National Agriculture

and Food Research Organization

Food and Agriculture for the Future

Swine wastewater treatment technology to reduce

nitrous oxide emission by using an aerobic

bioreactor packed with carbon fibres

NARO Institute of Livestock and Grassland Science

Animal Waste Management and Environment Division

Senior Researcher

Takahiro Yamashita

Outline

Current state of manure management in Japan・Amount of livestock waste

・Effluent regulations

・Amount of greenhouse gas emissions

・N2O generation from wastewater treatment processes

Objective

Development of technology that can reduce N2O

generated from wastewater treatment processes

「Swine wastewater treatment technology using an aerobic bioreactor packed with carbon fibers to reduce nitrous oxide emissions」-new technology for reducing N2O emissions-

Livestock (pig, cattle, chicken)

Reference：Guidelines for the treatment and use of livestock manure

(Livestock Industry’s Environmental Improvement Organization)

Urine

Feces

13.4 L/head/day

0.13 kg/head/day

45.5 kg/head/day

Feces

Urine

3.8 L/head/day

2.1 kg/head/day

Feces

Urine purified in

treatment

Manure compost

Feces

Urine

Total manure: over

80,000,000 t / year

Soil as fertilizer

Purified water is discharged into rivers and other water bodies

The discharge of such water is

governed by several regulations

Water Quality Pollution Control Act

The wastewater from livestock farms negatively affects surrounding areas directly; it is therefore very important to adopt effective pollution-control measures. Effluents are regulated by the Water Quality Pollution Control Act in Japan.

Standards for the livestock industry

‘Living environment’ itemsEffluent standards

ItemsPermissible

limits

The general effluent standard

pH 5.8-8.6

Biochemical oxygen demand (BOD) (mg/L) 160

Chemical oxygen demand (COD) (mg/L) 160

SS (mg/L) 200

Coliform count (organisms/cm3) 3,000

Nitrogen (N) content (mg/L) 170 120

Phosphorus (P) content (mg/L) 25 16

The Act and its Regulations are applicable to barns on livestock farms with a total floor space of 50 m2 or

larger (pigs), 200 m2 or larger (cattle), and 500 m2 or larger (horses), and with an average effluent volume of

50 m3 or more per day.

the provisional standards are

expected to be tightened further to

match these general standards.

The effluent standard items above

are classified as ‘living

environment’ items, which are

regulated for effluent volumes of

50 m3 or more per day.

0

300

600

900

1200

1500硝酸性窒素規制濃度

(mg

N/L

)暫定基準

一律排水基準

Re

gu

late

d c

on

ce

ntr

ati

on

of

nit

rate

nit

rog

en

Prov. standard

Uniform effluent std. Prediction

If regulations on nitrogen

are tightened further

Background: Nitrogen effluent Control

low-cost nitrogen-removal technology

must be promptly developed.

Livestock farmers

Quickly

Because the general effluent standard for nitrate nitrogen is 100 mg/L, the

provisional standard will be strengthened further at the next

revision in 2016.

The current nitrate nitrogen regulation for livestock wastewater is the provisional standard of

700 mg/L (Fiscal Year 2013).

The cost of wastewater treatment will

increase, leading to lower earnings,

which may become a make-or-break

issue for livestock farmers.

Background: Climate Change

N2O emissions totaled

22,700,000 t, accounting for 1.6%

of the total GHG emissions.

N2O emissions in Japan (FY 2013)

The global warming potential of N2O is 298-times larger than that of CO2

(The IPCC Fourth Assessment Report)

Improved wastewater treatment

technology for greenhouse gas

emission reduction is needed.

Activated sludge treatment

N2O

Agriculture accounts for almost

half of the total emissions, and

40% of this (or 20% of the total)

are emissions from livestock

waste management, which

includes wastewater treatment.

Agriculture

Fuel combustion

Waste

Industrial process

Biological Nitrogen Removal

NH4+

N2O

NO

NO2-

NO3-

N2

Nit

rifi

cati

on

Den

itrification

[Anaerobic]If oxygen is not present

CO2N2↑

NO3-

Organic

matter

Denitrifying

bacteria

NH4+O2

NO3-

Nitrifying

bacteria

[Aerobic]If oxygen is present

Time

Concentr

ation

NH4+

NO3-

Time

Concentr

ation

NH4+

NO3-

NH4+

N2O

NO

NO2-

NO3-

N2

Most of the nitrogen in barn

wastewater, particularly soluble nitrogen, exists as NH4

+.Barn

When both reactions proceed efficiently, N2O is not emitted into the air. However, in

the conventional activated sludge method, N2O is emitted due to various factors.

