[Study Case] Reducing Iron, Manganese, and Color Levels in PDAM Water Treatment Systems Using DMI65 Filter Media in Central Java

A. Introduction

To improve the quality of clean water for the community, PDAMs in various regions in Central Java use various raw water sources, ranging from river water, reservoirs, and springs, to underground well water. Underground water sources are chosen especially in locations far from large rivers or where reservoirs are not yet available.

However, underground wells’ raw water sources often contain high concentrations of iron (Fe) and manganese (Mn). This content varies between locations, depending on the soil composition and rocks around the underground flow.

Underground well water usually looks clear and colorless when it is first taken, although it often smells of rust. This is because the iron and manganese are still dissolved. However, after a few minutes of contact with air, the water turns cloudy yellow to reddish brown due to oxidation.

The increased dissolved oxygen changes iron (Fe2+ to Fe3+) and manganese (Mn2+ to Mn4+), so the water changes color and requires further treatment to meet health and hygiene standards.

Conventional methods, such as aeration and sedimentation with coagulants-flocculants, are increasingly considered less efficient. In addition to requiring high investment, chemical, energy, and maintenance costs, this method is not optimal for raw water with high manganese levels.

Since 2007, PDAM has switched to DMI65 media filter technology in several locations in Central Java, which is a more efficient solution and produces more stable water quality.

B. Technical Data

DMI65 media filter is a special media sand that accelerates the oxidation reaction of iron (Fe), manganese (Mn), arsenic (As), aluminum (Al), and hydrogen sulfide (H₂S) in water.

Image 1. DMI65 Media Sand

This media has superior characteristics:

• Can remove iron up to > 20 ppm
• Easy operation without requiring a large area
• Saves electricity and labor costs because it does not require high energy
• Media life span can reach 8 years or more with good maintenance
• Does not require regeneration chemicals such as KMnO₄, as required by other filter media

Table 1. Technical Specifications of DMI65 Media

Table 2. Operating Condition Specifications

Graph 1. Services Pressure Drop

Graph 2. Backwash Bed Expansion 

Table 3. Water Quality Resulting from DMI65 Media Filter Processing

The results of the water treatment process using the DMI65 Media Filter in the PDAM Raw Water Treatment Installation System can reduce ≥ 98% of the Iron (Fe) and Manganese (Mn) parameter values ​​contained in the water.

Image 2. NSF/ANSI Validation Certificate

Table 4. Results of the implementation of the DMI65 media filter including discharge capacity, operating linear velocity and raw water conditions.

The implementation of the DMI65 media filter at the PDAM Central Java Drinking Water Treatment Plant uses a linear velocity filter operation that varies from 7 m/hour to 16 m/hour following the parameter values ​​of Iron (Fe) and Manganese (Mn) contained in the raw water source.

C. DMI65 Media Filter Mechanism

The DMI65 filter media works based on the principle of simultaneous reduction and oxidation (redox) reactions, where a reduction reaction is impossible without an oxidation reaction. This media acts as a catalyst that “helps” chemical reactions occur without experiencing permanent changes to its structure.

To optimize the oxidation process of iron (Fe) and manganese (Mn) ions dissolved in water, the DMI65 media is designed to operate with oxidants such as chlorine. This oxidant functions to remove electrons from iron and manganese ions, thus changing both into a form that is easier to filter by the media. For the oxidation process to run perfectly, the free chlorine content in the filter output water needs to be maintained between 0.1 and 0.3 ppm.

Various types of oxidants can be used in this process, such as:

• Sodium Hypochlorite (NaOCl)
• Blazing powder
• Chlorine Gas
• Stabilized Chlorine (SDIC, TCCA)
• Other oxidants, such as Hydrogen Peroxide (H₂O₂), Chlorine Dioxide (ClO₂), or Ozone, provided that residual levels can be measured and maintained.

NaOCl not only functions as an oxidant, but also prevents the growth of bacteria or slime on the surface of the media. The surface of the manganese oxide catalyst in the media must be kept clean so that the ions in the water can interact directly with the surface of the media. NaOCl, as a source of oxygen that is more reactive than molecular oxygen, increases the efficiency of the oxidation process. The table below shows safe levels for other water constituents that can interfere with surface interactions.

Table 5. Safe Levels for Water Constituents

DMI65 Media Initial Activation

Before being used for the first time, DMI65 media must go through an activation process. This process requires a sodium hypochlorite solution with a concentration of 12.5% ​​as much as 10 liters for every 1 m³ of media. Activation is done by soaking the media in the solution for 12-24 hours. The purpose of this soaking is to remove the outer layer of the media that can inhibit the oxidation reaction.

