Onion and garlic waste clean up heavy metals

Indian researchers have discovered a use for onion and garlic waste from the food industry: mopping up hazardous heavy metals, such as arsenic, cadmium, iron, lead, mercury and tin.

Biotechnologists from the GGS Indraprastha University in Delhi, published a paper outlining how waste from the processing and canning of onion (Allium cepa) and garlic (Allium sativum) could be used as an alternative remediation material for removing toxic elements from contaminated materials including industrial effluent.

The biotechnologists’ research showed that at 50°C, the efficiency of the clean-up process is largely dependent on pH and equilibration time usually occurs within half an hour. A pH of 5 was optimal.

The extraction process was most effective for lead, one of the most troublesome metallic environmental pollutants. The researchers found they could extract more than 10 milligrams per gram of Allium material from a test solution containing 5 grams per litre of mixed metal ion solution, amounting to recovery efficiency of more than 70%.

Once the extraction is complete, the absorbed metals can be released into a collecting vessel using nitric acid and the biomass re-used.

“The technique appears to be industrially applicable and viable,” the researchers wrote. “This may provide an affordable, environmentally friendly and low-maintenance technology for small and medium-scale industries in developing countries.”

The research paper was published in Volume 49, No. 3/4 of the International Journal of Environment and Pollution, pp 179-196.