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International Seminar - University of Palermo 20 May 2016

Donatella Caniani 1

Università di Palermo

Dipartimento di Ingegneria Civile,

Ambientale, Aerospaziale, dei

Materiali (DICAM)

Innovative wastewater

treatment technologies

for energy saving and

environmental

protection

May 20, 2016 - Palermo

Innovative wastewater

treatment technologies

for energy saving and

environmental

protection


Emissioni di gas serra dalla

digestione aerobica dei

fanghi: risultati

sperimentali e modellistici

Donatella Caniani

Innovative wastewater treatment technologies

for energy saving and environmental protection


Outline

1. GHG emissions in wastewater utilities1. GHG emissions in wastewater utilities

4. Biological processes for GHG production4. Biological processes for GHG production

6. 6. Aerobic Digestion (Aerobic Digestion (AeDAeD) ) ModellingModelling

77. . Experimental resultsExperimental results

22.. LiteratureLiterature AnalysisAnalysis

33.. AttentionAttention towardstowards aerobicaerobic digestiondigestion

55.. BiologicalBiological processesprocesses forfor NN22OO productionproduction




Schematic diagram of the modified

BSM2 plant and sources of modelled

GHG emissions.

(C. Sweetapple et al., 2013)Off – site emissions

(indirect emissions)

1. 1. GHG emissions in wastewater utilitiesGHG emissions in wastewater utilities

On – site emissions

(direct emissions)

•• ONON--SITE EMISSIONS: BIOLOGICAL PROCESSES DURING WASTEWATER TREATMENT.SITE EMISSIONS: BIOLOGICAL PROCESSES DURING WASTEWATER TREATMENT.

•• OFFOFF--SITE EMISSIONS: ENERGY CONSUMPTION,CHEMICALS SITE EMISSIONS: ENERGY CONSUMPTION,CHEMICALS PRODUCTION AND PRODUCTION AND TRANSPORTATION, TRANSPORTATION, SLUDGE SLUDGE

TRANSPORTATION, DISPOSAL OR TRANSPORTATION, DISPOSAL OR REUSE.REUSE.




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Nitrous oxide is a

POWERFUL GREENHOUSE GASPOWERFUL GREENHOUSE GAS

GWP (Global GWP (Global WarmingWarming PotentialPotential))

Carbon dioxide(CO2) = 1

Methane (CH4) = 24

Nitrous oxide (N2O) = 289 (IPCC, 2006)

WHAT IS NITROUS OXIDE ? WHAT IS NITROUS OXIDE ?

1. GHG emissions in wastewater utilities


Donatella Caniani 2




2. LITERATURE ANALYSIS. STRENGTHS & WEAKNESSES..

4. The knowledge on modelling about

activated sludge processes (ASM) with

nitrous oxide emissions is increased.

STRENGTHSSTRENGTHS WEAKNESSESWEAKNESSES

1. The knowledge on CO2 and CH4 formation during biological

processes is very rich.

2. The knowledge N2O formation during nitrification,

denitrification and nitrifier denitrification processes is

increased.

3. The infleunce of design variables on amount of emissions is

clear.




STRENGTHSSTRENGTHS WEAKNESSESWEAKNESSES

1. Lacking of a standard protocol for gas sampling and

measurement in liquid and gas phase, including aerobic

digestion

2. Lacking of a model for sludge aerobic digestion

3. Lacking of experimental measurement at pilot scale and full

scale of aerobic digestion

Attention towards aerobic digestionAttention towards aerobic digestion

2. LITERATURE ANALYSIS. STRENGTHS & WEAKNESSES..




3. Attention towards aerobic digestionBiologicalBiological Systems: Systems: ActivatedActivated sludgesludge tank (AS) and tank (AS) and AerobicAerobic digestordigestor ((AeDAeD))

WWTP in Rionero in Vulture (Pz)

AA fractionfraction ofof nutrientsnutrients andand organicorganic pollutantspollutants areare removedremoved throughthrough thethe biologicalbiological activityactivity ofof bothboth

heterotrophicheterotrophic andand autotrophicautotrophic bacteria,bacteria, whichwhich survivesurvive inin thethe tanktank underunder specificspecific biochemicalbiochemical andand

physicalphysical conditionsconditions..

SubmergedSubmerged

aerationaeration devicesdevices

The AS is the core unit of a WWTP where

the actual contaminants biological removal

takes place.

