substrates diffuse through the liquid film into the slime film where biological
oxidation and synthesis occur. End products and sludges appear in the filter effluent.
6.2 Low-Rate, High-Rate, and Super-Rate Filters
Trickling filters are classified by hydraulic and organic loading as low-rate, highrate, and super-rate (Figs. 3.16, 3.17, and 3.18). Super-rate filters are also referred to
as roughing filters. There is no rigid dividing line between the various rate trickling
filters [109]. However, some rather general ranges are given in Table 3.5 to differentiate the various types of trickling filters by the hydraulic and organic loadings.
Hydraulic loading is the rate of application of wastewater to the surface, usually
expressed in millions of gallons per day per acre of surface area (mgad) gallons per
day per square foot (gal/d/ft
2 ) or cubic meters per day per square meter (m
3 /d/m
2 ).
Organic loading is in pounds of BOD per acre-foot per day lb/ac.ft/d, pounds of
BOD per cubic yard per day (lb/yd
3 /d), pounds of BOD per 1000 cubic foot per day
(lb/1000 ft
3 /d), or kilograms of BOD per cubic meter per day (kg/m
3 /d).
Accordingly, a low-rate filter is one designed for the applied loadings of not more
than 0.4 kg BOD/m
3 /d (25 lb BOD/1000 ft
3 /d) and 4.08 m
3 /m
2 /d (100 gal/ft
2 /d). The
Fig. 3.16 Standard (low-rate) and high-rate trickling filters. (Source: US EPA)
120
L. K. Wang et al.
oxidation and synthesis occur. End products and sludges appear in the filter effluent.
6.2 Low-Rate, High-Rate, and Super-Rate Filters
Trickling filters are classified by hydraulic and organic loading as low-rate, highrate, and super-rate (Figs. 3.16, 3.17, and 3.18). Super-rate filters are also referred to
as roughing filters. There is no rigid dividing line between the various rate trickling
filters [109]. However, some rather general ranges are given in Table 3.5 to differentiate the various types of trickling filters by the hydraulic and organic loadings.
Hydraulic loading is the rate of application of wastewater to the surface, usually
expressed in millions of gallons per day per acre of surface area (mgad) gallons per
day per square foot (gal/d/ft
2 ) or cubic meters per day per square meter (m
3 /d/m
2 ).
Organic loading is in pounds of BOD per acre-foot per day lb/ac.ft/d, pounds of
BOD per cubic yard per day (lb/yd
3 /d), pounds of BOD per 1000 cubic foot per day
(lb/1000 ft
3 /d), or kilograms of BOD per cubic meter per day (kg/m
3 /d).
Accordingly, a low-rate filter is one designed for the applied loadings of not more
than 0.4 kg BOD/m
3 /d (25 lb BOD/1000 ft
3 /d) and 4.08 m
3 /m
2 /d (100 gal/ft
2 /d). The
Fig. 3.16 Standard (low-rate) and high-rate trickling filters. (Source: US EPA)
120
L. K. Wang et al.