digestates utlilization in agriculture - a holistic analysis - prof. eberhard hartung

Digestate u*liza*on in agriculture

(a holis*c analysis) E. Hartung

Ins*tute of Agricultural Engineering -‐ Kiel University

Agenda: •  Mo+va+on & Challenges •  Substrate variability & AD effects •  Fer+lizer use & effect on Soil proper+es •  GHG & … •  “Other” u+liza+on •  Conclusions

Mo*va*on Development biogas plants in Germany

plants installed electrical output (GW)

48 % NaWaRo 44 % solid & fluid manure

2 % bio-‐waste

6 % residual materials

Substrate Input of German biogas plants

Substrate Output / Digestates

“Mo*va*on” -‐ 2 Statements

Today, the general op*ons for the digestate use are: •  landscaping, •  combus*on •  and fer*liza*on (mostly in agriculture), the last of which is oVen the most aWrac*ve op*on due to organic and nutrient content (Hahn & Hoffstede, 2010). The common applica*ons of digestate include •  fer*lizers, •  growing media, •  soil improvers, •  combus*on and •  landfill (Jansen, 2011).

Challenges

Origin, composi*on & pre-‐/post-‐treatment of digestates / type of diges*on process: •  nutrients, pH & heavy metals, organic dry maWer content •  chemical, physical & biological contaminants

Legisla*on of digestate u*liza*on in agriculture as fer*lizer: •  quality criteria & threshold defini*ons •  applica*on limits (*me periods, maximum nutrient loads, minimum storage

capaci*es, etc.) •  fer*liser applica*on plan/management & applica*on techniques

Environmental effects of applied digestates: •  effects on soil proper*es, •  odour, ammonia & GHG-‐emissions, pathogens •  leaching of nutrients & contaminants

Substrate Quality

Legisla+ve Limits

Environmental Effects

Challenges

Addi*onal challenges: •  area used for the cul*va*on of energy crops is in general not enough for the

applica*on of the digestates -‐> high demand for “addi*onal applica*on areas” •  low dry maWer (poor transportability) and low & strongly varying nutrient

content •  high storage-‐, transporta*on-‐ and applica*on –costs •  high pH, instable fer*lising effect, loss of nutrients

Substrate Quality

Legisla+ve Limits

Environmental Effects

Lukehurst et al., 2010; hWp://www.en.esbjerg.aau.dk/digitalAssets/80/80457_task37_digestate_brochure9-‐2010.pdf

Nutrients present in plant & animal products

Substrate variability

Substrates used for biogas produc*on (can) include (Al Seadi, et al., 2008): •  Animal manure and slurry; •  Agricultural residues and by-‐products; •  Diges*ble organic wastes from food and agro industries (vegetable and animal origin); •  Organic frac*on of municipal solid waste (MSW) and from catering (vegetable and animal

origin); •  Sewage sludge (WWTP); •  Dedicated energy crops (e.g. maize, miscanthus, sorghum, clover); and •  Organic waste from other industries e.g. paper, leather and tex*le industries.


Substrate variability

Makádi et al., 2012; hWp://cdn.intechopen.com/pdfs-‐wm/31331.pdf

Substrate variability & AD effects

Due to anaerobic diges*on (AD) part of the organic nitrogen supplied with the feedstock is converted to ammonium, although the total nitrogen content in digestate remains the same as in the feedstock (Lukehurst et al., 2010).


Fer*lizer use & Effect on Soil proper*es


Substrate variability & AD effects

The amounts of organic dry maWer and the carbon content of digestate are decreased by the decomposi*on of easily degradable carbon compounds in digesters (S*nner et al., 2008)



Effect of digestate on soil pH: •  in case of long term digestate applica*on monitoring of soil pH is necessary •  soil acidifica*on due to digestates seem to depend on soil type/texture •  loamy soils will show rather a pH decrease compared to sandy soils

