Advances in poultry litter disposal technology – a review

Review paper

Advances in poultry litter disposal technology – a review

B.P. Kelleher a,*, J.J. Leahy a, A.M. Henihan a, T.F. O’Dwyer a,D. Sutton b, M.J. Leahy c

a Chemical and Environmental Science Department, University of Limerick, Limerick, Irelandb Materials and Surface Science Institute, University of Limerick, Limerick, Ireland

c Department of Physics, University of Limerick, Limerick, Ireland

Accepted 6 August 2001

Abstract

The land disposal of waste from the poultry industry and subsequent environmental implications has stimulated interest into

cleaner and more useful disposal options. The review presented here details advances in the three main alternative disposal routes for

poultry litter, specifically in the last decade. Results of experimental investigations into the optimisation of composting, anaerobic

digestion and direct combustion are summarised. These technologies open up increased opportunities to market the energy and

nutrients in poultry litter to agricultural and non-agricultural uses. Common problems experienced by the current technologies are

the existence and fate of nitrogen as ammonia, pH and temperature levels, moisture content and the economics of alternative

disposal methods. Further advancement of these technologies is currently receiving increased interest, both academically and

commercially. However, significant financial incentives are required to attract the agricultural industry. � 2002 Elsevier Science

Ltd. All rights reserved.

Keywords: Poultry litter; Composting; Anaerobic digestion; Direct combustion

1. Introduction

Waste from the poultry industry includes a mixture ofexcreta (manure), bedding material or litter (e.g. woodshavings or straw), waste feed, dead birds, broken eggsand feathers removed from poultry houses. Other wastesinclude those from cage, conveyer belt and water-flushing systems. The litter and manure component ofthis waste has a high nutritional value and is used as anorganic fertiliser, thus recycling nutrients such as ni-trogen, phosphorous and potassium. These components(poultry litter) have traditionally been land spread onsoil as an amendment. However, over-application of thismaterial can lead to an enriching of water nutrients re-sulting in eutrophication of water bodies, the spread ofpathogens, the production of phytotoxic substances, airpollution and emission of greenhouse gases. Eutrophi-cation has been suggested as the main cause of impairedsurface water resources, US EPA (1996). Bitzer andSims (1988) reported that excessive application ofpoultry litter in cropping systems can result in nitrate

(NO3) contamination of groundwater. High levels ofNO3 in drinking water can cause methaemoglobinaemia(blue baby syndrome), cancer, and respiratory illness inhumans and fetal abortions in livestock, Stevenson(1986). Alternative, environmentally acceptable, dis-posal routes, with potential financial benefits, may lie inlarge-scale biomass to energy schemes that can alsoprovide an easier to handle fertiliser as a by-product.Three options have been considered and in some casesimplemented: centralised anaerobic digestion, compo-sting and direct combustion with combined heat andpower. The cost of transporting feedstock has, in allcases, been the limiting factor.

2. Characterisation

The three wastes of primary concern in poultry pro-duction are the bedding litter used for poultry housing,the manure resulting from poultry production and deadbirds common to all operations. This review looks atdisposal options for the first two materials. The com-position of both litter and manure is predominantlywater and carbon (C) with smaller amounts of nitrogen

Bioresource Technology 83 (2002) 27–36

*Corresponding author. Tel.: +353-61-213012; fax: +353-61-202568.

E-mail address: [email protected] (B.P. Kelleher).

0960-8524/02/$ - see front matter � 2002 Elsevier Science Ltd. All rights reserved.

PII: S0960-8524 (01 )00133-X

(N) and phosphorous (P) and trace levels of chlorine(Cl), calcium (Ca), magnesium (Mg), sodium (Na),manganese (Mn), iron (Fe), copper (Cu), zinc (Zn) andarsenic (As). Poultry litter refers to the bedding materialused during the poultry production cycle. Materials usedas litter include straw, sawdust, wood shavings, shred-ded paper and peanut or rice hulls. During the pro-duction cycle accumulating manure is mixed with litterand at the end of the cycle both are removed together.Chemical and physiochemical characterisation of

poultry manure are summarised in Table 1 (Guerra-Rodriguez et al., 2001). Nitrogen exists in several formsand is constantly transformed by microbial activity,and changes in temperature, pH, moisture and oxygenconcentration. The concentration of ammonia nitrogenis important when considering any of the three disposaltechniques. Poultry manure contains significant con-centrations of organic nitrogen due to the presence ofhigh levels of protein and amino acids. Of the nitrogenin fresh manure, 60–80% is typically in organic form,such as urea and protein. Depending on environmentalconditions a large percentage of this organic nitrogen(40–90%) is converted to ammonia within a year.Ammonia exists as either gas (NH3) or in an ionisedstate ðNH4Þþ, which is water-soluble. NH3 gas can belost to the atmosphere while NH4 can be transformedby microorganisms to nitrate (a process known as ni-trification). Nitrate is highly mobile in water and canbe present in runoff. During anaerobic digestion ofpoultry manure the concentration of endogenous am-monia-nitrogen rises considerably. While some mem-bers of an anaerobic microorganism population can useammonium ions, an excess of ammonium can inhibitthe destruction of organic compounds, the productionof volatile fatty acids, and methanogenesis (Krylovaet al., 1997). The presence of ammonium ions alsocontributes to a corrosively high pH and leads tohandling, storage and disposal problems. The minimi-sation of ammonia content is desirable for any treat-ment of poultry litter.

