AGRICULTURAL BIOMASS WASTES: UTILIZATION ROUTES

G.E. Timbers and C.G.E. Downing

Engineering Research Service, Agriculture Canada, Ottawa, Ontario KIA 0C6

Received 16 August 1977

Timbers, G.E. and C.G.E. Downing. 1977. Agricultural biomass wastes: Utilization routes. Can. Agric. Eng. 19: 84-87.

The amount ofbiomass produced by Canadian agriculture is estimated at 118 X 106 tonnes. Ofthis total, approximately 73%isconsidered marketable in the form of grain, animal products, fruitand vegetables. Whenthe unharvested biomassand wasteproducts areadded together, an estimated additional 30 X 106 tonnes of material canbecredited to agricultural production.Animals, which are the only means ofharvesting much ofthe biomass produced onourmarginal lands, provide notonly asourceof protein butalsoa source of manure. Theavailability of thismanure combined withthat ofplantwaste mustnot beoverlookedasa possible renewable energy source. Anaerobic digestion, pyrolysis and hydrolysis aremethods forutilizing thebiomass systemwastes. In today's energy-conscious society, the possibilities of converting these wastes into viable energy forms demandsimmediate investigation.

INTRODUCTION

Canada has a land area of some 900 X 106ha. The area of agricultural capabilitycomprises approximately 115 X 106 ha orroughly 13%of Canada's total area (Shieldsand Ferguson 1975). From these 115 millionha, the quantity of agricultural biomassproduced amounts to an estimated 118 X 106tonnes (Table I). When the unharvestedbiomass and waste products are considered,the magnitude of this renewable resourcecan be seen. The amount of waste biomassoutlined in Table II has certain assumptionsmade in regard to availability (Downing1975). Biomass crops could, of course, begrown specifically for energy purposes within the farm sector following the "fuelplantation" concept (Szego and Kemp1973). Production of liquid, solid or gaseousfuels from biomass is possible based onconventional crops, short rotation forestry(including hybrid poplars) or in the futureon crops specifically developed for highbiomass yields. Agricultural cereal production as a source of renewable energy hasbeen considered in the past. Fuel ethanolproduction from wheat was studied byClark, D.S. et al. (Ethanol from renewableresources and its application in automotivefuels, published by the Minister responsiblefor the Canadian Wheat Board, 1971)during a period of grain surplus. Theyestimated that even for a 10% alcohol blendwith gasoline at 1971 usage rates, a rawmaterial equivalent to 221.6 million bu ofwheat would be required for the alcoholproduction. It is evident that such usage offood or feed material is not appropriate intoday's hungry world. Faced with a rapiddepletion of non-renewable fossil fuel, agriculture should be looking within itself tomake certain that efficient use is made of allavailable resources.

Contribution no. 551 from Engineering ResearchService.

84

TABLE I AGRICULTURAL PRODUCTION OF BIOMASS AS FOOD AND FEED

Product Quantity Energyf

X 106 tonnes X 1012 BTU X 106 G. joules

Cereal grains 33.3 549. 579.Oilseeds 2.2 42.4 44.8Forages 35.2 559. 590.Pasture 43.1 595. 627.7Fruit, vegetables and

potatoes 4.15 9.6 10.1Dairy products 9.2 19.9 21.Meat and poultry 2.0 21. 21.6Total of plant origin 117.95 1755. 1851.6

fl GJ = 109 joules = 9.47 X 105 BTU = 2.39 X 105 kcal.

TABLE II AVAILABLE CANADIAN BIOMASS PRODUCTION WASTES AND RESIDUES

Product Quantity Energy*

X 106 tonnes X 10'2 BTU v X 106 G. joules

Animal wastej 12.6 263.6 278.2Crop residue§ 16.9 234. 246.9Total 29.5 497.6 525.1

tGJ = 109 joules =9.47 X 105 BTU = 2.39 X 105kcal.JAnimal waste is based on the assumption that cattle in the east are in pasture approximately 1 3 timeand that cattle in the west are largely on range and therefore only '/4 of the manure is available.

§Crop residue averaged at '/: ton per acre. Straw is available at over 1ton per acre in the east but muchless in the west.

The Resources

The waste products of Canadian agricultural production have, at least in theory, atremendous potential for energy. Estimatesindicate that the gross energy content ofthese residues exceeds 0.5 X 109 GJ annu

ally. This total is about 7% of the totalannual Canadian usage (7.4 X 109GJ or 7 X1015 BTU primary energy). While it isevident that only a portion of this energycould ever be recovered, the magnitudeproduced demonstrates that it must beconsidered as a potential energy source.