Effect of digestate on soil organic maWer (OM) content: •  inconsistent results with respect to soil organic maWer decrease/increase •  tendency that OM losses duet to intensive cul*va*on of energy crops can not

be “compensated” by digestate applica*on (limited by maximum nutrient loads) •  but digestates have advantages compared to the ini*al (input) substrate •  higher lignin content in digestates leads to increased reten*on *me in soil

Fer*lizer use & Effect on Soil proper*es Effect of digestate on soil organic maWer (OM) content: •  inconsistent results with respect to soil organic maWer decrease/increase •  tendency that OM losses duet to intensive cul*va*on of energy crops can not be “compensated” by

digestate applica*on (limited by maximum nutrient loads) •  but digestates have advantages compared to the ini*al (input) substrate •  higher lignin content in digestates leads to increased reten*on *me in soil

plant material

slurry

digestates

material dry maLer %

humus reproduc+on kg Humus-‐C (t substrate)-‐1

straw green fer*lizer

cupngs

fluid

caWle

pig

VDLUFA, 2005

solid


Liebetrau et al., 2013; hWps://www.dbfz.de/web/fileadmin/user_upload/Referenzen/Abschlussberichte/Endbericht03KB027_final_TIB_31_07_2013.pdf

type

of d

igestate

Percentage of total N

slow biodegradable (humus reproduc+on effec+ve) easily biodegradable fast biodegradable

Fer*lizer use & Effect on Soil proper*es Effects of a commonly prac*ced humus supply with 500 Häq (kg Humus-‐C) ha-‐1 a-‐1 of different digestates & composts (1 Häq is equivalent to 1 kg of produced soil carbon due to humifica*on per t of supplied substrate)


type

of d

igestate

N-‐Amount in kg/ha

slow biodegradable (humus reproduc+on effec+ve) easily biodegradable fast biodegradable

Limit 170 kg/ha

Limit 120 kg/ha

Fer*lizer use & Effect on Soil proper*es Effect of digestate on soil pH: •  in case of long term digestate applica*on monitoring of soil pH is necessary •  soil acidifica*on due to digestates seem to depend on soil type/texture •  loamy soils will show rather a pH decrease compared to sandy soils

Effect of digestate on soil organic maWer (OM) content: •  inconsistent results with respect to soil organic maWer decrease/increase •  tendency that OM losses duet to intensive cul*va*on of energy crops can not be “compensated” by

digestate applica*on (limited by maximum nutrient loads) •  but digestates have advantages compared to the ini*al (input) substrate •  higher lignin content in digestates leads to increased reten*on *me in soil

Effect of digestate on microbiological ac*vity of soil: •  should be a sensi*ve indica*on of changes in physical & chemical soil proper*es •  digestates are supposed to promote microbiological ac*vity e.g. due to higher

amounts of easy degradable carbon •  digestates contain growth regulators & influence enzyme ac*vi*es

Fer*lizer use & Effect on Soil proper*es Effect of digestate on microbiological ac*vity of soil: •  should be a sensi*ve indica*on of changes in physical & chemical soil proper*es •  digestates are supposed to promote microbiological ac*vity e.g. due to higher amounts of easy

degradable carbon •  digestates contain growth regulators & influence enzyme ac*vi*es

•  But effects depend very much on type of digestate, soil texture, crop rota+on and fer+lizer management, … ; much more systema+c research in long +me experiments are necessary!


GHG & Ammonia emissions & … General Ques*ons? •  focus on processes &/or applica*ons •  focus on whole produc*on chain (e.g. energy & nutrient balances, LCA

studies) •  which model, included boundary/limi*ng condi*ons & set values are

used •  which assump*ons were made

GHG & Ammonia emissions & …


GHG

emission

s [kg CO

2-‐eq

/Mg Inpu

t sub

strate]

different fermenta*on processes / facili*es

digestate applica+on digestate storage compos+ng / post roo+ng emissions past bio-‐ filter electricity demand BGP & CHP emissions fermenter

emissions CHP

credit digestate

credit heat recovery

credit electricity

Balance

GHG & … Odour: •  diges*on reduces significantly many odour compounds (unpleasant odours) Ammonia emissions & N leaching depends on: •  type of digestate & nutrient content •  storage & applica*on technique, pre-‐/post-‐treatment of digestate •  soil type & soil moisture, crop rota*on & crop yield •  *me & amount of applica*on, weather condi*ons, etc. …. Veterinary Safety, Plant pathogens & Weed seeds: •  anaerobic diges*on (AD) is very effec*ve in lowering pathogen loads with

respect to veterinary safety •  few studies show a reduc*on poten*al for pant pathogens due to (mesophilic)

