Energy Production in WWT

Fakultät für Ingenieurwissenschaften

FB Maschinenbau / Verfahrens- und

Umwelttechnik

Prof. Dr.-Ing. Wolfgang Pfeiffer

E-Mail: [email protected]

www.hs-wismar.de

Energy Production in WWT

Thermal disintegration of surplus sludge – results of pilot and full scale

investigations at WWTP Grevesmühlen with the Haarslev HCHS system

IWAMA 2nd International Capacity Development Workshop

14. Februar 2017, DWA Nordost, Boltenhagen

Utility company „Zweckverband Grevesmühlen“

Thermal sewage sludge disintegration

Results of bench scale experiments

Results of pilot scale investigations

Full scale results

Results of dewatering in full scale

Influence on sludge drying

Potential savings

Summary and conclusions

Table of contents

Hochschule Wismar – Prof. Dr.-Ing. Wolfgang Pfeiffer

DBU research project (AZ 31037-23)

Quelle: ZVG; Ausbauzustand des Klärwerks 2002

WWTP Grevesmühlen

Capacity 45.000 PE (current extencion to 65.000 PE)

central sludge treatment plant for 100.000 PE (also for

external WWTPs Dassow, Lüdersdorf, Boltenhagen, …)

Co-fermentation of sludges from grid traps (hotels,

restaurants) and industrial pre-treatment plants (mainly food

industry – i.e. dairy and bread)

Production of 200% of electricity of WWTP consumption

Coverage of the power consumption of pumping stations

and water work Wotenitz of Grevesmühlen

Savings of some 100.000 €/a electricity costs


Energy balance – WWTP Grevesmühlen

4

Quelle:

Zweckverband

Grevesmühlen


Basics of sewage sludge disposal

5

A WWTP, that can not dispose its sewage sludge environ-

mentally sound, does not make sense (Karl Imhoff, 1925)

Dried digested sludge is the ideal initial situation for an

environmentally sound and cost optimal solution for sewage

sludge disposal as dried digested sludge is:

almost indefinitely storable

most reduced in quantity –weight and volume

high in calorific value

but:

Drying of digested sludge is energy intensive


Basics of sewage sludge treatment

6

Tasks of the optimization of the sewage sludge treatment are:

Increase of the degree of degradation in anaerobic

digestion

Less dry matter, more biogas

Improval of the dewatering characteristics

Less sludge mass, less water to evaporate

An approach to optimize sewage sludge treatment is:

Thermal sewage sludge disintegration

Hochschule Wismar – Prof. Dr.-Ing. Wolfgang Pfeiffer 7

Basics of sewage sludge disintegration

Tasks of the thermal sewage sludge disintegration are:

Destruction of (intact) cells

making available the cell juice for anaerobic degradation,

improving the dewatering characteristics of the sludge

Decomposition of sewage sludge components

making sewage sludge components available for anaerobic

degradation,

improving the dewaterability due to a reduction of the water

binding capacity of the sludge components

Pinnekamp observed already in the 1980 an improval of the biogas

production due to thermal disintegration and demonstrated the

potential of thermal sewage sludge disintegration.

(Treatment at 120 – 170 °C for 0,5 h +40% biogas from SS)


Bench scale experiments

2014

Discontinuos and continuos experiments

for several month investigating the effects

of thermal disintegration of SS on

anaerobic digestion

8

2006

First experiments in the wastewater lab of

Hochschule Wismar

Investigation of the influence of a thermal

pre-treatment of SS (surplus sludge) on

anaerobic digestion


Disintegration at 120 °C

No significant effects on

biogas production in

anaerobic sewage sludge

digestion

9

Mehranfall an Faulgas (120 °C)

-2000

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Datum

Me

hra

nfa

ll in

ml/d

Fermenter 1

Fermenter 2

Fermenter 3

Mehranfall an Faulgas (140 °C)

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Datum

Me

hra

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n m

l/d

Fermenter 1

Fermenter 2

Fermenter 3

Disintegration at 140 °C

Significant effects on the

anaerobic digestion

20 % increase in biogas

production

0

5000

10000

15000

20000

25000

30000

35000

40000

Fau

lgasan

fall

in

ml

Datum

Faulgasanfall akuum. (120 °C)

Fermenter 0

Fermenter 1

Fermenter 2

Fermenter 3

0

10000

20000

30000

40000

50000

60000

70000

akku

m. F

au

lgasan

fall (

ml)

Datum

Faulgasanfall akkumuliert (140 °C)