The microorganisms (generally bacteria,

called activated biomass) are able to digest

the wastewater under aerobic conditions,

reducing the organic carbon and nutrients

(N and P) loads.




BiologicalBiological Systems: Systems: ActivatedActivated sludgesludge tank (AS) and tank (AS) and AerobicAerobic digestordigestor ((AeDAeD))

In AeD the excess sludge is maintained in

aerobic conditions with retention time of

approximately 20 days without feeding

exogenous organic substrate. In this way, a

decrease in the sludge concentration is

observed due to its endogenous

respiration.

DECAY RATE

SubmergedSubmerged

aerationaeration devicesdevices

SurfaceSurface aerationaeration

devicesdevices


3. Attention towards aerobic digestion


Donatella Caniani 3




AttentionAttention towardstowards the the AerobicAerobic DigestionDigestion ((AeDAeD). ). WhyWhy??


Experimental measurements of direct GHG emissions from

aerobic digesters (AeD) were yet not available in literature.

Estimating the contribution of AeDs to the WWTP eFP and CFP is

important for knowing their impact through CO2 equivalent

(CO2,eq)emissions, in particular regarding N2O.

The interest towards the contribution to the WWTP CFP of AeD

is linked to its popularity in small to medium sized WWTPs

(5000-50000 IE) in Italy as excess sludge treatment.

Small to medium sized plants normally characterized by

conventional treatment schemes are usually neglected in

scientific literature, even though they are very popular in

isolated villages, especially in rural areas.

Similarly to what occurs in biological tanks, CO2 is produced by

bacterial endogenous respiration, accumulates in the liquid

phase and is then stripped during aeration . N2O is also

generated and its production depends mainly on nitrogen (N)

availability.





AerobicAerobic DigestionDigestion vs vs AnaerobicAnaerobic DigestionDigestion

AeDAeD advantagesadvantages.

1. High VSS removal efficiency

2. Sludge reuse in agriculture

3. Better management conditions

4. Low cost in construction

AeDAeD disadvantagesdisadvantages.

1. High energy demand for aeration

2. No energy recovery

3. Sensitive to operational conditions (T, pH, TSS..)

4. High cost in management





4. Biological processes for GHG production11.. OrganicOrganic CarbonCarbon OxidationOxidation byby meansmeans ofof heterotrophicheterotrophic aerobicaerobic bacteriabacteria

CCxx(H(H22O)O)xx + O2 → CO2 + H2O + e-Red.Ox.

ATPATP

CCxxHHyyNNzzOOtt

(C(C55HH77NONO22,, asas suggestedsuggested byby

HooverHoover && PorgesPorges inin 19521952))

Cx(H2O)x electron donor

O2 electron acceptor

ATP energy needed for generation

CxHyNzOt new cells

CO2 product of the reaction

catabolic

pathway

anabolic

pathway

N, P, S, K,

Ca, Mg

22.. EndogenousEndogenous decaydecay

CxHyNzOt + O2 → CO2 + NH3 + H2ORed.Ox.

C5H7NO2 + 5O2 → 5CO2 + NH3 + 2H2O

(organic

substrate)

The organic substrate in wastewaters is represented by:

ProteinsProteinsCarbohydratesCarbohydrates OilsOils, , fatsfats and and greasesgreases

Fossil carbon from soaps,

detergents, petroleum

derived ecc..




NN22O O emissionsemissions fromfrom activatedactivated sludgesludge reactorreactor duringduring BNR (BNR (BiologicalBiological NitrogenNitrogen RemovalRemoval) )

processesprocesses. . TheyThey are are classifiedclassified asas on on –– site site emissionsemissions , or , or directdirect emissionemission. . (C. Sweetapple et al., 2013; J. Porro et al., 2011; X. Flores – Alsina et al., 2013)

33.. OrganicOrganic CarbonCarbon OxidationOxidation byby meansmeans ofof autotrophicautotrophic aerobicaerobic bacteriabacteria

CO2 + H2O + E → Cx(H2O)x + O2

NitrificationNitrification pathwaypathway: oxidation of NH4+ to NO3

- via NO2-

N2O from secondary chemical reactions

44.. OrganicOrganic CarbonCarbon OxidationOxidation byby meansmeans ofof heterotrophicheterotrophic anoxicanoxic bacteriabacteria ((DenitrificationDenitrification))

Cx(H2O)x + NO3- → CO2 + N2+ H2O + e-

Red.Ox.

