Anaerobic Mono-Digestion of Turkey Manure: Efficient Revaluation to Obtain Methane and Soil Conditioner

Rolando Chamy, Elba Vivanco, Carlos Ramos

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DOI: 10.4236/jwarp.2011.38067                

Abstract

This work demonstrates the possibility to make a full valuation of a solid waste such as turkey manure, to obtain methane and a soil conditioner/fertilizer from turkey manure anaerobic digestion in a mesophilic pilot-scale continuous stirred tank reactor at different organic loading rates (OLR) (from 0.5 to 2.5 kgVS/m³d). The application of the anaerobic mono-digestion for the turkey manure treatment was an efficient alternative, because high volatile solids removal and methane were obtained in addition to obtaining a stabilized solid waste that can be applied as soil conditioner, based on its nutritional parameters and humic substances content. In this way, the turkey manure anaerobic digestion can be applied avoiding the co-digestion of the manure with other wastes and allows a process devoid of pollutant emissions, obtaining two products. The reactor operation depends on the OLR, and its operation does not allow an OLR above 1.5 kgVS/m³d. Higher OLR produced a decrease in the TS and VS removals and methane productivity.

Keywords

Methane, Biomethanization, Solid Wastes, Turkey Manure, Soil Conditioner, Fertilizer

1. Introduction

The anaerobic digestion is a biological process, involving different kinds of microorganisms, which is accomplished by four sequential steps (hydrolysis, acidogenesis, acetogenesis and methanogenesis). In this manner, organic matter is transformed into biogas, mainly made up by methane, 60% - 70% of the biogas. Due to environmental, energy, economic and legal considerations, the anaerobic digestion for solid waste treatment is a process that, in most of the cases, is the best way to transform the organic matter into value-added products, like methane and a stabilized sludge with soil conditioner characteristics, avoiding the disposal of the solid waste in a dump or landfill, incineration and composting [1,2]. However, the solid waste anaerobic digestion is a complex process, from a kinetic and process point of view, due to the high solid content, low moisture and waste composition, which makes the hydrolytic phase to be the limiting step. For the solid wastes biomethanization, the continuous stirred tank reactor (CSTR) is the main industrial-scale reactor type used, due to the simplicity of the process, the reactor operation and the lower investment cost [3]. An important operation parameter is the organic loading rate (OLR), because it affects the hydraulic retention time (HRT). Maintaining the reaction volume, an increase on the OLR, produces a decrease in HTR, so the reaction time must be proper to convert the waste to methane.

The possibility to generate a process without pollutant emissions and obtaining value added products are part of the current focus of environmental biotechnology. In this sense, anaerobic digestion achieves these objectives, due to the possibility to convert waste (low-cost raw material) into biofuels (hydrogen and/or methane) and an effluent (stabilized waste) can be used as fertilizer or soil conditioner. Therefore, the waste is completely up-valued in its energy and fertilizer potentials, which today in Chile is not totally exploited.

Until now, the literature reports the application of anaerobic digestion only to obtain methane and doesn’t show how the operational parameters of the reactor affect the production of biogas and a soil conditioner/fertilizer. Also, according to the literature, the anaerobic manure monodigestion cannot be achieved, the co-digestion of manure with other wastes being the only viable process.

This work demonstrates the possibility to completely up-valuate the raw turkey manure, without its co-digestion, to obtain methane and a soil conditioner/fertilizer from the turkey manure anaerobic mono-digestion in a pilot-scale continuous stirred tank reactor, evaluating the operation of the CSTR at different organic loading rates.

2. Materials and Methods

2.1. Inoculum

Anaerobic sludge from an industrial-scale CSTR for the treatment of sludge from a sewage wastewater plant (activated sludge system) was used as inoculum. The main characteristics of the inoculum are show in Table 1, which was characterized by low concentration of ammonium and acetic acid. The methanogenic activity of the sludge was 0.14 [gCOD_CH4/gVSSd].

