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  • Environmental Energy Company 1www.makingenergy.com360-923-2000

    Dairy Waste AnaerobicDigestion Handbook

    Options for RecoveringBeneficial ProductsFrom Dairy Manure

    Dennis A. Burke P.E.June 2001

    Environmental Energy Company6007 Hill Street

    Olympia, WA 98516

  • Environmental Energy Company iwww.makingenergy.com360-923-2000

    Table Of Contents

    Anaerobic DigestionDairy Waste Handbook ................................................................................................... 1Introduction......................................................................................................................... 1Dairy Operations................................................................................................................. 3

    Housing System .............................................................................................................. 3Free Stall Barns........................................................................................................... 3Corrals......................................................................................................................... 4Milk Barn .................................................................................................................... 4Open Lot ..................................................................................................................... 5

    Transport System ............................................................................................................ 5Flush Systems ............................................................................................................. 6Scrape Systems ........................................................................................................... 6Front end Loader......................................................................................................... 6Vacuum Systems......................................................................................................... 7

    Bedding ........................................................................................................................... 7Manure Processing.......................................................................................................... 8

    Holding Tanks and Chopper Pumps ........................................................................... 8Primary Screens .......................................................................................................... 9Gravity Separators .................................................................................................... 10Primary Holding Ponds............................................................................................. 13Secondary Holding Ponds......................................................................................... 14

    Summary ....................................................................................................................... 14Anaerobic Digestion ......................................................................................................... 16

    Bacterial Consortia........................................................................................................ 16Factors Controlling the Conversion of Waste to Gas ................................................... 17

    Waste Characteristics................................................................................................ 17Dilution of Waste.................................................................................................. 18Foreign Materials .................................................................................................. 19Toxic Materials ..................................................................................................... 20Nutrients................................................................................................................ 20

    Temperature .............................................................................................................. 20

  • Environmental Energy Company iiwww.makingenergy.com360-923-2000

    pH.............................................................................................................................. 21Hydraulic Retention Time (HRT)............................................................................. 21Solids Retention Time (SRT).................................................................................... 21Digester Loading (kg / m3 / d)................................................................................... 23Food to Microorganism Ratio................................................................................... 23End Product Removal ............................................................................................... 24

    Digester Types .............................................................................................................. 24Processes that are not Appropriate for Digesting Dairy Manure.............................. 25Processes that can be used for Digesting Dairy Manure........................................... 27

    Anaerobic Lagoons (Very Low Rate)................................................................... 27Completely Mixed Digesters (Low Rate) ............................................................. 28Plug Flow Digesters (Low Rate)........................................................................... 30Contact Digesters (High Rate) .............................................................................. 31Sequencing Batch Reactors (High Rate)............................................................... 32Contact Stabilization Reactors (High Rate).......................................................... 32Phased Digesters ................................................................................................... 33Hybrid Processes................................................................................................... 35

    Qualitative Analysis of Anaerobic Processes ............................................................... 35Solids Concentration Limitations ............................................................................. 35Digestion of the Entire Waste Stream....................................................................... 35Foreign Material Processing ..................................................................................... 36Odor Control ............................................................................................................. 36Stability, Flexibility, and Reliability......................................................................... 36Nutrient Concentration and Retention ...................................................................... 37Additional Substrate Processing ............................................................................... 37Energy Production .................................................................................................... 38

    Conventional Digesters......................................................................................... 38Lagoons................................................................................................................. 40High Rate Anaerobic Reactors.............................................................................. 40

    Cost of Anaerobic Processes for Dairy Waste.......................................................... 42Alternative Waste Management Systems ......................................................................... 44

    Existing Manure Handling............................................................................................ 44Housing ......................................................................................................................... 45Collection...................................................................................................................... 45Treatment ...................................................................................................................... 47Post-Treatment.............................................................................................................. 48Final Disposal ............................................................................................................... 49Evaluation ..................................................................................................................... 49

    References......................................................................................................................... 51

  • Environmental Energy Company 1www.makingenergy.com360-923-2000

    Dairy Waste Anaerobic

    Digestion Handbook

    Dennis A. Burke P.E.

    Introduction

    The rapid growth in the size of dairy operations has resulted in new laws andregulations governing the handling and disposal of manure (Mitchell andBeddoes 2000). Requirements for nutrient management plans, manure solidsdisposal, and odor control (HouseBill 2001) make it necessary that new manuremanagement approaches be considered. One of the more promising methods isanaerobic digestion.

    Anaerobic digestion is a natural process that converts biomass to energy.Biomass is any organic material that comes from plants, animals or their wastes.Anaerobic digestion has been used for over 100 years to stabilize municipalsewage and a wide variety of industrial wastes. Most municipal wastewatertreatment plants use anaerobic digestion to convert waste solids to gas. Theanaerobic process removes a vast majority of the odorous compounds (Lusk1995),(Wilkie 2000),(Wilkie 2000). It also significantly reduces the pathogenspresent in the slurry (Lusk 1995). Over

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