ATPATP

CCxxHHyyNNzzOOtt

(C(C55HH77NONO22))

Cx(H2O)x electron donor

NO3- electron acceptor

ATP energy needed for generation

CxHyNzOt new cells

CO2 product of the reaction

catabolic

pathway

anabolic

pathway

N, P, S, K,

Ca, Mg

e-

N2O as intermediate

4. Biological processes for GHG production


Donatella Caniani 4




5. 5. BiologicalBiological processesprocesses for Nfor N22O productionO production

NITRIFICATIONNITRIFICATION DENITRIFICATIONDENITRIFICATION

Nitrification is the oxidation of NH4+ to NO3

- via NO2-, as represented by following

reactions:

AutotrophicAutotrophic aerobicaerobic bacteriabacteria..

The inorganic carbon is their only carbon

source.

The energy for their growth is taken from

reactions (chemoautotrophicchemoautotrophic bacteriabacteria).

NH4+ + 3/2 O2 NO2

- + 2H+ + H2O

NO2- + ½ O2 NO3

-

IT IS PERFORMED BY:

Secondary nitrifiers or nitrite –

oxidizing bacteria (NOB)(NOB) that

oxidize the NO2- to NO3

-

Primary nitrifiers or ammonium

– oxidizing bactiera (AOB)(AOB) that

oxidize the NH4+ to NO2

-

NitrosomonasNitrosomonas

NitrobacterNitrobacter

REACTION REACTION

ENVIRONMENTENVIRONMENT

Aerobic

nono == -- 33 nono == ++33

nono == ++ 55

NH3 + 3/2 O2 HNO2 + H2O

HNO2 + ½ O2 HNO3

Red.Ox.

Red.Ox.






NH4+ + 3/2 O2 NO2

- + 2H+ + H2ONitrosomonas

NH4+ + ½ O2 NH2OH + H+

NH2OH + O2 NO2- + 2H+ + H2O

Reazioni Reazioni

intermedieintermedieIntermediate:

NH2OH

HYDROXYLAMINE

N2O is formed during the chemical

decomposition of intermediates,

such as hydroxylamine and nitrite.

N2O is also produced during the

incomplete oxidation of NH2OH

because of formation of nitrosyl

radical (NOH).

Outline of the pathway and enzymes involved. (N. Wrage et al., 2001)

ENZYMES CATALYSING






The denitrification is è the stepwise reduction of NO3- to N2. Denitrification involves

several types of heterotrophic microbes that reduce the nitrate to nitrogen gas, producing

nitrite, nitric oxide (NO), and nitrous oxide (N2O) as intermediates .

HeterotrophicHeterotrophic facultativefacultative bacteriabacteria ((PseudomonasPseudomonas)).

The organic carbon is used for both anabolic and

catabolic pathways.

The NO3- is used in place of oxygen as an

electron acceptor in anoxic conditions.

REACTION REACTION

ENVIRONMENTENVIRONMENT

Anoxic

IT IS PERFORMED BY

C10H19O3N + 10 NO3- 5N2 + 10CO2 + 3H2O + NH3 +10OH-

Red.Ox.

NN22O O isis anan intermediate in the intermediate in the denitrificationdenitrification

pathwaypathway. . ItIt isis notnot a a productproduct of of chemicalchemical

reactionsreactions!!Outline of the denitrification pathway and enzymes

involved. (N. Wrage et al., 2001)

ENZYMES CATALYSING

DENITRIFICATION - 4 4 STEPSSTEPS




NITRIFIER DENITRIFICATIONNITRIFIER DENITRIFICATION

More than 35 years ago, it was proposed that same nitrifiers (AOB) could not only nitrify,

but denitrify as well; this pathway of nitrification, called nitrifiernitrifier denitrificationdenitrification, might

contribute to a major part of the loss of ammonium in the form of NO ed N2O.

It is a pathway in which the oxidation of NH3 to NO2- is followed by reduction of NO2

- to

N2O and N2, withoutwithout NONO33-- productionproduction.

Nitrifier denitrification: hypotetical pathway and probable enzymes. (N.

Wrage et al., 2001)

This sequence of rections in

perfermed by autotrophicautotrophic

ammoniumammonium –– oxidizingoxidizing bacteriabacteria;

Nitrosomonas europaea is the

best studied.

