9-Wastewater Sludge Characteristics

8/22/2019 9-Wastewater Sludge Characteristics

1/19

Characteristics of Wastewater

Treatment Sludge

By

Ricardo B. Jacquez

Professor

CAGE Department

NMSUAssistant: Maung Myint


2/19

Important Relations for Sludge Calculations

Ws = weight of the dry solids

Wf = weight of the fixed solids

Wv = weight of the volatile solids

Ss = specif ic gravity o f dry so l ids

Sf = specific gravity of fixed solids (2.5)

Sv = specific gravity of volatile solids (1.2)

v

v

f

f

s

s

S

W

S

W

S

W


3/19

Sludge volume = V

Ws= weight of dry solid [lb or gm]r = unit weight of water = 62.4 lb/ft3 = 1000 kg/m3

Swet.sludge = specific gravity of wet sludge

sludgewet

Srsolid

WsV

.100

%


4/19

Sources of wastewater sludge

Primary clarifier

Secondary clarifiers:

activated sludgebio-towers


5/19

Typical domestic wastewater sludge,

Ws=1

Wf=0.3 Wv=0.7

Sf=2.5 Sv=1.2

42.12.1

7.0

5.2

3.01

s

s

v

v

f

f

s

s

SS

S

W

S

W

S

W


6/19

Typical sludge has 96.5% water, 3.5% solid,

and specific gravity of solid=1.42.

Determine the specific gravity of typical wetsludge?

0.101.142.1/5.31/5.96 5.35.96

/%/%

%%

.

.

sludgewet

sludgewet

S

SssludgeinsolidSwwater

sludgeinsolidwaterS


7/19

Primary clarifier solids

Mp=E Q [MGD] SS [mg/L] 8.34 [lb/MG(mg/L)]

Mp = mass of primary solids, [lb/day]

E = efficiency of primary clarifier (see Fig)SS = suspended solid concentration in influent

[mg/L]

Q = flow rate [MGD]


8/19

(from Peavy, Rowe, and Tchobanoglous, 1985, p. 228)


9/19

Secondary clarifier solids

Ms=YQ[MGD] BODR [mg/L] 8.34[lb/MG mg/L]

Ms=mass of secondary solids [lb/day]Y =yield coefficient (see Fig. 5-37)

BODR=BOD removed [mg/L]

Q = flow rate [MGD]


10/19

Volume of sludge

sludgewetofgravityspecif icS

gallbwaterofweightunitr

daygalsludgeofvolumeV

SrwaterMMV

Srsolid

MMV

sludgewet

sludgewet

SP

sludgewet

SP

.

.

.

]/34.8[

]/[

)100/%100(

)100/(%


11/19

Typical solids content of sludge

Type of sludge Sludge concentration %

Un-thickened Thickened

Separate

Primary sludge 2.5 - 5.5 8 - 10

Trickling-filter sludge 4 - 7 7 - 9

Activated sludge 0.5 - 1.2 2.5 - 3.3

Pure O2

sludge 0.8 - 3 2.5 - 9

Combined

Primary and trickling-

filter sludge 3 - 6 7 - 9

Primary and modified-

aeration 3 - 4 8.3 - 11.6

Primary and air-activated sludge 2.6 - 4.8 4.6 - 9


12/19

Ex. Reduction of volume by sludge thickening

A wastewater-treatment plant consists of

primary treatment units followed by an

activated-sludge secondary system. The

primary and secondary sludges are mixed,

thickened in a gravity thickener, and sent to

further treatment. A schematic of the system isshown in the next slide.

Influent SS=200mg/L Primary sludge =5%

Influent BOD=225mg/L

Effluent BOD=20mg/L Thickened sludge=4%

Flow Q = 5 MGD Secondary sludge=0.75%


13/19

Primary clarifier diameter = 82 ft

Aeration volume = 102,400 cft = 766,180 gal

Influent Primary Aeration Secondary

clarifier clarifier

Sludge return

Liquid

Return Thickener Thickened sludgeto sludge-treatment facilities

MLSS in aerator 3,500 mg/L


14/19

1. Mass and volume of primary sludge

a) area of primary clarifier = A = 3.14 D2/4

A = 3.14 (82 ft)2

/ 4 = 5,283 ft2

b) overflow rate = Q/A = 5.0 x 106/5283 ft2

=950 gpd/ft2 (42 m/s)

c) from Fig. 5-13, the efficiency of clarifier isEss = 58% EBOD = 32%

d) mass of primary solids removed is Mp

Mp=Ess Q SS

=0.58(5 MGD)(200 mg/L)(8.34lb/MG mg/L)

Mp=4,840 lb/day


15/19

e) volume of primary sludge

daygalV

gallb

dlbV

Srsolid

MV

sludgewet

P

/600,11

)0.1(/34.8)100/5(

/840,4

)100/(% .


16/19

2. Mass of secondary solids

b) from Fig. 13.1 (text, pg 651), Y=0.48

c) mass of secondary solid Ms

Ms=Y BOD5

Q

=0.48(5MGD)133mg/L(8.34lb/MG mg/L)

Ms = 2,660 lb/day

29.0/3500766.0

/22532.015

/

LmgMG

LmgMGD

M

F

masssludge

dayappliedBOD

M

F


17/19

d) volume of secondary sludge

3a. Total mass of solids MT=Mp +Ms

MT= 4,840 + 2,660 = 7,500 lb/day

3b. Total volume of sluge VT =Vp +Vs

VT= 11,600+ 42,600 = 54,200 gal/d

daygalV

gallb

dlbV

Srsolid

MV

sludgewet

s

/600,42

)0.1(/34.8)100/75.0(

/660,2)100/(% .


18/19

4a) mass of solids sent to sludge treatment

Neglect the solids in the thickener

supernatant, the mass of solids in thethickened sludge is equal to 7,500 lb/day.

4b) volume of thickened sludge

daygalV

gallb

dlbV

Srsolid

MV

sludgethickened

thickened

/500,22

)0.1(/34.8)100/4(

/500,7

)100/(% .


19/19

5. Volume reduction (%) by thickening

%58100200,54

500,22200,54

100

reductionvolume

V

VVreductionvolume

T

thickenedT

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9-Wastewater Sludge Characteristics