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Can livestock farming reduce its emissions?

Methanisation: “good for the environment and energy autonomy”

Anaïs Marechal, science journalist
On April 6th, 2022 |
4 min reading time
Julien Thual
Engineer coordinating methanisation at ADEME
Key takeaways
  • Livestock effluent (wastewater) is responsible for about 10% of greenhouse gas (GHG) emissions from livestock farming. These emissions are linked to their storage and treatment method.
  • As of 1 January 2022, there were 1175 methanisation units in France, of which 805 were using agricultural effluents in 2021.
  • Methanisation has continues to develop over recent years, with a strong dynamic that has notably allowed the addition of 1.5 TWh installed capacity per year.It is essential to regulate this use in order to avoid competition with food.
  • In France, this share is limited by law to 15% of cultivated areas and is currently between 3 and 6%.

Emit­ting methane (CH4) and nitrous oxide (N2O), live­stock efflu­ents (waste­water) are respon­si­ble for about 10% of green­house gas (GHG) emis­sions from live­stock farm­ing1. These emis­sions are linked to the way in which they are stored and treat­ed. Mit­i­ga­tion solu­tions include reduc­ing stor­age time, sep­a­rat­ing the sol­id and liq­uid phas­es, cov­er­ing pits or using nitri­fi­ca­tion or ure­ase (urine trans­for­ma­tion) inhibitors. 

The last method cur­rent­ly under devel­op­ment is methani­sa­tion. This con­sists of recov­er­ing the methane pro­duced by the anaer­o­bic decom­po­si­tion – with­out oxy­gen – of organ­ic mat­ter. The bio­gas can be trans­formed into elec­tric­i­ty and heat in cogen­er­a­tion units or inject­ed direct­ly into the gas net­work. The residue, called diges­tate, is used to fer­tilise and improve the soil. Methani­sa­tion units using live­stock efflu­ents can be installed on the farm, on top of exist­ing slur­ry pits or cen­tralised with­in a region.

How is the agricultural effluent methanisation sector faring?

On 1st Jan­u­ary 2022, there were 1175 methani­sa­tion units in France, 805 of which were using agri­cul­tur­al efflu­ents in 2021. Methani­sa­tion units treat­ing house­hold and indus­tri­al waste are not real­ly evolv­ing, while those at waste­water treat­ment plants are mov­ing towards bio­methane injec­tion. On the oth­er hand, on-farm and cen­tralised instal­la­tions are increas­ing sig­nif­i­cant­ly and have the great­est poten­tial in France: the num­ber of on-farm instal­la­tions has risen from 38 units in 2010 to 661 in 2020. There are a few large-scale anaer­o­bic diges­tion projects, but the new facil­i­ties are main­ly small to medi­um-sized, pro­cess­ing between 10,000 and 20,000 tonnes of waste per year.

His­tor­i­cal­ly, the anaer­o­bic diges­tion sec­tor has focused on the cogen­er­a­tion of elec­tric­i­ty and heat, which rep­re­sents 72% of on-farm and cen­tralised units in 20202 . How­ev­er, for the past five years, the trend has been towards inject­ing bio­methane into the gas net­work. At the farm lev­el, the use of bio­methane for injec­tion rose from 41 to 114 units between 2018 and 2020. The same dynam­ic can be observed for cen­tralised instal­la­tions, which went from 15 to 55 injec­tion units over the same period.

How can we explain this newfound enthusiasm for biomethane injection?

First­ly, the desire to sub­sti­tute import­ed nat­ur­al gas with bio­methane rather than elec­tric­i­ty. In the cur­rent con­text, bio­methane has the major advan­tage of pro­vid­ing a renew­able and inde­pen­dent ener­gy source for France and Europe. Anoth­er argu­ment in favour of bio­methane injec­tion is ener­gy effi­cien­cy. Elec­tric­i­ty cogen­er­a­tion alone is 35% effi­cient, ris­ing to 50% or even 55% if we also make use of the heat. Bio­methane injec­tion has an ener­gy effi­cien­cy close to 85%.

Val­i­da­tion of the tech­nol­o­gy’s per­for­mance has opened the way to wider dis­sem­i­na­tion of this type of project. Today, reg­u­la­tions require that the fea­si­bil­i­ty of an injec­tion instal­la­tion be stud­ied as a pri­or­i­ty. How­ev­er, these projects are more expen­sive: the aver­age invest­ment is €5.5 mil­lion com­pared to €2 mil­lion for cogeneration.

What role can methanisation play in reducing the climate impact of livestock farming?

