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# Sludge Digester

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If a mixed primary & waste activated sludge is treated in a digester that will destroy 60% of the VSS, determine the sludge volume (a) before digestion, (b) after digestion and, (c) the percent reduction in sludge volume for 2,500 lb (dry basis) of combined primary/waste activated sludge with the following characteristics:

https://brainmass.com/engineering/environmental-engineering/sludge-digester-539606

#### Solution Preview

Sludge (S) contains three parts: Water (W), Volatile Suspended Solids VSS (V) and Fixed Suspended Solids FSS (F).

Given,
mass of VSS + FSS = mv + mf = M = 2500 lb

a.
Before digestion
% of VSS (pv) = 65%, = (mv/ms)*100 => mv/ms = 0.65 [Here, ms: mass of sludge]
% FSS (pf) = 4% = (mf/ms)*100 => mf/ms = 0.04
% solid pM = pv + pf = 65 + 4 = 69%
Hence, %Water (pw) = 100 - pM = 100 - 69 = 31% = (mw/ms)*100 => mw/ms = 0.31

Specific gravity of VSS Sv = 1.0
Specific gravity of FSS Sf = 2.5
Specific ...

#### Solution Summary

Solution to a numerical problem related to sludge treatment.

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