ANAEROBIC DIGESTION. Break the ice. Sergi Astals & Joan Mata B A. EPROBIO - Foggia - June 2011 XARXA DE CENTRES DE SUPORT A LA INNOVACIÓ TECNOLÒGICA

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1 ANAEROBIC DIGESTION Break the ice Sergi Astals & Joan Mata EPROBIO - Foggia - June 2011 DEPARTAMENT D ENGINYERIA QUÍMICA B A GRUP DE RECERCA EN BIOTECNOLOGIA AMBIENTAL IT XARXA DE CENTRES DE SUPORT A LA INNOVACIÓ TECNOLÒGICA 1

2 INDEX OF CONTENTS What is anaerobic digestion? Anaerobic digestion advantages Which waste can be digested? What is biogas? Biogas as a renewable source of energy 2

3 What come to your mind when you listen anaerobic digestion? 3

4 What is anaerobic digestion? AD is a biological technology which, in the absence of oxygen, decomposes organic matter. The breakdown of the biodegradable organic matter produce stable organic residues and biogas (a mixture of methane (CH 4 ) and carbon dioxide (CO 2 )). Anaerobic conditions requires the absence of oxidizers compounds*: - Oxygen (O 2 ) - Nitrate (NO 3- ) and nitrite (NO 2- ) - Sulphates (SO 2-4 ) * Substances that have the ability to oxidize other substances. They gain electrons, they are reduced, so other compounds have to loss it (oxidized). 4

5 What is anaerobic digestion? AD take place in the nature where organic matter is present and the oxygen concentration is negligible: - Stomachs of ruminants - Sediments of lakes - Landfills - Sewers - 5

6 Anaerobic digestion advantages The main advantages of the AD technology are: - Stabilize organic matter - Feasible for a wide variety of waste and flow rates - Reduce greenhouse gases emission global warming - Low sludge production - Positive energy balance Energy from biogas Low operational cost - No or very little use of chemicals 6

7 Which wastes can be anaerobically digested? AD has long been used to stabilize organic wastes before its final disposal. Today, AD is a consolidated technology used to stabilize: - Sewage sludge from wastewater treatment plants - Municipal solid wastes (MSW) - Industrial wastewaters - Agricultural wastes - animal manure - crops waste 7

8 What industrial wastewaters are anaerobically digested? AD is used as an end of pipe treatment for: Agro-food industry: Sugar, potato, starch, fruit, vegetables, dairy, bakery Beverage: Beer, soft drinks, wine, fruit juices, coffee Pulp and paper industry: mechanical pulp, straw, bagasse Others: pharmaceutical, chemical, municipal sewage, landfill leachate 8

9 What is biogas? Biogas is a methane rich flammable gas that results from the decomposition of organic waste materials. Which gases can be found in biogas: > Mayor compounds: - Methane (CH 4 ) [60 70 %] - Carbon dioxide (CO 2 ) [40 30%] > Minor compounds: - Hydrogen sulphide (H 2 S) > odour problems - Ammonia (NH 3 ) > odour problems - Hydrogen (H 2 ) - 9

10 Biogas energy value Biogas can be used in a combustion heat and power unit (CHP) to produce electricity and another form of energy (steam or hot water). > Methane lower heating value is 35,800 KJ/m 3 > Natural gas* heating value is 37,300 KJ/m 3 Biogas lower heating value range from 21,300 to 23,400 KJ/m 3 as function of the % CH 4 An estimation of the lower heating value of biogas can be done by: Biogas heating value (kj/m ) = 35,800 % CH 100 * Natural gas is a mixture of methane, propane and butane

11 Biogas energy value Exercise a: How much water can be heat to 80 ºC with 1 m 3 of biogas? Exercise b: How much water can be boil with 1 m 3 of biogas? Exercise c: How much water can be boil with 1 m 3 of biogas is the burner efficiency is 0.75? Data of water: Initial temperature = 25 ºC Latent heat vaporization (λ)= 2,260 KJ/m 3 Heat capacity (C) = 4.18 KJ/(Kg ºC) Biogas lower heating value = 22,400 KJ/m 3 11

12 Biogas energy value Exercise a: KJ 4.18 = Kg º C X = Kg Exercise b: KJ KJ 4.18 = Kg º C Kg X = 8.64 Kg ( º C) X( kg) 22,400 KJ ( º C) X( kg) X( Kg) 22,400 KJ Exercise c: KJ KJ 4.18 Kg º C Kg X = 6.48 Kg ( º C) X( kg) X( Kg) = 22,400 KJ

13 Energy conversion factors 1 KWh = 3600 KJ 1 KJ = ktep* 1 KWh = ktep * tep: tonne of oil equivalent (the amount of energy released by burning one tonne of crude oil) 13

14 Biogas uses Biogas, as a renewable source of energy, is becoming more important as petrol cost continue to rise. Even some AD plant still burn the biogas in flares, digester gases are used as fuel for: - Heating anaerobic digesters and plant buildings - To operate cogeneration unit - To operate blowers, pumps, Household and/or communities AD can use biogas for: - heat water - cook EurObserv ER light 14

15 Biogas as renewable source of energy Energy crisis of 1970s and 2000s promoted the development of the AD. While the interest for the environment protection, mainly the depuration of the surface water is increasing. 15

16 EurObserv ER 2008 Landfill gas Urban sewage and industrial effluents Agricultural waste, MSW, OFMSW, co-digestion plants 16

17 EurObserv ER 2008 and 2010 Landfill gas Urban sewage and industrial effluents Agricultural waste, MSW, OFMSW, co-digestion plants 17

18 EurObserv ER 2010 The biogas sector has never before aroused so much attention as it does today. Interest has been fired by the introduction of regulatory directives - Council Directive 1999/31/EC of 26 April 1999on the landfill of waste - Council Directive 2008/98/EC on waste - Council Directive 2009/28/EC of 23 April 2009 on the promotion of the use of energy from renewable sources Biogas is mainly produced form waste treatment. However, energy crops are growing Biogas production has been stimulated to farm holders to reduce their energy dependency and diversify their incomes. Countries want to reduce their dependency on natural gas, purify biogas to obtain biomethane which can be injected in the natural gas grid 18

19 Biogas price Country Installed Power (kw) / kwh Bonus Spain < 500 0,140 > 500 0,100 < 150 0,117 plus 0.07 /kwh using energy crops Germany ,092 plus 0.01 /kwh if a 30% of manure is used ,083 plus 0.03 /kwh for CHP unit ,078 < 100 0,165 minus 25% for co-digestion Austria , ,125 > ,103 France < 150 0,093 plus 0,02 for methanisation > ,078 19