Anaerobic Co-digestion of Biomass for Methane Production : Recent Research Achievements

Wei Wu CE 521

Introduction

Anaerobic Digestion

 Anaerobic digestion (AD) Organic Matter + H 2 O + Bacteria   CH 4 + CO 2 + NH 3 + H 2 S 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

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—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

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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 Crop or Crop residues

Low C/N ratio– high ammonia High alkalinity Rich in macro/micro nutrient 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

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

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

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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

Increased by 65 %

Case 1

Manure + 30% sugar beet tops Cow manure alone Increased by 58 % Manure + 30% grass Cow manure alone Increased by 16 % 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%

Gelegenis et al., 2007

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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

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