1. 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
Evaluation of Energy Recovery from Food Processing Waste and Wastewater using Life Cycle Assessment – Case Study on Tofu Industry
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YeeShee Tan
Yasuhiro Fukushima
Environmental System Engineering Lab
Department of Environmental Engineering
National Cheng Kung University (Taiwan)

2. Food Processing Waste/wastewater
Introduction
Food Industry
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
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.
There are many food industry companies have been established. while producing the food, the food processing waste/wastewater will be emitted. For the current situation in Taiwan, these waste/wastewater contain high chemical oxygen demand that is around 15,000 mg/L which 150 times greater than the standard. This also implies the high potential of energy production. Furthermore, these waste/wastewater are not properly treated as there are many small factories distributed in residential area without a centralized treatment system and the waste/wastewater are deluded as non-toxic substance. So, with this characteristic of food industry, recent advancement is to recover energy from food processing waste/wastewater while eliminating pollution by using biological technologies, such as hydrogen fermentation, anaerobic digestion, etc. as the climate change, water quality and the distributed energy collection are drawing attention nowadays. By the energy recovery process, it can potentially reduce GHG emissions that avoided by treatment, COD, and produce energy in household and factory scale.
Food Processing Waste/wastewater

3. Cost Maintenance Space Safety Environment
Objectives
To develop a design support system for an energy recovery from food processing waste/wastewater.
Cost
Maintenance
The objectives of this study is to develop a design support system for an energy recovery from food processing waste and wastewater. For the design system, the design scheme will be cost (How much they can earn?), space (Do they have enough space for the equipment installation?), environment (Is it really good to the environment?), Maintenance (Do they need some professional skill for the maintenance?), Safety (Is it safe?), Usage of the energy (How can the energy be used after it has been produced?) and etc. However, in this study, the part that we are going to support is the environment, especially focus on the GHGs emission and the COD.
Space
Safety
Food Industry
Environment
Usage of the energy
GHGs, COD
Design system

4. Methodology Food Industry Environment Synthesis
Process synthesis is established to synthesize an energy recovery process that deal with food processing waste/ wastewater
Food Industry
For the design system that considering environment scheme, the elements for methodology are synthesis and evaluation. Process synthesis is established to synthesize an energy recovery process that deal with food processing waste/wastewater while comparative LCA is conducted to evaluate the potential of GHGs emission by the waste-to-energy process. When doing the evaluation, basis process is needed. Therefore the most conventional energy production is selected as a benchmark. Takes hydrogen fermentation as an example, if it is chosen as the energy recovery process, hydrogen production by steam reforming or electrolysis will be chosen as a reference.
Evaluation
Basis for Evaluation
Comparative LCA is conducted to evaluate the potential of GHGs emission by the waste-to-energy process.
The most conventional energy production is selected as a benchmark

5. Case study 1 kg Tofu 1.5 L Wastewater Tofu factory 3.03 kg Dreg
A small scale tofu factory (Residential area, Tainan)
1 kg Tofu
Tofu factory
To apply the methodology, a case study of small scale tofu factory that located in residential area of Tainan has been chosen. To produce 1 kg of tofu, there are 1.5 L wastewater and 3.03 kg dregs will be emitted by the tofu factory.
1.5 L Wastewater
Carbohydrates: 10,456 mg/L
3.03 kg Dreg
Carbohydrates: 7,306 mg/L

6. Process Synthesis Characteristics of waste/wastewater
Types of energy recovery
Condition and constraints of process
Carbohydrates
Hydrogen dark fermentation
Dark fermentation
Input: Carbohydrates
Output: Volatile fatty acid (VFA) effluent, CO2 & H2
Hydrogen photo fermentation
Next is the elaboration of process synthesis. To synthesize the process, first we have to know the characteristics of waste/wastewater and the types of energy recovery that can be used. Different types of food processing waste/wastewater have to be treated by different types of energy recovery process, such as , carbohydrates rich waste/wastewater should be fed into hydrogen photo fermentation, hydrogen dark fermentation and anaerobic digestion, oil rich waste/wastewater should be recovery by biodiesel production, sugar rich waste/wastewater has to be subjected to bioethanol production. As I mentioned in the previous slide, tofu wastewater and dregs are contain with high carbohydrates, hence these three processes will be the candidate process for the synthesis. Once we know the types of energy recovery that can be used, the condition and constraints of the process have to be known to ensure the reliability of process. There are such as, for dark fermentation, carbohydrates will be the preferred input while the output will be VFA contained effluent, CO2 and H2. for photo fermentation, VFA is the preferred input and CO2 and H2 will be the output. Besides that, it is highly rely on the availability of light source. And for anaerobic digestion, volatile fatty acid is more preferred than carbohydrates as an input while emitting CO2 and CH4.
Anaerobic digestion
Photo fermentation
Input: VFA
Output: CO2 & H2
Rely on availability of light source.
Oil
Biodiesel production
Sugar
Bioethanol production
Anaerobic digestion
Input: VFA
Output: CO2 & CH4