3. Methods of disposal

3.1. Composting

Composting is the aerobic degradation of biode-gradable organic waste. It is a relatively fast biodegra-dation process, taking typically 4–6 weeks to reach astabilised material. The composted material is odourlessand fine textured with a low moisture content and can beused as an organic fertiliser. Composted poultry litter iseasy to handle and pathogen free. Disadvantages arecited as loss of nitrogen and other nutrients duringcomposting, equipment cost and labour, odour andavailable land (Sweeten, 1988).Moisture and C/N ratio have a major influence on a

successful composting process. For poultry waste, a lowC/N ratio contributes to large ammonia losses (Grayet al., 1971). A high moisture content, of more than75%, inhibits a quick start to the composting process.The moisture content (or the degree of material drying)is a major influence on the decomposition rate and thetendency to stabilise, since the metabolic heat generationduring decomposition drives evaporation. Factors thatcontribute to moisture loss include evaporation, leach-ing and aeration, natural or forced. Rynk et al. (1991)reported that moisture content should be maintainedbetween 40% and 60% during the composting process,although Fernandes et al. (1994) have reported thatsuccessful composting of poultry manure mixed withpeat or chopped straw has been obtained in a passivestatic-pile at high initial moisture levels (73–80%).Ammonia emissions during the composting of

chicken litter represent significant environmentalchange. Elwell et al. (1998) carried out studies on thecomposting of poultry litter without added amend-ments. They found that while overly wet material canhamper initial operation, the general progression driesthe material and produces a granular output that isbelow 20% (wt%) moisture and can be bagged and/orsold commercially. More importantly the study reportedthat there was very high ammonia production relative tomore conventional manure composting. Kithome et al.(1999) measured NH3 volatilisation during compostingof poultry litter and evaluated the potential of differentadditives to reduce the loss of NH3 using a laboratory-composting simulator. Various amendments were addedto the poultry manure including two natural zeolites,clay, coir (mesocarp of coconut fruit), CaCl2, CaSO4,MgCl2, MgSO4 and Al2ðSO4Þ3. Composting lasted from49 to 56 days and volatilised ammonia was trapped in a0.3 M H2SO4 solution. The composted materials wereweighed and analysed for moisture content, total N andNHþ

4 . NH3 volatilisation loss for the unamended ma-nures ranged from 47% to 62% of the total manure N.However, a layer of 38% zeolite placed on the surface ofthe manure reduced NH3 losses by 44%, whereas 33%

Table 1

Chemical and physiochemical characterisation of poultry manure,

Guerra-Rodriguez et al. (2001)

Solid poultry

manure

Organic matter content, % dry matter 85.38

pH 8.8

Moisture, % wet weight 48.69

Total nitrogen, % dry weight 3.56

Inorganic nitrogen, % dry weight 1.74

Ammonia nitrogen, % dry weight 1.76

OCC/nitrogen ratio 10.89

TCC/nitrogen ratio 12.24

P2O5, % dry weight 0.71

K2O5, % dry weight 3.79

28 B.P. Kelleher et al. / Bioresource Technology 83 (2002) 27–36

coir placed on the surface of the manure reduced NH3

losses by 49%. Composting poultry manure with theaddition of 20% alum reduced NH3 losses by 28%. Theaddition of zeolites, coir and alum produced compostswith high NHþ

4 concentrations ranging from 17% to53% of total N. 20% CaCl2 decreased NH3 volatilisationbut did not result in increased NHþ

4 or NO�3 concen-

trations. The 38% zeolite and 33% coir-amended com-posts had total N concentrations of 17% and31% g kg�1, respectively. The zeolite and coir amend-ments were therefore proposed to be the most successfulfor reducing NH3 losses during composting of poultrymanure.Raviv et al. (1999) found that the addition of

squeezed grapefruit peels to poultry litter compost wasfound to have a beneficial effect on the characteristics ofthe end product. Unamended composting of poultrymanure in an aerated pile resulted in overheating (>65�C) and rapid loss of total volatile solids (TVSs) and ofnitrogen. The addition of 5% (on a dry weight basis) ofsqueezed grapefruit peels lowered the pH of the aqueousphase of the raw materials from 6.6 to 5.8 and enabledthe temperature of the pile to be controlled below 60 �C.Amendment with the peels also resulted in an increase inthe amount of conserved nitrogen by approx. 80%. Incontrast nitrogen was conserved more than the TVS ona relative basis in the peel mixture but conserved lessthan the TVS in the poultry manure alone. The authorssuggest that previously released NHþ

