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180 8. GRANULAR MEDIA FILTRATION
TABLE 8.4 Example of Single-Stage Dual Granular Media Gravity Filtration System for 50,000 m3/day
(13.2 MGD) Desalination Plant
Component/Parameter
FEED WATER
• Design flow rate, m3/day (MGD) • Turbidity, NTU
• SDI5
DESIGN CHEMICAL DOSAGES
• Ferric chloride, mg/L
• Polymer, mg/L
• Sulfuric acid, mg/L: Target pH: 7.6
FILTER CELLS
• Number
• Width, m (ft)
• Length, m
• Filter cell area
• Total filter cell depth
• Total filter media depth
• Water depth above the filter bed
TOP-LAYER FILTER MEDIA
• Type
• Depth
• Effective size
• Uniformity coefficient
• Specific density, tons/m3
BOTTOM-LAYER FILTER MEDIA
• Type
• Depth
• Effective size
• Uniformity coefficient
• Specific density, tons/m3
FILTER PERFORMANCE PARAMETERS
• Average surface loading rate
• Maximum surface loading rate with 2 units out of service • Filtration cycle
BACKWASH RATE
• Average
• Maximum
Specifications/Design Criteria
122,093 (32.3 MGD) 0.3e10 (max 20) 6e10 (max 12)
10 (0.5e30 mg/L) 0.25 (0.0e1.0 mg/L) 8 (0e30 mg/L)
12
4 (13.2 ft)
15 (49.2 ft)
60 m2 (649.44 ft2) 6.0 m (19.7 ft) 1.8 m (5.3 ft)
2.0 m (6.6 ft)
Anthracite 1.0 m (3.3 ft) 1.0 mm
1.3
1.55
Sand
0.8 m (3.3 ft) 0.6 mm
1.3
2.65
7.1 m3/m2 h (2.9 gpm/ft2) 8.5 m3/m2 h (3.5 gpm/ft2) 24e48 h
20 m3/m2 h ( 8 gpm/ft2) 50 m3/m2 h (20 gpm/ft2)