Backwash and Filter Preparation

After the activation process is complete, the DMI65 filter tank must undergo a backwash process to clean excess NaOCl and fine particles that may have been carried over during media production. Since manganese oxide is the active substance in the media, the backwash process requires sufficient time until the manganese content in the wash water reaches 0.03 ppm and free chlorine residual is formed. 

After the backwash process is complete, the filter is ready for use in the service stage.

Media Durability and Replacement

Although DMI65 media has an average service life of between 5 and 8 years, physical abrasion between sand grains can cause a decrease in filtration properties. This usually occurs before the degradation of the catalytic surface layer. However, even when the physical filtration function of the media has decreased, DMI65 is still able to oxidize iron and manganese ions. With proper maintenance, this media remains a reliable and efficient choice for clean water treatment.

D. Process of Reducing Iron (Fe) Levels

Iron in the form of Ferro ions (Fe²⁺) is easily dissolved in water, and is usually found in the form of Ferro Bicarbonate. To remove this dissolved iron, an oxidation process is required that changes Ferro into Ferric Hydroxide (Fe³⁺) in water with a neutral pH. The Ferric Hydroxide that is formed then settles on the surface of the DMI65 filter media and can be removed through a backwash process (reverse flow washing).

The oxidation reaction of Ferro Bicarbonate by Sodium Hypochlorite (NaOCl) with the help of DMI65 media which acts as a catalyst takes place very quickly, even instantly. The following is the equation for the redox reaction that occurs:

2Fe(HCO3)2 + NaOCl + H2O → 2Fe(OH)3 + 2CO2 + NaCl

The catalytic surface of DMI65 media (M in solid black circle) is coated with manganese oxide which allows the adsorption of ions in water. This process is known as metal oxide surface hydroxylation, where ionized water molecules are attracted to ions on the catalyst surface. The following are the steps of the reaction that take place:

1. Water Molecule Absorption

Oxygen from water molecules is first attracted to manganese metal (M) on the surface of DMI65 media. This triggers water molecules to break down into hydroxide ions (OH⁻) and hydrogen ions (H⁺).

2. Dynamic Process on the Catalyst Surface

This reaction occurs dynamically and not simultaneously on the entire catalyst surface. The attached hydroxide matrix and hydrogen ions will be released continuously, creating an ideal environment for Ferro (Fe²⁺) oxidation.

3. Transformation of Ferrous to Ferric Hydroxide

The dissolved Ferrous ions are attracted to the oxygen on the catalyst surface. This brings the Ferrous into close chemical bond with the hydroxide ions, which then transforms into Ferric Hydroxide (Fe³⁺).

4. Formation of Ferric Hydroxide Crystals

The formed Ferric Hydroxide has a more balanced electrical charge, making it easier to move away from the catalyst surface. This Ferric Hydroxide is insoluble in water, so it precipitates in the form of aggregate crystals with a minimum size of 3 nanometers. These aggregates clump into larger groups and are easily filtered by the DMI65 media layer.

This process is not only efficient but also ensures that the Ferro ion is converted into a more stable form (Ferri Hydroxide), which can then be completely removed through backwash. With the help of DMI65 media, this reaction is fast and effective, making this technology very reliable in treating water with high iron content.

E. Process of Reducing Manganese (Mn)

DMI65 media is designed with a catalytic surface containing manganese oxide (MnO₂), which allows chemical bonding between manganese atoms and oxygen from water. However, the manganese oxidation process is different from iron oxidation because manganese hydroxide (Mn(OH)₂) has a higher solubility than ferrous hydroxide (Fe(OH)₃). This difference affects the mechanism of manganese removal from water.

The manganese oxidation process by Sodium Hypochlorite (NaOCl) produces manganese dioxide (MnO₂), not oxyhydroxide as in iron. The following is the equation of the redox reaction that occurs:

Mn(HCO3)2 + NaOCl → MnO(OH)2 + NaCl + 2CO2

The manganese dioxide formed has a higher oxide valence, but the precipitation and removal of manganese is not greatly aided by the concentration of hydroxide anions. Therefore, to increase the efficiency of the manganese oxidation process while reducing chemical requirements, more reactive oxygen sources such as ozone or aeration are often used as alternatives. Sufficient dissolved oxygen can reduce the amount of Sodium Hypochlorite required.