How to Treat Livestock Wastewater?

Return sludge

wa

ste

wate

r

Wa

ter

treatm

ent

Sludge from the

initial sedimentation

tank (used as

fertilizer)

Initial

sedimentation

tank

Final

sedimentation

tank

Aeration tank

Organic matter removal by

microorganisms

wastewater is separated into solid and liquid fractions by physical treatment such as gravitational

sedimentation.

In the next tank, containing floc-like activated sludge, the pollution

materials, or organic matters, are decomposed by microorganisms.

the wastewater is again separated into solid and liquid

fractions, and the resulting liquid is discharged as treated

water.

Excess sludge (used as

fertilizer)

Return sludge

wa

ste

wate

r

Wa

ter

treatm

ent

Sludge from the

initial sedimentation

tank (used as

fertilizer)

Initial

sedimentation

tank

Final

sedimentation

tank

Aeration tank(activated sludge tank)

Organic matter removal by

microorganisms

Excess sludge (used as

fertilizer)

N2O Generation During Wastewater Purification

N2O generation

NH4+ NO2

-

NO3-

Nitrifying bacteria

NO2- and NO3

- accumulation

Aerobic conditions

Formation of Aerobic & Anaerobic Conditions Using Biofilms

Activated sludge (microorganisms) adhere to

carbon fibers to form aerobic superficial layers

and anaerobic deep layers.

Interior of the

activated sludge tank Carbon fibers

NH4+ NO3

- N2

Nitrification

(aerobic)

Denitrification

(anaerobic)

Activated sludge

Microorganisms adhere

to carbon fibersN2O

Microorganisms adhere to the carriers

installed in the activated sludge tank, to

form biofilms consisting of aerobic

superficial layers and anaerobic deep layers.

This allows the microorganisms to grow,

and simultaneously accelerates both the

(aerobic) nitrification and (anaerobic)

denitrification reactions. Such a smooth

oxidation-reduction reaction is considered

to inhibit the production of N2O.

Deep

anaerobic

layers

Superficial aerobic

layers

Carrier

Approx. 400 mL of wastewater supplied through

the reactor bottom every 6 hours

Overview of Experimental Device

Activated sludge reactor(control)

Carbon fiber reactor (fixed bed type)

Fiber size:

Φ7 μm

(6 m3/m3.h)

P

Water treatment

Carbon fibersAir

Swine wastewater P B

Water treatment

Air

Swine wastewater P B

Activated sludge(MLSS: Avg. 5000)

55cm

5 cm5-cm interval

5 cm

Mesh cylinder (flat)Mesh cylinder

11 layers of carbon fibers in 4 directions

Water treatment

Reactor water volume: 10 L(Diameter: 15 cm)

Swine wastewater

Ventilation flow

(aeration strength)

Reduced N2O generation

Average BOD load:0.3 kg/m3/day

Thermostatic

chamber (20 °C) operation

Experimental Results (Water Quality)

0

500

1000

1500

2000

2500

流入水 炭素繊維

リアクター

処理水

活性汚泥

リアクター

処理水

BO

D (

mg/

L)BOD

0

50

100

150

200

250

300

流入水 炭素繊維

リアクター

処理水

活性汚泥

リアクター

処理水

溶解性窒素

(mg

/L)

NO3-N NO2-N NH4-N

Water quality data for Days 73 – 176 of operation

The carbon fiber reactor was found to inhibit the accumulation of nitrate

nitrogen more than the activated sludge reactor.

So

lub

le n

itro

ge

n

Influent Influent Water

treated in

carbon

fiber

reactor

Water

treated in

activated

sludge

reactor

Water

treated in

carbon

fiber

reactor

Water

treated in

activated

sludge

reactor

Experimental Results (Gas Generation)

0

200

400

600

800

1000

1200

温室効果ガス発生量

（g-

CO

2e

q/m

3/d

ay）

N2O

CH4

活性汚泥法 炭素繊維法

N2O

CH4

Carbon fiber method was therefore

found to be capable of significantly

reducing N2O emissions.

