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Int. J. Engg. Res. & Sci. & Tech. 2015 Patrick Mukumba and Golden Makaka, 2015

BIOGAS PRODUCTION FROM A FIELD BATCHBIOGAS DIGESTER USING COW DUNG AS A

SUBSTRATEPatrick Mukumba1* and Golden Makaka1

Biogas can be a solution to South Africa energy needs especially to rural areas of Eastern CapeProvince that have plenty of biogas substrates from cattle, donkeys, goats, sheep and chicken.The effectiveness of cow dung for biogas production was investigated using a field batch biogasdigester. The cow dung was collected from University of Fort Hare Dairy farm and was analyzedfor total solids, volatile solids, total alkalinity, calorific value, total alkalinity, pH, Chemical OxygenDemand and Ammonium Nitrogen. The biogas composition was analysed using a Gas Analyzer.In the experiment, it was observed that the biogas production from the cow dung increasedexponentially with time and ceased after certain days of degradation. The alkalinity values werewithin the normal range, above the threshold alkalinity of 500 mg/L for anaerobic digestion andstable ammonium-nitrogen levels in cow dung improved anaerobic digestion process. The studyrevealed that cow dung produced biogas yield with an average methane yield of 50%. In addition,the study revealed further that cow dung as an animal waste has great potentials for generationof biogas and its use should be encouraged due to its early retention time and high volume ofbiogas yields.

Keywords: Anaerobic digestion, Digester, Cow dung, Biogas, Methane yield

*Corresponding Author: Patrick Mukumba [email protected]

1 University of Fort Hare, Physics Department, Private Bag X1314, Alice 5700, South Africa.

Int. J. Engg. Res. & Sci. & Tech. 2015

ISSN 2319-5991 www.ijerst.comVol. 4, No. 2, May 2015

© 2015 IJERST. All Rights Reserved

Research Paper

INTRODUCTIONSouth Africa has a warm climate and in mostlocations ambient temperature is sufficient tomaintain the biogas fermentation process and noartificial heating is required in biogas digestersand the biogas installations are generally basedon psychrophilic and mesophilic anaerobicdigestion process. The Anaerobic Digestion (AD)of organic raw materials converts organic matter

into biogas and digestate (Tani et al., 2006; Zhanget al., 2007). Biogas generally consists of amixture of methane, carbon dioxide, nitrogen,oxygen, hydrogen sulphide and traces of othergases (Ward et al., 2008).

The following are some of the factors affectingthe biogas fermentation process of organicsubstances under anaerobic conditions; thequantity and nature of organic matter, the

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temperature, acidity and alkalinity of substrate andthe flow and dilution of material.

The use of biogas from biomass for energyproduction is considered to be one of the mostpromising alternative, sustainable and renewableenergy sources (Cherubini and Strømman, 2011).The anaerobic digestion process consists of aseries of metabolic reactions that includehydrolysis, acidogenesis, acetogenesis andmethanogenesis performed by a wide range ofmicroorganisms and producing a biogascontaining mainly methane and a digestedsubstratum (digestate), that can be used asorganic fertiliser or raw material for biofertilisers(Themelis and Ulloa, 2007). Unlike fossil fuels,biogas from AD is permanently renewable, as itis produced from biomass, which is a living formof storage of solar energy through photosynthesis(Al Seadi et al., 2008).

Biogas has proved to be one of the reliablesources of energy because it is cheap andreduces greenhouse gas emissions. In addition,it reduces the smell of manure by turning itsvolatile organic compounds into odourlessmethane and carbon dioxide. Biogas is one ofthe most untapped sources of natural andsustainable energy available. Although biogas isused all over the world, however this technologyin South Africa is still premature.

Biogas technology has the followingadvantages (Brown, 1987, Silayo, 1992 andLekule, 1996); It provides an alternative sourceof energy thus reducing the rate of deforestation,relatively cheap source of energy, improves crop-livestock-tree system through nutrient cycling,reduces time and workload of collecting fuelwood, reduces kitchen smoke-pollution therebypromoting human health, promotes good health

through safe treatment of manures, as arenewable source of energy, it provides a reliablepower supply that is environmentally friendly andis a rich source of nitrogen, phosphorus (P),potassium (K) and other macro- andmicronutrients.

The biogas digesters available in South Africaare of three main types namely; Balloon (tube)digester, Floating drum digester and Fixed domedigester. In this research a cylindrical biogasdigester was designed, constructed and fed withcow dung and monitored to see its performancecharacteristics.

