Overview
Manganese sand filters, as specialized equipment in the field of groundwater treatment, achieve highly efficient removal of iron and manganese ions in water through the synergistic effect of catalytic oxidation and filtration interception of manganese sand filter media. They are a crucial pretreatment unit for municipal water supply, industrial circulating water, and geological engineering. The technological core lies in utilizing the MnO₂ active groups on the surface of manganese sand (with a catalytic efficiency of ≥95%) to oxidize soluble Fe²⁺ and Mn²⁺ into insoluble hydroxides, and then purify the water quality through the interception of the filter layer. Compared with the traditional aeration oxidation method, this equipment can increase the iron and manganese removal rate to over 98% and reduce the floor area by 40%. It is especially suitable for the treatment of groundwater with an iron content of ≤10mg/L and a manganese content of ≤2mg/L, and has become the mainstream choice for ensuring the safety of urban and rural drinking water and improving the quality of industrial water.
Core Working Principle and Structural Design
I. Analysis of the Catalytic Oxidation Mechanism
1. Chemical Reaction Process
- Iron removal: 4Fe²⁺ + O₂ + 10H₂O → 4Fe(OH)₃↓ (The reaction rate is increased by 3 times under the catalysis of manganese sand).
- Manganese removal: 2Mn²⁺ + O₂ + 2H₂O → 2MnO₂↓ + 4H⁺ (The oxidation efficiency is the best when pH ≥ 7.5).
The MnO₂ on the surface of manganese sand forms catalytic active sites. When groundwater containing iron and manganese passes through the filter layer, dissolved oxygen rapidly reacts with metal ions under the catalytic action, and the generated hydroxides attach to the surface of manganese sand, forming an "active filter membrane" with self-catalytic ability, which extends the filtration cycle to twice that of the traditional process.
2. Filtration Interception System
The particle size of manganese sand is usually 0.6 - 2.0mm, with a bulk density of 1.8 - 2.2t/m³, forming a filter bed layer with a porosity of 40% - 45%. When water flows downward through the filter layer, precipitates such as Fe(OH)₃ and MnO₂ are intercepted, and the turbidity of the effluent water is ≤1NTU, the iron content is ≤0.3mg/L, and the manganese content is ≤0.1mg/L.
II. Structural Design Advantages
1. Corrosion-Resistant and Pressure-Bearing Tanks
They are made of Q235B carbon steel lined with fiberglass (with a thickness of ≥5mm) or 304 stainless steel materials, with a pressure resistance of 0.6 - 1.0MPa, adapting to the groundwater environment with a pH value of 6.5 - 8.5, and having a service life of more than 15 years.
2. Water Distribution and Backwashing Systems
- The upward flow water distributor adopts ABS or stainless steel wedge-shaped screen pipes, with a slit width of 0.25mm, ensuring the uniform distribution of water flow.
- The backwashing adopts a gas-water mixed mode (with a water flow rate of 15 - 20L/(㎡·s) and an air flow rate of 10 - 15L/(㎡·s)). Combined with the collision and friction of manganese sand particles, it can remove iron and manganese oxides in the filter layer. The backwashing cycle is usually 24 - 48 hours.
3. Active Filter Membrane Regeneration Design
When the filter layer is penetrated (when the iron in the effluent water is >0.3mg/L), short-term intensive aeration (DO ≥ 6mg/L) combined with low-intensity backwashing (with a water flow rate of 10L/(㎡·s)) can restore the catalytic activity on the surface of manganese sand and reduce the frequency of filter media replacement.
Analysis of Typical Application Scenarios
1. Iron and Manganese Removal in Urban and Rural Drinking Water
The iron content in the groundwater in a hilly area is 6.8mg/L, and the manganese content is 0.8mg/L. After being treated by a manganese sand filter (with a filtration rate of 8 - 10m/h and a manganese sand particle size of 0.8 - 1.2mm), the iron content in the effluent water is 0.1mg/L, and the manganese content is 0.05mg/L, meeting the requirements of the "Standards for Drinking Water Quality" (GB 5749 - 2022). The equipment is equipped with an aeration device (with a jet aeration oxygen dissolution efficiency of ≥85%), and the treatment cost is only 0.12 yuan/ton, reducing the operating cost by 40% compared with the traditional lime softening method.
2. Anti-Scaling Treatment of Industrial Circulating Water
In the circulating cooling water system of a thermal power plant, the manganese sand filter (with a treatment flow of 300m³/h and a filter layer thickness of 1.2m) removes Fe²⁺ (with a content of 2.5mg/L) in the water to prevent the formation of iron scale on the heat exchanger, maintaining the heat transfer coefficient at 3500W/(㎡·K), which is 20% higher than that without treatment. The equipment reduces the number of acid pickling times by 3 times a year and saves 180,000 yuan in chemical costs.
3. Reuse Treatment of Mine Wastewater
The iron content in the mine water of a certain coal mine is 5.2mg/L, and the manganese content is 0.5mg/L. After adopting the "manganese sand filtration + disinfection" process, the iron content in the effluent water is ≤0.3mg/L, and the manganese content is ≤0.1mg/L, meeting the requirements of the "Pollutant Discharge Standards for the Coal Industry" (GB 20426 - 2006). The water is reused for underground dust removal, saving 120,000 tons of water annually. The filter media is filled with a mixture of magnetite and manganese sand (with a volume ratio of 1:3) to enhance the interception ability of fine particles.
