Evaluating magnetic nano-ferrofluid as a novel coagulant for surface water treatment

In the area of environmental remediation, nanomaterials offer the potential for the efficient removal of pollutants and biological contaminants. With the rapid development of nanotechnology, nano-ferrofluid or magnetic fluids are currently being widely studied in water treatment field. The utilization of iron oxide nanomaterials or magnetic nanoparticles (MNs) has received great attention due to their unique properties, such as biocompatibility, small size, high surface area to volume ratio, and easy separation from solution using an external magnetic field. However, a few works have been conducted on coagulant and enhancing coagulation process using simple nano-ferrofluid without any modification. In the present study, at first, we synthesized nano-ferrofluid; then, after characterizations, we use the magnetic fluid for water treatment. For this purpose, we choose Karun River in the southwest of Iran as a model and water samples are collected. Then, they are treated with a small amount of magnetic fluid. In this process, the effect of this nanomaterial on turbidity, hardness, alkalinity, removal of some important heavy metal cations, and important anions like phosphate, population of coliform bacteria and fecal coliform bacteria, and amount of chemical oxygen demand (COD) is investigated separately. Also, the effect of some important parameters such as time and rate of mixing steps, pH, temperature, and reusability of these nanomagnetic particles as a coagulant is investigated and the interesting and applicable results are obtained. In general, the combination of removing important hazardous ions with 1 μg mL− 1 such as Cd2 +, Co2 +, Mn2 +, Fe2 +, Pb2 +, Zn2 +, Ni2 +, and Cu2 + cations (more than 90%), great ability in decreasing turbidity (about 90%), excellent antibacterial efficiency (98% of fecal coliform bacteria and 97% of coliform bacteria were removed), decreasing COD (about 60%), green and cheap preparation, ease of use, and decreased time of separating those with external magnetic field compared to available commercial coagulants. To the best of our knowledge, most of available coagulants can only decrease turbidity. Notably, in decreasing turbidity, MNs have the same efficiency over the pH range (4.0-8.0) and temperature range (15-45 °C) in real samples. Meanwhile the most coagulants do not have these properties simultaneously.