RESPONSE TO PRE-TREATMENTS AND DIGESTION INTENSIFICATION ... · PDF fileRESPONSE TO PRE-TREATMENTS AND DIGESTION INTENSIFICATION OF SEWAGE SLUDGE ... CEMENT COMPOSTING ... the SP increased

RESPONSE TO PRE-TREATMENTS AND DIGESTION INTENSIFICATION OF SEWAGE SLUDGE

Negral L., Marañón E.1, Fernández-Nava Y., Castrillón L.

University Institute of Industrial Technology of Asturias. University of Oviedo. 33203 Gijón, Spain

Le, S., Miller, K., Carlines, I.

United Utilities Group PLC, Warrington, WA5 3LP United Kingdom

1corresponding author: [email protected]

mailto:[email protected]

http://www.end-o-sludg.eu/

INTRODUCTION

• SEWAGE SLUDGE BACKGROUND

• PRETREATMENTS

Ultrasound

Enzymatic Hydrolysis

Grinding

• ORGANIC MATTER SOLUBILIZATION

• ENHANCED ANAEROBIC DIGESTION

• CONCLUSIONS

18/10/2013 BIOCHARS COMPOST DIGESTATES BCD 2013 2


AGRICULTURE

DEWATERING + CHEMICAL

STABILIZATION

ANAEROBIC DIGESTION + DEWATERING

AEROBIC DIGESTION + DEWATERING

DEWATERING + HEAT

DRYING + COMPOSTING CEMENT

MANUFACTURING

DEWATERING + HEAT DRYING

ANAEROBIC DIGESTION +


AEROBIC DIGESTION +


DEWATERING + INCINERATION

SEWAGE SLUDGE-BACKGROUND (I)

BIOCHARS COMPOST DIGESTATES BCD 2013 18/10/2013

LANDFILL DEWATERING

DESTINATION

3


SEWAGE SLUDGE-BACKGROUND (II)

4

107 tonnes (dry matter) Europe/year

Hydrolysis is the rate-limiting stage of AD

Anaerobic digestion stabilizes the sludge while leads to energy recovery and production of digestate

Classical HRT ≈ 20 days

> 50% of Total Operating Costs in WWTPs


PRE-TREATMENT FOR HIDROLYSIS

ENHANCEMENT

> 95% moisture


SEWAGE SLUDGE-BACKGROUND (III)

5 BIOCHARS COMPOST DIGESTATES BCD 2013 18/10/2013

Sludge contains recalciltrant organic fraction (bacterial cell wall) which is difficult to biodegrade

COMPLEXORGANICMATTER

MONOMERSHydrolysis Acidogenesis

VolatileFatty Acids

CH3COOH

H2 + CO2

CH4 + CO2

CH4 + CO2

MethanogenesisAcetate-utilizing

methanogens

MethanogenesisHydrogen-utilizing

methanogens

Aceto

genesis

Acetogenesis

Rate limiting-step

Pre-treatments boost the biodegradability and methane yield


PRE-TREATMENTS (I)


BIOLOGICAL

Enzymatic hydrolysis

Hydrolytic bacteria

THERMAL

60-180ºC

Freeze/thaw

CHEMICAL

Oxidation

Acid addition

Alkali addition

MECHANICAL

Ultrasound

Centrifugation

High pressure

Grinding Combination of different pre-treatments


PRE-TREATMENTS (II)

7

Ultrasound

Ultrasonic equipment used:

Hielscher UP 400S, 24 kHz, 400 W

Sonotrode H22, made of titanium, Ø 22 mm

Different input energies: 50 – 21000 kJ/kg TS



PRE-TREATMENTS (III)


Enzymatic hydrolysis (EH) achieved by promoting endogenous enzymes at 42ºC for 48 hours under anaerobic conditions: Inverted Phase Fermentation (IPF) ®

2 phases separated from the raw sludge: a top thickened layer «Solid Phase (SP)» and a bottom clarified layer «Liquid Phase (LP)»

Subsequent Anaerobic Digestion (AD) of the LP and the SP

LP contains soluble organic matter (high in VFA), readily biodegradable

SP may be submitted to pre-treatment to enhance biodegradability


PRE-TREATMENTS (IV)


SP pre-treatment: grinding in alkaline media

Milling paremeters: 1:3 ratio sludge cake to water 100 rpm, 4 days 1:1 ratio grinding media to sludge cake 5% NaOH (dry basis), adjusted to pH 8 with HCl after milling

In theory, the higher the rate of soluble COD release from the sludge substrate, the greater the eventual methane yield from digestion

Grinding mill Zirconium oxide grinding media


SOLUBILIZATION (I)


Short-term evolution of SCOD (1 day fermentation, 37ºC) after ultrasound disruption for secondary sludge

The numbers in legends indicate the specific energy applied in kJ/kgTS

Untreated 3407 6814 10599 14006 20819

For applied energy of around 7000 kJ/kgTS, the increase in CODs range from 90% for primary sludge to about 40000% for secondary sludge

0

5

10

15

20

25

Initial Ultrasound Fermentation

SCO

D (

g/L

)


0

5

10

15

20

25

Initial Enzymatichydrolysis

Fermentation

SCO

D (

g/L

)

SOLUBILIZATION (II)


Short-term evolution of SCOD (1 day fermentation, 37ºC) after IPF for secondary sludge

SP = Solid Phase; LP =Liquid Phase

Solubilization by IPF led to 1500% increase for primary sludge and 20000% for secondary sludge)

Thickening of the sludge, with solid concentration factors above 2 achieved in the SP


ENHANCED ANAEROBIC DIGESTION (I)


Continuous digestion of Sludge Liquor

Digestion was carried out in 5 L

UASB reactors at 37ºC

Optimum HRT reduced to 1 day!!

