Micromixing Efficiency of Particles in Heavy Metal Removal Processes under Various Inlet Conditions

Evangelos Karvelas,Christos Liosis,Ioannis Sarris,Lefteris Benos,Theodoros Karakasidis

doi:10.3390/w11061135

Abstract

Water quality problems are a persistent global issue since population growth has continually stressed hydrological resources. Heavy metals released into the environment from plating plants, mining, and alloy manufacturing pose a significant threat to the public health. A possible solution for water purification from heavy metals is to capture them by using nanoparticles in micromixers. In this method, conventionally heavy metal capture is achieved by effectively mixing two streams, a particle solution and the contaminated water, under the action of external magnetic fields. In the present study, we investigated the effective mixing of iron oxide nanoparticles and water without the use of external magnetic fields. For this reason, the mixing of particles and the contaminated water was studied for various inlet velocity ratios and inflow angles of the two streams using computational fluid dynamics techniques. The Navier-Stokes equations were solved for the water flow, the discrete motion of particles was evaluated by a Lagrangian method, while the flow of substances of the contaminated water was studied by a scalar transport equation. Results showed that as the velocity ratio between the inlet streams increased, the mixing of particles with the contaminated water was increased. Therefore, nanoparticles were more uniformly distributed in the duct and efficiently absorbed the substances of the contaminated water. On the other hand, the angle between two streams was found to play an insignificant role in the mixing process. Consequently, the results from this study could be used in the design of more compact and cost efficient micromixer devices.

Highlights

Industrial, municipal, and agricultural growth has tremendous effects on ground and surface water resources due to the resulting pollution [1,2,3,4,5,6]
In addition to convenient magnetic properties, iron oxide (e.g., Fe3 O4 ) nanoparticles possess many advantages—for instance, low toxicity, low price, and high surface to volume ratio, which are associated with their ability regarding surface chemical modification and can show enhanced capacity for metals uptake in water treatment procedures
We investigated an efficient alternative to obtaining efficient mixing of the magnetic nanoparticles with the polluted water in a Y-shaped micromixer; from each branch arrives a water stream contaminated by heavy metals and a particle solution stream, which are inserted in a microfluidic duct

Summary

Introduction

Industrial, municipal, and agricultural growth has tremendous effects on ground and surface water resources due to the resulting pollution [1,2,3,4,5,6]. There are sustainable solutions for the treatment of wastewater [9,10] nanotechnology has been identified as one of the most promising technologies that could play an important role in resolving many of the problems involving water purification and quality since nanoparticles covered with appropriate chemical substances for heavy ion removal possess an increased surface to volume ratio and constitute an efficient removal method [11,12,13,14,15]. In addition to convenient magnetic properties, iron oxide (e.g., Fe3 O4 ) nanoparticles possess many advantages—for instance, low toxicity, low price, and high surface to volume ratio (depending on the particle size), which are associated with their ability regarding surface chemical modification and can show enhanced capacity for metals uptake in water treatment procedures. Surface modification achieved by the attachment of inorganic shells or/and organic molecules stabilizes the nanoparticles, eventually preventing their oxidation, and provides specific functionalities that can be selective for ion uptake

Methods

Results

Discussion

Conclusion