Theoretical Insight into the Biodegradation of Solitary Oil Microdroplets Moving through a Water Column

In the aftermath of oil spills in the sea, clouds of droplets drift into the seawater column and are carried away by sea currents. The fate of the drifting droplets is determined by natural attenuation processes, mainly dissolution into the seawater and biodegradation by oil-degrading microbial communities. Specifically, microbes have developed three fundamental strategies for accessing and assimilating oily substrates. Depending on their affinity for the oily phase and ability to proliferate in multicellular structures, microbes might either attach to the oil surface and directly uptake compounds from the oily phase, or grow suspended in the aqueous phase consuming solubilized oil, or form three-dimensional biofilms over the oil–water interface. In this work, a compound particle model that accounts for all three microbial strategies is developed for the biodegradation of solitary oil microdroplets moving through a water column. Under a set of educated hypotheses, the hydrodynamics and solute transport problems are amenable to analytical solutions and a closed-form correlation is established for the overall dissolution rate as a function of the Thiele modulus, the Biot number and other key parameters. Moreover, two coupled ordinary differential equations are formulated for the evolution of the particle size and used to investigate the impact of the dissolution and biodegradation processes on the droplet shrinking rate

Technoeconomic Analysis of the Recovery of Phenols from Olive Mill Wastewater through Membrane Filtration and Resin Adsorption/Desorption

Olive mill wastewater is an important agro-industrial waste with no established treatment method. The authors have developed a phenol separation method that could potentially cover the treatment cost of the waste. The purpose of this study was to identify any economic hotspots in the process, the operational cost and examine the margin of profit for such a process. The equipment cost was scaled for different treatment capacities and then used to estimate the fixed capital investment and the yearly operational cost. The highest purchased equipment cost was identified for the membrane filtration system, while the cost for resin replacement was identified as the highest operational cost. The lifespan of the resin used in the adsorption step was identified as an economic hot spot for the process, with the phenols separation cost ranging from 0.84 to 13.6 €/g of phenols for a resin lifespan of 5–100 adsorption/desorption cycles. The lifespan of the resin proved to be the single most important aspect that determines the phenols separation cost. The price range that was calculated for the product of the process is very promising because of the typical value of antioxidants and the low concentration of phenols that are needed for food supplements and cosmetics

A Performance Comparison of Pilot-Scale Sand Filtration and Membrane Filtration of Glafkos River Water

Surface-water treatment plants use the flocculation–precipitation method followed by gravity filters to remove suspended solids. In the present work, the replacement of gravity filters with ultrafiltration membrane units is suggested to improve the efficiency of water treatment and to reduce fixed and operational costs. A parametric pilot-scale study was conducted to compare the filtration efficiency of a deep bed and a membrane module for water-simulating river water of various turbidity degrees. Suspensions of kaolinite were prepared to simulate turbidity of the Glafkos River, Achaia Region of Greece and were filtered using a laboratory sand-bed column and a pilot ultrafiltration (UF) membrane unit. Operational parameters such as the particle concentration ratio, the flow rate, and the filter head loss were studied in the case of the granular bed. In the case of membrane filtration, the permeate flux, turbidity, and membrane permeability loss due to fouling were tested. A discussion in terms of the operational cost and environmental impacts was performed. Filtration capacity of the sand filter is a decreasing function of the flow rate and it was found less efficient than membrane ultrafiltration for increased turbidity or increased particle concentration values. Membrane ultrafiltration could achieve long-term economic profit while it is characterized by minimum environmental impact since the use of chemical reagents and the production of waste sludge are limited

Theoretical Insight into the Biodegradation of Solitary Oil Microdroplets Moving through a Water Column

In the aftermath of oil spills in the sea, clouds of droplets drift into the seawater column and are carried away by sea currents. The fate of the drifting droplets is determined by natural attenuation processes, mainly dissolution into the seawater and biodegradation by oil-degrading microbial communities. Specifically, microbes have developed three fundamental strategies for accessing and assimilating oily substrates. Depending on their affinity for the oily phase and ability to proliferate in multicellular structures, microbes might either attach to the oil surface and directly uptake compounds from the oily phase, or grow suspended in the aqueous phase consuming solubilized oil, or form three-dimensional biofilms over the oil–water interface. In this work, a compound particle model that accounts for all three microbial strategies is developed for the biodegradation of solitary oil microdroplets moving through a water column. Under a set of educated hypotheses, the hydrodynamics and solute transport problems are amenable to analytical solutions and a closed-form correlation is established for the overall dissolution rate as a function of the Thiele modulus, the Biot number and other key parameters. Moreover, two coupled ordinary differential equations are formulated for the evolution of the particle size and used to investigate the impact of the dissolution and biodegradation processes on the droplet shrinking rate

Heterogeneous nucleation and growth of calcium carbonate on calcite and quartz

The precipitation of calcium carbonate as a binding salt for the consolidation of loose sand formations is a promising approach. The heterogeneous nucleation and growth of calcite were investigated in supersaturated solutions. The ionic activities in the solutions tested were selected so that they included both supersaturations in which crystal growth took place only following the introduction of seed particles and supersaturations in which precipitation occurred spontaneously past the lapse of induction times. In the latter case the supersaturation conditions were sufficiently low to allow the measurement of induction times preceding the onset of precipitation. The stability domain of the calcium carbonate system was established at pH 8.50, 25 °C, measuring the induction times in the range between 30 min and 2 h. The rates of precipitation following the destabilization of the solutions were measured from the pH and/or concentration–time profiles. The induction times were inversely proportional and rates proportional to the solution supersaturation as expected. The high-order dependence of the rates of precipitation on the solution supersaturation suggested a polynuclear growth mechanism. Fitting of the induction time–supersaturation data according to this model yielded a value of 64 mJ/m2 for the surface energy of the calcite nucleus. In the concentration domain corresponding to stable supersaturated solutions, seeded growth experiments at constant supersaturation showed a second-order dependence on the rates of crystal growth of calcite seed crystals. Inoculation of the stable supersaturated solutions with quartz seed crystals failed to induce nucleation. Raising supersaturation to reach the unstable domain showed interesting features: calcite seed crystals yielded crystal growth kinetics compatible with the polynuclear growth model, without any induction time. The presence of quartz seed crystals reduced the induction times and resulted in nucleation in the bulk solution. The kinetic data in the latter case were consistent with the polynuclear growth model and the surface energy for the newly forming embryo was calculated equal to 31.1 mJ/m2, because of the dominantly heterogeneous nature of the process