1. Oxidation Mechanism in DMI65 Media

Manganese hydroxide (Mn(OH)₂) will be attracted to the catalytic surface of DMI65 (M) media on the oxygen side. For the oxidation process to run perfectly, oxygen molecules must be available near the surface to support the transfer of oxygen to the catalytic lattice. However, statistically, this reaction is slower compared to the oxidation of iron (Fe) via hydroxide.

2. pH Factors and Anoxic Conditions

Increasing pH can help accelerate manganese oxidation and removal. However, under anoxic conditions (low dissolved oxygen), manganese can dissolve back into the water or leach from the catalytic surface of the media. This causes manganese contaminants that should be removed to re-enter the system. Therefore, anoxic conditions must be avoided to protect the catalytic layer of the DMI65 media. The optimum pH for manganese oxidation is between 7.0 and 8.0.

3. The Relationship of Iron to Manganese Removal

The presence of iron in water can facilitate the removal of manganese through the coprecipitation mechanism. Because the atomic radius of manganese (127 picometers) is almost the same as iron (127 picometers), manganese ions can bind together with iron ions in the oxidation process. This coprecipitation produces less stable backwash sludge because manganese tends to move more easily in solution.

4. Conclusion of Manganese Oxidation Process in DMI65 Media

• The manganese oxidation process requires sufficient oxidants and dissolved oxygen conditions for high efficiency.
• An optimal pH of 7.0–8.0 must be maintained to prevent re-dissolution of manganese.
• The presence of iron in the water can assist the manganese removal process through coprecipitation.
• Successful manganese precipitation produces manganese dioxide (MnO₂), which is easily filtered and removed through backwash.

With proper design and maintenance, DMI65 filter media provides an effective solution for reducing manganese levels in water, even under complex operational conditions.

F. DMI65 Media Filter Implementation

Before implementing the DMI65 media filter, there are several important initial steps to ensure the design and operation of the water treatment system are in accordance with the needs. These steps include analyzing the raw water conditions, the desired water quality targets, the raw water discharge, and the existing water treatment installation (WTP) system.

Initial Analysis and Important Parameters

1. Raw Water Condition

The condition of raw water needs to be analyzed in depth, including parameters such as iron (Fe), manganese (Mn), pH, turbidity, and ammonia (NH₃) content. The Fe and Mn parameters are the main references for determining the linear velocity to be used in the DMI65 media so that the filter tank design can be adjusted to meet processing needs.

2. Water Quality Targets

The expected water quality will determine the configuration of the DMI65 filter system, whether using a series configuration for a more intensive process or parallel to increase production capacity. The filter media bed depth must also be adequate to achieve optimal results.

3. Raw Water Discharge

The raw water discharge is needed to calculate the DMI65 filter capacity, which includes the cross-sectional area of ​​the filter tank based on the selected linear velocity. Here is the formula for calculating the tank parameters:

4. Bed Depth and Freeboard of Filter Tank

The minimum recommended bed depth (media thickness) is 60–70 cm. Based on experience, the optimal DMI65 media thickness is 100 cm to maintain water quality stability even though the filter is already clogged. Freeboard (empty tank space) for media expansion during backwash is recommended at least 40% of the bed depth, but 50% provides optimal results to prevent media sand from coming out during the backwash process.

Implementation in Water Treatment System

Modification of Existing System

DMI65 media can be implemented by replacing sand media in existing treatment systems, both in pressurized filter tanks and gravity filters. This step provides economic benefits because it reduces the need for investment in new tanks. Before replacement, the dimensions of the filter tank and strainer (nozzle) specifications must be reviewed to ensure compatibility with the DMI65 design requirements.

Example of Implementation Results:

The use of DMI65 media in an existing system equipped with chlorine injection in the filter inlet line produces better water quality, with significant reductions in Fe and Mn levels, while maintaining operational cost efficiency.

New Processing System

In the new system, the installation design can be adjusted to the specific needs of the raw water source. Here are two implementation options:

1. From the Well Directly to the DMI65 Filter

Water from the well is directly channeled to the DMI65 filter, and the results are channeled to the reservoir tank for distribution.

Advantages: Reduces electricity costs by using only one well pump for filter operation.

Disadvantages: Requires an interconnect switch (flow switch) between the well pump and the chlorine injection pump so that chlorine injection follows the life cycle of the well pump, especially if the operation is not running for a full 24 hours.

The results of the water quality of the DMI65 Filter processing process with the concept of going directly from the well to the DMI65 Filter:

2. From Well to Buffer Tank Then to DMI65 Filter

Water from the well is first stored in the buffer tank before being processed by the DMI65 filter. The filtration results are then channeled to the reservoir tank for distribution.

