Table 4.

Summary of the main advantages and disadvantages of common chemical and biological treatments for Cr (VI) removal. nZVI, nanoscale zero-valent iron.

Treatment	Advantages	Disadvantages	References
Chemical reduction with nanoscale zero-valent iron	High efficiency; high reactive surface area; easy to inject in aquifers.	Low stability; aggregation of nZVI particles; ecotoxicological effects on native organisms.	[111,112,113]
Adsorption coupled with ion exchange	Selective process; possible reuse of raw materials as green sorbents.	Complexity of adsorbents preparation; sludge generation; large amount of chemical required; waste generation; resin exhaustion; costly.	[126,131,169]
Electrocoagulation	High efficiency rate also with high chromium initial concentration; quicker and more sustainable than chemical coagulation processes; almost zero waste generation.	Skilled man-power requirement, several parameters influence its efficiency	[122,170,171]
Bioremediation	Cost-effective; ecological; sustainable; highly efficient with low and moderate pollutant concentration in large volume; no secondary pollution	Possibly inhibited by high pollutant concentrations;	[10,22,23]