Protection of Historical Mortars through Treatment with Suspensions of Nanoparticles

Mortars, which are very important elements for the integrity of historic monuments, consist mainly of calcium carbonate and silicates in different proportions. Chemical dissolution due to exposure in open air is very important for the degradation of mortars. Inorganic nanoparticles with chemical and crystallographic affinity with mortar components are expected to be effective structure stabilizers and agents offering resistance to chemical dissolution. In the present work, we have developed and applied suspensions of amorphous calcium carbonate (ACC), silicon oxide (am-SiO2) and composite nanoparticles by the precipitation of ACC on am-SiO2 and vice versa. The application of suspensions of the synthesized nanoparticles on three different historical mortars of Roman times (1st century AD), retarded their dissolution rate in solutions undersaturated with respect to calcite, in acid pH (6.50, 25 °C). All three test historic mortars, treated with suspensions of the nanoparticles prepared, showed high resistance towards dissolution at pH 6.50. The ability of the nanoparticles’ suspension to consolidate the damaged mortar was the key factor in deciding the corresponding effectiveness in the retardation of the rate of dissolution. The combination of ACC with am-SiO2 nanoparticles showed high efficiency for protection from the dissolution of calcite rich mortars

Protection of Historical Mortars through Treatment with Suspensions of Nanoparticles

Mortars, which are very important elements for the integrity of historic monuments, consist mainly of calcium carbonate and silicates in different proportions. Chemical dissolution due to exposure in open air is very important for the degradation of mortars. Inorganic nanoparticles with chemical and crystallographic affinity with mortar components are expected to be effective structure stabilizers and agents offering resistance to chemical dissolution. In the present work, we have developed and applied suspensions of amorphous calcium carbonate (ACC), silicon oxide (am-SiO2) and composite nanoparticles by the precipitation of ACC on am-SiO2 and vice versa. The application of suspensions of the synthesized nanoparticles on three different historical mortars of Roman times (1st century AD), retarded their dissolution rate in solutions undersaturated with respect to calcite, in acid pH (6.50, 25 °C). All three test historic mortars, treated with suspensions of the nanoparticles prepared, showed high resistance towards dissolution at pH 6.50. The ability of the nanoparticles’ suspension to consolidate the damaged mortar was the key factor in deciding the corresponding effectiveness in the retardation of the rate of dissolution. The combination of ACC with am-SiO2 nanoparticles showed high efficiency for protection from the dissolution of calcite rich mortars

Impact of Microbial Uptake on the Nutrient Plume around Marine Organic Particles: High-Resolution Numerical Analysis

The interactions between marine bacteria and particulate matter play a pivotal role in the biogeochemical cycles of carbon and associated inorganic elements in the oceans. Eutrophic plumes typically form around nutrient-releasing particles and host intense bacterial activities. However, the potential of bacteria to reshape the nutrient plumes remains largely unexplored. We present a high-resolution numerical analysis for the impacts of nutrient uptake by free-living bacteria on the pattern of dissolution around slow-moving particles. At the single-particle level, the nutrient field is parameterized by the Péclet and Damköhler numbers (0 < Pe < 1000, 0 < Da < 10) that quantify the relative contribution of advection, diffusion and uptake to nutrient transport. In spite of reducing the extent of the nutrient plume in the wake of the particle, bacterial uptake enhances the rates of particle dissolution and nutrient depletion. These effects are amplified when the uptake timescale is shorter than the plume lifetime (Pe/Da < 100, Da > 0.0001), while otherwise they are suppressed by advection or diffusion. Our analysis suggests that the quenching of eutrophic plumes is significant for individual phytoplankton cells, as well as marine aggregates with sizes ranging from 0.1 mm to 10 mm and sinking velocities up to 40 m per day. This microscale process has a large potential impact on microbial growth dynamics and nutrient cycling in marine ecosystems

Hydroxytyrosol Enrichment of Olive Leaf Extracts via Membrane Separation Processes

Antioxidants isolated from plant materials, such as phenolics, have attracted a lot of attention because of their potential uses. This contributes to the idea of the biorefinery, which is a way to produce useful products from biomass waste. Olea europaea byproducts have been extensively investigated for their large contents in phenolics. Oleuropein is a phenolic compound abundant in olive leaves, with its molecule containing hydroxytyrosol, elenolic acid, and glucose. In this work, olive leaf extracts were treated using different combinations of ultrafiltration and nanofiltration membranes to assess their capacity of facilitating the production of hydroxytyrosol-enriched solutions, either by separating the initially extracted oleuropein or by separating the hydroxytyrosol produced after a hydrolysis step. The best performance was observed when an ultrafiltration membrane (UP010, 10,000 Da) was followed by a nanofiltration membrane (TS40, 200–300 Da) for the treatment of the hydrolyzed extract, increasing the purity of the final product from 25% w/w of the total extracted compounds being hydroxytyrosol when membrane processes were not used to 68% w/w