ainiaAnaerobic co-digestion of cattle manure with rice straw. Gracia Silvestre, Paz Gómez, Andrés Pascual and Begoña Ruiz

ADSW&EC 2011 Vienna 29.08.2011

CONTENTS

• Introduction

• Objectives

• Materials and Methods

• Results and Discussion

• Conclusions

INTRODUCTION

Rice Straw production

15000 Ha rice cultivation (part in a natural park).

30% of national production.

Around 100.000 t/year

Some figures about rice in Region Valencia…

INTRODUCTION

Traditional management of rice straw

Open-air burningAir pollution

Reincorporation to fieldsWater pollution

NATURAL PARK

INTRODUCTION

Rice fields2005

OBJECTIVES

Rice straw management

Traditional Alternative

BurnBury (“fanguejat”)

Anaerobicdigestion

Atmopshere andwater pollution

Sustainablemanagement

• 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.

PARTICULAR OBJECTIVES

OBJECTIVES

The aim of this research is to define a sustainable system for using the rice straw as substrate for anaerobic digestion in theconditions of the region of Valencia (Spain).

MATERIALS AND METHODS. Substrates

Rice straw samples

Cow manure samples

Inoculum

Origin: rice field in Valencia (Spain)Grinded to 2-3 cm with agriculturalchopper.

Origin: cow farm in Valencia.

Origin: biogas plant in Valencia (co-digestion of cow manure andvegetal co-substrates at 38ºC and 3 kgVS·m-3·d-1.

MATERIALS AND METHODS. Pre-treatments

Rice straw

Water

Oven 105ºC

Thermalpretreatment A

1 w.u.

6 w.u.Thermal

pretreatment B

1h

2h

BMP test

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-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)

RESULTS AND DISCUSSION. Pretreatments

MethaneBiogasBiogas

Substrates

58 ± 468 ± 5616 ± 43RS thermal pretreat (2h)

55 ± 462 ± 4616 ± 38RS thermal pretreat (1h)

58 ± 2399 ± 33547 ± 45RS untreated

(%)(NL/Kg)(NL/KgVS)

• 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.

Maceration of rice straw sample at 105ºC (1 h and 2 h)

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.

122117156153Methane (m3/tvs)22181312Methane (m3/t)

8.07.97.97.6pH<100<100<100<100VFA (mg/L)

72676665Methane (% biogas)0.830.680.56 0.54Biogas (m3/m3d)24252634HRT (days)4.93.93.62.3OLR (KgVS/m3d)5210Rice straw (%)

PIVPIIIPIIPIParameters*

RESULTS AND DISCUSSION

*Average values. SD are available in the proceedings.

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.

CONCLUSIONS

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.

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