AD •  few studies show a reduc*on poten*al of the viability of weed & crop seeds due

to (mesophilic) AD

GHG & … Veterinary Safety, Plant pathogens & weed seeds: •  anaerobic diges*on (AD) is very effec*ve in lowering pathogen loads with respect to veterinary

safety •  few studies show a reduc*on poten*al for pant pathogens due to (mesophilic) AD •  few studies show a reduc*on poten*al of the viability of weed & crop seeds due to (mesophilic) AD


“Other” u*liza*on Separa*on before or past anaerobic fermenta*on: •  separa*on efficiency depends very much on type of digestate & type of

separa*on technique •  high investment costs, energy efficiency of separa*on process needs to be

improved

“Other” u*liza*on Separa*on before or past anaerobic fermenta*on: •  separa*on efficiency depends very much on type of digestate & type of separa*on technique •  high investment costs, energy efficiency of separa*on process needs to be improved


“Other” u*liza*on Separa*on before or past anaerobic fermenta*on: •  separa*on efficiency depends very much on type of digestate & type of separa*on technique •  high investment costs, energy efficiency of separa*on process needs to be improved digestate post processing (high treatment & investment costs): •  solid-‐liquid separa*on:

•  solid frac*on compos*ng -‐> soil improver-‐growing material (SIGM) •  liquid frac*on -‐> Liquid fer0lizer

•  stripping (ammonium sulphate fer0lizer) •  pelle*zing (fer0lizer pellet/solid fuel)

“Other” u*liza*on digestate post processing (high treatment & investment costs): •  solid-‐liquid separa*on:


•  stripping (ammonium sulphate fer0lizer) •  pelle*zing (fer0lizer pellet/solid fuel)

Primary energy demand in kWh/t raw digestate

GHG emissions in kg CO2eq/t raw digestate

Haverinen, 2014, hWps://aaltodoc.aalto.fi/bitstream/handle/123456789/13544/master_Haverinen_Aleksi_2014.pdf?sequence=1

“Other” u*liza*on Separa*on before or past anaerobic fermenta*on: •  separa*on efficiency depends very much on type of digestate & type of separa*on technique •  high investment costs, energy efficiency of separa*on process needs to be improved digestate post processing (high treatment & investment costs): •  solid-‐liquid separa*on:


•  stripping (ammonium sulphate fer0lizer) •  pelle*zing (fer0lizer pellet/solid fuel) •  ion exchange, struvite precipita*on •  membrane filtra*on •  drying •  soil improver (carboniza*on, biochar produc*on)

Conclusions •  U*liza*on of digestates in agriculture is a very broad field/topic •  Up to now most digestates are used as fer*lizer & effect: •  environment •  soil proper*es

•  Alterna*ve digestate u*liza*on are mostly characterized by high treatment & investment costs

•  Future goals: •  Achieve more knowledge on effects of digestate applica*on •  Op*mize (automated) side-‐ & plant-‐specific applica*on •  Improve cost-‐effec*ve separa*on and carboniza*on techniques •  U*lize fluctua*on of renewable energy produc*on for digestate

treatment

Digestate u*liza*on in agriculture

(a holis*c analysis) E. Hartung

Ins*tute of Agricultural Engineering -‐ Kiel University

Agenda: •  Mo+va+on & Challenges •  Substrate variability & AD effects •  Fer+lizer use & effect on Soil proper+es •  GHG & … •  “Other” u+liza+on •  Conclusions

digestates utlilization in agriculture - a holistic analysis - prof. eberhard hartung

Government & Nonprofit

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