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OBJECTIVES Rice straw management Traditional Alternative Burn Anaerobic Bury (“fanguejat”) digestion Atmopshere and Sustainable water pollution management
OBJECTIVESThe aim of this research is to define a sustainable system forusing the rice straw as substrate for anaerobic digestion in theconditions 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.
MATERIALS AND METHODS. SubstratesRice 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.
MATERIALS AND METHODS. Pre-treatmentsRice 1 w.u. Thermal 1h BMP teststraw pretreatment A Oven 105ºC 2h ThermalWater 6 w.u. pretreatment B
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
MATERIALS AND METHODS. Co-digestionPlug-flow digester with a working volume of 900 LOperation temperature 38ºCControl parameters: TS, VS, pH, NH4+-N and VFABiogas production was measured by gas counter Kromschröder BK-2,5CH4 and H2S content was measured by Dräger MultiwarnThree different mixtures of cow manure and rice straw were analyzed (1%,2% and 5% rice straw)
RESULTS AND DISCUSSION. PretreatmentsMaceration 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.
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.
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.
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.