Mercury containing wastewater mainly comes from non-ferrous metal smelter, chemical plant, pesticide plant, paper mill, dye plant and thermal instrument plant. The methods of removing inorganic mercury from wastewater include sulfide precipitation, chemical coagulation, activated carbon adsorption, metal reduction, ion exchange and microorganism. Generally, the alkaline mercury wastewater is usually treated by chemical coagulation or sulfide precipitation. The wastewater containing mercury can be treated by metal reduction. Low concentration mercury containing wastewater can be treated by activated carbon adsorption, chemical coagulation or activated sludge. Organic mercury wastewater is difficult to treat. Organic mercury is usually oxidized to inorganic mercury first and then treated.