1. Anaerobic Co-digestion of Biomass for Methane Production : Recent Research Achievements
Wei Wu
CE 521
Today I am going to review recently published papers on the topic of anaerobic co-digestion of biomass for methane production

2. Introduction
Many of you may heard the term of bio-renewable energy. Like,using corn to make ethanol is a good exmaple of coverting biomass to produce renewable energy. Biomass can be defined as organic matter formed by photosynthetic capture of solar energy and stored as chemical energy which includes crops and crops residues, animal manure, organic wastes as shown in this picture. The solar energy stored in biomass could be released as biogas through anaerobic digestion. Biogas could be then used to produce electricity and heat as renewable energy.

3. Anaerobic Digestion Anaerobic digestion (AD)
Organic Matter + H2O + Bacteria
CH4 + CO2 + NH3 + H2S
Traditionally
Single substrate and single purpose
Manure was digested to produce energy
Sewage sludge should be stabilized
Industrial waste water should be pre-treated
Recently
Co-digestion of two or more substrate and multi-purpose
As we learned in the class, anaerobic digestion is a process that bacteria break down organic matter in absence of oxygen and produce biogas consisting of methane, carbon dioxide, and other trace gases (ammonia, h2s). In the past, anaerobic digestion was single substrate, and single purpose treatment. …. After year 2000, co-digestion of two or more substrate has become a hot topic.

4. Co-digestion Co-digestion Two or more substrates
Major amount of a main basic substrates (e.g. manure or sewage sludge) + Minor amount of a singe, or a variety of additional substrates
Multi-purpose process serving at the same time
Waste upgrading
Energy production
Improvement of fertilizer quality
Co-digestion is anaerobic digestion of two or more substrates. The most common situation is a ….. Because of time, today I am going to focus on co-digestion animal manure with other waste streams. Co-digestion has become a mutli …for… and other

5. Co-digestion—Cont. Factors impact the production of biogas
The type of waste being digested
Its concentration
Its temperature
The presence of toxic materials
The pH and alkalinity
The hydraulic retention time
The solids retention time
The ration of food to microorganism
The rate of digester loading
The rate at which toxic end products of digestion are removed
The rate and efficiency of the anaerobic digestion process is controlled by the following factors

6. Benefits of Co-digestion
Improved nutrient balance and digestion performance
A nutrient ratio of TOC:N:P = 300:5:1 to achieve optimal digestion performance
Manure
Low C/N ratio– high ammonia
High alkalinity
Rich in macro/micro
nutrient
Crop or Crop residues
High C/N ratio– high carbon content
Low alkalinity
Lack of macro/micro
nutrient
Improve the C/N ratio, buffering capacity and more biodegradable substrate
Co-digestion have been shown to …. Most bio-waste can be utilized as a single substrate in anaerobic digestion. However, …should be maintained to achieve….Manure contents low ….Crop or Crop residues in the other hand, contains. Co-digestion of Manure and crop or crop residues improve the C/N ratio, manure provides buffering capacity and also more biodegradable substrate are avaialble for digestion. Therefore decreasing the risk of ammonia inhibition and increasing biogas production.

7. Benefits of Co-digestion
Effective utilization of digester volumes
Help to utilize the availability of free capacities
Co- digestion of energy crops and manure resulted in the doubling of the plant capacity from 500 kW to 1000 kW retaining the digester volume (Lindorfer et al., 2007)
The wide distribution of sewage treatment plants minimizes transportation costs
Equalization of particulate, floating, settling, acidifying etc. wastes, through dilution by manure
Adding co-substrate in existing digesters…. Additionally…., Also waste with p…. Could be equalized through

8. Continuously stirred tank reactors (CSTRS) under mesophilic conditions
Co-digestion
Types of digester
Mesophilic AD
Approximately 30-35° C
Retention time of
15 – 30 d
Thermophilic AD
Exceed 55 ° C
Retention time of
12-14 d
Continuously stirred tank reactors (CSTRS) under mesophilic conditions
There are two types of digesters used to digest animal manure with other compatible waste stream. Mesophilic AD usually occurs at temperatures of …and requires a …..Thermophilic AD ….. Thermophilic AD may be able to destroy a larger number of pathogens, however, it costs more and more complicate to operate. Most laboratory scale studies I reviewed were using ….

9. Co-digestion
Source of organic waste streams can be co-digested with manure
Food Industry
Waste from potato, sugar beet, meat, and dairy processing
Grain Industry
Damaged grain
Paper Industry
Newspaper and recycled paper
Domestic Wastes
Livestock Wastes
Crop Residues
Corn stover and switchgrass
Many source of ….including

10. Manure + 30% sugar beet tops
Case 1
Increased by 65 %
Increased by 58 %
Increased by 16 %
Manure + 30% sugar beet tops
Cow manure alone
Manure + 30% grass
Cow manure alone
Now, I want to show your some case studies. Anaerobic co-digestion of grass ….with cow manure were evaluated using CSTR. They found that highest methane yields occurred when cow manure mixed with 30% of crop. This gragh showed that methane production. As we can see, compare to digestion of cow manure alone, co digestion of manure and sugar beet tops increased methane production by 65%...
Manure + 30% oat straw
Cow manure alone
Lehtomaki et al., 2007

11. Case 2 Whey co-digestion with diluted poultry manure
For an hydraulic retention time of 18 days at 35 ° C and organic loading rate of 4.9 g COD/L
Biogas production increased by 40%
Different fraction of whey co-digestion with diluted poultry manure were …using
Gelegenis et al., 2007

12. Case 3
Co-digestion of solid slaughter house waste, fruit-vegetable wastes, and manure
Possibility to treat combined waste of
Manure (cattle and swine)
Solid slaughterhouse wastes (rumen, paunch content, and blood from cattle and swine)
Fruit-vegetable wastes
Co-….were studied. They found that combined waste of ….using anaerobic co-digestion process give the possiblity of treating those wastes, which otherwise can not be successfully treated separately.
Alvarez et al., 2007

13. Drawbacks of Co-digestion
Increased digester effluent chemical oxygen demand (COD)
Additional pretreatment requirements
Increased mixing requirements
Wastewater treatment requirements
High utilization degree required

14. Conclusion
Co-digestion offers several possible ecological, technological, and economical advantages
There is very limited research, specifically in the U.S., that characterizes the digestibility of a number of the waste streams
The potential economic impact of fully utilizing alternative waste streams with AD of manure seems to be great, but economic analysis must be done to quantify this information
Quick conclusion,summary