Greensand Filter Media

Greensand filter media removes iron, manganese, and hydrogen sulfide from municipal water supplies through catalytic oxidation and physical filtration. This naturally occurring glauconite sand, enhanced with manganese dioxide coating, oxidizes dissolved metals at the grain surface before capturing precipitated particles within the filter bed. Typical installations achieve 95-99% iron removal efficiency at loading rates of 2-5 gpm/ft². The primary limitation is frequent potassium permanganate regeneration requirements, typically every 1-3 days depending on influent iron concentrations, which increases operational complexity and chemical costs compared to conventional multimedia filtration.

• Iron and Manganese Removal: Primary application in municipal groundwater treatment plants (1-25 MGD). Follows raw water intake and pre-chlorination, upstream of clearwell storage. Selected for simultaneous Fe/Mn oxidation and filtration in single unit, reducing footprint versus separate oxidation/filtration systems. Typical loading rates 2-5 gpm/sf

• Post-Lime Softening Polishing: Secondary filtration after lime softening clarifiers in hard water regions. Removes residual hardness minerals and improves turbidity to <0.1 NTU. Positioned between sedimentation and chlorine contact, upstream of distribution. Chosen for dual-media properties handling variable solids loading from upstream clarifier upsets

• Arsenic Removal Enhancement: Tertiary treatment in plants with elevated arsenic (>10 ppb). Follows pre-oxidation with chlorine or permanganate. Greensand's manganese dioxide coating provides adsorption sites for arsenic species. Typically sized for 3-4 gpm/sf loading with 6-8 hour contact time

• Radium Reduction: Specialized application for radium removal in groundwater systems. Operates downstream of aeration but upstream of pH adjustment. Selected for natural affinity of manganese oxides for radium isotopes, achieving 80-90% removal efficiency in properly conditioned systems

Daily Operations: Operators monitor headloss progression (typically 2-4 feet clean bed to 8-10 feet terminal), effluent iron/manganese levels (<0.3 mg/L Fe, <0.05 mg/L Mn), and turbidity (<0.1 NTU). Backwash initiation triggered by headloss or runtime (24-72 hours typical).

• Filter Media Bed: Manganese-coated glauconite sand, typically 24-30 inches deep. Effective size 0.30-0.35mm, uniformity coefficient <1.6. Density 85-90 lb/ft³. Selection based on raw water iron/manganese concentrations and required service run length. Standard municipal sizing: 2.5-4.0 tons per filter cell

• Underdrain System: Typically Leopold or Johnson wedgewire blocks with 0.020-0.030" slot openings. Provides uniform backwash distribution and prevents media loss. Sized for 15-20 gpm/sf backwash rate. Stainless steel construction preferred for oxidizing environment. Includes gravel support layers: 6" coarse (1/4-1/2"), 6" fine (1/8-1/4")

• Backwash System: Air scour (3-5 cfm/sf) followed by water wash (12-15 gpm/sf). Includes wash water storage tank (typically 10-15% of daily production), backwash pumps, and waste handling. Automated sequence controllers manage 15-20 minute cycles. Surface wash systems optional for enhanced cleaning

• Regeneration Equipment: Potassium permanganate feed system for media reactivation. Includes day tank (50-100 gallons), metering pumps, and contact piping. Feed rate 0.25-0.5 lb KMnO₄ per lb iron removed. Chemical storage sized for 30-day supply with secondary containment

• Hydraulic Loading Rates: Standard filtration: 2-5 gpm/ft² (typical municipal range), High-rate filtration: 5-8 gpm/ft² (requires careful evaluation), Backwash rate: 12-15 gpm/ft² minimum for adequate bed expansion

• Bed Specifications: Media depth: 24-30 inches typical, 36 inches maximum, Effective size: 0.30-0.35 mm (uniformity coefficient <1.6), Minimum freeboard: 50% of bed depth above media surface, Contact time: 5-8 minutes minimum at design flow

• Water Quality Parameters: Influent iron: 0.3-15 mg/L (higher concentrations require pre-oxidation), Influent manganese: 0.05-5 mg/L, pH range: 6.2-8.5 (optimal 6.8-7.2 for manganese removal), Dissolved oxygen: >25% saturation required

• Operational Criteria: Backwash frequency: 24-72 hours typical, Regeneration cycle: 1-4 weeks depending on throughput, Filter run length: 2,000-8,000 gallons per ft² between backwashes, Head loss trigger: 6-8 feet typical

• What is the required iron/manganese removal efficiency and influent concentrations? Concentrations >10 mg/L iron or >2 mg/L manganese may require pre-oxidation with chlorine or potassium permanganate. Without pre-treatment, breakthrough occurs within 24-48 hours. Engineers need raw water analysis with seasonal variations and target effluent goals

• Should the system use continuous regeneration or intermittent potassium permanganate feed? Continuous feed (0.05-0.25 mg/L KMnO₄) maintains coating but increases chemical costs 40-60%. Intermittent regeneration reduces costs but requires 4-8 hour contact time and temporary service interruption. Decision depends on redundancy and acceptable downtime

• What backwash system design accommodates greensand's density and expansion characteristics? Greensand specific gravity (2.4-2.7) requires 12-15 gpm/ft² minimum backwash rate versus 8-10 gpm/ft² for sand. Inadequate rates cause media stratification and channeling. Underdrain design must handle 50% higher flow rates than conventional media

• How will seasonal temperature variations affect filtration performance? Water temperatures <50°F reduce oxidation kinetics by 30-40%, requiring longer contact times or increased permanganate dosing. Systems in northern climates need temperature compensation in control algorithms

• MasterFormat Section 40 05 23 - Filtration Media: Primary specification section for greensand procurement including gradation requirements, chemical composition, and performance testing

• Related sections include 40 05 13 (Filter Underdrains) and 40 30

• Material/Equipment Verification: Verify NSF/ANSI 61 certification for potable water contact, Confirm effective size (0.30-0.35mm) and uniformity coefficient (<1.60), Request certificate of analysis showing manganese oxide content

• Installation Requirements: Requires specialized underdrain systems for backwash distribution, Media depth typically 24-30 inches minimum, Gravel support bed essential (6-12 inches)

• Field Challenges: Media segregation during placement, Proper conditioning with potassium permanganate solution

• Coordination Issues: 4-6 week lead times for bulk quantities, Chemical feed system integration for regeneration

• Inversand Company - Manganese Greensand Plus (standard municipal grade)

• Culligan - Filox-R and Culligan Greensand (residential/small municipal)

• ResinTech - MangOX media (synthetic alternative gaining municipal acceptance)

• Inversand remains the dominant supplier for large municipal installations, with over 70% market share in North America

• Birm Media - Lower cost ($800-1,200/cf vs $1,500-2,000/cf for greensand), but requires dissolved oxygen >2mg/L and pH >6.8

• Catalytic Carbon - Handles wider pH range, removes chloramines simultaneously, costs $2,500-3,500/cf

• Membrane Systems - Higher capital cost but eliminates backwash waste, preferred for smaller plants (<2 MGD) with space constraints

Establish relationships with regional Inversand distributors early - they provide critical technical support during startup. Consider bulk purchasing across multiple filter cells to reduce unit costs by 15-20%. Always order 10% excess media for future maintenance needs. Coordinate permanganate feed system installation with electrical contractors to avoid conflicts. Pre-condition media off-site when possible to accelerate commissioning schedules.