In this report, the management and
disinfection of manure with a low-tech, cheap, plastic
digester is described. The efficacy of disinfection was
monitored by carrying out microscopy and culture analysis
of the raw and treated manure slurries to establish the
microbial presence in both

A.S. Sambo (7230107)

K.A. Yongabi (7230101)

M.O. Agho (7230110)

P.L. Harris (7230104)

English

Loughborough University Institutional Repository

YONGABI, HARRIS, SAMBO and AGHO7429th WEDC International Conference Abuja, Nigeria, 2003Managing cow dung with a low tech, cheap plastic digesterK. A. Yongabi, P. L. Harris, A. S. Sambo, M. O. Agho, NigeriaTOWARDS THE MILLENNIUM DEVELOPMENT GOALSIntegrated farming has traditionally involved, among otherthings, the use of crop residues as feeds and the use ofanimal manure as fertilizer for the fields. While this inter-sectoral transfer of materials is necessary for sustainableagriculture, the use of untreated manure has tended tospread pathogens to animals, crops, soil, and water bodies(Jones and Mathew, 1975). The result is the exacerbationof communicable diseases like typhoid, malaria, diarrhoeaand Dysentery, Cholera etc.  This has been particularly truefor Nigeria where the use of untreated manure is rampant,especially in the northern part of the country.The use and disposal of animal wastes is one of the majorsanitation problems in rural parts of most developingcountries, and this is particularly true for Nigeria. Outsideof the pathogenic bacteria contained in untreated manure,a host of parasitic worms that also affect man, e.g. TaeniaSaginata and Fasciola hepatica, are known to be present.Some of the long-surviving pathogenic bacteria that havebeen reported to be present in raw manure include Salmo-nella spp, Escherichia coli, Campylobacter spp, Listeriamonocytogenes etc (Jones, 1980; Larsen and Munch, 1982;Robinson, 1982; Theresa et al, 1993).  Jones in 1980 alsoreported that bacteria associated with manure depends onthe species, population size, ability to survive, storage,capacity to remain virulent as well as survive on grass fora considerable period of time, serotype, slurry composi-tion, temperature and pH.One of the most common processes for ‘sterilizing’manure and producing biogas is anaerobic digestion, andsome of the popular types are the Chinese-dome under-ground and Indian digesters. While anaerobic digestion iswidely in use in Asia for the management of agriculturalwaste, the use of these digesters is minimal in Africa. Someof the reasons precluding the use of these digesters espe-cially in the rural communities in Nigeria, for instance, arethe cost of construction and the required skillful mainte-nance of the digesters. In this report, the management anddisinfection of manure with a low-tech, cheap, plasticdigester is described. The efficacy of disinfection wasmonitored by carrying out microscopy and culture analysisof the raw and treated manure slurries to establish themicrobial presence in both.Materials and methodsDigester  design and constructionThe digester was housed in an open top wooden trough of0.3 m depth, with unequal length rectangles at top andbottom. The trough is 1.8 m at the top and 1.26 m long atthe bottom. The widths at the top and bottom are 0.8 m and0.45 m respectively.A 1 m wide and 2.34 m long polyethylene sheet, withopen ends, was laid as bedding on the floor of the trough.The polyethylene sheet was folded at both ends longitudi-nally and pushed gently through PVC pipes (0.65 m longinlet pipe of 0.11 m diameter; and 0.54 m long outlet pipeof 0.09 m diameter). The edges of the polyethylene werewrapped round the file-smoothed mouth of the pipes andfastened in position with rubber bands. At every stage, carewas taken to avoid having a hole in the polyethylene sheet.Figure 1. Overview of the digester being checked forleakages with waterFigure 2. Collected gas being shown in a plastic bagafter four weeks of digestionYONGABI, HARRIS, SAMBO and AGHO75Sample Collection (Cow Dung)The cow manure was collected with a spade into a bucketfrom the Range Farm of the School of Agriculture andAgricultural Technology, Abubakar Tafawa Balewa Uni-versity, Bauchi.Slurry PreparationTwo 10 L buckets of fresh cow dung were added and stirredinto 40 L of well water to make slurry. 