Review paperAdvances in poultry litter disposal technology – a reviewB.P. Kellehera,*, J.J. Leahya, A.M. Henihana, T.F. O’Dwyera,D. Suttonb, M.J. LeahycaChemical and Environmental Science Department, University of Limerick, Limerick, IrelandbMaterials and Surface Science Institute, University of Limerick, Limerick, IrelandcDepartment of Physics, University of Limerick, Limerick, IrelandAccepted 6 August 2001AbstractThe land disposal of waste from the poultry industry and subsequent environmental implications has stimulated interest intocleaner and more useful disposal options. The review presented here details advances in the three main alternative disposal routes forpoultry litter, specifically in the last decade. Results of experimental investigations into the optimisation of composting, anaerobicdigestion and direct combustion are summarised. These technologies open up increased opportunities to market the energy andnutrients in poultry litter to agricultural and non-agricultural uses. Common problems experienced by the current technologies arethe existence and fate of nitrogen as ammonia, pH and temperature levels, moisture content and the economics of alternativedisposal methods. Further advancement of these technologies is currently receiving increased interest, both academically andcommercially. However, significant financial incentives are required to attract the agricultural industry.  2002 Elsevier ScienceLtd. All rights reserved.Keywords: Poultry litter; Composting; Anaerobic digestion; Direct combustion1. IntroductionWaste 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 ofNO3in 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. Characterisatio nThe 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 nitrogenBioresource 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: S0 9 6 0 - 8 5 24 (0 1) 00 13 3- 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 ofpoultry 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. NH3gas can belost to the atmosphere while NH4can 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 disposal3.1. CompostingComposting 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,