5. Biological processes for N2O production


Donatella Caniani 5




The two pathway model (Poquet et al., 2016)

OXIDATIONOXIDATION PROCESSESPROCESSES

oror

HYDROXYLAMINEHYDROXYLAMINE PATHWAYPATHWAY

REDUCTIONREDUCTION PROCESSPROCESS

oror

NITRIFIER DENITRIFICATION NITRIFIER DENITRIFICATION

PATHWAYPATHWAY

Red.

Ox.

2e-

O2Red.

3e-

Byproduct of incomplete oxidation

Final product of AOB

denitrification

Aerobic environment, O2 as electron acceptor Anoxic environment, NO2- as electron

acceptorENZYMES:

AMO – Ammonia monooxygenase

HAO – Hydroxylamine oxidoreductase

Nor – Nitric Oxide reductase coupled with copper ions

NirK – Nitrite reductase coupled with copper ions

Major contributor to

nitrous oxide production

in WWTPs.

H2O

Ox.

Red.

oxidation

red

uct

ion

1e-

2e-

1e-

1e-

NITRIFIER DENITRIFICATIONNITRIFIER DENITRIFICATION

5. Biological processes for N2O production




6. AeD modellingAEROBIC DIGESTORAEROBIC DIGESTOR

Basic concepts of ASMN (Hiatt & Grady, 2008) Basic concepts of ASMN (Hiatt & Grady, 2008) –– 2 steps nitrification, 4 steps 2 steps nitrification, 4 steps denitrificationdenitrification

++

PoquetPoquet Model (Model (PoquetPoquet et al., 2016) et al., 2016) –– NitrifierNitrifier DenitrificationDenitrification

AEROBIC DIGESTORAEROBIC DIGESTOR

Basic concepts of ASMN (Hiatt & Grady, 2008) Basic concepts of ASMN (Hiatt & Grady, 2008) –– 2 steps nitrification, 4 steps 2 steps nitrification, 4 steps denitrificationdenitrification

++

PoquetPoquet Model (Model (PoquetPoquet et al., 2016) et al., 2016) –– NitrifierNitrifier DenitrificationDenitrification

The wastage flow rate is 385 m3d-1

Few modifications were performed for the necessities of the study: 18 components and 19

processes were modelled.

MODEL LAYOUTMODEL LAYOUT

MatlabMatlab--SimulinkSimulink




6. AeD modelling. Basic concepts of ASMN (Hiatt & Grady, 2008) STATE VARIABLES – AeDMG1

1 SS

M(COD) L-3

Readily biodegradable substrate

2 SI Soluble non – biodegradable (inert)

organic matter

3 XS Slowly biodegradable substrate

4 XI Particulate non – biodegradable (inert)

organic matter

5 XB,H Active heterotrophic biomass

6 XB,A

OB

Active AOB biomass

7 XB,N

OB

Active NOB biomass

8 XD Inert particulate from biomass decay

9 SO Dissolved oxigen

10 SNO3

M(N) L-3

Nitrate

11 SNO2 Nitrite

12 SNO Nitric oxide

13 SN2O Nitrous oxide

14 SNH Ammonia nitrogen

15 SNS Soluble biodegradable organic

nitrogen

16 XNS Particulate biodegradable organic

nitrogen

17 SALK Molar units Alkalinity

PROCESSES – AeDMG1

R1 Aerobic growth of heterotrophs

R2 Anoxic growth of heterotrophs, nitrate to nitrite

R3 Anoxic growth of heterotrophs, nitrite to nitric oxide

R4 Anoxic growth of heterotrophs, nitric oxide to nitrous

oxide

R5 Anoxic growth of heterotrophs, nitrous oxide to nitrogen

R6 Decay of heterotrophic

R7 Aerobic growth of autotrophic, AOB

R8 Aerobic growth of autotrophic, NOB

R9 Mixotrophic growth of NOB

R10 Decay of autotrophic, AOB

R11 Decay of autotrophic, NOB

R12 Ammonification of soluble organic nitrogen

R13 Hydrolysis of entrapped organics

R14 Hydrolysis of entrapped nitrogen organic

4 4 StepsSteps

forfor

DenitrificDenitrific

ationation

4 4 StepsSteps

forfor

DenitrificDenitrific

ationation

2 2 StepsSteps

forfor

NitrificatiNitrificati

onon

2 2 StepsSteps

forfor

NitrificatiNitrificati

onon




Poquet Model (Poquet et

al., 2016)

NEWNEW POCESSESPOCESSES ANDAND STATESTATE VARIABLESVARIABLES

Five steps for nitrifier denitrification were added, as show below.

