Porous media grain size distribution and hydrodynamic forces effects on transport and deposition of suspended particles.

The effects of porous media grain size distribution on the transport and deposition of polydisperse suspended particles under different flow velocities were investigated. Selected Kaolinite particles (2-30µm) and Fluorescein (dissolved tracer) were injected in the porous media by step input injection technique. Three sands filled columns were used: Fine sand, Coarse sand, and a third sand (Mixture) obtained by mixing the two last sands in equal weight proportion. The porous media performance on the particle removal was evaluated by analysing particles breakthrough curves, hydro-dispersive parameters determined using the analytical solution of convection-dispersion equation with a first order deposition kinetics, particles deposition profiles, and particle-size distribution of the recovered and the deposited particles. The deposition kinetics and the longitudinal hydrodynamic dispersion coefficients are controlled by the porous media grain size distribution. Mixture sand is more dispersive than Fine and Coarse sands. More the uniformity coefficient of the porous medium is large, higher is the filtration efficiency. At low velocities, porous media capture all sizes of suspended particles injected with larger ones mainly captured at the entrance. A high flow velocity carries the particles deeper into the porous media, producing more gradual changes in the deposition profile. The median diameter of the deposited particles at different depth increases with flow velocity. The large grain size distribution leads to build narrow pores enhancing the deposition of the particles by straining.

Desorption of zinc, copper and lead ions from loaded flax fibres.

Biosorption is an efficient and cost-effective method for heavy metals' remediation. However, saturated biosorbents may pose a serious problem for the environment. Flax fibres have shown very good adsorption capacities to remove zinc, copper and lead ions from contaminated aqueous solutions. In this study, adsorption-desorption cycles were conducted with loaded flax fibres in batch mode to recover heavy metals using four types of solutions: hydrochloric acid solution, nitric acid solution, sodium hydroxide solution and ultrapure water. Desorption kinetic studies, conducted with loaded flax fibres, showed very fast desorption of zinc, copper and lead when using nitric and hydrochloric acids with a selectivity sequence of Zn (totally desorbed) > Cu (94%) > Pb (80-73%). Desorption kinetic was slower with the use of sodium hydroxide and showed much lower desorption rates of Zn (62%) > Pb (12%) > Cu (7%). Desorption of zinc and copper from previously loaded fibres from binary metal ion system in lead solution was also investigated. Different concentrations ranging from 0.04 to 0.20 mmol/L were tested. The obtained results demonstrated a significant release in the order Zn (18-90%) > Cu (2-42%), while lead was still efficiently adsorbed. Retention efficiencies of zinc and copper and adsorption efficiency of lead resulted in the same adsorption efficiencies of the three metal ions onto flax fibres in the ternary metal ion system.

Bio-Based Adsorption as Ecofriendly Method for Wastewater Decontamination: A Review.

Intense human activities have for years contributed to the pollution of the environment by many dangerous pollutants such as heavy metals, pesticides, or polycyclic aromatic hydrocarbons. There are many conventional methods used to control pollution, with practical and/or financial drawbacks. Therefore, in recent years, an innovative, easy-to-implement and inexpensive adsorption method has been developed to recover waste and clean up water from micropollutants. Firstly, this article aims to summarize the issues related to water remediation and to understand the advantages and disadvantages of the methods classically used to purify water. In particular, this review aims to provide a recent update of the bio-based adsorbents and their use. Differently from the majority of the reviews related to wastewater treatment, in this article several classes of pollutants are considered. Then, a discussion about the adsorption process and interactions involved is provided. Finally, perspectives are suggested about the future work to be done in this field.

Potential of using Alfa grass fibers (Stipa Tenacissima L.) to remove Pb2+, Cu2+, and Zn2+ from an aqueous solution.

