Page 424 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Rapid Filtration 379

TABLE 12.12
Performance Data for Three Filters at Ames, Iowa
Filter Effluent
Parameter Filter
Parameter Units Influent Dual Media Tri-Media Coarse Sand
BOD (mg=L) 30.38 12.68 12.99 14.46
Soluble BOD (mg=L) 9.67 7.21 7.27 7.78
Suspended solids (mg=L) 34.08 7.05 6.82 9.46
TOC (mg=L) 19.86 12.02 12.77 12.99
SOC (mg=L) 13.41 12.00 11.83 12.98
Turbidity (FTU) 17.60 4.80 6.78 4.66
Media Characteristics
Anthracite d 10 (mm)=UC 1.03=1.57 1.03=1.57
Depth in mm (in.) 381 (15 in.) 381 (15 in.)
Sand d 10 (mm) 0.49=1.41 0.49=1.41 2.0=1.52
Depth in mm (in.) 229 (9 in.) 229 (9 in.) 1168 (46 in.)
Garnet d 10 (mm) 0.27=1.55
Depth in mm (in.) 76 (3 in.)
Source: Adapted from Cleasby, J.L. and Lorence, J.C., J. Environ. Eng. Div., Proc. Am. Soc. Civil Eng., 104(EE4), 759, 1978.
Notes: BOD, biochemical oxygen demand (5 day is understood unless subscripted otherwise). Soluble BOD ¼ BOD from filtrate of
filter paper. Suspended solids ¼ solids retained on filter paper after oven drying. TOC, total organic carbon. SOC, soluble
organic carbon. Turbidity measured by light scattering instrument calibrated by formazin standard (formazin is a chemical made
commercially available for this purpose). Filter influent is from secondary clarifier that follows trickling filter treatment from
2
Ames, Iowa WWTP. Filter effluent is from each of three filters operated in parallel at 7.8 m=h (3.2 gpm=ft ).

In filtration of wastewater by depth filtration, the media measurement, flow measurement, and online turbidity and
selection, its depth, and backwashing are all important. A sum- online particle counting (or whatever else may be of interest,
mary of performance of three filter designs is given in Table with fewer and fewer limitations). Equipment catalogs and
12.12. The available headloss for each filter was 1.83 m (6 ft) internet web sites and local (or regional) representatives are
and length of runs were about 12 h for dual media and tri-media sources of information.
filters and about 24 h for the coarse sand filter. In comparing the
three filter designs, the coarse sand had only slightly higher
12.8.2 PACKAGE FILTRATION SYSTEMS
effluent suspended solids than the dual media and mixed media
filters, with effluent turbidity levels being about the same. The A package plant is a small unit that has all of the components
d 10 ¼ 2.0 mm size for the coarse sand was also found to be most required to facilitate operation as a system. For small systems,
appropriate in terms of floc capture per unit of headloss. The such as for populations up to 5000, package plants are often
most effective backwash procedure was subfluidization of the used rather than a generic design. For fewer than 1000 per-
bed coupled with air-wash. sons, a package plant would be strongly favored over a
generic design. A variety of proprietary pilot plants are on
the market and a few examples are described here.
12.8 PROPRIETARY EQUIPMENT
In every generic unit process various kinds of ancillary items 12.8.2.1 Deep Bed Filtration—Parkson DynaSandt
of equipment are required for the process to function, for The Parkson DynaSand Filter has been installed for municipal
example, pipes and valves, surface-wash, under-drain blocks, water treatment, industrial water treatment, industrial waste-
media support, etc. At the same time, proprietary firms have water treatment, and treatment of municipal wastewater. The
produced ‘‘package’’ water treatment systems. The discussion Dyna Sandt filter is a continuous backwash upflow, deep bed
here is intended to indicate the kinds of products available. granular media filter. The filter media is cleaned continuously
by recycling the sand internally by means of an air lift pipe and
sand washer with the clean sand redistributed on the top of the
12.8.1 ANCILLARY EQUIPMENT
bed. Units were installed at the Coors=Golden, Colorado, was-
The support equipment includes surface-wash nozzles, pipes tewater treatment plant (WWWTP) for final polishing of was-
and valves, media, backwash systems, air scour systems, tewater effluent before discharge to the adjacent Clear Creek.
under-drain systems, control systems, and instrumentation. Bed depths of 1016–2032 mm (40–80 in.) are available
The latter may include water level measurement, pressure and sizes from 0.914 to 3.43 m (3 ft-0 in.–11 ft-3 in.) diameter.