2.2. Waste Characteristics

The waste used was raw turkey manure, provided by a turkey breeding, and composed, mainly, by manure, chips and feathers. Chips were part of the layer on which the turkeys are confined. The manure was collected, approximately once a month; and it was stored in a refrigeration chamber (4˚C) to avoid changes on its initial composition. Table 2 shows manure composition, which has high solid concentration (51.2% (w/w)), of which 71.5% was organic matter, expressed as volatile solids. Also, high ammonium concentration was found. The chemical oxygen demand (COD) was 1.1 gO₂/gTS.

2.3. Reactor

The study was made in a pilot-scale CSTR with 2.0 m³ of total volume (1.6 m³ active volume). The experimental pilot scale set-up consisted on a fiberglass reactor (6.0 mm thickness) and a circular steel lid (8.0 mm thickness). The heating was automatically fixed at 37˚C. The mixing was maintained at 85 rpm through a gear motor (1 HP power) and the system consisted on a stainless steel central axis with 4 inclined blades (45˚) and 4 fiberglass baffles. The digester is located in Quillota (V region,

Table 1. Inoculum characteristics.

Table 2. Turkey manure characteristics.

Chile), at the School of Agronomy of Pontificia Universidad Católica de Valparaíso. Figure 1 shows the reactor scheme.

2.4. Experimental Procedure

The reactor was inoculated with anaerobic sludge, filling the digester up to the reaction volume (1.6 m³). Then, the reactor was airtight closed and the mixing was started. Later, nitrogen gas was injected to remove the oxygen inside the reactor. Once the reactor was loaded with sludge, the heating system was activated (programmed to 37˚C). The reactor feeding was semi-continuous, i.e., fresh waste was added once per day to the reactor. Five organic loading rates were analysed (see Table 3). An increase in the OLR produced a decrease in the HRT. During the reactor operation, total solids (TS), volatile solids (VS), ammonium () concentrations, and biogas production and composition were determined periodically. At different OLR, the generated effluent (solid fraction, obtained by solar drying, and liquid fraction, obtained by filtration) was evaluated as fertilizer and soil conditioner, by means of determination of macro and micronutrients and humic content. The length of each organic loading rate depended on the stability of the reactor behaviour.

2.5. Analytical Methodology

The TS and VS concentrations were measured according to Standard Methods [4] and the NH₄⁺ concentration was quantified by the utilization of a selective electrode

Figure 1. Overall scheme of the pilot-scale reactor, indicating the valve arrangement and the mixer system, heating and sampling.

Table 3. Average values of the operational parameters during each OLR studied for the pilot-scale CSTR operation in the anaerobic treatment of turkey manure.

(Cole-Parmer, model: 27502-03). The methane and carbon dioxide content were analysed with gas chromatography: PerkinElmer chromatograph (Clarus 500 model, packed column, thermal conductivity detector). The methane and biogas volume were expressed in standard pressure and temperature conditions (1 atm and 0˚C). Macro and micronutrients were determined according to [5] and the humic and fulvic content was analyzed through [6]. The methanogenic activity was measurement according to [7].

3. Results and Discussion

3.1. Solids Removal

Figure 2 shows the CSTR behaviour at the different OLR studied, with respect to the total and volatile solids removal. Table 3 presents the data obtained. An increase in the organic loading rate produced a gradual decrease in the TS and VS removals, which had the same trends. During the start-up (OLR of 0.5 kgVS/m³d), first fluctuation occurred and later stabilization occurred. For the second OLR (1.0 kgVS/m³d), the TS and VS removals maintained relatively constant, with an average removal of over 80% for TS and 90% for VS. When the CSTR was operated from an organic loading rate of 1.5 up to 2.5 kgVS/m³d, the total and volatile solids removals decreased gradually with an increase in the OLR. The minimal VS removal was 66% (for the OLR of 2.5 kgVS/m³d), which was higher than reported for manure in pilot and industrial-scale CSTR (50% - 58% of VS removal) [8-10]. The process could be negatively affected in terms of the low hydraulic retention time, which could not allow the proper metabolism/degradation of the recalcitrant substances, thus avoiding to obtain higher removal. Another fact could be the solids and ammonium concentrations inside the reactor. During the organic loading rates of 0.5 and 1.0 kgVS/m³d, the TS and NH₄⁺ maintained under 40.0 and 4.0 g/L for total solid and ammonium,