This study used alfa grass fibres as a natural low-cost adsorbent to remove lead, copper, and zinc ions from aqueous solutions. The adsorbent was characterized by FTIR, SEM, BET surface area, ATG, and XRD techniques. The effects of pH, contact time, initial metal concentration, and adsorbent dosage on the adsorption efficiency were evaluated in batch experiments. The results showed that the adsorption of all metals was fast, and optimal removal efficiency was achieved within 25 min of contact time using 5000 mg/L of Alfa fibres at pH 6.3. The adsorption selectivity order was Pb2+ > Cu2+ > Zn2+ with Pb2+ removal efficiencies up to 97.6%. The adsorption kinetics were best explained by a pseudo-second-order kinetic model. The experimental adsorption data fitted very well with the Langmuir isotherm model, and less well with the Freundlich and Temkin isotherm models. The maximum adsorption capacities were respectively 14.492, 11.904, and 8.695 mg/g for Pb2+, Cu2+, and Zn2+. The results of this study indicated that Alfa fibres could be used as effective adsorbent for the removal of Pb2+, Cu2+, and Zn2+ from aqueous solutions.

Effect of natural geotextile on the cotransport of heavy metals (Cu2+, Pb2+, and Zn2+) and kaolinite particles.

A cotransport study of heavy metals and kaolinite particles in sand column with and without flax geotextiles was carried out. The objectives were to evaluate the potential role of kaolinite in heavy metals transfer and to analyse the influence of flax geotextiles on the transfer of these pollutants. The adsorption rates of heavy metals on the kaolinite particles were, respectively, 53%, 65% and 25% for copper, lead, and zinc. The injection of kaolinite with heavy metals resulted in a significant decrease in the retention efficiency of copper and lead in the filter. The presence of kaolinite in the injected solution has virtually no influence on the effectiveness of zinc fixation in the filter. The retention of heavy metals is in the order of Zn > Cu > Pb with a significant drop of retention efficiency of 34% for copper, 67% for lead, and less than 1% for zinc. The presence of kaolinite in the injected solution reversed the retention order of heavy metals when metals solution was injected alone. Flax geotextiles increase the ability of the filter to retain soluble and attached heavy metals. It improves the sand retention capacity and it retains soluble and attached metals in its structure.

Nonwoven flax fibres geotextiles effects on solute heavy metals transport in porous media.

Filtration tests were carried out in laboratory columns filled with crushed sand with and without flax geotextiles to study the transfer and retention of soluble heavy metals. Divalent cations of copper, zinc and lead were simultaneously and continuously injected in filtration columns. Results show that, when geotextiles discs are present the retention of metals in sand is favoured and retention profiles are modified. In addition, and unlike synthetic geotextiles, flax fibres geotextiles contribute to the retention of a significant fraction of the cationic metal pollutants in their own structure. The overall metals retention efficiency of the filter is improved. Competition between cationic metals for adsorption on retention sites occurs in the column in the order Pb > Cu > Zn. Most of the lead is retained in the inlet of the column while copper and even more zinc migrate deeper in the column.

Competitive and non-competitive zinc, copper and lead biosorption from aqueous solutions onto flax fibers.

Competitive and non-competitive batch experiments were conducted on flax fibers to study Zn2+, Cu2+, and Pb2+ ions biosorption performance. Biosorption efficiency was dependent on contact time, pH, and biosorbent concentration. The results under competitive conditions were different from those obtained in non-competitive form. A high affinity of lead, with a selectivity sequence in general of Pb > Cu > Zn was observed. The biosorption data fitted very well the Langmuir model for lead in both types of solutions and for zinc and copper in the monometal form. The fit with the Freundlich model was not as successful, except for copper in the ternary system. Regarding zinc under competitive conditions, the sorption process was quite difficult and thus the equilibrium data could not fit well the adsorption models. The maximum adsorption capacities (mmol.kg-1) were respectively 112, 122 and 71, for Pb, Cu and Zn in the single metal ion solution and 82, 57 and 8 only in the ternary, showing thus a high competition between metal ions when added simultaneously. Overall, lead could still be efficiently removed in spite of the presence of other ions while zinc would be overcome in the presence of lead and copper.

Assessment of clogging of managed aquifer recharge in a semi-arid region.

