Thick and solid fractions from animal slurries as Thick and solid fractions from animal slurries as
an alternative to crop silage for biogas production an alternative to crop silage for biogas production Thick and solid fractions from animal slurries as
Thick and solid fractions from animal slurries as
an alternative to crop silage for biogas production an alternative to crop silage for biogas production
Solid-liquid separation
✔ Paolo MANTOVI, Claudio FABBRI, Mariangela SOLDANO, Sergio PICCININI
✔ Centro Ricerche Produzioni Animali – CRPA, Reggio Emilia, Italy
The solid-liquid separation of slurries allows to concentrate total solids and the organic matter in the solid fraction that could be profitably recycled to produce energy by anaerobic digestion, as an alternative to crop silage.
Trials have been carried out by CRPA using the most diffuse separation techniques, in real scale farms (cattle, pigs), to evaluate separation efficiencies for various parameters (TS, VS, TKN, P).
Biochemical Methane Potential
Anaerobic digestion at real scale
The Biochemical Methane Potential (BMP) was assessed by batch digestion at lab scale (Fig. 1) for solid fractions derived from slurries of milking cows (screw press) and thick fraction derived from pig slurries (flotation). Both fresh solid fractions and the same materials stored for 1 month were tested (Table 1).
Figure 1 – Batch digestion at lab scale
Experiences are ongoing, to replace maize silage quota in real scale biogas plants.
In terms of energy, a ton of solid fraction from cattle slurry, resulted equivalent to around 0.4 t of maize silage (Fig. 2), because of its higher water content (80% vs. 67% for silage) and the lower degradability of VS (60% vs. 80%, Fig. 3).
The lower VS degradability causes TS increase in the digestate (Fig. 4).
The concentration of TS in the digesters should be monitored in order to exceed critical levels (≈ 100 g/kg). Studies are ongoing to control this effect.
Table 1 – Results of the BMP tests on solid and thick fractions (average data at 30 days) Type of solid fraction Nm3 biogas /
t VS
Nm3 CH4 / t VS
Nm3 CH4 / t fm
CH4 in biogas
VS
degradability From cattle slurry with straw, fresh
(21.2% TS, 0.91 VS/TS) 375 214 41 57.1% 47.3%
From cattle slurry with sawdust, fresh
(20.9% TS, 0.93 VS/TS) 352 188 36 53.4% 49.7%
From cattle slurry with sawdust, 1 month after separation
(19.7% TS, 0.88 VS/TS) 151 80 14 53.1% 23.9%
From pig slurry, flotation
(8.0% TS, 0.74 VS/TS) 389 275 16.3 70.8% 42.3%
(UNI EN ISO 11734:2004)
ManuREsource2013 ManuREsource2013
International conference on International conference on
Manure management and valorization Manure management and valorization December 5-6, 2013, Bruges, Belgium December 5-6, 2013, Bruges, Belgium ManuREsource2013
ManuREsource2013
International conference on International conference on
Manure management and valorization Manure management and valorization December 5-6, 2013, Bruges, Belgium December 5-6, 2013, Bruges, Belgium
Figure 4 – Total solids concentration of digestate (primary digester) Figure 3 – Volatile solids degradability under anaerobic conditions
Figure 2 – Energy equivalence under anaerobic conditions.
At the biogas plant we can replace 1 ton of silage maize with around 2.5 tons of solid fraction from fresh cattle slurry
+2.5 -1
Solid fraction
cattle slurry Maize silage
Agri-multitasking project, financed by Lombardy Region (Italy), under Rural Development Programme 2007-2013. Contact:
Agri-multitasking project, financed by Lombardy Region (Italy), under Rural Development Programme 2007-2013. Contact: p.mantovi@crpa.itp.mantovi@crpa.it
