Let’s Break Down This Classic Iron and Manganese Removal Case.

Project Overview

    This project is an off-grid photovoltaic EDR demonstration water treatment project jointly implemented by the United States Bureau of Reclamation (USBR) and Indian research institutions. Commissioned in        2019, it serves as a standard reference case for solar-powered brackish water desalination in rural India.

     Project Location: Chelluru Village, on the outskirts of Hyderabad, Telangana, India Project Type: Off-grid photovoltaic power supply + EDR electrodialysis reversal desalination project for domestic water       supply Design Capacity: 6–10 m³/d of purified water, meeting the village’s daily drinking water demand and supplementary water for small-scale irrigation.

Raw Water Quality (Field Test Data):

• Groundwater TDS: 1300–1600 mg/L (brackish water)
• Total Iron: up to 1.8 mg/L (severely exceeding standard)
• Total Manganese: 0.35 mg/L (exceeding standard)
• Minor hydrogen sulfide, natural organic matter and colloidal sediment present
• Water Quality Characteristics: Reductive groundwater. Ferrous iron and manganous manganese exist in fully dissolved form, which is colorless and transparent and easily overlooked visually.

Core Project Pain Points & Operational Failure Experience: The project initially omitted complete pretreatment, including aeration and iron/manganese removal stages, feeding raw water directly into the        EDR unit. After only 2 months of operation, problems emerged: yellow-brown iron-manganese deposits formed on EDR membrane surfaces, membrane resistance rose, water production declined                    significantly, and desalination efficiency dropped sharply.

    The system was later retrofitted with a full pretreatment package, with the key addition of aeration and manganese greensand iron & manganese removal system. The equipment resumed stable operation        and has run continuously year-round ever since.

II. Complete Process Flow (Actual On-site Operation Sequence)

    Deep well water intake → Forced mechanical aeration system → Settling & equalization tank → Quartz sand filtration → Manganese greensand catalytic iron & manganese removal system (core          stage) → Activated carbon filtration → 5 μm cartridge security filtration → Intermediate clean water tank → Photovoltaic EDR desalination main unit

III. Process Units: Operation, Principles & Functions (Detailed Engineering Version)

    1. Deep Well Water Intake Unit

    Equipment Configuration: Submersible deep well pump, pipeline coarse strainer, motorized inlet valve, simple water quality monitoring probes. On-site Operation: Extract deep groundwater at constant      flow rate. The inlet intercepts large impurities such as leaves, gravel and coarse sediment to prevent pump abrasion and downstream pipeline clogging. The system monitors raw water turbidity and baseline      salinity in real time for water quality comparison before and after treatment. Core Function: Stabilize water source, protect the entire downstream equipment, and supply uniform influent for subsequent          pretreatment.

2. Forced Spray Aeration Unit (Mandatory Precondition for Iron & Manganese Removal)

    Equipment Configuration: Vertical spray aeration tower, low-pressure blower, water distribution spray nozzles. On-site Operation: Groundwater is evenly sprayed from the tower top and falls downward;      the blower continuously supplies sufficient air to achieve full water-air contact and extend gas-liquid exchange duration.

    Underlying Principle (Key): Iron and manganese in groundwater exist as dissolved divalent ions, colorless and transparent, and cannot be trapped by any filter media. Oxygen must be introduced via            aeration to drive chemical reactions:

• Ferrous iron → oxidized to ferric hydroxide (yellow-brown flocs, filterable)
• Manganous manganese → oxidized to solid manganese dioxide particles (filterable)

    Secondary Benefits: Remove hydrogen sulfide odor, release carbon dioxide, slightly raise pH, and create favorable water conditions for the catalytic reaction of manganese greensand filter media.