100 L of slurry wasprepared this way and introduced to the digester, leavingsome space for gas to collect. The system was then left to‘run’.Microbial analysisThree 10 ml samples of the slurry were collected asepticallyusing a sterile stainless steel spatula into sterile test tubes.The test tubes were well sealed with cotton wool andtransported to the laboratory for microbial analyses.Using the standard technique reported by Harrigan andMcCance (1976), one milliliter of the cow dung slurry wasaseptically transferred into 9 mls sterile distilled water togive a one in ten dilution (1:in 10 dilution).  The diluent wasthen serially diluted using 9 ml of sterile distilled water upto 106 dilution.  Using a sterile pipette, 1 ml each of 10-1, 10-3 and 10-5 dilutions were carefully and aseptically inocu-lated in triplicates by the pour plate techniques (i.e. 1mlmixed onto molten agar) onto Salmonella shigella Nutri-ent, MacConkey, Eosine Methylene Blue agars for bacterialisolation, and on potato dextrose, Sabaraud dextrose andmalt extract agars for fungi isolation.  All the plates wereincubated at 37 oc for 24 hours for bacteria and at 35oc forfour days for fungi.The described procedure was followed in performing themicrobial analyses for the fresh well water sample, wellwater sample that had been left on the shelf for four weeks,and the treated slurry after four weeks of digestion atmesophilic temperatures and gas collection had begun.MicroscopyThree smears of each sample were made on clean, grease-free slides and examined under the microscope using X100and X400 magnifications and the findings were recordedfor both slurry and water samples.Plate readingFollowing incubation at 24 and 96 hours for bacteria andfungi respectively, the plates were read off.  The culturalcharacteristics such as shape of colonies, colours etc. wereobserved macroscopically and recorded.  Then discretebacterial colonies from each plate were gram stained andobserved microscopically at 1500 magnification accordingto Cheesbrough (1984).  Equally discrete fungal colonieswere picked using a sterile inoculating needle and smearedin Lactophenol Cotton Blue and examined microscopicallyusing X400 magnification.  The cell morphologies as wellas unique differential features were recorded.  The charac-teristics features collated were compared with taxonomicalkeys specified in Bergey’s manual of Determinative Bacte-riology (Buchanan and Gibbons, 1980) to give identify tothe bacterial isolates and for fungi identity, characteristickeys described in Barnett and Hunter (1972) were used.Results and discussionThe Microscopy analysis results (Table) revealed the pres-ence of a few ova of helminthes in the raw slurry. In thetreated slurry, these ova are not only absent but theHelminthes larvae that are present are dead. Cattle playhost to a number of parasitic diseases that also affect man.Nwaedozi (2001) reported that Trichiuris trichiura andAscaris lumbricoides amongst others are some of theintestinal parasites of solid wastes from slums and low-income neighbourhoods in Nigeria.  Animals are usuallyintermediate hosts to a number of disease-causing agents inman, e.g. Taeniasis (Tapeworm disease) caused by Taeniasaginata primarily infects pigs while Fasciola hepatica hascow as an intermediate host.  Apart from being zoonotic,these infective worms also lead to low production in animalhusbandry.  The absence of the ova in the digested slurrysuggests that the digestion of manure in the describedpolyethylene bag is an effective way of breaking the cycle ofinfection in animals and the re-infection of man through hisactivities in agriculture.Table 1. Microscopy analysis Fresh well water Well water (After 4 weeks on the shelf at 35oC) Raw slurry Treated slurry (after 4 weeks of digestion) Yeast cells ? ? ? ? Motile bacteria ND ? ? ? Ova of Helminth ND ND ? ND Dead larvae of Helminth ND ND ND ? Free-living protozoa (Euglena, Amoeba, Paracium, Spirogyra) ND ND ND ? Key: ND – Not detected; “ - presentYONGABI, HARRIS, SAMBO and AGHO76The presence of the actively motile, free-living organismsin the treated slurry (and not in the raw slurry) is aninteresting observation, and their path/role in anaerobicdigestion may need further study. These organisms – Eu-glena, Paramecium, Amoeba, and Spirogyra – are unicellu-lar, non-parasitic organisms that are sometimes classifiedin the kingdom, Protista.  