Which results of measurement are obligatory

required for an optimized operation of a wastewater

treatment plant?

Speaker: Prof. Dr.-Ing. habil. Holger Scheer

Emscher Gesellschaft für Wassertechnik mbH, Essen

(Essen, Germany)

Presto-Seminar “Advanced Technologies and Ope-

ration of WWTP for an efficient nutrient removal“

May 23rd 2012

in St. Petersburg

_________________________________________________________________________________

Prof. Dr.-Ing. habil. Holger Scheer - Tel.: 0049 (0)201/3610-0 - E-Mail: scheer@ewlw.de

Content

1. Determination of representative measurements

2. Correct sampling in the influent

3. Important data required for optimization of operation

4. Real load of a wastewater treatment plant

4.1 Current rate of the connection

4.2 Real sludge load

5. Example for optimization of energy costs

6. Example for optimization of use of precipitant

7. Example from the field of sludge treatment

8. Summary

1. Determnination of representative measurements

Usability guaranteed? (accuracy, systematics...)

Sufficient frequency in a represantive period (including the weekends)

Analytic quality control of the lab (if needed, external control)

Daily composite samples available for the needed parameters?

Sampling point suitable (e.g. because of internal material flows).

For the optimal operation of a wastewater treatment plant a possibly large database

is needed.

Records of: Amount of wastewater

Weather conditions

Wastewater temperature

Concentration of certain parameters

Check the parameters on:

Place of the sampling

In practice only 3 places for representative sampling:

Raw sewage influent

Effluent of the primary treatment, influent in the biological treatment

Outlet into the surface water

2. Correct sampling

Continuous (online) measurement of the concentrations of important parameters

in influent desirable, but not possible to realise without great technical effort.

Therefore Higher effort for sampling and analysis

Possibilities of the sampling:

Sample collectors in proportion to volume and stream-flow

Sample collectors linked to the stream-flow need a measurement signal

of the stream-flow.

Generally daily composite samples are collected.

Sample collectors in proportion to time

Used, when approach to the measurement signal to complex.

The sample collectors need a cylinder switchover for daily 12 2h composite samples

Daily CS Manual rating of the 2-h-CS with inflow of belonging intervalls.

Manual sampling

Grab samples taken every half an hour or hour combined into a 2h sample.

After that same as sampling in proportion to time.

2. Correct sampling in the influent Q

[m

³/h]

Influent

BO

D5 C

onc.

Rainfall event

0 Time of day 24 - h 0 Time of day 24 - h

Time-proportional

Flow-proportinal

With sampling in one cylinder in proportion to time

Combined wastewater influent with low concentration rated as dry weather

Result of measurement often to high because of wrong sampling!

3. Important and required data for the operation optimization

During the time period of one year :

1. Date and day

2. Mark dry weather days

3. Wastewater temperature in the efluent of the reactor

(As an alternative in the influent or efluent of the primary treatment)

4. Daily wastewater run off Qd in m³/d

5. Dry weather run off QD,d in m³/d

6. Measured concentration in mg/l from 24 h-composite sample of the

influent of the biological treatment

• COD, homogenized, CCOD

• COD of the filtration of the sample, SCOD

• BOD5, homogenised, CBOD

• Filtratable substances, XSS

• Kjeldahl nitrogen, TKN, homogenized, CTKN

• Ammonia nitrogen, SNH4

• Nitrate nitrogen, SNO3

• Total phosphor, homogenized, CP

• Acid capacity, SCA, in mmol/l

Recommendation

according to

ATV-DVWK-A 198

Tabular compilation D

ate

Day

Weath

er

Waste

wate

r te

mpera

ture

All

days

DW

da

ys

CO

D.

CO

D f

iltra

te (

SC

OD)

CO

D h

om

og

. (C

CO

D)

BO

D5 h

om

og

. (C

BO

D)

Filt

rata

ble

su

bst. (

XS

S)

TK

B h

om

og

. (C

TK

N)

Am

mo

nia

nitro

. (S

NH

4)

Nitra

te n

itro

. (S

NO

4)

Ph

osp

ho

r,ho

mog

. (C

p)

Acid

ca

pa

c. (S

CA)

Influent Concentration

average

Tabular compilation

Sludge water COD loads Ratios

Da

te

Day

Qd,s

ludgew

.

SN

H4

,slu

dge

w.

Sta

rt

Sto

p

(Bd,C

OD

)

Weekly

avera

ge

Bd,C

OD

,WA

2 W

eeks a

vera

ge

Bd,C

OD

,2W

A

SC

OD/C

CO

D

CB

OD/C

CO

D

XS

S/C

CO

D

CT

KN/C

CO

D

SN

H4/C

CO

D

CP/C

CO

D

SK

S/C

CO

D

average

4. Current load in a wastewater treatment plant

WWTP-clasification in size class/definition of the size:

Decisive:

BOD5-load influent in 85 % of the dry weather days (85 %-fractile value)

Beware: Check the current rate of connection regularly!

