Wastewater Calculations - Mathematics and Statistics for the Environment - page 734

Solution: First convert lb/hr solids loading to tons/hr solids loading:

3100 lb/hr
2000 lb/ton

= 1.55 tons/hr

Now calculate pounds flocculant per ton of solids treated:

r)
Solidstreated (ton/hr)

Flocculant (lb/h 12 lb/hr

1.55 ton

Flocculant dosage(lb/ton) = = = 7.8 lb/ton

s/hr

24.14.2.2.6 Total Suspended Solids
The feed biosolids solids are comprised of two types of solids: suspended solids and dissolved sol-
ids. Suspended solids will not pass through a glass fiber filter pad. Suspended solids can be further
classified as total suspended solids (TSS), volatile suspended solids, or fixed suspended solids and
can also be separated into three components based on settling characteristics: settleable solids,
floatable solids, and colloidal solids. Total suspended solids in wastewater is normally in the range
of 100 to 350 mg/L. Dissolved solids will pass through a glass fiber filter pad. Dissolved solids can
also be classified as total dissolved solids (TDS), volatile dissolved solids, and fixed dissolved sol-
ids. Total dissolved solids are normally in the range of 250 to 850 mg/L.
Two lab tests can be used to estimate the total suspended solids concentration of the feed bio-
solids to the filter press: total residue test (measures both suspended and dissolved solids concen-
trations) and total filterable residue test (measures only the dissolved solids concentration). By
subtracting the total filterable residue from the total residue, we obtain the total nonfilterable residue
(total suspended solids), as shown in Equation 24.155:

Total residue (mg/L) - Total filterable residue (mg/L) = Total nonfilterable residue (mg/L) (24.155)

■ EXAMPLE 24.122
Problem: Lab tests indicate that the total residue portion of a feed biosolids sample is 22,000 mg/L.
The total filterable residue is 720 mg/L. On this basis, what is the estimated total suspended solids
concentration of the biosolids sample?
Solution:

Total residue (mg/L) - Total filterable residue (mg/L) = Total nonfilterable residue (mg/L)

22,000 mg/L - 720 mg/L = 21,280 mg/L Total suspended solids

24.14.3 r otary v aCuum F filter2 d eWatering C alCulations
The rotary vacuum filter (Figure 24.10) is a device used to separate solid material from liquid. The
vacuum filter consists of a large drum with large holes in it covered with a filter cloth. The drum
is partially submerged and rotated through a vat of conditioned biosolids. This filter is capable of
excellent solids capture and high-quality supernatant or filtrate; solids concentrations of 15 to 40%
can be achieved.

24.14.3.1 Filter Loading
The filter loading for vacuum filters is a measure of lb/hr of solids applied per square foot of drum
surface area. The equation to be used in this calculation is shown below:

Solidstofilter (lb/hr)

Surface area (ft )

2 =

(24.156)

Filterloading (lb/hr/ft)

2