4 may have beenbiologically immobilised in the mixture.Kirchmann and Lundvall (1998) concluded that

composting of animal wastes, including poultry wastes,should be restricted to those that need to be hygenised.This followed laboratory tests to study the effect ofdifferent solid manure treatments concerning NH3 lossesduring storage and after application to soil. Compostingresulted in drastically higher NH3 emissions than didanaerobic decomposition during incubation. However,application of the composted material to soil resulted inlow NH3 losses, as NH4–N concentrations were low.Significantly, the study found that the largest reductionin NH3 losses from poultry excreta was achieved if theexcreta were dried prior to storage and incorporatedinto soil. In contrast, composting caused significantlyhigher NH3 emissions.Despite these NH3 losses Gagnon and Simard (1999)

reported that the addition of poultry litter compost to asandy loam soil resulting in comparatively high soilmineral N content at the end of incubation. Of a numberof different composts, including dairy, sheep and horsederived material, poultry litter compost resulted in thehighest soil Mehlich-3 P content.More evidence of the volatilisation of ammonia and

of nitrogen-containing compounds from compostedpoultry manure was provided by Mondini et al. (1996).A comparison of the carbon and nitrogen contents of

composting and active drying poultry litter providesevidence that while there was an N and C reduction inthe composted material, C content remained the sameand N actually increased in the dried poultry litter. Ahumification index showed a decreasing trend in bothproducts, indicating the formation of humic substancesin both processes, although at different rates. The or-ganic matter of the composted material showed muchhigher levels of stabilisation.A study was undertaken by Georgakakis and Krintas

(2000) to investigate and optimise a composting systemknown as the Hosoya system in composting poultrymanure in a typical layer poultry farm in Greece.The hosoya system is one of the two treatment sys-

tems that have been applied for the treatment of wastes.The other is the Okada system and both are of Japaneseorigin. Both systems are based on the operation ofspecially designed manure turning and chopping me-chanical system (MTCM). The system consists of a se-ries of rotating metallic knives or forks with which thewaste is completely turned, aerated and gradually pu-shed to the end of the installation. This installationconsists of an open, shallow, oval shaped concretechannel about 80–100 m long and 4–6 m wide. It canserve about 100 000–120 000 layers. A greenhouse-typeshelter covers the channel consisting of a metallic skel-eton covered by hard plastic sheets. This covering en-sures that the sun will warm the air inside during sunnydays in winter and early spring. During warmer times ofthe year excess solar heat loads are removed by openinglarge doors and windows on the sidewalls of the shelter.The channel is filled with the waste material up to a

total depth of 1.0–1.2 m. In both systems the MTCMrolls along rails placed on the top of the channel side-walls. The main difference between the two systems isthat, with the Okada, the channel is straight while theHosoya is oval shaped. As a result, in the Okada themanure is pushed straight forward by the MTCM fromthe entrance at the one end of the channel to the exit atthe other end. The Hosoya system results in continuousmixing of the manure around the oval channel and onlya part of it, equivalent to that entering the channel,leaves the system. The MTCM in the Hosoya systemcompletes a full run along the oval channel in approx.2 h including a period of 15–20 min for maintenance orstandby. On a daily basis, a maximum of 12 full runscan then be completed. One complete run results in thedisplacement of 1.5 m of manure along the channel or amaximum of 18 m after 12 runs completed in 24 h.Therefore, the minimum travelling time for fresh ma-nure to reach the exit of the 80 m long channel is 4.44days. Fresh manure is batch fed daily to the ovalchannel and an equivalent quantity of final material isremoved from the exit, in order to keep the totalquantity in the channel constant and at the requireddepth. During the turning and pushing of manure by the

B.P. Kelleher et al. / Bioresource Technology 83 (2002) 27–36 29

MTCM, surrounding air is incorporated and moisture islost by evaporation.The Hosoya system controls the initial moisture

content by mixing the incoming fresh manure with therecirculated dry old material in the channel and thishelps to start the composting process. Moisture controlof the material in the oval channel is necessary to avoidblockages of the MTCM operation (Hosoya & Co.,1996).A particle size of less than approx. 12 mm is formed

from the initially muddy-textured raw material due tothe turning effect of the MTCM in the oval channel. Thereduction of particle size enhances degradation due tothe greater surface area available to microbes and anincrease in void space for oxygen.Georgakakis and Krintas studied the performance of

the Hosoya system by taking samples of poultry manureduring a run and analysing them for moisture content,and total and volatile solids. The temperature of thematerial and temperature and relative humidity of thesurrounding air were also monitored. The resultsshowed that the composting process could not be com-pleted in the Hosoya system. The initial turning andmixing results in a large temperature drop but there isinsufficient time for composting to take place. The au-thors recommend that this system could be used as apreliminary treatment for materials with high moisturecontent before more traditional techniques are used.Brodie et al. (2000) carried out comparative trials

between static piles and turned windrows and provideddata to support which method shows the best potentialfor producing commercially viable compost. The studyfound that, provided the basic raw materials are thesame, including such properties as porosity, nutrient andmoisture balance, then the composting process is for-giving and that both static and machine turned compostprocessing are suitable for poultry litter composting atless than optimal C:N ratios.

