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

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.

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.

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

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

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.

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

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 ….

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

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

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

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

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

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