Activated

sludge method

Carbon fiber

method

Am

ou

nt

of

gre

en

ho

use

gas g

en

era

ted

Amount of greenhouse gas generated by

wastewater purification treatment

The carbon fiber reactor successfully reduced N2O generation by 98% or

more, compared to the activated sludge reactor (with continuous aeration)

0

100

200

300

400

500

600

700

800

0 24 48 72 96 120 144 168

NH

3, N

2O

an

d C

H4

(mg/

m3)

経過時間(hrs)

ASリアクター(130～136日)

NH3

N2O

CH4

Time

0.03 gN2O-N/gTN-load

7180.5 mg-CO2

equivalent/day

Activated sludge reactor

0

100

200

300

400

500

600

700

800

0 24 48 72 96 120 144 168

NH

3, N

2O

an

d C

H4

(mg/

m3)

経過時間(hrs)

CFリアクター(130～136日)

NH3

N2O

CH4

Time

339.4 mg-CO2

equivalent/day

0.0003 gN2O-N/gTN-load

Carbon fiber reactor (fixed bed type)

*Measurement every 15 minutes

Amount of gas generated in reactors (Days 130 – 136 of operation)

Reactions Inside the Treatment Tank

Activated sludge method

(conventional method)

In activated sludge

NH4+ NO3

- accumulated

N2O

Aeration tank

Nitrifying

bacteria

Carbon fiber

method

Aeration

tank

Biofilms

Carb

on

fiberNH4

+

Superficial

layer Deep layer

N2

NO3-

Carbon fiber

Biofilms

Activated

sludge

Activated

sludge Activated

sludge

Activated

sludge

Activated

sludgeActivated

sludge

Activated

sludge

Denitrifying

bacteria

Nitrifying

bacteria

Denitrifying

bacteria

Application of this technology will lead to …

Global warming reduction

N2O generation

Nitrogen reduction

Eutrophication reduction

Lakes and inner bays

Livestock farmers

Wastewater treatment Increasing the safety of

drinking water

Thank you for your attention

Causes of Nitrous Oxide (N2O) Generation in Wastewater Treatment

NH4+ NO3

- N2

N2O

Low DO

condition

Nitrification Denitrification

High

NO2-

concent

-ration

- Insufficient aeration

- Organic matter high-

load operation

- Insufficient aeration

- Low SRT

- Low water temperature

- High ammonia concentration

High DO

conditionLow

COD/N

High

NO2-

concent-

ration

- Influence of excess

aeration by nitrification- COD restriction

- NO2- inflow from

the nitrification

process

- Properties of influent

- Influence of excess

sedimentation in the

up-stream process

When the COD/N ratio is 3.5 or less, 20 – 30%

of N load is discharged as N2O.

(Itokawa et al., 2001)

When the DO concentration is 1 mg/L or less,

10% of N load is discharged as N2O.

(Goreau et al., 1980)

- Decrease in pH due to

accumulated NO2

Reaction Path of Biological Nitrogen Removal in Purification

N2

N2O

NO

NO2-

NO3-

Anammox

bacteria

NH4+

N2ONO

Aerobic

reaction

Anaerobic

reaction

Nitrification process

Denitrification

process

Denitrifying

bacteria

Ammonium

oxidizing

archaebacteria

Nitrite

oxidizing

bacteria

Ammonium

oxidizing

bacteria

In either process, of denitrification or nitrification,

N2O may be discharged.

Denitrifying

bacteria

Denitrifying

bacteria

Denitrifying

bacteria

Ammonium

oxidizing

bacteria

Ammonium

oxidizing

bacteria

- FY 2013Lab scale

Carbon fiber reactorActivated sludge reactor

FY 2014Bench scale

Carbon fiber reactorActivated sludge reactor

Size 10 L 1 m3 (125 cm deep)

Amount of carbon fiber to supply; or Amount of activated sludge (mg/L)

55 cm (11-layer, 4 directions, 5 cm);

or 5000

6 pieces (90 cm);or

5000

Sewage to supply Swine wastewater Swine wastewater

BOD load (kg/m3/day) 0.3 0.3

BOD/N ratio Average 6 Approximately 2.5

Aeration amount 1 L/min (6 m3/m3・h) 50 L/min (3 m3/m3・h)