3.2. Anaerobic digestion

Anaerobic digestion is used worldwide as a unittreatment for industrial, agricultural and municipalwastes. It involves the degradation and stabilisation ofan organic material under anaerobic conditions by mi-crobial organisms and leads to the formation of meth-ane and inorganic products including carbon dioxide:

Organic matterþH2O

!anaerobesCH4þCO2þNew biomassþNH3þH2Sþheat:

The organic components of poultry litter can beclassified into broad biological groups: proteins, carbo-hydrates and lipids or fats. Carbohydrates make up thebulk of the biodegradable material and include cellulose,starch and sugars. Proteins are large complex organic

materials composed of hundreds of thousands of aminoacid groups. Lipids or fats are materials containing fattyacids. The anaerobic treatment of poultry litter involvestwo distinct stages (Williams, 1999). In the first stage,complex components, including fats, proteins andpolysaccharides, are hydrolysed and broken down totheir component subunits. This is facilitated by facul-tative and anaerobic bacteria, which then subject theproducts of hydrolyses to fermentation and other met-abolic processes leading to the production of simpleorganic compounds. This first stage is commonly re-ferred to as acid fermentation and in this stage organicmaterial is simply converted to organic acids, alcoholsand new bacterial cells. The second stage involves theconversion of the hydrolysis products to gases (mainlymethane and CO2) by several different species of strictlyanaerobic bacteria and is referred to as methane fer-mentation. The two stages are illustrated in Fig. 1.Anaerobic digestion is a relatively efficient conversion

process for poultry litter producing a collectable biogasmixture with an average methane content of 60%. Sys-tems are usually site specific but must have a certainminimum amount of poultry litter to supply a givensystem. The methane produced by this process can beused as a fuel for boilers, as a replacement for naturalgas or fuel oil and can also be fired in engine-generatorsto produce electricity for on-farm use or sale to elec-tricity companies.The residual sludge is stable and can be used as a soil

fertiliser. For larger operations the gases would need tobe scrubbed to remove impurities but may then becompressed and sold commercially to fuel companies.The poultry litter contains a higher fraction of biode-gradable organic matter than other livestock wastes andthis includes high levels of organic nitrogen due to thehigh content of protein and amino acids. The concen-tration of endogenous ammonia-nitrogen rises consid-erably during anaerobic digestion of poultry litter. Whilea certain amount of ammonium ions can be utilised bysome anaerobic bacteria, an excess of ammonium caninhibit the destruction of organic compounds, the pro-duction of volatile fatty acids and methanogenesis.Krylova et al. (1997) found that an excess of ammonia-nitrogen in a fermentation medium can cause inhibitionof the anaerobic process in the following ways: (1) freeammonia, which is more toxic for anaerobic microflorathan ammonium ion, is formed during the fermentationprocess; (2) amination of a-ketoglutaric acid from themetabolic pool of the tricarboxylic acid cycle can causedifficulties in the metabolism of organic compounds and(3) the release of ammonia-nitrogen may result in accu-mulation of volatile fatty acids. For these reasons, theminimisation of levels of ammonia is an important pri-ority during the anaerobic treatment of poultry litter.A possible solution to solve this problem is to dilute

the material to 0.5–3.0% total solids, which has the effect


of eliminating ammonia inhibition. Unfortunately thismethod results in a large increase in volume of wasteand renders the method economically non-viable.However, Bujoczek et al. (2000) varied the amounts offresh chicken manure and anaerobically digested sludge(poultry manure stored anaerobically for half a year) toinvestigate the highest solids level at which digestion wasstill feasible. The efficiency of conversion to methanewas found to decrease with increasing organic loads tothe digester. The highest solids content at which diges-tion was successful was approx. 10% total solids. Itodoand Awulu (1999) found that methane yield decreasedafter a threshold of 5% total solids was reached. Thesame investigation provided evidence that methane yieldfrom the anaerobic digestion of poultry waste washigher than that from the digestion of piggery and cattlewaste. Similar work by Callaghan et al. (1999) agreedwith these findings.Facilitated by the addition of exogenous NH4Cl, it

was demonstrated by Krylova et al. (1997) that almostall nitrogen becomes ammoniacal during anaerobic di-gestion of poultry litter. The results also indicated thatmethane production was stable between ammoniumlevels of 2–10 g l�1 but that higher ammonium levelsresulted in significant reductions in both biogas andmethane production (10–30 g NH4Cl l

�1). High levels ofammonium (>30 g l�1) resulted in a decrease in thenumbers of all physiological microbial groups (espe-cially proteolytic and methanogenic). However, the au-thors also studied the effect of addition of powderedphosphorite ore [10% (w/v)] on methane production andconcluded that this addition resulted in enhancedmethane production at NH4Cl concentrations up to30 g dm�3. NH4Cl also changed the composition of the

methanogenic consortium while there was a partial re-covery in the numbers of proteolytic and methanogenicbacteria. Phospherite addition had a positive effect up to50 g dm�3 of NH4Cl but at concentrations above thisthere was irreversible inhibition of methanogenesis thatcould not be eliminated by the addition of phosphorite.There have been several approaches to improving

digester performance including optimising temperature,total solid content and retention time and the additionof adsorbents and surfactants. Desai et al. (1994) andDesai and Madamwar (1994a,b) looked at these possi-bilities and concluded that the production of total gases,including methane, from digestion of poultry littermixed with cheese whey was optimal under the followingconditions:• Retention time was kept to approx. 10 days, a load-ing rate of 6.0 g total solid/litre of digester per daywas used and a total solid content of 6% (w/v) waspresent.

• 4 g l�1 of an adsorbent was added (in this case silicagel). There was then a twofold enhancement in totalgas production.

• The addition of surfactants, such as sodium laurylsulfate, results in an increase in digestion.Alternatively, when 20 mM of FeSO4 was added to a

daily-fed poultry-litter digester, it increased methano-genesis by 42% and increased the turnover rate of totalsolids, volatile solids and volatile fatty acids and thenumber of methanogens (Rao and Seenayya, 1994).These approaches deserve consideration although theeconomics of such additives could be inhibitory.An attempt to use solar power to provide tempera-

tures in the thermophilic range (40–60 �C) and usestones to store the heat required was made by Itodo et al.