The model is more complex than the proviuos one. However it is able to describe the

proceses for N2O production in a better way, without understimations in emission

evaluation.

The new state variable is

the Hydroxilammine

(NH2OH).

It is fundamental in N2O

emission evaluation.

6. AeD modelling


Donatella Caniani 6




6. AeD modelling

SensitivityClasses

Index

Sensitivity

I 0.00≤|I|<0.05 Small or Negligible

II 0.05≤|I|<0.20 Medium

III 0.20≤|I|<1.00 High

IV |I|≥1.00 Very High

MODEL CALIBRATIONMODEL CALIBRATION

SensitivitySensitivity AnalisysAnalisys –– MorrisMorris MethodMethod

RANKINGRANKING

MO

DE

L M

OD

EL

PA

RA

ME

TE

RS

PA

RA

ME

TE

RS

MODEL OUTPUTSMODEL OUTPUTS




mu_H

Y_H

etaAOB_ND0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Si

di

COD

COD



6. AeD modelling: sensitivity results




mu_H

Y_H

etaAOB_ND0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Si

di

TSS

TSS







mu_H

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Si

di

NH4

NH4





Donatella Caniani 7




mu_H

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Si

di

NO3

NO3







mu_H

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Si

di

NO2

NO2







6. AeD modelling: sensitivity resultsMODEL CALIBRATIONMODEL CALIBRATION


mu_H

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Si

di

N2O




6. AeD modelling: sensitivity resultsMODEL CALIBRATIONMODEL CALIBRATION


mu_H

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Si

di

NH2OH

Serie1


Donatella Caniani 8




7. Experimental results.

EVALUATE THE N2O EMISSIONS FROM BIOLOGICAL TANKS USING THE OFF-GAS METHOD. Rionero in Vulture WWTP (Pz), March 2015Activated Sludge Tank

At least the 2% of the entire surface must be covered with

the floating hood to obtain a representative result.

Aerobic Digestor




77.. ExperimentalExperimental resultsresults.. Rionero in Vulture WWTP (Pz), March 2015.

EVALUATE THE N2O EMISSIONS FROM AN ACTIVATED SLUDGE TANK

A reinforced polyethylenepolyethylene floatingfloating hood (1 x

0.7 x 0.4 m, L x W x H) with a cross sectional

area of 0.7 m2 was used to capture the gas

fluxes. Dissolved gases within the liquid are

transported by aerationaeration strippingstripping into the gas

in the hoodhood headspaceheadspace.

SuperSuper--Inert Multi Foil bags (4 L volume)Inert Multi Foil bags (4 L volume) were used to collect off-gas samples and carry

out off-line measurements of NN22O and COO and CO22 concentrations (Gori et al., 2015). The gas bags

were equipped with a vacuum pump vacuum pump and connected to the hood headspace to collect a

gas sample. The main advantage of Multi Foil gas bags was the good sample storage

properties allowing a safe transporsafe transportation for reliable GC-ECD and GC-FID laboratory gas-

chromatographic analyses.

The hood headspace was connected to an

off off –– gas analyzer gas analyzer and the gas flow rates gas flow rates

were measured by a hot wire anemometer.




EVALUATE THE N2O EMISSIONS FROM AN AEROBIC DIGESTOR WITH SURFACE AERATORS

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The off-gas hood was used to collect the exhaust gas in the hood headspace but

due to the presence of surface aeration, there was no relevant off-gas flow rate

leaving the liquid surface and was impossible to collect gas samples immediately.

Therefore, the floating hood was positioned in one location. In order to measure

the relative flux of the gases leaving the liquid volume, a portion of the Teflon tube

was siphon shaped and filled with water.

After about twenty hours keeping the hood in one position, the displacement of

the water level was measured and gas bags were sampled. This methodology

allowed to accumulate a measurable amount of gas in the hood headspace for

both GHG concentrations and flux.

Rionero in Vulture WWTP (Pz), March 2015.

7. Experimental results.




7. 7. Experimental results. Experimental results. Rionero in Vulture WWTP (Pz), March 2015.

