environmental aspects of ad of sewage sludge

EPROBIO Foggia 10 July 2010

Environmental Aspects of AD of Sewage Sludge


BIOSOLIDS

LANDAPPLICATION

ANAEROBICDIGESTION

DEWATERING

COMPOSTING

DEWATERING

THERMALDRYING

CO-DIGESTION

INCINERATION

GASIFICATION

LANDFILL

CLAY FACTORY

Ashes

LANDFILL

BIO-DRYING

OTHERORGANICWASTES

CEMENT FACTORY

ATAD


BIOSOLIDS

LANDAPPLICATION

ANAEROBICDIGESTION

DEWATERING

COMPOSTING

DEWATERING

THERMALDRYING

CO-DIGESTION

INCINERATION

GASIFICATION

LANDFILL

CLAY FACTORY

Ashes

LANDFILL

BIO-DRYING

OTHERORGANICWASTES

CEMENT FACTORY

ATAD

ANAEROBIC DIGESTION

• First application of AD

• Advantages

• Possibilities (heat / power)

• Configurations to improve the performance

• Co-digestion


Options to improve AD


Options to improve AD process

1) Hydrolysis: Pretreatments

• Thermal

• Mechanical (ultrasonic)

• Chemical (ozonation, H2O2,etc.)

• Biological (enzymatic)

2) Temperature: TAD

• Increase T of AD to reduce HRT and to incrase

OLR

3) Balance between acidogenic and

methanogenic step

• Two-phase digestion

4) Nutrient balance

• Co-digestion with other wastes

At any option, the improvement will depend on:

- Sludge characteristics (PS/SS)

- HRT used

- Temperature of operation (normally MAD)


Mechanical

Biological

Thermal

Chemical

Several effects:

-Solubilization

-Degradation

Improvent of biodegradability

Two interest: Increased biogas yield

Less residual sludge

Improvement options: 1) pre-treatments


Mètode Cond. de operació Desint. (%) Biogas incr (%)

Avantatges Desavantatges

Ultrasònic 10-15 106 J/kg ST 100 30 completa

desintegració intensiva energia

Tèrmic 150-200 ºC/ 30 min. 30-55 15-50 Procés flexible corrosió, olors

Termoquímic 80-150 ºC/30min NaOH (hasta pH12)

5-60 20-55 Relativament

simple

Corrosió, olor, subseguint

neutralització

Biològic* 5-10%; 37-55 ºC & 10-30 hr

5-50 10-20 operació simple,

baixos costs

baixos rendiments,

olors

Oxidatives O3 0.1-0.3g/gSV H2O2 0.5-2g/gSV

90 20-250 Alta eficiència

de desintegració

pH baixo, corrosió, alt cost

* recalcitrància de la part proteica

Improvement options: 1) pre-treatment


TREAMENTS ULTRASONIC vs THERMAL

Increase (%) on methane production

• More effectiveness:

- Mesofílic conditions - For secondary sludge

• Difference on Investment and operating costs.

PretreatmentUS

(11.000 kJ/kg)TT

(145ºC/ 30 min)

MAD PS 21.3 11.7

SS 30.0 17.9

TADPS 12.5 16.7

SS 21.4 18.3



9

PPCP’s

9(Esplugas, M. 2010)


*

AOX, LAS, PCB’s, PAH, DEHP, NP/NPE

Their removal has been studied under different operating conditions

* Results are complex as depend of the contaminant and

conditions

Removal or transformation (%) of NPE and DEHP with US (■) and TT (■) pretreatments

0

10

20

30

40

50

60

70

80

90

100

DEHP NP NP1EO NP2EO NPE

E(%

)

0

10

20

30

40

50

60

70

80

90

100


E(%

)

0

10

20

30

40

50

60

70

80

90

100


E(%

)

0

10

20

30

40

50

60

70

80

90

100


E(%

)

PS SS

55-71%53-65%

* In any case there is an improvement



0

20

40

60

80

100

TT-MAD TT-TAD US-MAD US-TAD

Treatment

E (

%)

0

20

40

60

80

100

TT-MAD TT-TAD US-MAD US-TAD

Treatment

E (

%)

(a) (b)