It is likely that these organismsmay be present in their dormant stage in grass fibres that arethe usual components of cattle manure. With digestionthough, the manure is broken down and a number ofnutrients are released to provide hatching conditions forthe organisms from dormancy to vegetation. The signifi-cance of the presence of these organisms in the treatedslurry is that the cow must have fed on grass containingviable cells of Euglena, Paramecium, Amoeba, andSpirogyra.Similarly, the microscopic examination of the well waterthat was used in making the slurry before feeding onto thedigester revealed the presence of yeasts, and the same is truefor the raw and treated slurries (please see Table).The pH of the raw and treated slurries was 7.0.  Jones(1980) reported that the operational parameters of anaero-bic digesters such as temperature, total solids, hydraulicretention time, volatile fatty acid concentrations and pHare important in determining the rate of gas production,and hence digestion.  The well water, which was used inmaking the slurry, was kept on the laboratory bench forfour weeks (for as long as biodigestion took place). Afollow up microscopy analysis of the well water, four weeksafter storage on laboratory shelf at 35oC, revealed thepresence of motile bacteria in addition to yeast cells.The Figure below gives a profile of the two slurries andwell water in terms of the number of counts of Aerobicmesophilic bacteria, Yeast, Escherichia coli, and Coliform.It is obvious from the Figure that digestion eliminates E.coli and significantly decimates Coliform and other Aero-bic mesophilic bacteria. Faecal pathogens have tradition-ally being tied to a number of ailments. E. coli and Coliformare particularly known to be indicators of diarrhoea-causing agents. With digestion, manure is made safer forapplication to the fields, as feeds in fish production, and asfeed supplement for animals.This observation tallies with the reports of Dahiya andVasudevan (1986) and Gadre et al (1986) who observedthat anaerobic digestion is a good option in the treatmentof waste.  Similarly, Kunte et al (1998) reported that animalwastes show the presence of pathogenic bacteria such asSalmonella spp, Escherichia coli, Campylobacter spp, andListeria monocytogenes etc and that they can survive for aconsiderable length of time in raw slurry.The elimination of E. coli, ova of helminthes and thedrastic decline in the number of Coliform count and otherbacteria in the anaerobic digester may be traceable to anyof the following factors; pH and accumulation of volatilefatty acids, anoxic conditions, temperature or a combina-tion of all of these factors.  In an independent study,Tappouni in 1984 reported that maximum biogas produc-tion during semi-continuous digestion correspond to arapid decline in the numbers of bactericidal effect of longchain fatty acids accumulated within the digester.Besides, it is suggested that other metabolites producedby anaerobic bacteria may have had antimicrobial activi-ties, thus leading to the reduction and elimination of thepathogens observed in this study.  Furthermore, the possi-bility of the unicellular protozoa feeding on the bacteriaand yeast cannot be dismissed.The yeast count was drastically less in the treated slurry.Similarly, fungi - Aspergillus niger and Rhizopus sp -isolated from the raw slurry were absent in the treatedslurry.  Aspergillus niger and Rhizopus sp are commonubiquitous fungi that cause decay of fruits and vegetables.In immuno-compromised patients, Aspergillus sp can causebronchopneumonia.  Their absence in the digested slurryattests to the fact that the treated slurry is safer for use asbiofertilizer than in the raw state.Incidentally, Aspergillus fumigatus and other Aspergilliwere isolated from the treated slurry.  These may becontaminants at the digester exit where the digested slurryis drained out.  