3. Settling & Equalization Tank

    Equipment Configuration: Integrated sedimentation tank, bottom blowdown valve, liquid level automatic control system. On-site Operation: Aerated water enters the tank with a retention time of no          less than 30 minutes. Large iron oxide flocs and suspended impurities generated by oxidation settle naturally. Operators open the bottom valve regularly every day for sludge discharge. Core Function:            Remove most iron oxide sludge in advance to greatly reduce the load on downstream filter vessels, extend the service life of quartz sand and manganese greensand media, and reduce backwashing                  frequency. It also stabilizes water flow and water quality to avoid impact from influent fluctuations.

4. Quartz Sand Filtration Unit

    Equipment Configuration: FRP pressure filter tank, refined quartz sand filter bed, automatic air-water backwashing system. On-site Operation: Water flows downward through the bed to trap residual        fine suspended solids, colloids and trace iron rust after sedimentation. The unit triggers automatic backwashing based on pressure differential: air scouring first loosens the filter bed, followed by water              rinsing  for contaminant discharge. Core Function: Further reduce effluent turbidity and protect the subsequent iron & manganese removal filter media from clogging and contamination, acting as a pre-          protection barrier for the iron-manganese removal system.

5. Manganese Greensand Catalytic Iron & Manganese Removal Unit (Most Critical Stage)

    Equipment Configuration: Special pressure vessel for iron & manganese removal, high-grade natural manganese greensand filter media, long-lasting catalytic film, intelligent backwashing system.                  Refined  On-site Operation: Control water flow through the filter bed at a steady rate, with the empty bed contact time (EBCT) strictly maintained above 7 minutes. A stable catalytic oxidation film forms        spontaneously on the manganese greensand surface, continuously performing secondary deep oxidation and adsorption interception for residual unoxidized ferrous iron and manganous manganese in the          water. When pressure differential inside the tank rises, the system automatically performs combined air-water backwashing to flush away saturated iron-manganese oxide sludge.

    Field Effluent Data:

• Influent total iron: 1.8 mg/L → Effluent total iron: ＜0.2 mg/L
• Influent total manganese: 0.35 mg/L → Effluent total manganese: ＜0.05 mg/L

    Irreplaceable Engineering Significance: EDR ion-exchange membranes are highly sensitive to iron and manganese. Once iron and manganese enter the membrane stack, they continuously oxidize and        deposit on the membrane surface, forming hard irreversible scaling layers that block ion channels. This leads to permanent reduction in water production, elevated membrane resistance and increased energy      consumption. This stage is the decisive link to protect EDR membrane stack lifespan and guarantee long-term stable system operation.

6. Granular Activated Carbon (GAC) Filtration Unit

    Equipment Configuration: Food-grade granular activated carbon filter tank On-site Operation: Water slowly penetrates the carbon bed; backwashing is performed periodically, and carbon media is              replaced once saturated. Core Function: Adsorb natural organic matter, tannins, color, trace odor and residual free chlorine in raw water. Organic matter is the primary culprit for organic fouling of EDR            membranes. Activated carbon can eliminate the source of organic contamination at the pretreatment stage.

7. 5 μm Precision Security Filtration

    Equipment Configuration: Precision filter housing, PP melt-blown filter cartridges On-site Operation: Trap fine powder shed from upstream filter media and trace solid particles; cartridges are replaced        periodically. Core Function: Final physical protection to prevent hard particles from entering the EDR membrane stack, avoiding physical scratches on membrane sheets and flow channel blockage.

8. Intermediate Clean Water Stabilization Tank

    On-site Operation: Store qualified pretreated clean water and interlock start-stop of upstream and downstream pumps. Core Function: Offset flow fluctuations caused by variable sunlight intensity of the      photovoltaic system, ensuring constant inlet pressure and flow rate for the EDR main unit and stable desalination working conditions.

9. Photovoltaic EDR Main Desalination System (Backend Core)

    Fully pretreated qualified water enters the solar-powered EDR electrodialysis reversal unit. The raw water TDS is reduced from 1600 mg/L to 300–500 mg/L, fully meeting drinking water standards and              agricultural supplementary irrigation requirements for rural India.