Methane yield rate up to: 2.3 m3CH4/m3

reactorday 70% COD removal for OLR of

18.5 kg COD/m3·day


ENHANCED ANAEROBIC DIGESTION (II)


Continuous digestion of Sludge Liquor in high load reactors (UASB)

Parameter Influent A Effluent A (% removal)

Influent B Effluent B (% removal)

HRT (day) 1 2

OLR (kgTCOD/m3·day) 18.5 12.9

TCOD (g/kg) 18.46 5.51 (71%)

25.71 9.80 (62%)

SCOD (g/kg) 10.61 2.07 (80%)

7.69 2.51 (67%)

m3 biogas/kgTCOD 0.19 0.15

m3 CH4/kgTCOD 0.13 0.09

m3 biogas/m3reactorday 3.52 1.95

m3 CH4/m3reactorday 2.34 1.19


ENHANCED ANAEROBIC DIGESTION (III)


Continuous digestion of the pre-treated SP in chemostats

The milled substrate was diluted with water and fed into chemostats (organic loading rates 1.0, 2.5 and 4.3 kgCOD/m3·day)

No inhibition/toxic effects observed in the digestion process

Digestion was stable when using pre-treated sludge as feed

Digestion was carried out using 5 L

chemostats at 37oC


ENHANCED ANAEROBIC DIGESTION (IV)

15 18/10/2013

Methane concentration

0

10

20

30

40

50

60

70

0 5 10 15

Time (days)

Meth

an

e c

on

cen

trati

on

(%

)

Control: 4.3 kgCOD/m3

C1: 4.3 kgCOD/m3

C2: 2.5 kgCOD/m3

C3: 1.0 kgCOD/m3

Biogas volume

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 5 10 15

Time (days)

Bio

gas v

olu

me (

ml)

Control: 4.3 kgCOD/m3

C1: 4.3 kgCOD/m3

C2: 2.5 kgCOD/m3

C3: 1.0 kgCOD/m3

The biogas volume and methane concentration were similar in the chemostats with the highest organic loading rates

Both the control and chemostat 1 had a loading rate of 4.3 kgCOD/m3, however the experimental chemostat produced 3.5 X more biogas than the control

The chemostat with the lowest loading rate (1.0 kgCOD/m3) and the control chemostat produced a similar quantity and quality of biogas, due to the limited availability of nutrients in their substrates


ENHANCED ANAEROBIC DIGESTION (V)


Continuous digestion of the pre-treated SP in chemostats Chemostat Digester influent Digester effluent COD reduction

TCOD

(mg/l)

SCOD

(mg/l)

TCOD

(mg/l)

SCOD

(mg/l)

TCOD

(%)

SCOD

(%)

Chemostat 1: loading rate 4.3 kgCOD/m3·day

60180 30200 36051 5503

40.1 81.8


35020 17540 25533 3486

27.1 80.1


23429 11734 17850 2203

23.8 81.2

Control Chemostat

4.3 kgCOD/m3·day

66240 3880 48304 4166

27.1 No SCOD

reduction


The novel pre-treatment IPF boosts the anaerobic digestion of sludge:

CONCLUSIONS: ENHANCED ANAEROBIC DIGESTION


The liquor from the sludge may be digested in high rate reactors (e.g.

UASB) The optimum HRT of the liquor is reduced to 1 – 2 days (18.5 – 13

kgCOD/m3·day)

Methane yield rates up to 2.3 m3CH4/m3reactor day

TCOD reductions of the liquor up to 71%

The grinding of the SP increased the biogas production to 3.5 X

TCOD reductions of pre-treated SP up to 40% at 4.3 kgCOD/m3·day


CONCLUSIONS: ENHANCED ANAEROBIC DIGESTION


>> COD & VS REMOVAL

>> BIOGAS PRODUCTION

<< PROCESS TIME

GREATER SUSTAINABILITY

IN SLUDGE MANAGEMENT



ACKNOWLEDGEMENTS

19

The research leading to these results has received funding from the

European Union Seventh Framework Programme (FP7-

ENV.2010.3.1.1-2 ENV) under Grant Agreement no. 265269.


We are grateful to the staff at the WWTPs for their generous

cooperation during the experiments








20

THANKS FOR YOUR ATTENTION!



Documents

RESPONSE TO PRE-TREATMENTS AND DIGESTION INTENSIFICATION ... · PDF fileRESPONSE TO PRE-TREATMENTS AND DIGESTION INTENSIFICATION OF SEWAGE SLUDGE ... CEMENT COMPOSTING ... the SP increased