Scientists develop low-cost method to remove toxic chromium from waste water using sunlight, smartphone

Indian researchers have developed a low-cost method to remove toxic chromium from waste water from industries, such as leather tanning and electroplating, by using ‘sunlight’ as a catalyst in combination with microfluidic technology.

A team from the Institute of Nano Science and Technology, Mohali, were successful in removing toxic chromium ions through a process called ‘continuous flow photoreduction’. They validated this process in waste water using titanium dioxide nanoparticles with the help of a smartphone based colorimetric technique.

Toxicity of chromium a serious concern

As per reports by WHO, the tolerable concentrations of chromium compounds in drinking water are limited to 0.05 mg/L for ‘hexavalent’ chromium and 5 mg/L for ‘trivalent’ chromium. Thus, it becomes imperative to reduce this hexavalent form of chromium to the trivalent form.

Hexavalent chromium is one of the most widely used heavy metals in metallurgy, chemicals, paints and textiles. Workers exposed to this are at increased risk of developing lung cancer, asthma, damage to the nasal epithelia and skin and related respiratory disorders.

Trivalent chromium is less toxic. Its presence in small quantities is not harmful.

Several chemical and physio-chemical methods, such as ion exchange, adsorption and bacterial and chemical reduction have been employed for the removal of hexavalent chromium, most of which are costly with low removal efficiencies.

Besides, the cost effectiveness of the process and the usage of renewable energy, with the microfluidics route, the reduction efficiency can also be tailored by fine-tuning the flow rate of the organic pollutant, reactor dimension and architecture precisely. One of the most advantageous features of using microreactors is the reusability of the photocatalyst without any recovery agents or cumbersome processes.

Various microfluidic parameters, such as reactor design, flow rate and channel length along with different catalyst phases, were fine-tuned to bring about superior degradation efficiency. A superior degradation efficiency of 95 percent was attained by utilising a serpentine microreactor coated with a photocatalyst.