Aspergillus spp are usually airborne.ConclusionThe polyethylene digester described in this study is cheap,low tech., and produces both biogas and disinfected slurrythat may be used as fertilizer for the fields or feeds forfishery production. The digester is easily constructed withlittle more than a sealing ability to mend leakages. Inaddition to the minimal maintenance skills required, thevisual access of the digester when the polyethylene bag istransparent makes this technology aptly suited for our ruralcommunities in disinfecting and managing solid waste inthe agricultural sector. With visual access, the progress ofdigestion is readily followed through colour changes in thedigester rather than solely through the familiar gas produc-tion rate. The average cost for a 95-liter polyethylenedigester is 45 USD, and all the materials are available inurban and rural markets across the country. Having theFigure 3. Microbial analysis in colony forming units permililitre (Cfu/ml)1240287010015000300030003000300030001000 1000 2000 3000 4000WellWaterRawSlurryTreatedSlurry Aerobic MesophilicYeastE. ColiColiformTNTC (Too Numerous to Count) arbitrarily approximated to 3,000Cfu/ml for convenience.YONGABI, HARRIS, SAMBO and AGHO77digester on a raised, mud platform with walls on the twolong sides may further reduce this cost.The introduction and practice of this technology in therural areas across the country would help to improvehygiene in the handling and processing of manure, and leadto the reduction in contamination of soils, water, andcrops. One other consequence of this is the improvement inpublic health arising from the safe management of manureand the application of the mineralized and ‘sterilized’product in increasing crop yields.AcknowledgementsThe authors gratefully acknowledge funding from theAbubakar Tafawa Balewa University and the CrawfordFund.  We also would like to thank C.D. Uzochukwu, D.J.Ubek, M. Audu, and S. Amana for their assistance with thiswork.ReferencesBarnett, H.L., and Hunter, B.B. (1972).  Illustrated generaof imperfect fungi, 3rd edition. Burgress Publishing Com-pany, Minneapolis, 241pp.Buchanan, R.E. and Gibbons, N.E. (1974).  Bergey’s Manualof DeterminativeBacteriology, Williams and Willims, Baltimore, USA.Cheesbrough, M. (1984).  Medical Laboratory Manual forTropical Countries,Butterworths, pp 78-79.Dahiya, A.K. and Vasudevan, P. (1986).  Biogas PlantSlurry as an Alternative to Chemical Fertilizers Biomass9, 67-74.Food and Aricultural Organization of the United Nations,Rome.Gadre, R.U., Ranade, D.R. and Godbole, S.H. (1986).  Anote on Survival of Salmonellas during anaerobic diges-tion of cattle dung.  Journal of Applied Bacteriology 60,93-96.Harrigan, W.F. and McCance, M.F. (1976).  Lab. methodin food and diary microbiology. Academic Press, Lon-don, 228pp.Itodo, I.N., Locas, E.B. and Kucha, E.I. (2001).  Interna-tional Journal of Engineering for International Develop-ment Vol. 3 No. 1 pp 15-21.Jones, P.W. (1980).  Health hazards associated with han-dling of animal wastes.  The Veterinary Record, 106, 4-7.Jones, P.W. and Mathews, P.R. (1975).  Examination ofSlurry for Cattle for Pathogenic Bacteria.  Journal ofHygiene, Cambridge 74, 57-64.Kaufman, R.K., Slater and Wellinger, A. (1982).  LowTemperature Methane generation from Animal Manure,In: Energy Conservation and use of renewable Energiesin the bioindustries, F. Vogt (ed.) Pergamon Press, pp371-382.Kunte, D.P., Yeole, T.Y., Chiplonkar, S.A., and Kanade,D.R. (1998) Inacivation of Salmonella typhi by highlevels of volatile fatty acids during anaerobic digestion.Journal of Applied Microbiology, 84, 138-142.Nwaedozie, J.M. (2001).  Reuse and Recycling of Waste(Case Study of Private Premises, Agricultural Lands andVegetable Oil Processing Industry) Nigerian Journal ofIndustrial Pollution Vol. 1 pp 82-90.Robinson, D.A. (1982).  Campylobacter infection in milk-ing herds.  In Campylobacter: Epidemiology, Pathogenesis,Biochemistry ed. Newell, D.G. P.274 Lancaster: MTPPress.Stout, B.A. (1983).  Biomass Energy Profiles, AgriculturalScience Bulletin, No. 54.Tappouni, Y.A. (1984).  The fate of Salmonella in anaero-bic digestion.  Ph.D Thesis, University College, Cardiff,UK.Theresa, E. Kearney, Larkin, M.J. and Levett, P.N. (1993).Effect of Slurry Storage and anaerobic digestion of patho-genic bacteria.  Journal of Applied Bacteriology, 74, 86-93.K A YONGABI, Vice Chancellor’s Office, FMEnv/ZERIResearch Centre, Abubakar Tafawa Balewa University,PMB 0248, Bauchi, Nigeria.M O AGHO, Vice Chancellor’s Office, FMEnv/ZERIResearch Centre, Abubakar Tafawa Balewa University,PMB 0248, Bauchi, Nigeria.P L HARRIS, Earth and Environmental Sciences, TheUniversity of Adelaide, Roseworthy Campus, Australia,5371.A S SAMBO.

Managing cow dung with a low tech, cheap plastic digester

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Managing cow dung with a low tech, cheap plastic digester

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