Fermenter 0

Fermenter 1

Fermenter 2

Fermenter 3

Bench scale experiments 2006


Full scale HCHS at WWTP Grevesmühlen

10

Preheater

Steam-

generator

dewatering

HCHS

Cooler

Economiser

Throughput 1 - 2 t/h dewatered SS

15 – 20% DM

Pressuriser

Hochschule Wismar – Prof. Dr.-Ing. Wolfgang Pfeiffer 11

HCHS-plant at WWTP Grevesmühlen

Fig. 1-3: WWTP

Grevesmühlen

Fig. 4: WWTP

Wola Dalza,

Łancut, Polen

1 2

3 4


Results – bench scale - discontinuous

12

Discontinuous experiments with dewatered SS

Biogas production is +30% as a result of disintegration with 160 °C

2014

t Ref/70°C

d ml/g VSS ml/g VSS % ml/g VSS % ml/g VSS %

1 14 215 338 157

2 9 360 412 114 432 120

4 13 315 358 114 447 142

5 14 330 440 133 436 132

6 16 378 500 132

sludge

sample

140°C 150°C 160°C

biogasproduction


Bench scale continuous experiments – series I

13

continuous bench scale experiments with app. 10% DM for 60 days

Increase in biogas production is +40 % with 160 °C disintegration


Continuous bench scale experiments - series II + III

14

Continuous bench scale experiments with app. 5% DM

Increase in biogas production is +28% with 160 °C disintegration

and HRT = 16 d


Pilot scale investigations

15

Operation of 4 pilot scale digesters

with Veff = 500 l

Investigation of the influence of thermal

disintegration on specific biogas

production [l/kg DMadded]

ht-FB1 – mixed sludge*

ht-FB2 – mixed sludge*

ht-FB3 – un-pre-treated surplus sludge

ht-FB4 – thermal disintegrated SS

* Mixture of primary sludge, Co-substrates, thermal

disintegrated and un-pre-treated surplus sludge

Increase of the portion of the thermal disintegrated

surplus sludge in 3 phases of 33% each


Pilot scale experiments - results

16

Continuous operation over 100 days with app. 5% DM

Increase in biogas production is +28% with 150 – 160 °C and HRT = 18 d


Pilot scale experiments - results

17

Increase in biogas production +28 %

Increase in oDM degradation +11 %-points (40,3 % 51,4 %)


Full scale operation – results – biogas production

18

Operation of digester FT2 with mixed sludge with

increasing portions of thermal disintegrated surplus

sludge in 3 phases


Full scale operation – results – ammonia conc.

19

Modest increase in NH4-N due to increased protein degradation


Full scale operation – results – COD in solution

20

Increase in COD in solution is app. 500 mg/l in centrate of centrifuge

Increase in COD in WWTP effluent is app. 5 mg/l


Full scale operation – results - dewatering

Dewatering was investigated with

a full scale HILLER centrifuge

Results:

Digested sludge with thermal

disintegrated surplus sludge

(FT2): 33% TR

Digested sludge with un-pre-

treated surplus sludge

(FT1): 25 % TR

Increase in DM is 8 %-points

Slightly less flocculant

consumption 14 kg/tDM with

25 m³/h throughput

Centrate with good quality

21


Belt dryer BD 3000/x

22

Partial / full drying

Granular product

Direct heating

Indirect heating

Fexible heat resource

Easy accessibility

Heat recovery

Modular units

Small waste gas flow

Feed of dewatered

slugde

Upper belt

Heat recuperator

Hot air feed to drying chambers

Dried sludge

Condensator

Waste

air

Incinerator

Drying chambers

Lower Belt


Einsparpotenziale

24

dewatering 1

Thermal Disintegration Belt dryer

PS

Co-generator

Biogas

Etherm

digester

Biogas-

production

+25%

dewatering 2

dewaterability

+8%-points -35% less

dewatered

diegested

sludge

Digester

volume

-37%

- 44% less water

evaporation

30% DM

95% DM

3,5% DM

~20% DM

SS

digested

sludge


Summary and conclusions

25

The quantity of dewatered digested sludge for disposal is reduced

by 35 %.

In combination with a thermal surplus sludge disintegration a full

drying of the sewage sludge becomes possible with the WWTP

internally produced heat with moderate digestion of co-substrates.

The required drying capacity and the required thermal energy for the

drying can be reduced by thermal surplus sludge disintegration by

almost 50 %.

For disinfection thermopilic digestion instead of disintegration of all

sludge might be considered

The research was finanically supported by DBU (German national

foundation for environmental protection) and Haarslev Industries

Thank you very much for your attention

Energy Production in WWT

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