**5.2 Passive technologies for the treatment of AMD**

The passive treatments of AMD rely upon biological, physical, and geochemical cycles to improve the nature of water. Primary passive methods can be compressively separated into biological and geochemical systems/reactors that use inorganic substances such as carbonates. The biological systems contain anaerobic and vertical flow wetlands, bioreactors. The geochemical systems include limestone drains, open limestone channels, limestone/steel slag leach beds, limestone sand. The selection of an effective passive treatment method relies on the water chemistry, flow rate, local topography, and characteristics of the site [25].

## **5.3 Treatment using various waste materials**

Active treatment methods are adopted in a wide range but they cause high establishment and absorbent expense. Also, some treatment methods associated with the active process like reverse osmosis, ion exchange requires pre-treatment of influent which is mentioned in the **Table 2**. Waste materials are generally economical than any other treatment method also reduces the environmental load. Various waste material which are generally used for the Treatment process of AMD are given in **Table 3**. They have the capacity and effectiveness to improve the pH of the AMD water and also to remove various pollutants from the wastewater. These waste materials provide a larger surface area, increasing the pH and adsorption rate to remove various pollutants at different concentrations [34, 35].
