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From Masselli, Masselli, and Burford. A simplification of textile waste survey and treatment. New England Interstate Water Pollution Control Commission. a% on weight of fiber, a weight percentage based on dried cloth weight. bOWF, weight percentage based on dried cloth.

0.10. As a general rule, one lb of oxygen is required per lb of BOD removed under conventional activated sludge operations with an F to M ratio of 0.3 to 0.5. For aerobic digestion with an F to M ratio of 0.1, approximately 1.5 lb of oxygen are required per pound of BOD removed.

Sludge Production

In the activated sludge process, soluble organic matter is converted to suspended solids in the form of bacterial cells.

The amount of sludge produced is a function of process loading and of BOD removal. Sludge production can be expressed within practical limits by equation 8.2(2):

lb of volatile suspended solids produced lb BOD removed

lb mixed liquor volatile suspended solids lb BOD applied per day

The value of "A" varies from 0.4 to 0.9, and the value of "B" from 0.01 to 0.1, depending on the waste being treated. An approximate expression for sludge production in many treatment applications is given in equation 8.2(3):

lb volatile suspended solids produced lb BOD removed lb mixed liquor volatile suspended solids

lb BOD applied per day

Based on conventional activated sludge operations, between 0.5 and 0.6 lb of excess sludge are produced per lb of BOD removed. With aerobic digestion, approximately 0.2 lb of excess sludge are produced per lb of BOD removed.

Aerobically digested sludge can be dewatered on vacuum filters with loadings of approximately 1 lb/sq ft/hr. Dewatering excess sludge from conventional activated sludge operations requires a heat treatment for sludge conditioning or a heavy dosage of conditioning chemicals to form a filter cake that will dewater and separate from a filter cloth.

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