Treatment method	Suitable for	Advantages	Disadvantages	Reference
Open limestone channels	Pre-treatment or post-treatment	Low operating and maintenance costs, no power consumption, can last for many years, simple and reliable	Coating, long channel required to achieve the desired retention time	[13]
Aerobic wetlands	Acid water containing Fe, Mn and SS	Low operating and maintenance costs, no power consumption, can last for many years	Cannot treat strongly acidic water efficiently (best for pH > 5.5)	[17]
Anaerobic wetlands	Acid water with low DO, Al, Fe³⁺ and SS contents	Low operating and maintenance costs, no power consumption, can last for many years	Coating on limestone surface due to presence of Fe and Al, large area and long retention time needed to remove Mn	[17]
Anoxic limestone drains	Acid water with low Al and Fe³⁺ contents	Low operating and maintenance costs, no power consumption, can last for many years, simple	Needs pretreatment, best for acid water with low DO, Al and Fe³⁺ to avoid armoring	[14]
Successive alkalinity-producing systems	Acid water with high contents of metals (Fe, Al, Zn, Cu)	Low operating and maintenance costs, no power consumption, can last for many years	Metal floc accumulation and degradation of organic layer, pretreatment required for acid water with high Fe³⁺ and SS contents	[14]