It has been iden­ti­fied as one of the main meth­ods for reduc­ing the GHGs asso­ci­at­ed with live­stock farm­ing. On aver­age, each project pre­vents the release of 2,600 tonnes of CO2 equiv­a­lent into the atmos­phere. INRAE has car­ried out the first life cycle analy­sis (LCA) of bio­methane from agri­cul­tur­al methani­sa­tion3. It estab­lish­es an envi­ron­men­tal eval­u­a­tion tak­ing into account ener­gy pro­duc­tion, efflu­ent man­age­ment and soil fer­til­i­sa­tion. Envi­ron­men­tal per­for­mance is improved by 60–85% for 16 of the indi­ca­tors con­sid­ered. No improve­ment is observed for 5 indi­ca­tors, and the sys­tem is less effi­cient for some indi­ca­tors, notably because of the increased use of elec­tri­cal ener­gy. The points for con­sid­er­a­tion are the con­trol of fugi­tive bio­gas emis­sions and the respect of good prac­tices for the spread­ing of digestates.

Methani­sa­tion also offers a solu­tion for treat­ing the ter­ri­to­ry’s bio-waste, diver­si­fy­ing agri­cul­ture, allow­ing organ­ic mat­ter to be returned to the soil and reduc­ing the use of min­er­al fer­tilis­ers. It is a major advan­tage for increas­ing our auton­o­my regard­ing soil fertilisation.

Do you think that methanisation will continue to develop?

Yes, we have seen a strong momen­tum over the past three years, with 1.5 TWh of addi­tion­al annu­al capac­i­ty installed each year. The objec­tive of the Mul­ti­an­nu­al Ener­gy Plan to reach 6 TWh in 2023 will be exceed­ed this year! We esti­mate the pro­duc­tion poten­tial at 30–35 TWh of bio­methane in 2030, and 90–130 TWh in 20504. There is also a high poten­tial in rela­tion to slur­ry pit cov­ers, these micro-methani­sa­tion units that only treat live­stock efflu­ents and use the bio­gas autonomous­ly on the farms. There are cur­rent­ly 40 of these units, while there are sev­er­al tens of thou­sands of slur­ry pits.

Is there enough biomass available? France Stratégie5 estimates that the existing deposits are half the size of those taken into account in the National Low-Carbon Strategy. 

Live­stock manure is the pri­or­i­ty resource to be used. This source must be sup­ple­ment­ed by more methanogenic sub­strates (such as plants) in order to find a good tech­ni­cal and eco­nom­ic com­pro­mise. In our prospec­tive work, the mobil­is­able resource in gross ton­nage is made up of 50% live­stock manure, 30% inter­me­di­ate crops and 20% oth­er waste. Inter­me­di­ate crops or cov­er crops are essen­tial to achieve our renew­able ener­gy pro­duc­tion objectives.

Some coun­tries, such as Ger­many, have cho­sen to pro­duce annu­al crops ded­i­cat­ed to ener­gy pro­duc­tion. It is essen­tial to reg­u­late this use to avoid com­pe­ti­tion with food. In France, this share is lim­it­ed by law to 15% of cul­ti­vat­ed areas and is cur­rent­ly between 3 and 6%.

Some local residents are opposed to the installation of anaerobic digestion units, complaining of noise and odour pollution and the risk of explosion. Is this an obstacle to the development of the sector?

Methani­sa­tion units are clas­si­fied instal­la­tions for envi­ron­men­tal pro­tec­tion and are there­fore sub­ject to numer­ous reg­u­la­tions for the pre­ven­tion of envi­ron­men­tal and pub­lic risks. Because of their orig­i­nal agri­cul­tur­al activ­i­ty, farm­ers are already used to man­ag­ing live­stock efflu­ents: only the man­age­ment of bio­gas is new and requires train­ing and rig­or­ous oper­a­tion. The risks in the event of an acci­dent main­ly con­cern farm staff and not local residents. 

I am more con­cerned about very large instal­la­tions, where the sus­tain­abil­i­ty of sup­plies and envi­ron­men­tal per­for­mance may be ques­tioned. The local inte­gra­tion of projects is not in favour of these installations.

Inter­view by Anaïs Marechal

1Ger­ber, P.J., Ste­in­feld, H., Hen­der­son, B., Mot­tet, A., Opio, C., Dijk­man, J., Fal­cuc­ci, A. & Tem­pio, G. 2013. Tack­ling cli­mate change through live­stock – A glob­al assess­ment of emis­sions and mit­i­ga­tion oppor­tu­ni­ties. Food and Agri­cul­ture Orga­ni­za­tion of the Unit­ed Nations (FAO), Rome.
2SINOE, Ser­vice mobil­i­sa­tion et val­ori­sa­tion des déchets, Chiffres clés du parc d’u­nités de méthani­sa­tion en France au 1er jan­vi­er 2021, May 2021
3Esnouf A., Brock­mann D., Cres­son R. (2021) Life cycle assess­ment of bio­methane from agri­cul­tur­al resources – LCA report. INRAE Trans­fert, 168pp.
4Transition(s) 2050, Ademe Edi­tions, Novem­ber 2021
5Mour­jane I. and Fos­se J. (2021), « La bio­masse agri­cole: quelles ressources pour quel poten­tiel énergé­tique », Work­ing Paper, n° 2021-03, July.

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