Table 6.

Current trends for AMD treatment.

Technology	Objective	Base Materials	Main Features
Fresh Water microalgae [91]	Clean up and biofuel production	AMD as flocculating agent	i)Harvesting of microalgae biomass done with AMD addition. ii)Improved settling velocity and reaction kinetics.
Organic carbon amendment [92]	Clean up	Primary treated AMD and rice bran	i)Year long stability in operation ii)Efficient removal of Cu, Zn and Cd metals iii)Cost effective carbon substrates for the SRB
Metallurgical slags [88]	Clean up	Metallurgical slags	i)Greatly increases pH ii)Sulfate and metal removal efficiency high, fast kinetics
Permeable reactive kiddle [93]	Clean up	Permeable reactive kiddle	i)Combination of steel slag, CIS and cement was most effective ii)1:20 PRK to AMD treatment ratio iii)Cost and complexity of system lowered
Bioelectrochemical process [94]	Clean up	AMD sludge	i)No addition of chemicals ii)Recovery of elemental sulfur iii)concomitant precipitation of rare earth elements iv)Less voluminous metal sludge with high settling rate