Fig. 1. Pathways in anaerobic digestion.


(1997). The tests resulted in a reduction in biogas yield.The problem of using solar energy in thermophilic di-gestion is that temperature fluctuation results in lowerbiogas yield, and digestion at thermophilic temperaturesis more sensitive to fluctuation than digestion at meso-philic temperatures. The storage of heat using stones forsupplemental heating during periods of low tempera-tures within the solar house was inefficient, as temper-ature varied from the mesophilic to the thermophilicrange. The authors recommend improvements to designfeatures to enable it to hold all the heat energy availableand enhance the application of solar energy in thermo-philic digestion.Codigestion of poultry waste with other manures can

have a beneficial effect on biogas production. The codi-gestion of hog and poultry waste was investigated byMagbanua et al. (2001). The study found that codiges-tion of the wastes was not only viable but that there wasalso a superior biogas yield from treatments of combinedwaste as opposed to the digestion of the wastes on theirown. The two wastes complimented each other with thehog waste supplying methanogens and poultry wasteproviding additional substrate. Problems that may resultin a material such as poultry litter being unsuitable fordigestion, such as a high or low pH, may be offset bycodigestion with another material. This is an importantconsideration when choosing a disposal option.

3.3. Direct combustion of poultry litter

The third alternative disposal route is direct com-bustion of poultry litter with the potential to provide forboth space heating of poultry houses and large-scaleschemes involving power generation or combined heatand power. Modern systems are efficient combustionfacilities with sophisticated gas cleanup, which produceenergy and reduce the waste to an inert residue withreduced pollution. The calorific value of poultry litterdecreases with increasing moisture content, air driedsamples having a typical value of 13.5 GJ/ton, which isabout half that of coal. Poultry litter has a low ash fu-sion temperature. This ash fusion can cause problemswhen using a conventional grate combustion system.Parameters such as combustion temperature, air mixtureand moisture content must be held within optimalspecifications for the efficient running of a combustionfacility and vary for combustion design. The processproduces an ash residue, which retains most of thephosphate and potash present in the fresh litter. Theoriginal nitrogen concentration is variable and loss tothe atmosphere on combustion as NOx is not considereda problem (Dagnall, 1993). The ash is stable, sterile,easier to handle and transport and more marketable asan organic fertiliser than conventional poultry litter.Combustion facilities may be classified by the type of

system used, the nature of the waste to be combusted

and their capacity. However, a broad division can bemade between mass-burn incineration and other types(Williams, 1999).

Mass-burn combustion: Large-scale incineration in asingle-stage chamber unit in which complete combustionor oxidation takes place. Typical volumes of waste arebetween 10 and 50 ton/h.

Other types of combustion: Other types of combustioninvolve small-scale volumes typically between 1 and 2ton/h. Examples include fluidised bed, cyclonic, rotarykiln and liquid and gaseous incinerators.The most successful conversion of poultry litter to

energy involves the use of mass burn combustion and, inparticular, step-grate combustion systems. Fibropower,Page and Allen (1993), officially opened their poultry-litter-fired power plant, thought to be the first com-mercial plant of its type in the world, at Eye in SuffolkUK in November 1993. The plant generates a grossoutput of 14 MWe. After in-house use of electricity, anet output of 12.5 MWe is supplied to a 33 kV powerline for distribution through local electricity networks.The poultry litter itself comes from barn reared broilerhens and is a mixture of wood shavings, straw andchicken droppings. The wood shavings and straw im-proves the burning process and permits control of themoisture content. The high calcium content of the litterproduces a self-cleansing effect and reduces the need tointroduce calcium as a cleaning agent for gaseousemissions. The escape of odours from the storage facilityis minimised by the use of negative pressure. Fuel is fedinto a boiler through a stepped-grate system, whichensures that the material has a residence time of 2 s at850 �C thereby killing pathogens and preventing theemission of odour. The system is fed by two unmannedcranes that mix the litter from the supplier farms beforeloading it on four elevators. The fuel is then movedthrough the furnace by the step-grate system. Aftercombustion, an electrostatic precipitator is used to en-sure low dust emissions.A sister company, Fibrowatt, constructed a 13.5 MW

facility in Glanford and a 38.5 MW unit in Thetford,England (Anonymous, 1996). The Eye and Glanfordprojects developed Fibrowatt’s expertise and experiencein the use of poultry litter as a fuel. The moisturecontent of the litter supplied to Eye was found to behigher than expected and resulted in problems. There-fore, new technology was introduced for the boiler usedat Glanford. The boiler is a Detroit stocker grate, achain grate with spreader stockers which blow the fuelinto the boiler and ensure that the majority of the fuel isburnt in mid-air. The plant at Eye employs a movinggrate which means that the litter is burnt on the floor ofthe boiler. The spreader stocker arrangement used inThetford is more effective and is now used at mostbiomass conversion facilities not using fluidised-bedtechnology.