7. Flow Chart of Process Synthesis
Start
Is the major content in
waste/wastewater carbohydrates? No
Recovery by other processes,
e.g. biodiesel production etc.
Yes
Recovery by dark fermentation
Is the effluent still at a
level above standard?
Next is the flow chart of the process synthesis. First we start with the question “Is the major content in waste/wastewater carbohydrates?”.To ask this as our case study is the carbohydrates rich tofu wastewater and dregs. If the answer is no, then we suggest to recovery by other processes, e.g. biodiesel production etc. while if the answer is yes, then it can be recovery by dark fermentation as carbohydrates is the preferred organic carbon. Then comes to the second question, “Is the effluent still at a level above standard, which is 100 mg/L, the standard of taiwan EPA?”, if the answer is no, then it can be discharged directly to the environment as it is clean enough while if the answer is yes, then addition processes is needed. The next question will be “are they contained with solid VFA?” as the effluent from dark fermentation contains high VFA and VFA is the preferred organic carbon for both photo fermentation and anaerobic digestion. But if it is contained with solid VFA, then it is better to recovery by anaerobic digestion, instead of photo fermentation, as solid content in the effluent will affect the transparency of the liquor. While if it doesn’t contained with solid, then it can be recovery by photo fermentation. The synthesis of process will be ended when the effluent is treated to a level below standard and can be discharged directly to the environment. No
Discharged directly to the environment.
Yes
Are they contained
with solid VFA? No
Recovery by photo fermentation
Yes
Recovery by anaerobic digestion
Is the effluent still at a
level above standard?
Yes No
Discharged directly to the environment.

8. Comparative Life Cycle Assessment
Soy
Tofu processing
Tofu
Wastewater/dreg
Wastewater/dreg
7,350 L wastewater
14,847 L diluted dreg
Evaluated scenario
Reference scenario
GHG
GHG
GHG
A framework for comparative life cycle assessment has been constructed to evaluate the amount of GHG emission that can be reduced by a waste-to-energy process. A candidate process system is synthesized, modeled, and evaluated in comparison with a reference scenario. Besides the tofu processing process included in both of the scenarios, the evaluated scenario consists of energy recovery from waste/wastewater (i.e. dark fermentation and anaerobic digestion), while the reference scenario include the most conventional waste/wastewater treatment for wastewater and dregs and energy production by reference mechanism. Tofu wastewater and dregs in the both scenarios has to be treated to a level below standards. Furthermore, the environmental interventions from the entire life cycle require attention. In our framework, namely: 1) emission from energy recovery (or production); 2) emission from waste/wastewater treatment plant; 3) emission from power plant; and 4) emission from production of feedstock are evaluated. Emissions from the common part are omitted because choice of treatment strategies does not affect the environmental interventions in this part of the life cycle. The common functional unit of the scenarios in this comparative LCA framework is the a) treatment of the food processing wastewater/waste, i.e 7350 L wastewater and 14,847 L diluted dreg, these amounts are the waste/wastewater that will be emitted by the tofu factory in a day and b) energy production, i.e. 30,760 L-H2 and 1,630 L-CH4, which can be produced in a day in that tofu factory.
Energy recovery from wastewater/dreg
Waste/wastewater treatment
Supplementary
feedstock
Effluent
GHG
GHG
Electricity
Electricity
GHG
GHG
GHG
Wastewater treatment
Energy production by reference mechanism
Effluent
Feedstock
Energy
( H2, CH4)
Energy
( H2, CH4)
30,760 L-H2
1,630 L-CH4

