Wastewater treatment: biological treatment

Introduction to Biological Treatment... Approximate composition of average sanitary wastewater mg/l based on 450 liter/capita/day.. Wastewater After primary settling After biological tre

Introduction to

Biological Treatment

Approximate composition of average sanitary

wastewater (mg/l) based on 450 liter/capita/day.

Wastewater

After primary settling

After biological treatment

Average characteristics of selected industrial wastewater

processing Meat packaging Synthetic textile Chlorophenolic manufacturer

Loadings on treatment plants are commonly expressed in units of pounds of BOD per day or pounds of solids per day in addition to the flow rate For example, each person contributes about 0.2 lb BOD/day in domestic wastewater

34 8 ) (

) /

concentrat ion mg l Q million gal per day day

per

Pounds

4 62 )

( )

/





concentrat ion mg l Q million ft per day day

per

Pounds

Example:

Industrial wastewaters have a total flow of 2,930,000 gpd, BOD of 21,600 lb/day and suspended solids of 13,400 lb/day Calculate the BOD and suspended solids concentration

Answer:

BOD= 884 mg/l

SS= 548 mg/l

Wastewater flow rate and BOD loading

0 400 800 1200

0 2 4 6 8 10 12 14 16 18 20 22 24

Time

0 40 80 120 160 200

0 2 4 6 8 10 12 14 16 18 20 22 24

Time

The sanitary and industrial waste from a community consists of

domestic wastewater from a sewered population of 7500 persons; potato processing waste of 30000 gpd containing 500 lb BOD; and creamery wastewater flow of 120,000 gpd with a BOD concentration

of 1000 mg/l Estimate the combined wastewater flow in gallons per day and BOD in mg/l Assume domestic wastewater flow is 120

gpcd and BOD loading is 0.2 lbpcd

Answer:

Potato 30,000 500

Sum 1,050,000 3,000

l

mg d

gal million

d lb conc

34 8 /

05 1

/

3000







Biological Reactions

Adopted from Rittman and McCarty, Environmental Biotechnology Applications, 2001

Lag phase

Log growth

Declining growth phase

Biomass (X)

Stationary phase

Endogenous phase

Time

Bacteria Growth Versus Substrate Decay in Batch Culture

Substrate (S) Concentration

Monod Kinetic Growth Function

S

µ

µmax

0.5 µmax

KS

S K

S

S

max





Biomass

specific

growth rate

Maximum

specific

growth rate

Half-saturation constant

Substrate concentration

Temperature range (oC)

Environmental Factors Affecting Growth

(1) Temperature

) 20

( 20



T k

(2) pH: Best range is

6.5-7.5 but growth

could still occur at

pH as low as 4 or

as higher as 9.

(3) Dissolved oxygen

• Aerobic (DO> 1.5-2.0 mg/l)

• Anoxic (DO<0.2 mg/l)

• Anaerobic (DO<<0.1 mg/l)

Processes

 Primary treatment

 Secondary treatment

 Advanced treatment

Primary Treatment

Grit Chamber

Thickner

Wastewater

influent

Effluent Disinfectant

Screens

Primary Settling tank

Anaerobic digester Dewatering Sludge

disposal

Contact tank

Primary treatment removes about 35% BOD and 60% SS

Secondary Treatment

Biological treatment can be conducted

by one of the following methods:

Activated sludge

Rotating biological contactors

Trickling filters

Overall removal after secondary treatment is

90% BOD and 90% SS

Biological treatment

Effluent

Contact tank

Secondary Settling tank

Disinfectant

Grit Chamber

Thickner

Wastewater

influent

Screens

Primary Settling tank

Anaerobic digester Dewatering Sludge

disposal

Advanced Treatment

May include:

Overall removal after advanced treatment is >95%

BOD and > 95% SS

Zakher WWTP Flow Sheet Diagram