MATERIALS AND METHODSSource of SubstrateFresh cow dung was collected from University ofFort Hare Dairy farm. Prior to loading the cowdung into the batch biogas digester, stones,leaves, sticks, waste feed and other foreignsubstances were picked from the cow dungwaste. Furthermore, water was added to thesubstrates, Total Solids (TS) of for the preparedsample was determined to find out the amount ofwater to be added to the substrates before feedinginto the batch digester. The most favourable TSvalue desired for better biogas production is 8%(Ituen et al., 2007).

Figure 1 shows the designed and constructed

Figure 1: Designed andConstructed Batch Biogas Digester


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biogas digester that was fed with fresh dung afterit was insulated with sawdust. In addition, Figure2 shows the plastered second wall of the batchbiogas digester that was constructed to keepsawdust, an insulating material for the batchbiogas digester.

the analytical determinations were performedaccording to the standard methods forexamination of water and waste water (ALPHA,2005). The temperature of slurry was measuredby type-K thermocouple, while the digital pH metermeasured the influent and effluent pH.

Biogas AnalysisThe biogas composition was analysed by thebiogas analyser. The biogas analyser consistedof Non-Dispersive Infrared sensor for sensingmethane and carbon dioxide and Palladium/Nickelsensor for sensing hydrogen and hydrogensulphide. Figure 3 shows the biogas dataacquisition system that includes a biogasanalyser.

RESULTS AND DISCUSSIONThe daily biogas yield of cow dung when thedigester was insulated is shown in Figure 4. Itwas observed that the biogas production fromthe cow dung increased exponentially with timeand ceased after a retention time of 31 days.

Figure 2: Designed AndConstructed Batch Biogas Digester

Substrate ParametersThe following parameters for the substrates weredetermined, pH, Total Solids (TS), Volatile Solids(VS), ammonia-nitrogen (NH4-N), Total Alkalinity(TA), temperature (T) and Caloric Value (CV). All

Figure 3: Data Acquisition System ThatIncludes A Biogas Analyser

Figure 4: Biogas yield for cow dung

The experiment was carried out under a biogastemperature range of 29 to 32°C and for aretention period of 31 days. From Figure 4 it wasobserved that the biogas production started toincrease from day 11 and kept increasing untilreaching the peak value of 0.5 m3 on day 19 andthen declined to 0.03 m3 on day 25. The results


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obtained were indicative of strong microbialactivities in the biogas digester. From day 11 today 18 the gas yield (Y) is approximated by theequation:

18t11for 0.462-0.052t Y ...(1)

While from day 19 to day 23, the gas yield isapproximated by:

23t19for 3.121-0.165tY ...(2)

The rapid biogas production between day 11and 19 was attributed to readily biodegradableorganic matter in the substrate and the presenceof high content of the methanogens. The totalvolume of biogas produced was 2.55 m3. The totalbiogas yield of 70% (1.71 m3) was attained in thefirst 19 days before the biogas yield declined.However, the biogas yield from day 19 to day 31was 30% (0.54 m3) of the total biogas production.It was observed that after day 23 of the experimentthe biogas digester produced less than 0.03 m3

biogas. Figure 5 shows that pH range decreasedwith time attaining a minimum value of 7.1, onday 16 as cow dung was converted to fatty acids.

0.48 m3 was achieved at pH 7.1 as shown inFigure 5. The best f it for the pH (R) isapproximated by the equation:

8.8047t2182.00.007tR 2 ...(3)

Figure 6 shows a COD graph for the cow dung.The initial COD entering the digester was 38456mg/L and decreased gradually to final value of27543 mg/L. This gives a total COD destructionof 10913 mg/L.

Figure 5: Relationship betweengas yield and pH range for cow dung

As from day 16 the pH started to increasegradually as the fatty acids were consumed bythe methanogens. The optimum biogas yield of

The optimum biogas of 0.48 m3 (Figure 5) wasproduced at a COD of 30987 mg/L. Themaximum biogas production was produced fromday 14 to day 17 because COD removal efficiencywas highest. The COD (S) best fit can beapproximated by the equation:

37213t51.7462t11.11132.6026tS ...(4)

Table 1 shows the biogas yield for cow dungafter the digester was insulated. The biogasproduced had methane content of 50% at anaverage temperature of 31°C.

From Table 1 it was observed that the biogasfrom cow dung had an average yield of 50%. Thissuggests that the performance of the digesterimproved by using sawdust as an insulatingmaterial for the biogas digester. Figure 7 showsthe relationship between biogas yield and NH4-N

Figure 6: Relationship between gasyield and COD range for cow dung

COD/

mg/

L


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for cow dung. The NH4-N concentrations for cowdung are ranged from 920 mg/L to 1090 mg/L.The highest biogas yield of 0.48 m3 was producedat NH4 – N concentrations of 925 mg/L. Theinhibiting concentrations of NH4 - N are reportedto be above 1500 mg/L (Calli et al., 2005, Chen etal., 2008, Fricke et al., 2007). Therefore, stableNH4 – N levels in cow dung improved anaerobicdigestion process.