Agricultural wastes, primarily as strawand manure, offer potential. Animal wastesconstitute a large volume of material; how

ever, it is not all available for use as anenergy source. Range and pasture cattlemanure is not available, but manure fromconfinement housing such as dairy and beeffeedlots, swine and poultry operations is notonly available but in many cases constitutesa removal problem. Crop residues are widelydistributed, thus incurring an energy penaltyin terms of collection. They are also requiredfor soil maintenance in many areas.

Utilization Routes

The obvious utilization of animal man

ures for fertilizer has a definite impact oninput energy requirements at the farm level.The Council for Agricultural Science and

CANADIAN AGRICULTURAL ENGINEERING. VOL. 19 NO. 2. DECEMBER 1977

Technology Report No. 41 (1975) indicatesthat manure could supply 19, 38 and 61% ofthe nitrogen, phosphorus and potassiumused annually in chemical fertilizers in theU.S.A. However, fertilizer use of manures,particularly from large confinement operations, is complicated by the energy costs fortransport and distribution, storage facilitiesrequired, odor problems and possibilities ofgroundwater contamination.

Anaerobic Digestion

Production of methane gas from manures through anaerobic digestion has beenpracticed in the past in Europe and is nowreceiving renewed attention as petroleumprices increase. In Germany during the1950's some farms generated methane fortractor fuel. Low petroleum prices laterrendered these operations uneconomic andthey were discontinued. More recently smallscale methane systems have been put intouse in India, Korea and Taiwan. The gasproduced is used on site for cooking pur-

ACID

FERMENTATION

METHANE

FERMENTATION

Figure 1. Methane production from organicwaste by two-stage microbial fermentation.

poses. Research in the U.S.A. has mushroomed and many laboratory and pilot-plant studies are underway investigatingeconomic feasibility and equipment factors.Agriculture Canada has been supporting amajor investigation of farm methane production through the work of H.M. Lapp atthe University of Manitoba (Lapp 1976,1977 Agriculture Canada/DSS Reports ofContracts 0SW5-0018 and OSW-0527).There, the equipment and techniques required for operation in our northern climateare being studied (Kroeker et al. 1975).

The anaerobic digestion of animal wasteto form methane-rich gas is a two-stepmicrobial fermentation. Initially, acid-forming bacteria break down the volatile solids toorganic acids which are subsequently utilized by methanogenic organisms to yieldmethane-rich gas (Fig. 1). Typical gas composition is: methane, 50-70%; CO,, 25-45%;N2, .5-3%; H2, 1-10% with traces of H2S.Heating value of the gas is in the 18-25MJ/m3 (500-700 BTU/ft3) range. Normaloperation of the anaerobic digestor requirestemperatures about 35C, which points up amajor drawback for use in the Canadianclimate. To maintain digestor temperaturesunder such cold conditions, a large portionof the methane produced is needed forheating purposes. The other major disadvantages of the digestion system for farmoperations are the high capitalization costsand the explosive properties of the methane.

On the positive side, integration ofmethane production facilities into the required waste handling facilities of large scale

WOOD WASTE

HYDROGENATION

confinement housing operations should befeasible. Large poultry, swine and dairyoperations near major centers must treatand dispose of the wastes in a manner whichminimizes the odor problem. Anaerobicdigestion stabilizes the waste and the digestor sludge is relatively odor-free and yetretains the fertilizer value of the originalmanure.

Methane is best suited to heating uses.This would work well with broiler operations where heating accounts for most of theenergy use.

Other uses for the gas include waterheating (dairy operations in particular)residence heating, and grain drying. Storagefacilities are a problem, particularly with theseasonality of gas production which is low inthe winter when the heating requirementsare high.

Increased efficiency of methane production should be possible through the use ofother lower grade energy sources, such assolar energy to maintain digestor temperature and wind-generated compressed air tooperate agitator and pump motors.

An extension of the anaerobic digestionfacility to include algal growth for single cellprotein (SCP) production has been suggested (Gasper et al. Paper No. 75-3545presented at 1975 A.S.A.E. Winter Meeting). In their system, algae are grown inculture tanks on the digestor effluent. TheSCP would find a use in feed formulations.

They also suggest the use of waste industrialheat to maintain digestor temperatures.

OIL SUBSTITUTENATURAL GAS

HEXOSES

IGLUCOSE

PENTOSES

IXYLOSE

AMMONIA

METHANOL

HYDROCARBONS

ACETIC ACID

METHANOL

ACETONE

PHENOL

CRESOLS

HYDROCARBONS

PHENOL

HYDROCARBONS

CRYSTALLIZATION HYDROGENATION

YEAST

VITAMINS

PROTEIN

FAT

GLYCEROL FURFURALETHYLENE GLYCOL

PROPYLENE GLYCOL

ALCOHOLS

ETHYL

BUTYL

ISOPROPYL

KETONES

ACETONES

HYDROGENATION

FERMENTATION

ACETIC GLYCEROL

BUTYRIC BUTYLENE

LACTIC GLYCOL

OIL

PHENOLS VANILLIN

HYDROCARBONS

Figure 2. Products available from the conversion of wood wastes (from Pulp and Paper Research Institute of Canada report OSY4-0093).

