Anaerobic Co-digestion of Anaerobic Co-digestion of Biomass for Methane Biomass for Methane

Production : Recent Research Production : Recent Research Achievements Achievements

Wei Wu Wei Wu

CE 521 CE 521

Introduction Introduction

Anaerobic Digestion Anaerobic Digestion Anaerobic digestion (AD)Anaerobic digestion (AD)

Organic Matter + HOrganic Matter + H22O + BacteriaO + Bacteria

CHCH44 + CO + CO22 + NH + NH33 + H + H22S S TraditionallyTraditionally

Single substrate and single purpose Single substrate and single purpose Manure was digested to produce energy Manure was digested to produce energy Sewage sludge should be stabilizedSewage sludge should be stabilized Industrial waste water should be pre-treatedIndustrial waste water should be pre-treated

Recently Recently Co-digestion of two or more substrate and multi-Co-digestion of two or more substrate and multi-

purpose purpose

Co-digestion Co-digestion Co-digestion Co-digestion

Two or more substrates Two or more substrates Major amount of a main basic substrates Major amount of a main basic substrates

(e.g. manure or sewage sludge) + Minor (e.g. manure or sewage sludge) + Minor amount of a singe, or a variety of additional amount of a singe, or a variety of additional substratessubstrates

Multi-purpose process serving at the Multi-purpose process serving at the same timesame time

Waste upgradingWaste upgrading Energy production Energy production Improvement of fertilizer qualityImprovement of fertilizer quality

Co-digestion—Cont.Co-digestion—Cont. Factors impact the production of biogasFactors impact the production of biogas

The type of waste being digestedThe type of waste being digested Its concentration Its concentration Its temperatureIts temperature The presence of toxic materialsThe presence of toxic materials The pH and alkalinityThe pH and alkalinity The hydraulic retention timeThe hydraulic retention time The solids retention timeThe solids retention time The ration of food to microorganism The ration of food to microorganism The rate of digester loadingThe rate of digester loading The rate at which toxic end products of The rate at which toxic end products of

digestion are removed digestion are removed

Manure

Low C/N ratio– high ammonia High alkalinity

Rich in macro/micronutrient

Benefits of Co-digestion Benefits of Co-digestion Improved nutrient balance and Improved nutrient balance and

digestion performance digestion performance A nutrient ratio of TOC:N:P = 300:5:1 to A nutrient ratio of TOC:N:P = 300:5:1 to

achieve optimal digestion performance achieve optimal digestion performance

Crop or Crop residues

High C/N ratio– high carbon contentLow alkalinity

Lack of macro/micronutrient

Improve the C/N ratio, buffering capacity and more biodegradable substrate

Benefits of Co-digestionBenefits of Co-digestion Effective utilization of digester Effective utilization of digester

volumes volumes Help to utilize the availability of free Help to utilize the availability of free

capacitiescapacities Co- digestion of energy crops and manure Co- digestion of energy crops and manure

resulted in the doubling of the plant capacity resulted in the doubling of the plant capacity from 500 kW to 1000 kW retaining the from 500 kW to 1000 kW retaining the digester volume (Lindorfer et al., 2007)digester volume (Lindorfer et al., 2007)

The wide distribution of sewage treatment The wide distribution of sewage treatment plants minimizes transportation costsplants minimizes transportation costs

Equalization of particulate, floating, Equalization of particulate, floating, settling, acidifying etc. wastes, settling, acidifying etc. wastes, through dilution by manurethrough dilution by manure

Co-digestionCo-digestion

Thermophilic ADThermophilic AD Exceed 55 ° CExceed 55 ° C Retention time Retention time

ofof

12-14 d 12-14 d

Types of digesterTypes of digester Mesophilic ADMesophilic AD

Approximately 30-35Approximately 30-35° C° C Retention time of Retention time of

15 – 30 d15 – 30 d

Continuously stirred tank reactors (CSTRS) under mesophilic conditions

Co-digestionCo-digestion Source of organic waste streams can be Source of organic waste streams can be

co-digested with manure co-digested with manure Food Industry Food Industry

Waste from potato, sugar beet, meat, and dairy Waste from potato, sugar beet, meat, and dairy processing processing

Grain Industry Grain Industry Damaged grainDamaged grain

Paper Industry Paper Industry Newspaper and recycled paperNewspaper and recycled paper

Domestic Wastes Domestic Wastes Livestock Wastes Livestock Wastes Crop ResiduesCrop Residues

Corn stover and switchgrassCorn stover and switchgrass

Case 1 Case 1

Lehtomaki et al., 2007

Cow manure alone

Cow manure alone

Cow manure alone

Manure + 30% sugar beet tops

Manure + 30% grass

Manure + 30% oat straw

Increased by 65 %

Increased by 58 %

Increased by 16 %

Case 2 Case 2 Whey co-digestion with diluted poultry Whey co-digestion with diluted poultry

manure manure For an hydraulic retention time of 18 For an hydraulic retention time of 18

days at 35 days at 35 ° C and organic loading rate of ° C and organic loading rate of 4.9 g COD/L4.9 g COD/L

Biogas production increased by 40% Biogas production increased by 40%

Gelegenis et al., 2007

Case 3 Case 3 Co-digestion of solid slaughter house Co-digestion of solid slaughter house

waste, fruit-vegetable wastes, and waste, fruit-vegetable wastes, and manure manure Possibility to treat combined waste of Possibility to treat combined waste of

Manure (cattle and swine)Manure (cattle and swine) Solid slaughterhouse wastes (rumen, paunch Solid slaughterhouse wastes (rumen, paunch

content, and blood from cattle and swine)content, and blood from cattle and swine) Fruit-vegetable wastes Fruit-vegetable wastes

Alvarez et al., 2007

Drawbacks of Co-digestion Drawbacks of Co-digestion Increased digester effluent chemical Increased digester effluent chemical

oxygen demand (COD)oxygen demand (COD) Additional pretreatment requirementsAdditional pretreatment requirements Increased mixing requirementsIncreased mixing requirements Wastewater treatment requirementsWastewater treatment requirements High utilization degree required High utilization degree required

Conclusion Conclusion Co-digestion offers several possible Co-digestion offers several possible

ecological, technological, and economical ecological, technological, and economical advantagesadvantages

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