Nitrous oxide emissions in wastewater treatment plants: biological processes, methods for

sampling and measurement, decision support systems for planning and management.

From electricity

generation

From organic

matter oxidationFrom N2O

Total CO2,eq

emissions

Plant

CFP

AS 0.26 0.14 0.007 0.4070.47

AeD 0.063 3·10-10 4·10-9 0.063

Gori et al. 2010 0.60.6 from AS

0.4 from AeD0.1 - 1.7

Corominas et al.

20100.524

0.376 from AS

0.389 from AD0.384 from AS - 1.673

Total plant CFP (all values in kgCO2,eq/ kgbCOD) and comparison with literature data

From electricity

generation

From organic matter

oxidationFrom N2O

AS 0.294 0.158 0.007

AeD 0.071 3·10-10 4·10-9

Flores-Alsina et al. (2011) -

scenario A0

0.311 without energy

recovery

0.380 from AS

0.079 from AD0.236 from AS


scenario A1


recovery

0.398 from AS



scenario A2


recovery

0.380 from AS

0.079 from AD0.158from AS


scenario A3


recovery

0.398 from AS


Plant CFP (all values in kgCO2,eq/ m3 of treated wastewater) and comparison with literature data

Emission factor: 0.00032 kgN2O-N/kgNH4-N Daily rate AS: 70 gN2O/d


Donatella Caniani 9




7. 7. Experimental results. Experimental results. Rionero in Vulture WWTP (Pz), March 2015.

• The value obtained for the emission factor is 0.00032 kgN2O-N/kgNH4-N, corresponding to

0.032%. The obtained value is inside the range indicated by Chandran (2011) for

AS, nevertheless closer to its lower bound. This is not because the plant is designed and

managed towards a low-emissions configuration, but most probably because many anoxic

zones are generated in the aerobic tank due to the poor performance of the aeration system.

• The daily rate of N2O emitted from the aeration tank is 70 gN2O/d that is a value typical

obtained for anoxic tanks, as shown for example by Ahn et al. (2010) for a Modified Ludzack -

Ettinger (MLE) configuration.

• The emissions from the AeD are smaller than those from AS mainly because of low off-gas

flow rates due to the installation of surface turbines instead of submerged diffusers.

However, the poor management of the AS compartment implies that the AeD receives higher

NH4 loads than in normal operative conditions and could become potentially the main

contributor to N2O emissions: nitrogen compounds accumulated in the AS are the potential

source of emissions along the sludge line (e.g. during following sludge treatment steps such

as thickening, dewatering, transportation and disposal).




7. Experimental results: pilot plantEVALUATE THE N2O EMISSIONS FROM AN AEROBIC DIGESTOR ON LAB SCALE

� IN 60 mL

� OUT 60 mL

� At first, 6 L of secondary sludge from the settler underflow of

the WWTP located in Potenza (Italy), serving 120000 PE, were

introduced in the digester was fed.

� Diffusers were introduced inside the tank to ensure an

adequate amount of DO to the microorganisms’ activities; a mixer

was also useful to avoid sludge sedimentation and consequently

the clogging of diffusers.

� The testing was performed in a 20-days monitoring campaign,

in order to reach the equilibrium conditions regarding the

biological activities. To ensure a discontinuous feeding, 60 mL of

new sludge were introduced every day.

� Analysis regarding COD, nitrogen compounds, TSS and VSS on

the influent and the underflow were performed during the testing

days.

Palermo 21/05/2016





� A simplified off-gas technique was used to

collect the off-gas.

� A hood was used to collect and conveying

the off-gas towards the flowmeter. The off-

gas flow rate was measured. However, at the

same time, Tedlar sampling bags were used to

take gas samples from the hood headspace:

eight bags a day were analyzed, one every 15

minutes.





mg/l COD TSS VSS NH4+ N-NO2

- N-NO3-

Influent sludge at first day test 6141.23 10720 8240 2.28 1.13 132.87

Discharged sludge after 20 days 5130.55 6780 4045 3.03 1.77 277.50

A 50.9 percent decreasing in VSS concentration and a

36.7 percent decreasing in TSS concentration were

observed, respectively, after 20 days, which are values

closer to the literature range for well performed systems

(38 - 50 per cent in VSS and 30 - 50 per cent in TSS,

Metcalf and Eddy, 2003).


