Getting most out of the thermaldrying of sewage sludgeto stay within the planetaryboundaries for the nitrogen cycle

16.01.2016

Ivan DeviatkinDoctoral student, Department of Sustainability Science, School of Energy Systems, Lappeenranta University of Technology

Planetary boundaries

1.0-2.5 mg N/L – limit to prevent eutrophication.

To keep it such, the planetary nitrogen fixationboundary is set to 62-82 Mt N/year.

Currently, the fixation rate is 121 Mt N/year, where82 Mt N comes from synthetic fertilizers.

Therefore, 20-26 Mt N from synthetic fertilizersshould be avoided.

Where to get N, if not a synthetic one?

Stream N content, mg/LLiquid manure fractions ≈ 3,500

Digested manure ≈ 3,500

Organic waste ≈ 1,200

Reject water from WWTP ≈ 750

Industrial waste streams *

Condensate from sludge drying *

N-fertilizer

N-food

N-wastewaterN-sludge

N-NO3

N2

N-Anam

mox

N-A

nam

mox

Shor

t circ

uit

N-H

aber

-Bos

ch

van Eekert, M., Weijma, J., Verdoes, N., de Buisonje, F., Reitsma, B., van den Bulk, J., van Gastel, J., 2012. Explorative research on innovative nitrogen recovery.

Great attention was drawn to N recovery from liquidflows neglecting direct recovery from gaseous flows!

Research idea (!) and questions (?)

(!) sludge drying and incineration is a commonpractice, so nitrogen recovery during thermal dryingof sludge (and similar streams) was seen favorable.

(?) how much N is released from sewage sludge, digestate, and biosludge from a pulp and paper mill

(?) what is the impact of T on the N release

(?) which recovery methods could be practiced

(?) intensifying N release through condensatestripping

Legend

N-NH3

Sewage sludge

(1)

(2)

(4)

(3)

Nitrogen fertilizer

Hot air/steam

Fumes for treatment

Energy

Ash for recycling

Solid flowLiquid flowGas flowEnergy flow

(1)(2)(3)(4)

- sludge bunker;- drier;- incineration plant;- absorber/adsorber.

drier

bunker recovery

Incineration plant

Nitrogen release during batch drying 1

Experimental setup on the Figure→

Sewage sludge Toikansuo WWTP, LPRDigestate Kouvolan Vesi Oy, KouvolaBiosludge UPM Kymmene, LPR

b a cd

e

fg

Legend:a – vessel with sludgeb – inlet pipec – outlet piped – electric ovene – thermometerf – praparation unitg – Gasmet analyzer

Nitrogen species Digestate Exhaust fumes Condensate

Total nitrogen (𝑁"#") Modified Kjeldahl test

n.d. Nitrogen (total) cell test

Soluble nitrogen (𝑁$#%) WE + Nitrogen (total) cell test

n.a. n.d.

Ammonium (𝑁𝐻'() WE + Ion chromatography

n.a. Ion chromatography

Ammonia gas (𝑁𝐻)) n.a. FTIR n.a.

Nitrogen release during batch drying 2

100°C 130°C 160°C

70°C 100°C 130°C 160°C

130°C 180°C 210°C

Sewage sludge

Digestate

Biosludge

0

10 000

20 000

30 000

40 000

50 000

60 000

Sewage sludge Digestate Biosludge

Total Nitrogen Soluble Nitrogen N-NH470°C 100°C 130°C160°C 180°C 210°C

19%

58%

7%

mg/

kg T

S

Nitrogen release during batch drying 3

100°C 130°C 160°C

70°C 100°C 130°C 160°C

130°C 180°C 210°C

Sewage sludge

Digestate

Biosludge

0

5 000

10 000

15 000

20 000

Sewage sludge Digestate Biosludge

Total Nitrogen Soluble Nitrogen N-NH470°C 100°C 130°C160°C 180°C 210°C

mg/

kg T

S

55%

4900 −6200

9000 −9900

1300 −1700

50%65%

Nitrogen release during continuous drying 1

Experimental setup on the Figure →

Two (+1) tests. Feeding at 1.38±0.17 kg/h.MC of raw sludge was 83.7±0.1% and of driedsludge – 31.1±0.1%.Each experiment lasted for 8 hours.

Ammonia measurement at 2h, 4h, 5h, 6h, 7h, 8h.Acid traps for NH3 capture. Ion chromatography.

Biochar was used for ammonia capture

Nitrogen release during continuous drying 2

0

400

800

1 200

1 600

2 000

0.00

0.30

1.00

1.30

2.00

2.30

3.00

3.30

4.00

4.30

5.00C

umul

ativ

e m

ass o

f dry

slu

dge,

g Test I Test II Test III

100

200

300

400

500

1h 2h 3h 4h 5h 6h

Drie

d sl

udge

out

put,

g·h-1

Test I Test II Test III

- calculated driedsludge output (280±10 g/h)

R² = 0,99413

R² = 0,99861

0,0

200,0

400,0

600,0

800,0

1000,0

1200,0

1400,0

0 1 2 3 4 5 6 7 8 9

Cum

ulat

ive

N in

exh

aust

fum

es, m

g

Time, h

So we get:

0.53±0.01 mg N/g dried sludge

0.21±0.01 g dried sludge/g wet sludge.

Therefore, we can get:

110±6 g N/t wet sludge.

Adsorption on biochar: organic materials doped with N

Absorption:• ammonium sulphate solution,• ammonium nitrate solution,• ammonium chloride solution,• etc.

Aqua ammonia

General recovery methods

Packed adsorption Packed absorption

Sprayed absorption Droplet absorption

Thus, there is the need to release 30% Nback for recovery!

Intensifying ammonia release

100%90%

TEST IITEST I

30% in condensate

70% goesfor recovery

Let us strip it!

14ºC 31ºC

Sludge is a reliable source of nitrogen as its amount is ever-growing worldwide.

When we incinerate sludge, we have a good possibility to recover nitrogen.

50-65% of soluble nitrogen is release as ammonia duringthe drying process.

Nitrogen released could be recovered by ad/absorption.

Moreover, great possibilities for symbiosis exist. The process could be retrofitted to:• a sludge incineration plant to get nitrogen released;• a WWTP for nitrogen stripping from condensate.

What do we get after all?

Legend

N-NH3

Sewage sludge

(1)

(2)

(4)

(3)

Nitrogen fertilizer

Hot air/steam

Fumes for treatment

Energy

Ash for recycling

Solid flowLiquid flowGas flowEnergy flow

(1)(2)(3)(4)

- sludge bunker;- drier;- incineration plant;- absorber/adsorber.

drier

bunker recovery

Incineration plant

1. Technical study on recovery possibilities

2. Economical analysis

3. Environmental impact assessment

Future research needs

Socialacceptance

Environmental impact

Economicconditions

SYSTEM ANALYSIS

Thank you for your attention!

Questions?