Thursday, March 13, 2014

Biogas - Digestate As Fertilizer

Treatment of animal manure and slurries in biogas plants results in biodegradation of organic matter to inorganic compounds and methane.
In practice, the anaerobic degradation rate of organic matter from animal manure and slurries is about 40% for cattle slurry and of 65% for pig slurry.

The degradation rate depends at large on feedstock type as showed in table 1.
Due to degradation of organic matter, digestate is easier to pump and easier to apply as fertilizer, with reduced need of stirring, compared to untreated slurry.







Dry mater [%] Total N [kg/t] NH4-N [kg/t] P [kg/t] K [kg/t] Ph
Cattle slurry 6 5 2.8 0.8 3.5 6.5
Pig slurry 4 5 3.8 1 2 7
Digested slury 2.8 5 4 0.9 2.8 7.5


Table 2 shows nutrient distribution in digestate made from household waste.


Dry matter Nges [%] P205 [%] K2O [%]
Milk products 4 – 8 0.6 – 0.7 0.7 – 1.8
Vegetable waste 5 – 15 3 – 4 0.6 – 0.8 1 – 1.1
Kitchen waste 10 – 20 1.6 – 4.2 0.3 – 1.5 0.4 – 1.1
Vegetable oil 10 – 15 3 – 6 1 – 3 0.1 – 0.2
Fat from waste 25 – 70 0.8 – 3.3 0.1 – 0.5 0.1 – 0.5


References:
Biogas Handbook, Teodorita Al Seadi, Dominik Rutz, Heinz Prassl, Michael Köttner, Tobias Finsterwalder, Silke Volk, Rainer Janssen. ISBN 978-87-992962-0-0
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