Researchers at University of Delhi are using garlic and onion to filter out heavy metals like arsenic, cadmium, mercury, lead, etc. The filter itself is made out of leftovers from processing garlic and onions at food canneries, and is reusable. When it absorbs as much contaminants as it can handle, and then nitric acid is applied to separate the metals into another vessel. The filter can then be reused all over again. Once the filter has outlived its usefulness, then it can be thrown into the food waste stream as feedstock for biofuel refineries. The process depends on achieving an efficient pH of 5, in a relatively low temperature of 50 degree Celsius only.