An electrostatic precipitator controls particulateemissions, in the Eye and Glanford plants. However, theThetford plant controls its emissions with the use of acyclone and baghouse in series, further reducing par-ticulate emissions. Due to the clean nature of poultrylitter, neither Eye nor Glanford employs equipment tolimit SO2 or HCL emissions. As an extra precaution theThetford facility decided to inject lime into the flue gasbetween the cyclone and the baghouse, minimising SO2

and HCL. The addition of lime results in a modified ashcomponent that adds a new dimension to its use as afertiliser.Construction of the Thetford power station began in

1996 and it was handed over to the owners in June 1999.Having proven the systems technical and economic vi-ability the operation was shut down after a year’s op-eration. The shutdown has provided an opportunity toimplement more process improvements. Recommis-sioning took place in February 2000 and it is expectedthat the plant will exceed the load factors experiencedwith the first two plants of 91.3% (Staff Report, ModernPower Systems, 2000). Another example of advancesincorporated into the Thetford plant is the use of spiralscrew feeders that transfer the litter to a conveyor belt,then to the steam generator where it is pneumaticallytransferred into the boiler furnace. This is a much moreefficient process than that of the two other plants wherecrane grabs are used to transfer the fuel from the de-livery bunkers to the boiler furnace. The litter is, asstated, combusted at more than 850 �C with a residencetime of 2 s. These conditions are usually specified for thereduction of dioxin. Small amounts of chlorine arepresent in the flue gas but the complete mechanisms to

generate furans, dioxin or long chain polymers do notoccur in the process. Fig. 2 shows a simplified schematicof how the process works.An alternative method of direct combustion of

poultry litter is by fluidised bed combustion. There arethree main types of fluidised beds, bubbling (Fig. 3),turbulent or circulating bed types. All designs consist ofa bed of sand in a refractory-lined chamber throughwhich primary combustion air is blown from below.Adjusting the airflow fluidises the sand particles. Cy-clones are placed within the freeboard to re-circulate thesand to the bed. The fluidised bed reactor facilitates thedispersion of incoming fuel, where it is quickly heated toignition temperature, and provides sufficient residencetime in the reactor for complete combustion. Fluidisedbeds are compact and have high heat-storage and heat-transfer rates and thus allow faster ignition of lowcombustible waste. Because of high heat-transfer rates,fluidised beds are good for heat recovery purposes(Williams, 1999).Annamalai et al. (1985) investigated the direct com-

bustion of poultry litter in a fluidised bed combustor.Their investigation concluded that:• Nearly perfect fluidisation was achieved.• Manure could be ignited at approx. 580 �C. However,complications arose due to the high moisture contentof the manure, especially in the feeder system. Thefuel, therefore, was dried before combustion to amoisture content of 11%.

• With heaters at zero setting, combustion was self-containing at fuel feed ratios above 2 g/s. For feedrates below 2 g/s, electrical heaters were necessaryto maintain the desired bed temperature.

Fig. 2. Flow diagram of poultry litter fuelled power plant, Staff Report, Modern Power Systems (2000).


• Oxidation efficiency increased when excess air wasvaried from )20% to 10%. Above 10% excess air,the efficiency decreased. The concentration of carbonmonoxide (CO) was insensitive to excess air increasesafter 10%.

• Carbon dioxide (CO2) concentration and oxidationefficiency increased when bed temperature was variedfrom 615 to 650 �C, while above 650 �C, the CO2 con-centration leveled off.

• If the level of CO was within acceptable limits, thenapprox. 10% excess air and a temperature of 650 �Cprovided optimum conditions for the combustion ofmanure by a fluidised bed unit.

Similar tests are reported by Abelha et al. (2002). With aview to using poultry litter as an energy resource (com-bined heat and power), combustion studies of poultrylitter on its own or mixed 1:1 with peat were carried out inan atmospheric bubbling fluidised bed. The highmoisturecontent of chicken litter provided uncertainty as towhether combustion could be sustained on 100% chickenlitter therefore, a mixture with peat was considered tohelp improve combustion. The study found that as longas the moisture content of chicken litter is kept below25%, the combustion will not need the addition of peat.The combustor was operated over a temperature range of700–1000 �C. The main parameters investigated were: (i)moisture content, (ii) air staging, and (iii) variations inexcess air levels along the freeboard.

The main conclusions were: (1) combustion was in-fluenced very much by conditions of fuel supply, (2)steady fuel supply was strongly dependent on themoisture content of the chicken litter, (3) temperatureappeared to influence the reduction of levels of un-burned carbon and hydrocarbons released from resi-dues, (4) air staging in the freeboard improvedcombustion efficiency by enhancing the combustion ofvolatiles released from residues in the riser and (5) NOx

emissions were influenced by air staging in the free-board.Particles collected from the bed and the two cyclones

were analysed to determine levels of heavy metals. Thepresence of relatively high K levels due to straw used inthe poultry litter and enrichment of K in ashes collectedfrom cyclones was observed. Leachability tests werecarried out with the ashes collected to verify whether ornot they could safely be used in agricultural lands. Theresults showed little tendency to leach.These studies illustrate that fluidised bed technology

can be used for the direct combustion of poultry litter.The minimisation of moisture content at low cost isobviously desirable and worthy of investigation for allcombustion techniques. The manipulation of diet tolower the moisture content of poultry litter may be anapproach worth considering. One such investigation wascarried out by Svihus et al. (1995). High moisture barley,which is sometimes included in the feed given to broiler

Fig. 3. Typical bubbling bed fluidised bed incinerator, Williams (1999).