CANADIAN AGRICULTURAL ENGINEERING, VOL. 19 NO. 2, DECEMBER 1977 85

developed to various degrees between laboratory and commercial scales. One veryinteresting process is the enzymatic hydrolysis of cellulose to glucose developed at theU.S. Natick laboratories (Spano et al. 1975).Over a period of several years they havedeveloped mutant strains of Trichodermaviride which produce useable cellulose enzymes. Milled cellulose waste is hydrolyzedto glucose (Fig. 6) which is then available forfurther treatment. Some pretreatment of thecellulose is necessary to improve the hydrolysis. Ball milling of the material exposesmore of the crystalline cellulose to theenzymes for hydrolysis. Up to 78% sacchar-ification of the cellulose has been achieved in

48 h and up to 66% in 24 h. The degree ofconversion depends on the feedstock andpretreatment. Because of the degree ofsophistication required in the hydrolysis

processes, these will be restricted to the largeindustrial operations and not be applied atthe farm level.

SUMMARY

Modern mechanization, fertilizer andpesticide production which have allowed thegreat strides in productivity are energyintensive, but a return to the "old days" ofhigh labor, low energy agriculture is notpossible with the demands being placed onthe production system. There is, however,the possibility of increasing agriculture's netenergy output/ input balance by utilizing thelarge quantities of waste produced. Thetechniques for utilizing biomass residue areavailable, at least in the pilot-plant scale.Much more work in Canada is needed on

both the conventional and energy economicsof using existing biomass production. The

GAS TO

PURIFICATION

AND RECYCLE

Pyrolysis

While methane generation offers the bestpossibility for energy recovery from agricultural wastes at the farm level, several highertechnology procedures can be applied. Pyrolysis processes (intermediate and high temperature), hydrogasification, and hydrolysiscan all be applied to agricultural waste (Fig.2). These technologies can be used forpreparation of chemicals from the biomassas well as energy recovery. Of particularinterest to agriculture are the preparation ofalcohols for fuel, ammonia for fertilizers,glucose for food and feed either directly orthrough the production of yeasts for SCP.

While the majority of pyrolysis researchhas been directed toward urban refuse, thesetechniques are equally applicable to agricultural and forestry waste products. Recentstudies in Canada outline the use of forestrywastes for fuel and chemical production.Pyrolysis of biomass material yields oil, charand low BTU gas (Fig. 3) The initial gas hasa heating value of 4-17 MJ/m3 (100-450BTU/ft3). The gas may be burned directly,upgraded to pipeline quality or used as afeedstock for the manufacture of other

products, including methanol. This latteroption is being seriously studied in Canada.The oil and char can be used to provide therequired heat for the pyrolysis or as stokerfuel. Agricultural residue, like straw, is verywidely distributed and of low density. Cerealgrain straw is available at near Vi ton percultivated acre with about 49 million acres

(20 X 106ha) presently cultivated in Canada.The problems of collection, transport andstorage of this material in adequate volumesto operate a large pyrolysis unit are evident.One approach to this problem has been thedevelopment of a mobile pyrolytic unit bythe Georgia Tech Engineering ExperimentStation (Tatom et al. 1975). Their mobileunit (Fig. 4) was built on two trailers whichcould be moved to small sawmills or other

sources of waste biomass. With a capacity of100 t/day a mobile unit could be set up at anindividual farm to process straw which hadbeen collected and stored. The straw couldthen be converted to useable grade fuel forfarm application or for sale. Gas from thepyrolysis was used to power the systemengine and generator and as a heat sourcefor the input feed drier. In agriculturalapplications where the straw has been air-dried and stored, drier capacity would belower and techniques for handling andstoring the gas would be required.

Hydrolysis

The use of waste biomass as a source offood or chemical raw materials has receivedconsiderable attention. Cellulosic materialswhich are produced in abundance can besubjected to chemical or enzymatic hydrolysis to yield glucose which can be usedeither directly as food or feed or alternatively used for fermentation (Fig. 5).Numerous hydrolysis processes have been

AS-RECEIVED

REFUSE

JZLPRIMARY U

SHREDDER

FINE

GRIND

UNRECOVERED

SOLIDS

TO DISPOSAL

^8WT °/o

INORGANIC

PROCESSING

SUBSYSTEM

♦ rCLEAN MAGNETIC

GLASS METALS

Garrett Pyrolysis Process

1 •^tJ

1M

i

CHAR OIL

WATER TO- PURIFICATION

AND DISPOSAL

86

REFUSE

FEED HOPPER

SEAL —

FEEDLOCK

SEAL

SHAFT

FURNACE

OXYGEN —;

COMBUSTION ZONE

MOLTEN

MATERIAL

WATER QUENCH

FUEL GAS PRODUCT

WASTE WATER

Union Carbide Purox Process

Figure 3. Schematic representation of two pyrolysis processes for treating biomass.