4. Purification of Water for Food Processing
The iron content in the source water of a mineral water factory is 1.5mg/L. After being treated by a manganese sand filter (with a filtration rate of 6m/h and a SiO₂ content in manganese sand of ≤3%), the iron content is reduced to 0.08mg/L, avoiding the appearance of an "iron smell" and turbidity in the mineral water after filling. The equipment is equipped with a PLC automatic control system, which dynamically adjusts the backwashing intensity according to the iron content in the influent water, extending the service life of manganese sand to 5 years.
Technical Advantages and Industry Value
1. High-Efficiency Catalysis and Stable Filtration
- The synchronous removal rate of iron and manganese is over 98%, and the effluent water indicators are better than national standards.
- The penetration cycle of the filter layer is as long as 72 hours, which is 3 times that of traditional quartz sand filtration, reducing the frequency of backwashing.
2. Low Energy Consumption and Economic Adaptability
- Low energy consumption: The electricity consumption for treating one ton of water is ≤0.05kW·h, which is only 1/10 of that of membrane treatment.
- Low investment cost: The equipment cost is about 1/3 of that of the ion exchange method, which is suitable for small and medium-sized water treatment projects.
3. Long Service Life and Easy Maintenance
- Manganese sand filter media can be regenerated and reused: 90% of the catalytic activity can be restored through acid pickling (with a 10% HCl solution), and the replacement cycle is 8 - 10 years.
- High degree of automation: Integrated with differential pressure sensing and automatic backwashing, it can achieve unattended operation.
Selection and Maintenance Guidelines
I. Key Selection Factors
- Adaptation to Iron and Manganese Contents:
When iron > 10mg/L or manganese > 2mg/L, pre-aeration or multi-stage filtration is required. For conventional groundwater (with iron ≤ 10mg/L and manganese ≤ 2mg/L), a single-layer manganese sand filter tank (with a filter layer thickness of 1.0 - 1.2m) is selected.
- Filtration Rate and Flow Design:
The filtration rate of a gravity filter is 8 - 10m/h, and that of a pressure filter is 10 - 15m/h. The equipment is configured at 1.2 times the maximum treatment flow.
- Material and Anti-Corrosion:
When the Cl⁻ content in groundwater is >500mg/L, a 316L stainless steel tank is selected. For ordinary water quality, carbon steel + fiberglass lining is selected.
II. Maintenance Optimization Strategies
1. Daily Operation Management
- Monitor the iron and manganese concentrations and turbidity of the influent and effluent water daily. When the iron removal rate drops by 10%, start backwashing.
- Control the pH value of the influent water to be ≥6.5. When it is lower than this value, add lime for adjustment (with an addition amount of 5 - 10mg/L).
2. Filter Media Regeneration Process
- When the surface of manganese sand turns black and the catalytic efficiency decreases, soak it in a 10% sulfuric acid solution (at a temperature of 40 - 50°C) for 2 hours, and then rinse it with clean water until the pH value is 6 - 7.
- Conduct sampling inspections of the MnO₂ content of manganese sand every year. When it is lower than 35%, partial replacement (with a replacement amount of 10% - 20%) is required.
3. Troubleshooting
- Excessive iron in the effluent water: Check whether the aeration oxygen dissolution is sufficient (DO should be ≥5mg/L) and whether there is channeling in the filter layer.
- Poor backwashing effect: Confirm the backwashing intensity (the water flow rate should be ≥15L/(㎡·s)) and clean the blockages in the water distributor.
Industry Development Trends
With the increasing demand for groundwater pollution prevention and resource utilization, manganese sand filters are developing in the directions of high efficiency, intelligence, and multi-functionality:
- Nanocatalytic Modification: Manganese sand loaded with MnO₂ nanoparticles has an increased catalytic efficiency by 50% and can handle high-concentration wastewater with an iron content of ≤15mg/L.
- Intelligent Coordinated Control System: Integrated with ORP sensors and AI algorithms, it can optimize the aeration intensity and backwashing strategy in real time, increasing the utilization rate of manganese sand by 20%.
- Integration of Composite Processes: Integrated with ultrafiltration membranes and activated carbon filtration to form an "iron and manganese removal - decarbonization - disinfection" integrated equipment, which is suitable for decentralized water supply scenarios.
Conclusion
Manganese sand filters have become the core equipment for the treatment of iron and manganese pollution in groundwater with the synergistic technology of catalytic oxidation - filtration interception. From the safety of urban and rural drinking water to the utilization of industrial circulating water, their characteristics of high efficiency, economy, and easy maintenance have solved the efficiency bottleneck of traditional processes. In the future, with the integration of nanomaterials and intelligent control technology, this equipment will play a more crucial role in the treatment of high-difficulty groundwater and water environment restoration, promoting the recycling of water resources to move towards precision and low carbon.
