Large quantities of water and various chemicals are used in the milling processes. Like mine water, these tailings waters must be treated and neutralized before they can be discharged to natural drainage basins. Treating acidic drainage from tailings ponds is a costly and long term liability. Treatment systems developed to do so can be defined as passive or active. Active systems use lime to neutralize acid water in conventional water treatment plants.
Passive systems use the natural ability of the ecosystems to heal themselves.
Research emphasis is now on the understanding and development of passive systems. This research focuses on the field of biotechnology and explores the possibilities offered by bacteria, plants, various organic materials, and engineered wetland. Bacteria Biological processes for cleaning contaminated soils and groundwaters use bacterial biodegradation to decompose organic contaminants into harmless compounds. Under some conditions bacteria can also be used to recover metals. For example, a group of bacteria eat and thrive on arsenic.