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	[1] I. Angelidaki, L. Ellegaard and B. Ahring, “Applications of the Anaerobic Digestion Process,” In: T. Scheper, Ed., Advances in Biochemical Engineering/Biotechnology 82, Springer-Verlag, Berlin Heidelberg, 2003, pp. 1-33.
[2]	W. Edelmann, “Products, Impacts and Economy of An- aerobic Digestion of OFMSW,” In: J. Mata-Alvarez, Ed., Biomethanization of the Organic Fraction Of Municipal Solid Wastes, IWA Publishing, London, 2003, pp. 265-301.
[3]	P. Vandevivere, L. De Baere and W. Verstraete, “Types of Anaerobic Digester for Solid Waste,” In: J. Mata-Al- varez, Ed., Biomethanization of the Organic Fraction Of Municipal Solid Wastes, IWA Publishing, London, pp. 111-140.
[4]	A. P. H. A., “Standard Methods for the Examination of Water and Wastewaters,” 20th Edition, American Public Health Association, Washington D.C., 1998.
[5]	A. Sadzawka, M. A. Carrasco, R. Grez, M. L. Mora, H. Flores and A. Neaman, “Recommended Analytical Meth- ods for the Chilean Soils,” Standards and Accreditation Committee, Chilean Society of Soil Science, Santiago (in Spanish), 2006.
[6]	D. S. Orlov and L. A. Grishina, “Practical Manual of Humus Chemistry,“ Moscow University Press, Moscow (in Russian), 1981.
[7]	J. Field, R. Sierra álvarez and G. Lettinga, “Ensayos Anaerobios”, Actas del 4 Seminario D. A. A. R.: De- puración Anaerobia de Aguas Residuales, Valladolid, 1988, pp. 52-81.
[8]	T. Espinosa-Solares, J. Bombardiere, M. Chatfield, M. Domaschko, M. Easter, D. A. Stafford, S. Castillo-An- geles and N. Castellanos-Hernandez, “Macroscopic Mass and Energy Balance of a Pilot Plant Anaerobic Bioreactor Operated under Thermophilic Conditions,” Applied Bio- chemistry and Biotechnology, Vol. 132, No. 1-3, 2006, pp. 959-968. doi:10.1385/ABAB:132:1:959
[9]	P. Kaparaju, I. Buendia, L. Ellegaard and I. Angelidakia, “Effects of Mixing on Methane Production during Ther- mophilic Anaerobic Digestion of Manure: Lab-Scale and Pilot-Scale Studies,” Bioresource Technology, Vol. 99, No. 11, 2008, pp. 4919-4928. doi:10.1016/j.biortech.2007.09.015
[10]	L. M. Safley, R. L. Vetter and D. Smith, “Operating a Full-Scale Poultry Manure Anaerobic Digester,” Bio- logical Wastes, Vol. 19, No. 2, 1987, pp. 79-90. doi:10.1016/0269-7483(87)90102-9
[11]	I. Angelidaki, X. Chen, J. Cui, P. Kaparaju and L. Elle- gaard, “Thermophilic Anaerobic Digestion of Source- Sorted Organic Fraction of Household Municipal Solid Waste: Start-Up Procedure for Continuously Stirred Tank Reactor,” Water Research, Vol. 40, No. 14, 2006, pp. 2621-2628. doi:10.1016/j.watres.2006.05.015
[12]	R. Chamy, P. Poirrier, M. C. Schiappacasse, D. Alkalay and L. Guerrero, “Effect of Ammonia Content in the Biodegradability of the Salmon Industry Waste,” Bio- process Engineering, Vol. 19, No. 1, 1998, pp. 1-5.
[13]	R. Chamy, C. León, E. Vivanco, P. Poirrier and C. Ramos, “Anaerobic Monodigestion of Poultry Manure, Effective Alternative against Codigestion: Determination of Operation Parameters for CSTR,” Proceedings of the 12th World Congress on Anaerobic Digestion, Guadala- jara, Mexico, 2010.
