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Basic Information about Mercury (Hg)

Physical and Chemical Properties

Mercury is the only metal that is liquid at room temperature. It has a melting point of -38.83°C and a boiling point of 356.73°C. Mercury has a high density (13.534 g/cm³ at 20°C) and good electrical conductivity. In water, mercury can be found in the form of elemental Hg(0), mercury ion Hg²⁺, and organomercury compounds such as methyl mercury.

Presence in Water and Health Effects

Mercury can enter waters through natural processes such as rock weathering and volcanic activity, as well as human activities such as mining, fossil fuel combustion, and industrial waste disposal. In water, mercury can accumulate in the aquatic food chain. Exposure to mercury can cause nervous system disorders, brain damage, kidney disorders, and reproductive problems. Methyl mercury in particular is highly toxic and can penetrate the placenta, harming the developing fetus.

Water Treatment Applications and Removal Methods

Some methods used to remove mercury from water include:

• Adsorption using activated carbon or specialized ion exchange resins
• Chemical precipitation using sulfides or hydroxides
• Membrane filtration such as nanofiltration or reverse osmosis
• Oxidation-reduction technologies
• Phytoremediation using specific aquatic plants

The selection of methods depends on the form of mercury present, the concentration, and the characteristics of the water being treated. Often a combination of several methods is required to achieve the desired level of removal.

Real World Application Example

At a coal-fired power generation facility in the United States, a flue gas desulfurization (FGD) wastewater treatment system uses a combination of chemical precipitation, filtration, and adsorption to reduce mercury levels. The process successfully reduced mercury concentrations from about 50 ppb to less than 10 ppt, meeting strict regulatory standards.

In Minamata, Japan, after the infamous mercury pollution tragedy, a large-scale remediation project was undertaken to clean up the polluted bay. Methods used included dredging of contaminated sediments, physical-chemical treatment, and long-term monitoring of water quality and marine biota.

Regulatory Guidelines and Standards

The World Health Organization (WHO) sets the maximum limit for mercury in drinking water at 0.006 mg/L. In Indonesia, based on the Minister of Health Regulation No. 492 Year 2010, the maximum limit of mercury in drinking water is 0.001 mg/L. For industrial wastewater, the maximum limit of mercury varies depending on the type of industry, but generally ranges from 0.002 - 0.005 mg/L in accordance with the Minister of Environment Regulation No. 5 Year 2014.

Environmental Impacts and Sustainability Considerations

Mercury is a persistent pollutant that can persist in the environment and bioaccumulate in the food chain. Improper management of mercury can cause long-term pollution to aquatic and soil ecosystems. Global efforts to reduce mercury use and emissions have been made through the Minamata Convention on Mercury. In the context of water treatment, the development of environmentally friendly technologies for mercury removal and safe mercury waste management is an important focus.

Future Trends and Research

Some current research and development directions in water treatment involving mercury include:

• Development of new nanomaterials for more effective mercury adsorption
• Bioremediation techniques using microorganisms or plants capable of accumulating or converting mercury
• Integration of real-time sensor technology for more accurate mercury monitoring
• Nature-based solutions for mercury remediation in natural environments
• Optimization of integrated water treatment processes for multi-contaminant removal including mercury

Water Treatment Fun Facts

• Some bacterial species have the ability to convert toxic mercury into a less harmful form through the process of demethylation, which is the basis for the development of mercury bioremediation.
• Rainwater can contain small amounts of mercury due to mercury emissions into the atmosphere, demonstrating the importance of a holistic approach to mercury management in the environment.
• The use of mercury in the chlorine-alkali process for the production of chlorine and caustic soda has led to significant mercury contamination at several industrial sites, requiring specialized water treatment technologies for remediation.