DEHP NPE

*

AOX, LAS, PCB’s, PAH, DEHP, NP/NPE

Their removal has been studied under different operating conditions

* Results are complex as depend of the contaminant and

conditions

* In any case there is an improvement



Improvement options: 2

Temperature


Thermophilic vs. Mesophilic AD

At low HRT TAD yields are much

higher

At high HRT yields are

similar

Values depend on type of sludge

-Pathogen removal higher in TAD (Biosolids Class A)

Better removal of Microcontamiinats % (AOX, LAS, PCB’s, PAH, DEHP,

NP/E)

- More VFA in supernatants

- Worse dewaterability

0102030405060708090

100

Mesophilicdigestion

Thermophilicdigestion

Substratesonication

Son+M_dig Son+T_digNap

htha

lene

and

pyr

ene

rem

oval

(%)


Temperature range alternance (Tartakovsky et al. 2007)

Incr. 50 % aprox. en CH4 prod.

TAD ranges are small to avoid methanogens

inhibition

Change of temperature


B A GRUP DE RECERCA EN

BIOTECNOLOGIA AMBIENTAL

DEPARTAMENT D’ENGINYERIA QUÍMICA

XARXA DE CENTRES

DE SUPORT

A LA INNOVACIÓ

TECNOLÒGICA

Improvement options 3) Two-

phase AD


To keep an equilibrium between acidogenic and methanogenic

phases

Can be considered as a biological

pretreatment of AD

Each phase has its own HRT and operting

Temperature

Keith et al., 2006

Acidogènic Methanogenic

Improvement options: 3) two-phase AD


M-M does not improve too much VS removal, but firts acidogenic phase reduces significantly the pathogenic

laod

Configuration HRT(d) VSrem (%)

Meso-Meso 3,5+6,5 50-55

Thermo-Meso 2,5+9 61

Thermo-Thermo 2,5 + 5 63



B A GRUP DE RECERCA EN

BIOTECNOLOGIA AMBIENTAL

DEPARTAMENT D’ENGINYERIA QUÍMICA

XARXA DE CENTRES

DE SUPORT

A LA INNOVACIÓ

TECNOLÒGICA

An example with hyperthermophilic conditions

was studied by Wang (1997) and Gavala (2003)

1st phase

70ºC

MAD

TAD

• Improvements: 30-50%

• For PS improvements for TAD

• For SS, improvements for MAD and TAD

HRT and T should be fixed for each

particular mixture

or



Improvement options: 4) Co-

digestion


Improvement options: 4) Co-digestion

• SS digesters are infra-used

• Biodegr. OM (High VS conc. Offers a good

opportunity) • A single infra-structure is

used

• Eventual nutrient deficit is

compensated

• Eventual inhibitors are diluted

Mata et al., 1989


Mata et al., 1989

IC

CAL

DIG

BIOGAS

MEZ

FD

SEL

FORSU

EFECTOS DE LA ADICION DE FORSU EN LOS FANGOS DE DEPURADORA SORE EL LA PRODUCCION DE GAS Y EL TIEMPO DE RESIDENCIA

0,0

20,0

40,0

60,0

80,0

100,0

120,0

140,0

160,0

180,0

200,0

0,0 2,0 4,0 6,0 8,0 10,0 12,0 14,0 16,0 18,0

PERCENTAJE DE INCREMENTO EN EL CAUDAL DE ENTRADA AL DIGESTOR

PO

RC

EN

TA

JE D

E IN

CR

EM

EN

TO

EN

LA

P

RO

DU

CC

IÓN

DE

BIO

GA

S O

DE

EL

EC

TR

ICID

AD

17,5

18,0

18,5

19,0

19,5

20,0

20,5

21,0Incremento biogas/electricidad

Nuevo Tiempo de Residencia

Improvement options: 4) Co-digestion


CONCLUSIONS

• DA can improve its yields (biogas productions and VS removal and digestate quality)

•Improvement can be carried out by pretreatments and a significant activity on this

field is underway.

• Improvement options are quite a few and should be carefully studied as many factors are

affecting


CONCLUSIONS

• Requirements of land application can favour TAD and possibly pre-treatmnes.

• Directive will have a high influence on these issues.

Co-digestion is a logical choice, depending on the surroundings, with

important benefits


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environmental aspects of ad of sewage sludge

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