**3. Methods for removal of heavy metals**

Since last many decades, various physical and chemical methods were employed to remove metals from environment. The list is given below [5, 13, 14, 22–24].

**Chemicals methods**: Chemical precipitation, electrochemical treatment, oxidation/reduction.

**Physical methods**: Ion exchange, membrane technology, reverse osmosis, and evaporation recovery, filtration.

**Biological methods**: Microorganisms including bacteria, fungi or algae.

However, these strategies were not the first choice as they are expensive, inefficient, laborintensive, or the treatment process lacks selectivity [25, 26]. The research on bioremediation or biosorption-based remediation techniques in the past decades has concluded that bioremediation is a natural process and cost effective [4, 27–31].
