Digestate handling

Logistics of biomass for biogas

Co-substrates

Surplus of P in Danish agricultureP Surplus

P overskud i marken(kg P/ha)

(Grant et al., 2005)

P overskud i marken(kg P/ha)

P overskud i marken(kg P/ha)

(Grant et al., 2005)

P Surplus

Plant Cattle Pig Mixed

What is this?

Typical composition of digestateTotal Nkg/ton

Total Pkg/ton

Kkg/ton

Degassed slurry

5.0 1.0 2.0

Liquid fraction

4.5 0.3 2.0

Solid fraction

8.0 8.0 2.0

Birkmose et al. (2013). Biomasse til biogasanlæg iDanmark

Solid

Logistics of biomass for biogas

Solid fraction

Co-substrates

Value of digestatePotential ValueKr/ton

56

47

156

Degassed slurryLiquid fractionSolid fraction

True value is lower because of: 1. Difficulties and costs during storage, 2. Uncertain availability of nutrients, 3. Administrative and legistrative problems, 4. Increased demand for catch crops, 5. Odour, 6. Supply and demand

Birkmose et al. (2013). Biomasse til biogasanlæg iDanmark

The goal

Feedstock (chemical

composition)

Retention time

Temperature

Soil

Precipitation

Oxygen

NH3

N2O

CO2

Main environmental impacts associated with digestate handling

• NH3 emissions during storage and land application

• Formation of the greenhouse gas N2O ad CO2 after land application

• Nitrate leaching• Phosphorus loss

NH3 volatilization

• High pH of digestate leads to high risk of ammonia volitilization

• Covered storage• Low dry matter content leads to fast

infiltration and therefore low ammonia volatilization

N2O emission

• N2O is formed in two processes, nitrification and denitrification

• Nitrification requires ammonia and oxygen• Defitrification require nitrate, organic matter

and absense of oxygen

Application of fertilizer and N2O emissions

Bouwman (1996)