Water temperature (°C) 20 Vary by season

GHG gas measurement 15-minute cycle 15-minute cycle

Carbon Fiber Supply Experiment at the Actual Facility

Partially supply

water by bypass

operation

Treated

water

Area for testing with

carbon fiber

Volume:

Approx. 1 m3

P

P

A

Wastewater draw-up

Pump

Aeration

Partially supply

water by bypass

operation

Treated

water

Area for comparison

(no carbon fiber)

Volume:

Approx. 1 m3

P

P

A

Wastewater draw-up

Pump

Aeration4.8 m3/h

BOD load: 0.3 kg/m3/day

6 pieces (90 cm)

Activated sludge amount

MLSS: 5000 mg/L

Barn wastewater pit

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70

NH

4-N

, N

O3-N

an

d N

O2-N

(m

g/L

)

Period（days）

Influent NH₄-N Effluent NH₄-N Influent NO₃-N

Effluent NO₃-N Influent NO₂-N Effluent NO₂-N

In the activated sludge (AS) reactor

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70

NH

4-N

, N

O3-N

an

d N

O2-N

(m

g/L

)

Period（days）

Influent NH₄-N Effluent NH₄-N Influent NO₃-N

Effluent NO₃-N Influent NO₂-N Efflent NO₂-N

In the carbon fiber (CF) reactor

0

100

200

300

400

500

0 10 20 30 40 50 60 70

NH

3, N

2O

an

d C

H4

(mg

/m3)

Period (days)

CFリアクター

NH₃

N₂O

CH₄

0

100

200

300

400

500

0 10 20 30 40 50 60 70

NH

3, N

2O

an

d C

H4

(mg

/m3)

Period (days)

ASリアクター

NH₃

N₂O

CH₄

Generated Gas and Water quality

0.008 g N2O-N/g TN-load 0.021 gN2O-N/g TN-load

Aeration tank 10L Carbon fiber

Biofilms

Carbon fiber

Biofilms

Aeration tank 700L

Non- contact aeration in the indoor

experiment with small-scale equipment Direct contact aeration in the scaled-up experiment

Microorganism Carriers: Carbon Fibers

When microorganisms adhere to non-carbon fibers, there is an energy barrier which

impedes and retards adhesion. However, it was found that this barrier is not present in

the case of adhesion to carbon fibers, which means that microorganisms can adhere

to such fibers more quickly and easily.

[Comparative rate test of microorganism

adhesion to various fibers]

- Carbon fiber (CF)

- Polyacrylonitrile (PAN)

- Aromatic polyamide (AP)

- Polyethylene (PE)

It was found that the rate of microorganism adhesion was 1.5 – 10 times

faster in the case of carbon fiber than other fiber types. (The carbon fiber

adhesion rate for Escherichia coli was 5 times that of polyamide fiber.)

Between any substances, there is mutual attraction caused by intermolecular forces.

In the case of microorganisms in water, there is greater attraction to carbon fiber

than to other fibers.

Under water, both

microorganism

cells and fibers

have a negative

electric charge.

It was found that the

negative electric charge on

carbon fiber is less than that

on other fibers.

Micro-organism

cells

--

-

- --

CF--

PAN----

AP----

PE----

Reference:Matsumoto S, Ohtaki A, Hori K. 2012. Carbon fiber as an excellent

support material for wastewater treatment biofilms. Environmental Science &

Technology 46, 10175–10181.

Carbon fiber method

Aeration tank

BiofilmsC

arbo

n fib

er

NH4+

Superficial

layerDeep layer

N2

NO3-

Carbon fiber

Biofilms

Intermittent aeration method in activated sludge treatment plants

. Osada et al. (1995) reported that less than 1% of influent nitrogen was emitted as N2O gas during the

intermittent aeration process. However, the intermittent aeration method produces lower degradation of organic

matter than standard activated sludge processes.

Activated

sludge

Activated

sludge Activated

sludge Activated

sludge

Activated

sludgeActivated

sludge

Activated

sludge

Activated

sludgeActivated

sludgeActivated

sludge

Activated

sludgeActivated

sludge Activated

sludgeActivated

sludge

Cycle

Aeration No aeration

Sedimentation

26

27