Effect of Temperature on Methane Production from Field-Scale Anaerobic Digesters Treating Dairy Manure

EFFECT OF TEMPERATURE ON THE METHANE PRODUCTION FROM FIELD SCALE

ANAEROBIC DIGESTERS TREATING DAIRY MANURE

Osman Arikan a, b, c, Walter Mulbry a, Stephanie Lansing b a USDA-ARS, Sustainable Agricultural Systems Laboratory, Beltsville, MD

b University of Maryland, Department of Environmental Science and Technology, College Park, MD, c Istanbul Technical University, Department of Environmental Engineering, Istanbul, Turkey

CONTENT

Introduction

Materials and Methods

Results

Conclusions

INTRODUCTION

Dairy Manure Production and Management

A dairy cow produces ~20-25 wet tons/year manure.

If improperly managed, dairy manures are of concern because of effects such as pathogens, nutrients, methane, and ammonia emissions.

Methane emissions from dairy manure in 2010 in the US were doubled comparing to values from 1990.

Manure management systems that prevent pollution and minimize fugitive methane emissions are becoming attractive.

INTRODUCTION

Why Anaerobic Digestion ?

results in the production of biogas that can be used as a renewable source of electricity.

reduces greenhouse gas emissions, odors and water contamination.

Digested manure solids can also be recycled on-farm as bedding material.

INTRODUCTION

Digestion Temperature Digestion temperature influences system heat requirements and methane production.

Three temperature conditions;

Temperatures of 35-37 °C are typically recommended.

Digesters require significant amount of heat energy to maintain temperatures at these levels.

There is limited information about methane production from dairy digesters at temperatures less than 35 oC.

Results are from lab-scale rather than field-scale systems.

- Psychrophilic (15-25 oC),

- Mesophilic (35-40 oC),

- Thermophilic (50-60 oC),

INTRODUCTION

Objective

to evaluate the effect of two relatively low digestion temperatures (22 and 28°C) on CH4 production using replicate continuously-fed, field-scale dairy manure digesters at two organic loading rates.

The results were compared with those from identical digesters operated at 35 oC.

MATERIALS and METHODS

Substrate

Manure was obtained from the USDA’s Dairy Research Unit within the Beltsville Agricultural Research Center (BARC).

Manure Treatment at the BARC Dairy

Solids separated manure

Solids

MATERIALS and METHODS

Characteristics of substrates used in the study

MATERIALS and METHODS

Field-scale (FS) Anaerobic Digesters

Anaerobic Digesters

Experimental Procedure

Period 1; All digesters were operated at steady state conditions for 42 days using solids-separated manure at 30 oC after start-up of 78 days.

Period 2; Pairs of digesters were maintained at one of three set temperatures (22 ± 2, 28 ± 2 and 35 ± 2 oC) and fed with solids-separated manure for 80 days.

Period 3; The digesters were subsequently operated under the same temperature regime but were fed with separated manure plus added solids for 56 days.

MATERIALS and METHODS

Analytical Methods

Temperature was continuously monitored within each digester using thermocouples.

The produced biogas was monitored using low-pressure cumulative gas meters.

Biogas samples were analyzed for CH4 using a TCD gas chromatograph.

Influent samples and effluent samples from the digesters were collected weekly and analyzed for total solids (TS), volatile solids (VS) and pH according to Standard Methods (APHA, 2005).

MATERIALS and METHODS

RESULTS

Organic loading rates (OLR) to the digesters

Suggested range1.4

2.6

solids-separated manure separated manure plus added solids

RESULTS

Weekly methane production

7.4

5.1

6.8

7.5

5.8

7.1

8.6

solids-separated manure separated manure plus added solids

RESULTS

Specific methane production

0.26

0.340.37

0.160.190.23

0.35

solids-separated manure separated manure plus added solids

RESULTS

Steady state data of the field-scale digesters

Farm digesters have major energy requirements for maintaining digester temperature at typical values of 35°C.

Our results suggest that anaerobic digesters treating dairy manure at 28°C can be nearly as effective as digesters operated at 35°C, even with a relatively short 17-day retention time.

Digesters operated at 22°C produced about 70% as much CH4 as 35°C digesters without affecting digester stability.

Addition of solids had limited contribution (20 to 30%) on methane production due to use of sawdust as bedding.

CONCLUSIONS

Jose Colina and Lorianny Rivera for assistance in operating the digesters and Anna Kulow for analyzing biogas and effluent samples.

ACKNOWLEDGMENTS

Investigating the fate and effect of antibiotics and feed additives during the anaerobic digestion of manure.

CURRENT WORK

THANK YOU!