chickens in Norway, was stored under different condi-tions to study the effect on the digestive tract and,consequently, the moisture content of the poultry ma-nure. The barley was preserved anaerobically by ensilingusing different additives, aerobically with propionicacid, or by drying. The contents of true protein, totalamino acids, total b-glucans and the moisture contentwere reduced when barley was stored in the moist stage.However, anaerobic storage, which produced lactic acidand ethanol fermentation, caused the strongest reduc-tion of these variables. Importantly, from a combustionand composting point of view, feeding high-moisturebarley, obtained through high moisture storage, resultedin less sticky droppings so the cleanness of the cages andfeathers was significantly improved. Dietary manipula-tion, as long as it does not adversely affect other phys-iological parameters, is worthy of investigation as amethod to reduce the moisture content of poultry ma-nure.Sondreal et al. (2001) concluded that the choice of

fuel and generating technology for new power plants,including the combustion of biomass, is influenced by anincreasingly complex combination of interrelated factorswhich include: (1) current and future governmentalpolicies on restructuring and deregulation of utilities,and environmental incentives like carbon emissiontaxes; (2) economic factors such as proximity to loadcentres, electricity, plant capital investment, fuel costand fuel price stability; and (3) existing technology, in-cluding environmental controls, for generation of powerand associated benefits and risks involved in its de-ployment, all of which is dependent on the fuel prop-erties.

4. Conclusions

Composting of poultry litter has been shown to besuccessful and the end material can be sold commer-cially as an organic fertiliser. The main disadvantagethat needs to be addressed is the loss of nitrogen, re-sulting in a material of less commercial and practicalvalue. This nitrogen loss contributes to an undesirablevolatilisation of ammonia to the atmosphere or nitrateto water bodies.Anaerobic digestion of poultry manure has also been

shown to be a viable disposal option. Operating condi-tions are important, however, as excessive levels ofammonia and/or high pH or temperature levels can in-hibit methane production. The addition of additivessuch as phospherite and the incorporation of adsorbentsor surfactants has resulted in encouraging results, al-though a cheaper method to enhance digestion is nee-ded. The other main consideration is, of course,economics. For anaerobic digestion of poultry waste tobe financially viable, a disposal fee to farmers and/or the

sale of the digested solid effluent as an organic fertiliserto retail markets is important.The moving grate combustion facilities used by Fi-

browatt in the UK have proven the technological via-bility of the process and have pointed the way forwardfor the use of poultry litter as a fuel. Fluidised bedtechnology can facilitate the use of poultry litter close towhere it is produced, either on its own or mixed withother domestic or industrial waste, to produce heat andpower. The use of poultry litter as a fuel has the addedbenefit that only trace concentrations of elements likenitrogen or sulphur are present in the gaseous productsof combustion thus leading to a dilution of emissions ofpollutants such as NOx and SO2. Other advantages as-sociated with fluidised bed technology are its ability toaccept fuels with a relatively high ash and moisturecontent, the low cost associated with fuel preparation,and operational flexibility with regard to ash collection.Rather than being a problem of waste, poultry litter

can and should be a source of energy and nutrients. Fuelcost, efficiency, capital cost and environmental andregulatory policies will be the principle limiting factorswhen it comes to making future decisions on disposaltechniques. There is also an onus on policy makers toprosecute persistent polluters thus compelling the pro-ducers of waste to consider alternative, cleaner disposaloptions.

Acknowledgements

This work would not have been possible without thehelp of the Kantoher Poultry Producer’s Association(KPPA) and in particular Jack O’Connor. Financialsupport was provided by the KPPA and the Environ-mental Protection Agency of Ireland (under the Na-tional Development Plan).

References

Abelha, P., Gulyurtlu, I., Boavida, J.S., Cabrita, I., Leahy, J.J.,

Kelleher, B., Leahy, M., 2002. Combustion of chicken litter in a

fluidised bed combustor. In: The Second International Mediterra-

nean Combustion Symposium, Sharm El-Sheikh, Egypt, January

6–11.

Annamalai, K., Madan, A., Sweetan, J., Lepori, W., Jenkins, P., 1985.

Combustion of feedlot manure in fluidised beds. In: Proceedings of

the International Conference on Fluidised Bed Combustion, vol. 2,

pp. 884–894.

Anonymous, 1996. Poultry litter to fir Europe’s biggest biomass plant.

Modern Power Systems 16, 23–26.

Bitzer, C.C., Sims, J.T., 1988. Estimating the availability of nitrogen in

poultry manure through laboratory and field studies. J. Environ.

Qual. 17, 47–54.

Brodie, H.L., Carr, L.E., Condon, P., 2000. Poultry litter composting

comparisons. Biocycle 41, 36–40.

Bujoczek, G., Oleszkiewicz, J., Sparling, R., Cenkowski, S., 2000. High

solid anaerobic digestion of chicken manure. J. Agr. Eng. Res. 76,

51–60.


Callaghan, F.J., Wase, D.A.G., Thayanithy, K., Forster, C.F., 1999.

Co-digestion of waste organic solids: batch studies. Bioresour.

Technol. 67, 117–122.

Dagnall, S.P., 1993. Poultry litter as a fuel. World’s Poult. Sci. J. 49,

175–177.

