YeeShee Tan Yasuhiro Fukushima

Environmental System Engineering LabDepartment of Environmental Engineering

National Cheng Kung University (Taiwan)

Evaluation of Energy Recovery from Food Processing Waste and Wastewater using Life

Cycle Assessment – Case Study on Tofu Industry

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食品生産における排水および廃棄物からのエネルギー回収プロセスの LCA —豆腐生産のケーススタディー

Introduction

Food IndustryFood Industry

Food Food Processing Processing

Waste/wasteWaste/wastewaterwater

Current situation: Contain high chemical oxygen demand (COD).

−15,000 mg/L, 150 times greater than the standard.

Not properly treated.– Small factory

distributed in residential area without a centralized treatment system.

– Waste/wastewater are deluded as non-toxic substance.

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Recent advancement: Recover energy from food processing waste/wastewater while eliminating pollution by using biological technologies.

– Climate change– Reduction of GHGs

emission– Water quality

– Reduction of COD– Distributed energy

collection– Energy production in

household and factory

ObjectivesTo develop a design support system for an energy

recovery from food processing waste/wastewater.

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Food IndustryFood Industry

Design system

GHGs, COD

Methodology

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Synthesis

Process synthesis is established to synthesize an energy recovery process that deal with food processing waste/ wastewater

Basis for Evaluation

The most conventional energy production is selected as a benchmark

Evaluation

Comparative LCA is conducted to evaluate the potential of GHGs emission by the waste-to-energy process.

Food IndustryFood Industry

Environment

3.03 kg Dreg3.03 kg DregCarbohydrates:

7,306 mg/L

1 kg 1 kg TofuTofu

1.5 L Wastewater1.5 L WastewaterCarbohydrates: 10,456 mg/L

Case studyA small scale tofu factory (Residential area, Tainan)

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Tofu factoryTofu factory

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Process SynthesisCharacteristics of

waste/wastewater

Types of energy recovery

Condition and constraints of

process

OilBiodiesel

production

SugarBioethanol production

Carbohydrates

Hydrogen photo fermentation

Hydrogen dark fermentation

Anaerobic digestion

Photo fermentationInput: VFAOutput: CO2 & H2

Rely on availability of light source.Anaerobic digestionInput: VFAOutput: CO2 & CH4

Dark fermentationInput: CarbohydratesOutput: Volatile fatty acid (VFA) effluent, CO2 & H2

Flow Chart of Process Synthesis

Start

Is the effluent still at a level above standard?

Is the major content in waste/wastewater carbohydrates?

Is the effluent still at a level above standard?

Are they contained with solid VFA?

Recovery by dark fermentation

Recovery by anaerobic digestion

Recovery by other processes, e.g. biodiesel production etc.

Discharged directly to the environment.

Recovery by photo fermentation

Discharged directly to the environment.

Yes

Yes

Yes

No

No

No

NoYes

Comparative Life Cycle Assessment

Wastewater/dreg

Tofu processing

Energy recovery from

wastewater/dreg

Evaluated scenario Reference scenario

Soy

Wastewater treatment

GHG

Tofu

Energy production by reference mechanism

Waste/wastewater treatment

Supplementary feedstock

Electricity

Effluent

Energy( H2, CH4)

GHG

GHG

Effluent

Electricity

Feedstock

GHG

GHG

GHG GHG

GHG

Wastewater/dreg

Energy( H2, CH4)

8 30,760 L-H2 1,630 L-CH4

7,350 L wastewater14,847 L diluted dreg

Evaluated Scenario

Hydrogen Dark-fermentation

Anaerobic Digestion

Effluent

Dilution

CO2

Tofu Wastew

ater

H2

CH4

Dreg

Anaerobic digestion sludge

Fermentation wastewater

CO2

Sludge

Wastewater treatment

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Reference Scenario

Steam reformin

g

Effluent

GHG

GHG

Power plant

Energy production by reference mechanism

Composting

Municipal wastewater treatment

Methane extracti

on

Tofu Wastew

ater

Dreg

Natural

gas

H2

Natural

gasCH4

GHG

Waste/wastewater treatment

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Result (1/2)

Dark fermentati

on

Anaerobic digestion

1,560Wastewater: 2,929Diluted dreg: 190

47Wastewater: 88Diluted dreg: 6COD (unit: mg/L)

7,877Wastewater: 14,793Diluted dreg: 960

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By interview and literature review, the process inventory can be collected.

3,600 L 19,000 L

30,760 L-H2/day 1,630 L-CH4/day

For a small tofu factory that produces 4900 kg tofu in a day,

Result (2/2)kg CO2-equiv./day

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Evaluated scenario

Reference scenario90

3,616

3,526

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100 tofu factories in Taiwan.– Assumed all are small scale factory in

residential area.

Climate change353 tons of CO2 equiv./day can be reduced.

Water quality14,514 ton COD and 3,476 ton COD can be treated

by dark fermentation and anaerobic digestion, respectively in a day.

Treated to a level below standard, i.e. 100 mg/L.Distributed energy production

3,076,000 L-H2/day and 163,000 L-CH4/day will be produced.

Discussion

Dark fermenta

tion

Anaerobic

digestion

ConclusionUsing case study, the design support system has been

developed.By synthesis

Compose of 2 processes, i.e. dark fermentation and anaerobic digestion.

By calculationSize of reactor

3,600 L for dark fermentation and 19,000 L for anaerobic digestion.

Productivity30,760 L-H2 for dark fermentation and 1,630 L-CH4 for

anaerobic digestion.COD removal

7,877 mg/L 1,560 mg/L 47 mg/LGHG emissions

3,526 kg-CO2 equiv. can be reduced.As a preliminary attempt, synthesis and evaluation of

the process is carried out. More detailed design scheme should be elaborated in the future study.

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YeeShee TanEmail: ys_ethene@hotmail.com

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