CONCLUSIONThese results on the production of biogas fromcow dung showed cow dung is a suitablesubstrate for biogas. In addition, the study revealedfurther that cow dung as an animal waste hasgreat potentials for generation of biogas and itsuse should be encouraged due to its earlyretention time and high volume of biogas yields.In the experiment, it was observed that the biogasproduction from the cow dung increasedexponentially with time and ceased after certaindays of degradation. Results indicated thataverage biogas yield for the cattle manure is 50%methane. Furthermore, the study has found thattotal alkalinity, ammonium-nitrogen, temperaturevariation, total solids concentration, chemicaloxygen demand, pH and agitation are the factorsthat affect quality and quantity of methane.

REFERENCES1. Al Seadi T, Rutz D, Prassl H, Köttner M,

Finsterwalder T, Volk S and Janssen R(2008), Biogas Handbook, Published byUniversity of Southern Denmark Esbjerg,Niels Bohrs Vej, DK-6700 Esbjerg,Denmark,pp. 9-10.

2. American Public Health Association (APHA),Standard methods for Examination of Water

Table 1: Biogas Composition For Cow DungAfter Biogas Digester Insulation

Gases Composition (%)

Methane (CH4) 50

Carbon dioxide (CO2) 40

Carbon monoxide (CO) 0

Hydrogen (H2) and other gases 10

Figure 7: Relationship Between BiogasYield and NH4-N for Cow Dung

The relationship between biogas productionand total alkalinity (TA) of cow dung is shown inFigure 8. The effluent total alkalinity for cow dungwas between 6235 mg/L- 6343 mg/L as shownin Figure 8. The highest biogas yield of 0.48 m3

was produced at TA level of 6325 mg/L. Therefore,alkalinity values were within the normal range,above the threshold alkalinity of 500 mg/L assuggested for anaerobic digestion (Fannin, 1987).

Figure 8: Relationship Between Biogas Yieldand Total Alkalinity for Cow Dung


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and Waste Water, Washington DC: WEF,2005.

3. Brown N (19897), Biogas systems indevelopment. Appropriate Technology, Vol.4, No. 3, pp. 5-7.

4. Calli B, Mertoglu B, Inac B and Yenigun O(2005), “Effects of free ammoniaconcentrations on the performance ofanaerobic bioreactors”, ProcessBiochemistry, Vol. 40, pp. 1285-1292.

5. Chen Y, Cheng J J, Creamer J S (2008),“Inhibition of anaerobic digestion process: Areview”, Bioresource Technology, Vol. 99,pp. 4044-4064.

6. Cherubini F and Strømman A H (2011), “Lifecycle assessmentof bioenergy systems:State of the art and future challenges”,Bioresource Technology, Vol. 102, pp. 437-451.

7. Fanni K F and Mah R (1987), Anaerobicdigestion of biomass, New York: ElsevierPublishing Co.

8. Fricke K, Santen H, Wallman R, Hütter A,and Dichtl N (2007), “Operating prob., 2007.

9. Ituen E E, John N M, and Bassey B E (2007),“Biogas production from organic waste inAkwa Ibom State of Nigeria”, AppropriateTechnologies for Environmental Protection

in the Developing World, Vol. 207, pp. 17-19.

10. Lekule F P and Sarwatt S V (1996), “Use ofbiogas as an alternative source of domesticenergy to reduce deforestation”, Paperpresented at the SPW/ EnvironmentalCourse.

11. Silayo V C (1992), Small biogas plants.Design, management and use. Agrotec,publications.

12. Tani M, Sakamoto N, Kishimoto T, andUmetsu K (2006), “Util izat ion ofanaerobically digested slurry combined withother waste following application toagricultural land”, In: International CongressSeries, Vol. 1293, pp. 331-334.

13. Themelis N J and Ulloa P A, “Methanegeneration in landfills”, Renewable Energy,Vol. 32, pp. 1243-1257.

14. Ward A J, Hobbs P J, Holliman and JonesD L (2007), “Optimisation of the anaerobicdigestion of agricultural resources”,Bioresource Technology, Vol. 99, pp. 7928-7940.

15. Zhang R, El-Mashad H M, Hartman K,Wang F, Liu G, Choate C and Gamble P,Characterization of food waste as feedstockfor anaerobic digestion.


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Int. J. Engg. Res. & Sci. & Tech. 2015 Patrick Mukumba and ...Int. J. Engg. Res. & Sci. & Tech. 2015 Patrick Mukumba and Golden Makaka, 2015 temperature, acidity and alkalinity of