounds. The concentrates were tested in hydroponic systems to examine their toxicity towards undesired herbs. The calculations of the cost of the overall process showed that fixed and operational costs could be recovered from the exploitation of OMW byproducts as water for irrigation and/or as bioherbicides.

In the present work, the effect of wettability on CaCO 3 precipitation was approached by monitoring crystal formation in microchips of different wettability degree. Solutions of calcium chloride and sodium bicarbonate were mixed in hydrophilic and neutral-wet Y-junction microchips, and the precipitation of CaCO 3 crystallites was monitored. Sequential pictures showed the formation and growth of CaCO 3 crystals as a function of time, and the precipitates were identified by Raman spectroscopy. The obtained results indicated that in hydrophilic microchips, the increase of supersaturation ratio value resulted in higher growth rates and aggregate formation. The neutral-wet microchip surfaces were found to accelerate the precipitation of CaCO 3 compared to hydrophilic surfaces, and in the case of neutral-wet surfaces, crystallites were formed mainly close to the wall surfaces. In hydrophilic microchips, calcite was the main precipitate, while aragonite formation was favored in neutral-wet microchips.

The dissolution of powdered Carrara marble was investigated in the absence and in the presence of (1-hydroxyethylidene)-1,1-diphosphonic acid (HEDP) at conditions of constant undersaturation at pH 8.25. The dependence of the rates of dissolution on the relative undersaturation suggested a surface diffusion controlled mechanism. According to this mechanistic information, the interaction of HEDP with calcitic Carrara marble was investigated. Two types of interaction of the HEDP with the marble suface were studied: preadsorption and addition of HEDP in the undersaturated solutions (1 µM to 1 mM). In both cases the rates of dissolution were drastically reduced depending on the concentration of the organophosphorus compound on the marble surface or in the undersaturated solutions. The rate reduction was attributed to the poisoning of the active dissolution sites through the uptake of HEDP on the calcite crystallites of the Carrara marble. The HEDP uptake by marble was measured quantitatively. The zeta potential was calculated from electrokinetic measurements of marble particle suspensions as a function of pH, pCa, and pCO3 2-. The potential-determining ions of the calcitic marble showed that the uptake of HEDP by the calcitic marble particles resulted in a shift of the surface potential to negative values and over a wide pCa range (2.0-4.5), causing charge reversal. The variation of the suspension pH did not result in significant changes of the surface potential. The examination of the morphology of the dissolving marble grains showed that the initially present small crystallites dissolved first, while in the presence of HEDP, which retarded dissolution, they were preserved.

The present work deals with the influence of pH and temperature on the spontaneous precipitation of calcium phosphate from simulated milk ultrafiltrate (SMUF) solutions. The pH range investigated is 5.7-7.0, and the temperature varied from 55 to 75 °C. It was found that the precipitates were prisms of hydroxyapatite (HAP) with low crystallinity preceded by amorphous calcium phosphate (ACP). Crystallinity improved with solution aging. Microscopic particles in the range of 200 nm were obtained at relatively high supersaturation (pH ) 6.8), whereas at relatively low supersaturation (pH ) 6.0), aggregates in the range of 1 µm were formed. Moreover, it was found that although the SMUF solution is also supersaturated with respect to magnesium phosphate, no magnesium salt was identified in the precipitates, thus precluding the coprecipitation of magnesium phosphate. At the same temperature, the supersaturation was regulated by adjusting the solution pH. Kinetics study of precipitation showed a parabolic dependence of the (initial) rates on the solution supersaturation, suggesting a surface diffusion-controlled mechanism with activation energy equal to 96 kJ mol -1 . The rates of precipitation were significantly reduced in the presence of citrate ions due to the decrease of the solution supersaturation caused by complexation of citrates with Ca 2+ ions. Additionally, a decreasing effect of citrates on the precipitation rate resulted from the adsorption of these species on the formed crystals, blocking some active sites of crystal growth and diminishing the constant of precipitation rate.

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