CANADIAN AGRICULTURAL ENGINEERING. VOL. 19 NO. 2. DECEMBER 1977

,aJET SAlVDUfT GfiS TofnULT,-C/CLOV£~ 6 BA/2X FEED £

rnuLTi-

CYCLOJUL

VAA7

-^r-^—\ \ \ \ \ \ \^f v * \v—n—t-

Trailer. II* CM/Q€ TO mix£i/e

Chine $ oil muTo STORAGE

Figure 4. Trailor mounted mobile pyrolysis unit (adapted from Taton).

problems of the wide distribution of material must be examined closely, and consideration given to integrating the use ofbiomass residue with urban waste and forest

biomass systems. Supplementary urbanwaste utilization systems with biomassmight make combined plants economical forsmaller population centers. Development ofanaerobic fermentation for on-farm use is

progressing. While methane is well suited toheating applications, from the farm operator's point ofview development ofmethodsfor its use in mobile equipment would bevery desirable. Safety standards and management procedures are needed for methaneproduction and storage facilities. In the areaof pyrolysis and hydrolysis operations basedon biomass residue utilization, more detailed studies are needed on availability,transport and storage problems and, ofcourse, economics.

Biomass production specifically for energy use, either in electrical generation oralternate solid, liquid or gaseous fuels, offers

many possibilities. Questions of land usepolicy will have to be addressed, especially ifagricultural land is to be used.

ACKNOWLEDGMENT

The authors would like to acknowledge theefforts of R.P. Hocking in the preparation of thispaper.

COUNCIL FOR AGRICULTURAL SCIENCE

AND TECHNOLOGY. 1975. Utilization of

animal manures and sewage sludges in foodand fiber production. Report No. 41.

DOWNING, C.G.E. 1975. Energy and agricultural biomass production and utilization inCanada. Proceedings of the 1975 CornellAgricultural Waste Management Conference,pp. 261-269.

KROEKER, E.J., H.M. LAPP, D.D.SCHULTE, and A.B. SPARLING. 1975.Cold weather energy recovery from anaerobicdigestion of swine manure. Proceedings of the1975Cornell Agricultural Waste ManagementConference, pp. 337-352.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 19 NO. 2, DECEMBER 1977

ENZYME

BROTH

FERMENTER

TRICHODERMA

VIRIDE

MILLED

CELLULOSE

REACTOR

CELLULOSE 30%

ENZYME

PH

TEMP.

0.1%4.8

50°C

GLUCOSE

SYRUP

GLUCOSE

FOR FOOD, FEED

OR CONVERSION

RECYCLE

ENZYME AND

UNREACTED

CELLULOSE

Figure 5. Schematic representation of NatickLaboratory's cellulose byconversionprocess (adapted from Spano).

CHEMICALCONVERSION

CHEMICAL

RAW

MATERIALS

CELLULOSE

ENZYME

HYDROLYSIS

MICROBIALCONVERSION

SINGLE

CELL

PROTEIN

FERMENTATION

ETHANOL

ACETONE

ANTIBIOTICS

ENZYMES

Figure 6. Uses for waste cellulose through bio-conversion (adapted from Spano).

SHIELDS, J.A. and W.J. FERGUSON 1975.Land resources, production possibilities andlimitations for crop production in the PrairieProvinces. Oilseed and Pulse Crops in Western Canada. Western Co-operative FertilizersLtd., Calgary, Alberta.

SPANO, L.A., J. MEDE1ROS, and M. MAN-DELS 1975. Enzymatic hydrolysis of cellulo-sic wastes to glucose. Pollution AbatementDivision, Food Sciences Laboratory, U.S.Army Natick Development Center, Natick,Massachusetts 01760.

SZEGO, G.C. and C.C. KEMP. 1973. Energyforests and fuel plantations. Chemtech. May.pp. 275-284.

TATOM, J.W., A.R. COLCORD, J.A.KNIGHT, L.W. ELSTON, and P.H. HAR-OZ. 1975. A mobile pyrolytic system-agricultural and forestry wastes into clean fuels. Proceedings of the 1975 Cornell AgriculturalWaste Management Conference, pp. 271-288.

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