[14]	I. Angelidaki and B. K. Ahring, “Anaerobic Thermophilic Digestion of Manure at Different Ammonia Loads: Ef- fects of Temperature,” Water Research, Vol. 28, No. 3, 1994, pp. 727-731. doi:10.1016/0043-1354(94)90153-8
[15]	I. Angelidaki and B. K. Ahring, “Thermophilic Anaerobic Digestion of Livestock Waste: The Effect of Ammonia,” Applied Biochemistry and Biotechnology, Vol. 38, 1993, pp. 560-564.
[16]	L. A. De Baere, M. Devocht, P. Van Assche and W. Ver- straete, “Influence of high NaCl and NH4Cl salt levels on methanogenic associations”, Water Research, Vol. 18, No. 5, 1984, pp. 543-548. doi:10.1016/0043-1354(84)90201-X
[17]	N. Krylova, R. E. Khabiboulline, R. P Naumava and M. A. Nagel, “The Influence of Ammonium and Methods for Removal during the Anaerobic Treatment of Poultry Manure,” Journal of Chemical Technology & Biote- chnology Vol. 70, No. 1, 1997, pp. 99-105.
[18]	T. Liu and S. Sung, “Ammonia Inhibition on Thermo- philic Aceticlastic Methanogens,” Water Science and Technology, Vol. 45, No. 10, 2002, pp. 113-120.
[19]	F. Omil, R. Méndez and J. M. Lema, “Anaerobic Treat- ment of Saline Wastewaters under High Sulphide and Ammonia Content,” Bioresource Technology, Vol. 54, 1995, pp. 269-278. doi:10.1016/0960-8524(95)00143-3
[20]	S. Sung and T. Liu, “Ammonia Inhibition on Thermo- philic Anaerobic Digestion,” Chemosphere, Vol. 53, No. 1, 2003, pp. 43-52. doi:10.1016/S0045-6535(03)00434-X
[21]	A. F. M. van Velsen, “Adaptation of Methanogenic Sludge to High Ammonia-Nitrogen Concentrations,” Water Research, Vol. 13, 1979, pp. 995-999. doi:10.1016/0043-1354(79)90194-5
[22]	G. N. Demirer and S. Chen, “Two-Phase Anaerobic Di- gestion of Unscreened Dairy Manure,” Process Biochem- istry, Vol. 40, No. 11, 2005, pp. 3542-3549. doi:10.1016/j.procbio.2005.03.062
[23]	J. Gelegenis, D. Georgakakis, I. Angelidaki, N. Chris- topoulou and M. Goumenaki, “Optimization of Biogas Production from Olive.Oil Mill Wastewater, by Codi- gesting with Diluted Poultry-Manure,” Applied Energy, Vol. 84, No. 6, 2007, pp. 646-663. doi:10.1016/j.apenergy.2006.12.001
[24]	K. Karim, R. Hoffmann, K. T. Klasson and M. H. Al-Dahhan, “Anaerobic Digestion of Animal Waste: Ef- fect of Mode of Mixing,” Water Research, Vol. 39, No. 15, 2005, pp. 3597-3606. doi:10.1016/j.watres.2005.06.019
[25]	K. Karim, R. Hoffmann, T. Klasson and M. H. Al-Dahhan, “Anaerobic Digestion of Animal Waste: Waste Strength versus Impact of Mixing,” Bioresource Technology, Vol. 96, No. 16, 2005, pp. 1771-1781. doi:10.1016/j.biortech.2005.01.020
[26]	A. Lehtom?ki, S. Huttunen and J. A. Rintala, “Laboratory Investigations on Co-Digestion of Energy Crops and Crop Residues with Cow Manure for Methane Production: Effect of Crop to Manure Ratio,” Resources, Conserva- tion and Recycling, Vol. 51, No. 3, 2007, pp. 591-609. doi:10.1016/j.resconrec.2006.11.004
[27]	Z. Pechan, O. Knappová, B. Petrovi?ová and O. Adamec, “Anaerobic Digestion of Poultry Manure at High Ammo- nium Nitrogen Concentrations,” Biological Wastes, Vol. 20, No. 2, 1987, pp. 117-131. doi:10.1016/0269-7483(87)90162-5