9. Evaluated Scenario Tofu Wastewater Dreg H2 Hydrogen Dilution
CO2 H2
Dilution
Hydrogen
Dark-fermentation
Fermentation
wastewater
CO2
In the evaluated scenario, dark fermentation and anaerobic digestion are chosen as the energy recovery methods. First, tofu wastewater is subjected to dark fermentation to produce H2 while emitting CO2 and fermentation wastewater. The fermentation wastewater is then treated with anaerobic digestion to produce CH4 as it still contains high COD. Effluent that is a level enough below standards and CO2 is discharged from this process. Fresh sludge that should be added to the dark fermentation and anaerobic digestion is cut-off because of its negligible amount. The dreg is diluted with the effluent from wastewater treatment plant with the ratio 1:4 and then fed into the dark fermentation. Sludge from the anaerobic digestion is added in this process to enhance the H2 production rate. The following process after the dark fermentation of diluted dreg is the same as the process used for treatment of the wastewater. Effluent from the designed process goes into the wastewater treatment plant although it is clean enough to be discharged directly into the environment.
Sludge
Anaerobic
Digestion
CH4
Anaerobic
digestion sludge
Wastewater treatment
Effluent

10. Waste/wastewater treatment Energy production by reference mechanism
Reference Scenario
Waste/wastewater treatment
GHG
Municipal
wastewater treatment
Tofu Wastewater
Composting
Dreg
Next is the reference scenario. As I mention in the previous slide. Reference scenario consists of two parts, that is waste/wastewater treatment and energy production by reference mechanism. For the waste/wastewater treatment, composting and municipal wastewater treatment are assumed while for energy production, hydrogen production by steam reforming and methane production by extraction from natural gas are chosen as the reference.
Energy production by reference mechanism
Natural gas
GHG
GHG
Power plant
Steam reforming
Methane extraction H2
Natural gas
CH4
Effluent

11. Result (1/2)
By interview and literature review, the process inventory can be collected.
For a small tofu factory that produces 4900 kg tofu in a day,
30,760 L-H2/day
1,630 L-CH4/day
For a small tofu factory that produces 4900 kg tofu in a day, it needs a 3600L of dark fermentation reactor and 19000L of anaerobic digestion reactor to produce L-H2 and 1630 L CH4. For the COD removal, 7877 mg/L of COD will be treated to 1560 mg/L by dark fermentation and be treated to 47 mg/L by anaerobic digestion, which is below a level of the standard, 100 mg/L
Dark fermentation
Anaerobic digestion
7,877
Wastewater: 14,793
Diluted dreg: 960
3,600 L
1,560
Wastewater: 2,929
Diluted dreg: 190
19,000 L 47
Wastewater: 88
Diluted dreg: 6
COD (unit: mg/L)

12. Result (2/2) Evaluated scenario 3,616 3,526 Reference scenario 90
kg CO2-equiv./day
3,616
3,526
For the GHG emission, from this graph, we can see that 90 kg-CO2 equiv. will be emitted by evaluated scenario while 3616 kg CO2 equiv will be emitted by reference scenario, telling us that 3526 kg-CO2eq. is reduced by waste-to-energy processes. For evaluated scenario, most of the emissions are direct ones from dark fermentation and anaerobic digestion. Others are contributed bythe power plant as electricity is needed for condition control such as temperature control, mixing etc. Lastly, the emission from wastewater treatment plant which is used for treating the effluent from the energy recovery plant is found negligible as the effluent is actually clean enough. For the reference scenario, most of the emission are from composting.
Reference scenario 90

13. Discussion 100 tofu factories in Taiwan.
Assumed all are small scale factory in
residential area.
Climate change
353 tons of CO2 equiv./day can be reduced.
Water quality
14,514 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.
Dark fermentation
Anaerobic digestion

14. Conclusion
Using case study, the design support system has been developed.
By synthesis
Compose of 2 processes, i.e. dark fermentation and anaerobic digestion.
By calculation
Size of reactor
3,600 L for dark fermentation and 19,000 L for anaerobic digestion.
Productivity
30,760 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/L
GHG 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.

15. Thanks for you attention!
YeeShee Tan