Advantages: The production capacity of the DMI65 filter can be greater than the well water discharge due to the residence time of the water in the buffer tank. If the well pump is damaged, the water in the buffer tank provides a time gap to continue the process.

Disadvantages: Requires more electricity because it involves 2-3 operational pumps.

G. DMI65 Media Filter Operating Procedure

The DMI65 filter media requires a structured operating procedure to ensure its effectiveness in reducing iron (Fe) and manganese (Mn) levels in raw water. The following are the operational stages that must be carried out.

1. Soaking Stage 

The soaking process aims to activate the DMI65 media before use, especially for new media. In new media, the outer matrix layer has a membrane that needs to be removed so that the media can function optimally.

Soaking Steps:

• The media is soaked with a solution of Sodium Hypochlorite (NaOCl) with a concentration of 12.5%.
• Solution dosage:
  • 10 liters of NaOCl for every 1 m³ of DMI65 media.
  • 10 ml of NaOCl for every 1 liter of DMI65 media.
• Soaking time: 12–24 hours.

After the soaking process is complete, the media must go through a backwash stage to clean the remaining NaOCl solution and fine particles from the media.

2. Backwash Stage

Backwash is done after the soaking process and when the DMI65 media starts to become saturated. Media saturation is indicated by:

• Increased Fe levels in filtered water.
• Decrease in filtered water flow rate.
• Increased pressure on the filter.

Backwash Steps:

• Chlorine injection is still carried out during backwash by maintaining residual chlorine in the output water in the range of 0.3–1 ppm.
• Velocity: 25–35 m/h or about 2.5 times the filtration speed.
• Process duration: several minutes to 15 minutes, depending on pump capacity.

Backwash Function:

• Cleans dirt from DMI65 media.
• Reactivates the media’s catalytic surface.

If the raw water used for backwashing has a high suspended solid content, the backwash process needs to be continued with a rinsing stage to ensure the cleanliness of the media.

3. Rinsing Stage 

Rinsing is performed after backwash to remove any remaining solid contaminants before the filter returns to normal operating mode.

Rinsing Steps:

• Rinsing duration:
  • 30 seconds for small bed depths.
  • 1 to several minutes for large bed depths.
• After rinsing, check the suspended solids in the filtered water to ensure that the media is ready to be reused.

In a processing system with raw water that is clean from suspended solids, the rinsing stage is not mandatory.

4. Filtration Stage

This stage is the main process where raw water is filtered through DMI65 media. This process aims to reduce Fe and Mn levels to the specified standards. 

Factors Affecting Filtration:

• Linear Velocity (LV):
  • The optimum LV ranges from 5–10 m/h for large systems.
  • Lower velocities provide longer contact times, thus increasing the efficiency of the catalytic oxidation reaction.
• Chlorine Injection:
  • During filtration, chlorine injection is still carried out by maintaining the residual chlorine in the filtered water in the range of 0.1–0.3 ppm.
• pH:
  • The optimal pH for the filtration process is 6.8–7.2.

Benefits of Optimal LV:

• Reduce backwash frequency.
• Reduce energy consumption.
• Maximize Fe and Mn removal efficiency.

H. Conclusion

Based on this case study, several key conclusions can be drawn regarding the implementation of DMI65 media filters in water treatment systems:

1. Effective and Efficient Ability

The DMI65 media filter has proven to be reliable in reducing iron (Fe), manganese (Mn), and color levels in water. This process is carried out with high efficiency, producing water quality that meets standards without requiring additional complex processing.

2. Flexibility and Low Operating Costs

The implementation of the DMI65 filter is very flexible, both for existing and new treatment systems. With lower operating costs, including savings in electricity, operator labor, and chemicals such as chlorine, the DMI65 filter is an economical solution for a variety of water treatment needs.

3. Wide Application and Long Service Life

The DMI65 filter can be applied for various purposes, including clean water treatment, drinking water, and industrial process water. In addition, the DMI65 media has a long service life, exceeding 8 years, thus providing long-term benefits for users with sustainable water treatment needs.

With reliable capabilities, economical operating costs, and flexible applications, the DMI65 media filter is the optimal solution to meet modern water treatment needs, both for domestic and industrial scales.

Ready to revolutionize your water treatment processes? Discover how media filter can efficiently remove iron, manganese, and color, ensuring optimal water quality with reduced costs and enhanced sustainability.

Contact us today to learn more about implementing this proven solution in your system and experience cleaner, safer water for your community or industry!