Donatella Caniani 10





NN22OO coverscovers thethe 7272 percentpercent ofof thethe totaltotal COCO22 equivalentequivalent emissionsemissions andand COCO22 onlyonly thethe 2828

percent,percent, consideringconsidering aa conversionconversion factorfactor ofof 289289 kgkgCOCO22/kg/kgNONO22 forfor NN22OO (IPCC(IPCC 20062006))..

testing days

CO2

kgCO2/kgbCOD·m2

N2O

kgN2O/kgbCOD·m2

CO2,e

kgCO2e/kgbCOD·m2

7/13/15 53.03 0.093 79.87

7/14/15 31.65 0.071 52.09

7/15/15 65.20 0.372 172.73

7/16/15 67.69 0.732 279.26

7/17/15 78.23 0.164 125.65

7/20/15 58.71 0.290 142.59

7/21/15 43.89 0.159 89.85

7/24/15 35.38 0.886 291.45

7/27/15 39.94 0.183 92.95

7/28/15 42.33 0.871 294.10

7/29/15 43.90 1.491 474.84

7/30/15 28.30 0.079 51.12

7/31/15 30.35 0.184 83.62

Assuming a conversion factor of 0.74 kgbCOD/kgCOD (Henze et al., 2000), the quantified emissions

from pilot AD are summarized in Table 2, showing an average value of 171171 kgCOkgCO22,e,e//kgkgbCODbCOD··mm22..

TheThe emissionsemissions areare

lowerlower thanthan thosethose

anan ASPASP andand higherhigher

thanthan thosethose anan

anaerobicanaerobic digester,digester,

inin whichwhich thethe

producedproduced COCO22 isis

convertedconverted inin

biogasbiogas withwith thethe

possibilitypossibility toto

recoverrecover energyenergy forfor

thethe plantplant..





testing days

Flux

(kgN2O/m2·d)

Emission fraction·10-3

kgN2O/kgNH4

7/13/15 468 0.018

7/14/15 317 0.009

7/15/15 1545 0.055

7/16/15 2909 0.102

7/17/15 612 0.022

7/20/15 1121 0.051

7/21/15 770 0.022

7/24/15 4190 0.131

7/27/15 879 0.027

7/28/15 4255 0.133

7/29/15 7150 0.210

7/30/15 396 0.010

7/31/15 867 0.025

Table 3 shows that the daily amount of N2O emissions depends of BNR processes,

computing the N2O emission fraction by means the normalization of the flux to the daily

influent Total Kjeldahl Nitrogen (TKN).

OnOn average,average, thethe calculatedcalculated

NN22OO emissionemission fractionfraction forfor thisthis

pilotpilot digesterdigester isis 00..006006

percent,percent, resultingresulting lowerlower thanthan

thethe rangerange proposedproposed byby

ChandranChandran ((20112011)) forfor ASPsASPs

whenwhen normalizednormalized toto influentinfluent

TKNTKN (from(from 00..0101%% toto 11..88%%))..




7. 7. Experimental results. Experimental results. Pilot plant.

Nitrous oxide emissions in wastewater treatment plants: biological processes, methods for

sampling and measurement, decision support systems for planning and management.

A link between the N2O emissions

and ammonia loads incoming in the

digester through the excess sludge

was found, by means performing

analysis of the sludge

characteristics during the testing

days.

As shown in figure, an increasing As shown in figure, an increasing

of emissions was observed when of emissions was observed when

ammonia decreased, proving the ammonia decreased, proving the

dependence of Ndependence of N22O emissions O emissions

from nitrification processesfrom nitrification processes

DODO concentrationsconcentrations inin thethe pilotpilot tanktank

werewere notnot constantconstant becausebecause ofof

lackinglacking ofof aa DODO controller,controller, andand

nitratesnitrates werewere accumulatedaccumulated inin thethe

liquidliquid phasephase contributingcontributing probablyprobably

toto NN22OO emissionsemissions..

EVALUATE THE N2O EMISSIONS FROM AN AEROBIC DIGESTOR ON LAB SCALE




7. Experimental results: pilot plant


Donatella Caniani 11




7. Future developmentsFULL – SCALE AEROBIC DIGESTER with submerged aerators

NO – AERATED TANKS (i.e. secondary settler)

MethodMethod forfor samplingsampling andand measurementsmeasurements

MethodMethod forfor samplingsampling andand measurementsmeasurements




[email protected]@unibas.it

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