Select a CBFP to dewater an anaerobic digester sludge. The sludge is primary plus waste activated sludge that has a solids concentration of 2.5% and a specific gravity of 1.02. The design sludge flow rate is 171.2 m³/d. The plant managers wish to operate on a two-shift basis, that is, 16 h/d to

Question

Select a CBFP to dewater an anaerobic digester sludge. The sludge is primary plus waste activated sludge that has a solids concentration of 2.5% and a specific gravity of 1.02. The design sludge flow rate is 171.2 m³/d. The plant managers wish to operate on a two-shift basis, that is, 16 h/d to minimize labor costs. Using Table 27-20, select an appropriate CBFP belt width.

Accepted Answer

a. Convert the sludge flow rate to units compatible with Table 27-20 taking into account that dewatering will take place over the 16 hour workday.
[latex]\frac{171.2 m^{3}/d}{16 h/d} [/latex] = 10.7 m³/h

b. From Table 27-20, select a 1.0 m width belt as a first trial.

c. Compute the solids loading rate using Equation 15-9 from Chapter 15.
[latex]\sout{V}_{sl} = \frac{M_{s}}{(ρ)(S_{sl})(P_{s})} [/latex] (15-9)
[latex]M_{sl} = (Q_{sl})(ρ)(S_{sl})(P_{s})[/latex]
= (10.7 m³/h)(1, 000 kg/m³)(1.02)(0.025) = 272.85 or 273 kg/h

This is within the range of 125–510 kg/h specified by the manufacturer.

d. Check the hydraulic and solids loading.

Hydraulic:
[latex]\frac{10.7 m^{3}/h}{1.0 m belt width} [/latex] = 10.7 m³/h ⋅ m or 178.3 L/min ⋅ m

Solids loading:
[latex]\frac{273 kg/h}{1.0 m belt width} [/latex] = 273 kg/h ⋅ m

The hydraulic loading is within the typical ranges of 80–190 L/min ⋅ m, and the solids loading is within the typical range of 180–320 kg/h ⋅ m given in Table 27-19.

Comments:
1. This is a trial selection. Other factors to be considered are polymer addition and the low percent solids of the feed.

2. For existing facilities, the use of pilot units is highly recommended.

Table 27-20 Typical continuous filter press manufacturer’s data
Hydraulic loading, m³/h	Solids loading, kg/h	Belt width, m
1–3	25–120	0.5
3–5	120–200	0.75
5–20	125–510	1.0
20–30	510–815	1.5
30–40	765–1,070	2.0
40–50	1,020–1,275	2.5
50–60	1,275–1,530	3.0
Note: These presses are representative but do not represent actual choices. Actual manufacturers’ data must be used for real world design.

Question 27.8: Select a CBFP to dewater an anaerobic digester sludge. The s...

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