Manganese (Mn)

1. Basic Information

2. Physical and Chemical Properties

Manganese is a reddish-gray hard and brittle metal. Some important properties of manganese:

• Melting point: 1247°C
• Boiling point: 2061°C
• Density: 7.43 g/cm³
• Water solubility: Insoluble as a metal, but some manganese compounds are soluble
• Oxidation numbers: +2, +3, +4, +6, +7
• Reactive to acids
• Easily oxidized in air

In solution, manganese is most commonly found in the form of Mn²⁺ ions. Manganese can also form complexes with a variety of organic and inorganic ligands.

3. Presence in Water and Health Effects

Manganese is naturally present in ground and surface water, usually at concentrations of 0.01-0.2 mg/L. Higher concentrations can be found near mining or industrial areas. Although manganese is an essential nutrient for the body, overexposure can cause health effects such as:

• Neurological disorders
• Respiratory problems
• Liver damage
• Reproductive disorders
• Decreased immune function

In addition, manganese in water can cause aesthetic problems such as brown stains on clothing and sanitary ware, as well as bad taste and odor in drinking water.

4. Water Treatment Applications and Removal Methods

Some commonly used methods for removing manganese from water:

• Oxidation and filtration: Manganese is oxidized to an insoluble form (MnO₂) using oxidants such as chlorine, potassium permanganate, or ozone, then removed through filtration.
• Ion exchange: Cation exchange resins can remove Mn²⁺ ions from water. Strong acid cation resins such as AmberSep™ G26 H are often used for water with low salt content.
• Use of manganese greensand: A special filtration media coated with manganese oxide to remove dissolved manganese.
• Reverse osmosis: Effective for removing manganese along with other contaminants.
• Water softening: Sodium-based softeners can remove some manganese.
• Aeration: Oxidizes dissolved manganese to an insoluble form that can be filtered.
• Biofiltration: Uses microorganisms to oxidize and remove manganese.

For water with higher salt content, chelating resins such as AmberSep™ IRC748 can be used due to their high selectivity to multivalent cations such as manganese.

5. Industrial Uses in Water Treatment

Manganese is used in several industrial water treatment applications:

• Potassium permanganate (KMnO₄) is used as a strong oxidant to remove iron, manganese, and sulfides from water.
• Manganese dioxide (MnO₂) is used as a filtration medium to remove iron and manganese from water.
• Some manganese-based catalysts are used in advanced oxidation processes for wastewater treatment.

6. Case Studies and Real World Application Examples

Example 1: Power Plant in West Java

A power plant in West Java faced problems with high levels of manganese (0.8 mg/L) in their raw water. They implemented a treatment system consisting of:

1. Aeration to partially oxidize the manganese
2. Addition of potassium permanganate for further oxidation
3. Filtration through multimedia media including manganese greensand
4. Final pH adjustment

The system successfully reduced manganese levels to below 0.05 mg/L, meeting water quality standards for power plant operations.

Example 2: Municipal Drinking Water Treatment System in Sulawesi

A city in Sulawesi had a groundwater source with manganese levels of 0.4 mg/L. They implemented a large-scale treatment system involving:

1. Pre-oxidation with chlorine
2. Coagulation and flocculation
3. Sedimentation
4. Rapid sand filtration with manganese greensand layer
5. Final disinfection

The system successfully reduced manganese levels to below 0.1 mg/L, meeting national drinking water standards and eliminating the colored and odorous water problems previously experienced by residents.

7. Regulatory Guidelines and Standards

Some guidelines and standards for manganese in water:

• WHO: Recommends a limit of 0.4 mg/L in drinking water based on aesthetic considerations.
• Indonesia: Permenkes No. 492 Year 2010 sets a maximum limit of 0.4 mg/L for manganese in drinking water.
• US EPA: Sets a secondary contaminant level of 0.05 mg/L based on aesthetic considerations.
• European Union: Sets a parametric value of 0.05 mg/L for manganese in drinking water.

Standards for industrial wastewater vary depending on the type of industry and local regulations, but generally range from 1-5 mg/L for discharge to water bodies.

8. Environmental Impacts and Sustainability Considerations

Some environmental and sustainability aspects related to manganese in water treatment:

• Accumulation in the environment: Manganese can accumulate in sediments and soil, potentially affecting aquatic ecosystems.
• Energy consumption: Some manganese removal methods, such as oxidation and filtration, require significant energy.
• Chemical use: Oxidants such as chlorine and potassium permanganate can have environmental impacts if not managed properly.
• Waste disposal: Manganese-containing sludge from water treatment processes needs to be managed and disposed of properly.
• Sourcing: Production of specialized filtration media such as manganese greensand requires mining and processing.

To improve sustainability, several approaches can be considered:

• Process optimization to reduce chemical and energy use
• Recycling and reuse of filter wash water
• Application of more environmentally friendly biological treatment technologies
• Recovery and utilization of manganese from processing sludge

9. Future Trends and Research in Water Treatment

Some promising research areas and trends in manganese treatment in water:

• Development of new adsorbents: Research on nanomaterials and composites for more efficient manganese removal.
• Bioremediation: Utilization of specialized microorganisms to oxidize and remove manganese from water.
• Advanced membrane technology: Development of manganese selective membranes for more effective removal.
• Electrochemical oxidation: A more efficient and environmentally friendly method to oxidize manganese.
• Integrated treatment system: Combining various technologies for optimal manganese removal along with other contaminants.
• Real-time monitoring: Development of sensors and online monitoring systems for more accurate and rapid manganese detection.
• Nature-based approach: Utilization of artificial wetlands and phytoremediation for manganese removal from wastewater.

10. Interesting Facts Related to Water Treatment

• Manganese is often referred to as iron's "twin brother" in water treatment due to its similar chemical properties and is often found together.
• Manganese-oxidizing bacteria can form biofilms on water distribution pipes, which sometimes causes "black water" when the biofilm is detached.
• Although generally considered a contaminant, manganese in low concentrations can actually be beneficial in wastewater treatment due to its role in microbial growth that aids in the degradation of organic pollutants.
• Some aquatic plants, such as water lilies, have been shown to be effective in absorbing manganese from polluted water, opening up possibilities for natural phytoremediation.
• Manganese greensand, a popular filtration media for manganese removal, is actually purple-black in color, not green as the name suggests.