Settling Tank - Dimension 1

1. Determine the area of settling tanks

a). Solid Flux Loading (SFL) Criteria

0.4 ~ 0.8 lb/ft²�h for average loading

1.2 lb/ft²�h = 29 lb/ft²�d < 50 lb/ft²�h for peak loading

b). Calculate area required

MLSS_r = 7,500 ~ 11,000 mg/l

R = 0.28 ~ 0.48

a). Calculate area at MLSS_r = 11,000 mg/l, SFL = 0.4 lb/ft²�h, R = 0.28

A = 14,000 ft²

R Q(gal/day) MLSS(mg/l) SFL(lb/ft²�h)

(ft²)

b). Calculate SFL at different operation conditions

Keep MLSS = 2,500 mg/l in aeration tank

Table of SFL at different operation conditions

Select A_L = 14,000 ft²

SFL, lb/ft2.h	0.4	0.41	0.43	0.45	0.46	Peak, 0.92	Satisfaction
Q mgd	5	5	5	5	5	10	All SFL satisfy the criteria
R	0.28	0.32	0.37	0.44	0.54	0.48
MLSSr	11,000	10,000	9,000	8,000	7,000	7,500
1+R	1.28	1.32	1.37	1.44	1.54	1.48
AL, ft2	13,900

 

c). Check surface overflow rate (SOFR) corresponding to the area decided by SFL

SOFR = (1+R)Q/A

At average flow, SOFR = (1+0.54) � 5 � 10⁶/14,000 � 550 gal/ft²�d,

< 800 gal/ft²�d, ok

At peak flow, for R = 0.48, SORF = (1+ 0.48) � 10 � 10⁶/14,000 � 1,100 gal/ft²�d,

< 1,200 gal/ft²�d, ok

R Q(gal/day) Area(ft²)

(ft²)