Finding the 85 % value

at least 40 values of dry weather days (in 3 years)

Optimization of the aeration plant

Weekly average of the loads

Forming the weekly average

at least 4 daily loads in one week

Known annual progression (e.g. low-load or high-load period)

intensive sampling can be reduceed to 4 – 10 weeks

4.1 Current rate of connection

Recommendation

according to

ATV-DVWK-A 131

4.2 Real sludge loading

The BOD5-sludge load BSS shows how much substrate of the biomass should be converted

per day:

[kg BSB5/(kg TS d)]

with BD = BOD5-daily load [kg BSB5/d] in influent of the aeration tank

VAT = Volume of the aeration tank [m3]

SSAT = Load of suspended solids in aeration tank [kg SS/m3]

Beware: Put in the correct values with correct reference!

AT SS

AT V

BOD d, B

BSS =

4.2 Real sludge loading

Often the current sludge loading is significantly beneath the designed sludge loading.

Current sludge loading << Required sludge loading

Optimization of the operation with the aim to reduce the total sludge amount

in the system

Two ways to reduce the sludge amount:

Reduce the current total solids in the aeration tank

Shut down of the aeration tank – if possible -

Required sludge loading depends on the wastewater temperature ( Beware:

Nitrification), results in SSAT:

[kg SS/m3]

(f(T)) SS

B AT

V D

B

needed AT, SS

=

Practical example to optimize the operation of the aeration tank

Required volume of the aeration tank VAT

Year 2010

0

1600

3200

4800

6400

Jan Feb Mrz Apr Mai Jun Jul Aug Sep Okt Nov Dez

VA

T

VAT present (4 tanks) VAT (2 tanks)

VAT (3 tanks) VAT required for max. load

5. Examples of optimization of energy cost

Wastewater treatment plant size: 100.000 PE

BOD5-load 6.000 kg BOD5/d

Volume of the aeration tank 16.000 m³

SSAT-content (needed) 3,0 kg SS/m³

SSAT-content (operation) 4,3 kg SS/m³

Assumption:

SSAT-reduction: SSAT= 1,0 kg SS/m³

Reduction of the O2 demand due to lowered 0,2 kg O2/ kg BOD5

endogenous respiration

Reduction of the O2-demand 31.000 kg O2/ Month

for one month

5. Examples of optimization of energy cost

-Value for pressure ventilation with = 0,65 (value quite good)

planar arrangement

Saving of O2-supply 48.000 kg O2 / Month

Oxygen entry ON= 1,4 kg O2 / kWh

Saving of kWh 34.000 KWh / Month

Costs per kWh 12 Cent

Monthly saving 4.000 Euro/Month

With operation optimization 20.000 Euro

after 5 months reduction

6. Optimization of use of precipitant

Required concentration of precipitant Estimate through ßPrec -value

XMe = required precipitant in [mg Me/l Wastewater]

XP,Fäll = Phosphor to percipitate in [mg P/l Wastewater]

AMMe = atomic mass of the metal (Me) in [mg/mmol]

AMP = atomic mass of the phosphor in [mg/mmol]

Reference value for ßPrec : simulataneous, pre and precipitation: ßPrec = 1,2

Flocculation filtration ßPrec = 2,5

If ßPrec = 1,2, resulting:

Percipitation with Iron: 2,16 [kg Fe/kg PFäll]

Percipitation with Aluminium: 1,05 [kg Al/kg PFäll]

Recommendation

according to

ATV-DVWK-A 202

] [mmol/mmol

P AM

Fäll P, X

Me AM

Me X

Prec β =

with

XP,Fäll Phosphor to precipitate

CP,ZB Pges in influent of the aeration tank (after prim. treatment)

CP,Mit Operation average in efluent of the clarifier

XP,BM needed Phosphor for cell building

XP, BioP biological P-Elimination

CP,Mit = 1,5 mg/l

Phosphor to precipitate: XP,Prec = CP,ZB - CP,Mit - XP,BM - XP,BioP [mg/l]

6. Optimization of use of precipitant

XP,Fäll = 8,9 – 1,5 – 2,2 – 3,3 = 1,9 mg/l

CP,ZB = 8,9 mg/l

XP,BM = 2,2 mg/l XP,Bio-P = 3,3 mg/l

7. Examples in the field of sludge treatment

Equation: V • SS = constant

V1 • SS1 = V2 • SS2 V1 / V2 = SS2 / SS1

Example:

Raw sludge from the primary treatment 2,5% SS

Raw sludge from the aeration tank 0,7% SS

Amount of sludge:

Primary treatment sludge 70 m³ / d

Surplus sludge 240 m³ / d

Total sludge 310 m³ / d

SS-content of the combined sludge: (70 • 2,5 + 240 • 0,7) / 310 = 1,1% SS

Through flow thickener:

Achievable solids (according to the design) 4,0 % SS

Real solids (on the plant) 2,5 % SS

V1 • TS1 = V2 • TS2

310 • 1,1 = V2 • 4,0 V2 = 85 m³/d

310 • 1,1 = V2 • 2,5 V2 = 135 m³/d 60% more water !

8. Summary

1. Measurements have to be representative

2. Mind correct sampling

=> often: less is more

3. Influent often not enough analysed

4. Wastewater treatment plants in many places not optimized

5. Technical optimization of the operation should be performed

6. In many places can the cost saving potential be achieved in a short

period of time

Prof. Dr.-Ing. habil. Holger Scheer

Emscher Gesellschaft für Wassertechnik mbH

Brunnenstraße 37

45128 Essen

Tel.: 0049 (0)201/3610 - 0 Fax: 0049 (0)201/3610 - 100

E-Mail: scheer@ewlw.de

Homepage: www.ewlw.de

Author´s address