Desai, M., Madamwar, D., 1994a. Anaerobic-digestion of a mixture of

cheese whey, poultry waste and cattle dung – A study of the use of

adsorbents to improve digester performance. Environ. Pollut. 86,

337–340.

Desai, M., Madamwar, D., 1994b. Surfactants in anaerobic digestion

of cheese whey, poultry waste, and cattle dung for improved

biomethanation. Trans. ASAE 37, 959–962.

Desai, M., Patel, V., Madamwar, D., 1994. Effect of temperature and

retention time of biomethanation of cheese whey-poultry waste-

cattle dung. Environ. Pollut. 83, 311–315.

Elwell, D.L., Keener, H.M., Carey, D.S., Schlak, P.P., 1998. Compo-

sting unamended chicken manure. Compost Sci. Utilisation 6, 22–

35.

Fernandes, L., Zhan, W., Patni, N.K., Yjui, P., 1994. Temperature

distribution and variation in passively aerated static compost piles.

Bioresour. Technol. 48, 257–263.

Gagnon, B., Simard, R.R., 1999. Nitrogen and phosphorus release

from on-farm and industrial composts. Can. J. Soil Sci. 79, 481–

489.

Georgakakis, D., Krintas, Th., 2000. Optimal use of the Hosoya

system in composting poultry manure. Bioresour. Technol. 72,

227–233.

Gray, K.R., Sherman, K., Biddlestone, A.J., 1971. In: Process

Biochem. 6, Part 1 & Part 2.

Guerra-Rodriguez, E., Diaz-Ravina, M., Vazquez, M., 2001. Co-

composting of chestnut burr and leaf litter with solid poultry

manure. Bioresour. Technol. 78, 107–109.

Hosoya & Co., 1996. Hosoya Manure Fermentation System. Hoyosa

& Co., 412 Fukaya, Ayase-Shi, Kanagawa-ken 252, Japan.

Itodo, I.N., Awulu, J.O., 1999. Effects of total solids concentrations of

poultry, cattle, and piggery waste slurries on biogas yield. Trans.

ASAE 42, 1853–1855.

Itodo, I.N., Lucas, E.B., Kucha, E.I., 1997. The effect of using solar

energy in the thermophilic digestion of poultry waste. J. Eng. Int.

Develop. 3, 15–21.

Kirchmann, H., Lundvall, A., 1998. Treatment of solid animal

manures: identification of low NH3 emission practises. Nutr.

Cycling in Agroecosyst. 51, 65–71.

Kithome, M., Paul, J.W., Bomke, A.A., 1999. Reducing nitrogen

losses during simulated composting of poultry manure using

adsorbents or chemical amendments. J. Environ. Qual. 28, 194–

201.

Krylova, N.I., Khabiboulline, R.E., Naumova, R.P., Nagle, M., 1997.

The influence of ammonium and methods for removal during the

anaerobic treatment of poultry manure. J. Chem. Technol.

Biotechnol. 70, 99–105.

Magbanua, B.S., Adams, T.T., Johnston, P., 2001. Bioresour. Technol.

76, 165–168.

Mondini, C., Chiumenti, R., da Borsa, F., Leita, L., De Nobili, M.,

1996. Changes during processing in the organic matter of

composted and air-dried poultry manure. Bioresour. Technol. 55,

243–249.

Page, B., Allen, W.H., 1993. Modern Power Systems 13, 57–61.

Rao, P.P., Seenayya, G., 1994. Improvement of methanogenesis from

cow dung and poultry litter waste digesters by addition of iron.

World J. Microbiol. Biotechnol. 10, 211–214.

Raviv, M., Medina, S., Shamir, Y., 1999. Cocomposting-a method to

improve results of poultry manure composting. Compost Sci.

Utilisation 7, 70–73.

Rynk, R., Kamp, M., Willson, G., Singley, M., Richard, T., Klega, J.,

Gouin, F., 1991. In: On-Farm Composting Handbook. Northeast

Regional Agricultural Engineering Service, 152 Riley-Robb Hall,

Cooperative Extension, Ithaca, NY 14853-5701, USA, p. 174.

Sondreal, E.A., Benson, S.A., Hurley, J.P., Mann, M.D., Pavlish, J.H.,

Swanson, M.L., Weber, G.F., Zygarlicke, C.J., 2001. Review of

advances in combustion technology and biomass cofiring. Fuel

Process. Technol. 71, 7–38.

Staff Report, 2000. Chicken runs provide the fuel for Fibrowatt’s

global ambitions. Modern Power Systems 20, 41–45.

Stevenson, F.J., 1986. Cycles of Soil. Wiley, New York.

Svihus, B., Selmer-Olsen, I., Brathen, E., 1995. Effect of different

preservation methods for high-moisture barley on feeding value for

broiler-chickens. Acta Agric. Scand. Sect. A. Animal Sci. 45, 252–

259.

Sweeten, J.M., 1988. Composting manure and sludge. In: Proc. Natl.

Poultry Waste Manage. Symp.. Department of Poultry Science,

The Ohio State University, Columbus, OH, pp. 38–44.

US Environmental Protection Agency, 1996. Environmental indicators

of water quality in the United States. EPA 841-R-96-002.

Williams, P.T., 1999. Waste Treatment and Disposal. Wiley, New

York.


Advances in poultry litter disposal technology – a review

Documents

Transcript of Advances in poultry litter disposal technology – a review