To overcome water scarcity issues in arid and semi-arid regions, Managed Aquifer Recharge (MAR) remains a viable and suitable solution to manage and restore aquifers. However, clogging represents a major issue that can affect the durability and efficiency of MAR structures. The aim of this study was to evaluate the extent of clogging in MAR sites (Berrechid, Morocco). To achieve this objective, two field-based studies were undertaken: the first one consists of implantation of sand-filled columns in the recharge sites to evaluate the surface and subsurface clogging. The second one consists of the implantation of pickets over a 750 m2 area in each recharge site to measure the extent of deposit thickness on the surface of the wadi bed. Results show that, despite the low rainfall (<1.4 mm/day) and the short period (91 days) of the study, the deposits thickness exceeds 3 cm in a large part of the MAR. The suspended solids concentrations measured in recharge sites ranged from 1.1 to 1.4 g/L. Due to the particles retention, the estimation of the saturated hydraulic conductivity (k) of the sand declines over 90% in the immediate entrance of the columns. The k values measured in situ during the drying period ranged from 10-5 to 10-6 m/s. The k values of the cake formed, without cracks, was about 10-8 m/s. The presence of cracks drives the entire infiltration. However, due to the high plasticity index of the MAR soil, a slight reduction of cracks opening during wetting cycles is observed. In addition, particles deposited in these cracks, would contribute actively to the reduction of infiltration. The results of this study clearly showed the MAR sites vulnerability in semi-arid regions due to physical clogging.

Modeling of the transport and deposition of polydispersed particles: Effects of hydrodynamics and spatiotemporal evolution of the deposition rate.

A time-distance-dependent deposition model is built to investigate the effects of hydrodynamic forces on the transport and deposition of polydispersed particles and the evolution of deposition rates with time and distance. Straining and the heterogeneity of the particle population are considered to play important roles in the decreasing distribution of deposition rates. Numerical simulations were applied in a series of sand column experiments at different fluid velocities for three different porous media. The effects of hydrodynamics forces are elaborated with the systematic variations of deposition dynamic parameters of the proposed model. With retention distributions with particle size as well as temporal and spatial evolutions of deposition rates, the transport and deposition mechanisms of polydispersed particles will be elucidated through the interplay of the variation of the particle size distribution of mobile particle populations and the geometrical change of the porous medium due to retention (straining and blocking).

Modeling of retention and re-entrainment of mono- and poly-disperse particles: Effects of hydrodynamics, particle size and interplay of different-sized particles retention.

In this paper, numerical simulations of experimental data were performed with kinetic rate coefficients to characterize the retention and re-entrainment dynamics under different hydrodynamic conditions for monodisperse and polydisperse latex particles (3, 10, 16µm and the mixture). The results show that drastic increase in fluid velocity provokes hardly any remarkable decrease in retention in the presence of large energy barriers (>2000kT). Systematical increases in deposition and re-entrainment dynamic rates were observed with fluid velocity and/or particle size. Increased irreversible deposition rate indicates straining and wedging dominate deposition in this study. Excess retention of 3µm particle in the polydisperse particle suspension was observed. The origins are reckoned that deposited larger particles may hinder the re-entrainment of smaller particles near the grain-to-grain contact and can provide additional sites of attachment.

Experimental investigation on removal of suspended particles from water using flax fibre geotextiles.

Natural geotextiles are increasingly used in geotechnical applications such as bank protection and short-term soil reinforcement. This study aimed to highlight the behaviour of natural flax fibre geotextiles towards the retention of suspended particles (SP) present in urban runoff and often polluted. Indeed, it is well known that a large fraction of the heavy metals are often associated with the SP. Long-term filtration tests were performed on four laboratory filter designs. The objective was to study the influence of a nonwoven flax fibre geotextiles on SP transfer through a sandy porous media under saturated conditions. The experiments consisted of injecting SP in a column filled with sand with and without flax fibre geotextiles at a constant flow rate. The results showed that nonwoven flax fibre geotextiles can increase flow homogeneity. Retention efficiency of SP at column scale as well as spatial deposition profile was modified by the presence of geotextile. The use of flax fibre geotextiles increases considerably the durability of the filtration system. Particle size analysis of the particles retained in the sand medium and in geotextiles shows that the coarser particles are mainly deposited at the entrance of the column, and in the geotextiles.