1. ainia
Anaerobic co-digestion of cattle manure with rice straw.
Gracia Silvestre, Paz Gómez, Andrés Pascual and Begoña Ruiz
ADSW&EC 2011 Vienna 29.08.2011

2. CONTENTS
• Introduction
• Objectives
• Materials and Methods
• Results and Discussion
• Conclusions

3. INTRODUCTION
Some figures about rice in Region Valencia…
15000 Ha rice cultivation (part in a natural park).
30% of national production.
Rice Straw production Around 100.000 t/year

4. INTRODUCTION
Traditional management of rice straw
Open-air burning
Air pollution
NATURAL PARK
Reincorporation to fields
Water pollution

5. INTRODUCTION
Rice fields
2005

6. OBJECTIVES
Rice straw management
Traditional Alternative
Burn Anaerobic
Bury (“fanguejat”) digestion
Atmopshere and Sustainable
water pollution management

7. OBJECTIVES
The aim of this research is to define a sustainable system for
using the rice straw as substrate for anaerobic digestion in the
conditions of the region of Valencia (Spain).
PARTICULAR OBJECTIVES
• Assessment of thermal pre-treatment of the rice straw to increase the
biogas potential (fibres difficult to digest)
• Study the rice straw co-digestion with cow manure in semi-continuous
plug flow pilot-scale reactor.
• Evaluation of the economic and energy balance of the process.

8. MATERIALS AND METHODS. Substrates
Rice straw samples
Origin: rice field in Valencia (Spain)
Grinded to 2-3 cm with agricultural
chopper.
Cow manure samples
Origin: cow farm in Valencia.
Inoculum
Origin: biogas plant in Valencia (co-
digestion of cow manure and
vegetal co-substrates at 38ºC and 3
kgVS·m-3·d-1.

9. MATERIALS AND METHODS. Pre-treatments
Rice 1 w.u. Thermal
1h BMP test
straw pretreatment A
Oven 105ºC
2h Thermal
Water
6 w.u. pretreatment B

10. MATERIALS AND METHODS. BMP tests
• VDI Standard 4630
“Fermentation of organic
materials”
• Digester volume: 2L
• Runs in triplicates
• Incubator at 38ºC ± 2ºC
• Manual mixing
• Biogas production: counter 1
mL resolution
• Gas analysis. CH4, CO2, O2,
H2, H2S

11. MATERIALS AND METHODS. Co-digestion
Plug-flow digester with a working volume of 900 L
Operation temperature 38ºC
Control parameters: TS, VS, pH, NH4+-N and VFA
Biogas production was measured by gas counter Kromschröder BK-2,5
CH4 and H2S content was measured by Dräger Multiwarn
Three different mixtures of cow manure and rice straw were analyzed (1%,
2% and 5% rice straw)

12. RESULTS AND DISCUSSION. Pretreatments
Maceration of rice straw sample at 105ºC (1 h and 2 h)
Biogas Biogas Methane
Substrates (NL/KgVS) (NL/Kg) (%)
RS untreated 547 ± 45 399 ± 33 58 ± 2
RS thermal pretreat (1h) 616 ± 38 62 ± 4 55 ± 4
RS thermal pretreat (2h) 616 ± 43 68 ± 5 58 ± 4
• The pre-treatment increased the biogas potential in 13%.
• The different maceration time did not show differences in the biogas
potential.
• Taking into account the methane concentration, the improvement
achieved by maceration 1 and 2 h was 6% and 13% respectively.
• Maceration pre-treatment implies water addition and the biogas potential
(on wet weigh basis) is lower than the untreated RS.

13. RESULTS AND DISCUSSION
Parameters* PI PII PIII PIV
Rice straw (%) 0 1 2 5
3
OLR (KgVS/m d) 2.3 3.6 3.9 4.9
HRT (days) 34 26 25 24
3 3
Biogas (m /m d) 0.54 0.56 0.68 0.83
Methane (% biogas) 65 66 67 72
Methane (m3/t) 12 13 18 22
Methane (m3/tvs) 153 156 117 122
VFA (mg/L) <100 <100 <100 <100
pH 7.6 7.9 7.9 8.0
*Average values. SD are available in the proceedings.
Biogas productivity was insignificantly increased in the period II in
comparison with the period I.
Biogas productivity increased 28% and 54% in period III and IV
respectively.
VFA and pH indicated that the process was developed in stable manner.
In period IV accumulation of the rice straw was observed inside the
digester.

14. CONCLUSIONS
Maceration pre-treatment slightly improves biogas
production per kgVS, but due to the high water
requirement, the biogas production per kg is lower
than untreated straw.
Anaerobic rice straw co-digestion with a cow manure
was technically feasible.
Biogas productivity increased in 4%, 28% and 54%
when addition of rice straw was 1%, 2% and 5% (on
weight basis).
The mixture 5% of rice straw showed problems of
solids accumulation in the digester.

15. ACKNOWLEDGEMENTS
This study is supported by the project “Evaluation of technic,
economic and environmental feasibility of the valorization of rice
straw through biogas production for sustainability improvement”
(nº04/10) financed by the Agroalimed Foundation.

16. Thank you for your attention!