Table 2.

Advantages and disadvantages of various waste and heavy metal removal and treatment methods.

Remediation techniques		Mechanism	Advantages	Disadvantages
Domain	Type of treatment
Physical techniques	Filtration	Separate mixture based on the size and solubility	• Easy operation	• Soluble compounds cannot be separated by conventional system
			• Low capital investment	• Preferred for liquid system
			• High efficiency	• Large-scale operation is costly
	Sedimentation	Settling of suspended particles based on gravity	• Simple and inexpensive	• High toxicity;
			• Effective	• Sediment removal and processing is costly
				• Chelating agent use and recycling is itself costly
				• Ineffective against trivalent metal ions including Fe3+, Al3+, and Cr3+
	Absorption	Immobilization of pollutants on resin surface and pores	• Simple and cost-effective	• Production of adsorbent is costly
			• High removal efficiency	• Again, discharge waste after regeneration of waste
			• Effective at a wide range of pH
Chemical techniques	Electro-catalytic oxido-reduction	Oxidation and reduction under the influence of electric field and catalyst	• Rapid and effective	• Formation of sludge or abduct material
				• Cost intensive
	Electro-deposition	High-energy electrons reduced metal ions into elements	• Rapid and effective	• Electrode cost is high
			• Can work at large scale as well	• Electrode replacement or regeneration is costly
	Flocculation	Form complex with pollutants and remove suspended material by precipitation or in the form of clump	• Easy to remove suspended particles and pollutants from liquid	• Suitable for liquid only
				• Use of chemical as flocculating agent for removal
				• Form sludge-like waste
	Dialysis and electrodialysis	Removal of solvents based on concentration based on concentration gradients. Electric field further improve the movement	• High rate of removal for charged metal ions under electric field	• Energy intensive
				• Scale-up is a tedious task
				• Only transfer pollutants from one phase to other
Biological techniques	Microbial accumulation	Microbes degrade complex and accumulate metals in cytoplasm	• Low-cost operation	• Only accumulate heavy metals in cell mass
			• Onsite and offsite operation possible	• Biomass degradation again releases pollutants
	Enzymatic degradation	Enzyme catalyze the degradation or biotransformation	• Enzyme recyclability and tolerance is a critical factor	• Cost intensive
			• Specific in action	• Complex process with multiple affecting factors
	Phytoremediation	Plants segregate selectively and accumulate within biomass in different organs	• Prolong storage of pollutants	• Slow in action
			• Effective and selective in action	• Dead matter valorization again releases bulk amount of pollutants in the environment
			• High tolerance