Ben

Leppard,

Charles

Griffin,

Kaylynn

Smalls

Anaerobic Digestion of Food

Waste From Clemson

University Dining Facilities

RECOGNITION OF PROBLEM

◼ According to the EPA, in the United States,

approximately 21% of waste that goes into

landfills and incinerators comes from food

waste; this is about 35 million tons of waste

(Resource Conservation).

◼ Clemson University produces about 675

tons of food waste per year

◼ Only about 270 tons per year are

composted.

http://www.epa.gov/foodrecovery

/

◼ Process:▪ Design an Anaerobic Digester to create biogas from Clemson food

waste

▪ Convert 50% of the food waste from Harcombe & Schilletter to biogas

◼ Structural:▪ Design reactor tank to withstand stresses

◼ Mechanical:▪ Achieve proper mixing in reactor and equilibrium tanks

▪ Pump feedstock at desired flow rate

GOALS OF THE PROJECT

CONSTRAINTS

◼ High Variability of Feedstock

◼ Highly Viscous Feedstock

◼ Limited Experience with Viscometer

QUESTIONS TO BE ADDRESSED

User

▪ How much food waste can the anaerobic digester handle?

▪ How much would it cost to operate the anaerobic digester?

▪ How much space will the anaerobic digester take up?

Client

▪ How much would it cost to fabricate the anaerobic digester?

▪ How much methane will be produced by the anaerobic digester?

▪ How long will it take before methane can be produced?

Designer

▪ Where is the anaerobic digester going to be placed?

▪ What is the composition of the food waste?

▪ Will other substrates need to be added to improve the anaerobic digester?

FEEDSTOCK DATA

Nitrogen: 1.0%

Carbon: 12.37%

C:N Ratio: 12.21%

Bulk Density:

399lb/cubic yard

Moisture: 75.28%

Ash:

3.2%

Dry

Matter:

24.7%

QUALITY OF FEEDSTOCK

◼ Light Metals

◼ Heavy Metals

◼ pH

◼ C:N Ratio

◼ TS/VS Concentration

ANALYSIS OF DATA

● Food waste had low C:N 12:21

● Desired range of 20:1 - 40:1

● Glycerol chosen as co-substrate because of high VS

content and carbon concentration

AGRICULTURE LAB VOLATILE SOLID

CALCULATION

%VS (Dry) = 100 - %ASH (Dry)

= 100 - 3.2%

= 96.8%VS

TEAM’S CALCULATION OF VOLATILE SOLID

GOVERNING EQUATIONS

NitrogenCarbon

C1=Food Waste

C2=Glycerol

C3=Mixed Stream

M1=Mass Flow Rate

C2:

MASS BALANCE

The team decide on a ratio of 30.1 because it was in the middle of the acceptable

range for carbon to nitrogen. Since we decided to use this ratio the flow rates became

CARBON NITROGEN RATIO

VOLATILE SOLID MASS BALANCE

C1=Food Waste

C2=Glycerol

C3=Mixed Stream

REACTOR SIZING

ORGANIC LOADING RATE

Determining the Organic Loading Rate is very important for designing an anaerobic

digestion. If the organic loading rate is too high, there is a risk of substrate

inhibition; it causes an accumulation of volatile free fatty acids which inhibits the

rest of the reactions; this is not good for the process.

ORGANIC LOADING RATE

ORGANIC LOADING RATE

BIOGAS PRODUCTION

ENERGY FROM BIOGAS

COMPUTER MODEL

Biogas Production

Time [Days]

Bio

ga

s [kg

]

Design Considerations

◼ Batch vs. Continuous

◼ Vertical vs. Horizontal

◼ Single vs. Multi-Stage

◼ Thermophilic vs. Mesophilic

POSSIBLE DESIGNS

Iron Oxide will be used to scrub the biogas of Hydrogen

Sulfide. When combined they form insoluble iron sulfide

Scrubbing of Biogas

ELECTRICITY GENERATION

CHP UNIT

Overall Design

SUSTAINABILITY MEASURES

◼ More ecologically friendly than landfilling or incineration

◼ Provides a valuable product from waste that is often disposed of

◼ Is a sustainable fuel source

◼ Reduces transportation costs to landfill (monetary, carbon, labor, equipment)

◼ Economically viable (net metering, disposal savings, carbon credits)

◼ Environmentally responsible (less need for landfill volume, reduced GHG

emissions,)

◼ Socially Equitable (localized waste disposal)

◼ Sustainable Materials: waste glycerol(adding carbon), waste food, used

equipment, water neutral process, carbon neutral process

TIME LINE

BUDGET

ANAEROBIC DIGESTION OVERVIEW

◼ Process where microorganism break

down organic compounds in anoxic

environments and produce biogas.

◼ Consist of 4 major parts

▪ Hydrolysis

▪ Acidogenesis

▪ Acetogenesis

▪ Methanogenesis

http://www.magheebioenergy.in/wp

-

content/uploads/2013/12/BiogasPr

edictionandDesignofFoodWastetoE

nergySystemELSEVIER20111.pdf

LITERATURE

C. Zhang, S. Haijia, J. Baeyens, and T. Tianwei. 2014 . Reviewing the anaerobic digestion of food waste for biogas production. Renewable and

Sustainable Energy Reviews. 38: 383-392.

●Role and optimal levels of important parameters, an approximate amount of food waste by country, average food waste

composition.

C. Drapcho, N. Nhuan, T. Walker. 2008. Chapter 9: Methane. In Biofuels Engineering Process Technology, 329-337. New York, N. Y.: McGraw Hill.

●It detailed the 4 steps that compose anaerobic digestion. It discussed possible enzymes that could be used to help

hydrolysis and fermentation. It stated that theoretically carbs yield lower methane. .While proteins and lipids yield higher

methane. A COD:N:P ratio of 300:5:1 was given as an adequate ratio for digestion.

EPA, L. Moody. Using Biochemical Methane Potentials and Anaerobic Toxicity Assays. Available at

http://www.epa.gov/agstar/documents/conf10/Moody_Final.pdf. Accessed on September 9, 2014.

●This is more information from Moody, an agricultural scientist at Iowa State, explaining the benefits of testing feedstock

prior to designing a digester.

Conclusion

◼ Digester was designed to handle a ton of food waste per day

◼ Produces 187,000 m3 of biogas per year

◼ Using a CHP unit, 333,000 kWh of electricity can be produced each year

REFERENCES

C. Zhang, S. Haijia, J. Baeyens, and T. Tianwei. 2014 . Reviewing the anaerobic digestion of food

waste for biogas production. Renewable and Sustainable Energy Reviews. 38: 383-392.

C. Banks. Anaerobic digestion and energy. University of Southampton. Available at:

http://www.valorgas.soton.ac.uk/Pub_docs/JyU%20SS%202011/CB%204.pdf. Accessed 8

September 2014.

C.J. Banks, Y. Zhang, Y. Jiang, S. Heaven. 2012. Trace element requirements for stable food waste

digestion at elevated ammonia concentrations. Bioresource Technology. 104: 127-135.

C. Chu, Y. Lu, K. Xu, Y. Ebie, Y. Inamori, H. Kong. 2008. A pH- and temperature-phased two-stage

process for hydrogen and methane production from food waste. Intl. J. Hydrogen Energy. 33(18):

4739-4746.