Microsoft Word - 5-Agra_13973.doc 570 Original Article Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 ANAEROBIC DIGESTION OF WASTEWATER FROM COFFEE AND CHEMICAL ANALYSIS OF BIOGAS PRODUCED USING GAS CHROMATOGRAPHY: QUANTIFICATION OF METHANE, AND POTENTIAL ENERGY GAS EXCHANGER DIGESTÃO ANAERÓBIA DA ÁGUA RESIDUÁRIA DO CAFÉ E ANÁLISE QUÍMICA DO BIOGÁS PRODUZIDO UTILIZANDO CROMATOGRAFIA GASOSA: QUANTIFIÇÃO DO METANO, POTENCIAL ENERGÉTICO E PERMUTABILIDADE GASOSA Claudio Milton Montenegro CAMPOS¹; Marco Antônio Calil PRADO²; Erlon Lopes PEREIRA³ 1. Programa de Pós graduação em Recursos Hídricos Aplicados em Sistemas Agrícolas, Universidade Federal de Lavras-UFLA, Lavras, MG. Brasil; 2. Programa de Pós graduação em Engenharia Agrícola, Universidade Federal de Lavras-UFLA, Lavras, MG. Brasil; 3. Engenheiro Agrícola. Mestre em Biotecnologia Industrial. Departamento de Biotecnologia. Escola de Engenharia de Lorena (EEL). Universidade de São Paulo - USP, EEL-USP, Lorena, São Paulo, Brasil. erlonlopes@gmail.com. ABSTRACT: Methane is the main constituent of biogas, being responsible for its calorific value. This work objective was to present the analysis of methane concentration in the biogas originated from anaerobic treatment system of wastewater of coffee wet processing (CWP) at laboratory scale, using coffee coconut. The methane concentration were performed by gas-solid chromatography (GSC) analyses. The system was composed of a column Restek RT-Q-PLOT, with the stage sets, the divinyl-benzene, nitrogen as mobile phase and a flame ionization detector (FID). The results of the concentration of methane in the biogas ranged from 48.60 to 68.14%. The upper and lower calorific values were 25,654 and 23,777 kJ.m-3, respectively. For interchangeability, obtained a Wobbe number of 7,851 kcal.m-3, resulting in their interchangeability with piped gas (city gas). KEYWORDS: Bioenergy. Methane. Anaerobiosis calorific power. Renewable energy. INTRODUCTION Analyses of the chemical composition of the biogas by gas chromatography has several advantages over other methods and has high resolving power and good speed of separation, and allows continuous monitoring of the effluent in the column, the exact quantitative measurement and repeatability and reproducibility analysis with automation of the analytical procedure and data processing (Prado and Campos, 2008; Campos et al., 2010). Columns Rt-Q-PLOT are suitable for analysis of hydrocarbons such as methane and solvents such as alcohols, and showed good stability up to 310oC, excellent permeability, providing low pressure variations, suitable for ambient temperatures and allowing rapid analysis with peaks well defined (PRADO et al., 2010). The calorific value of a fuel can be experimentally determined using a calorimeter, or may be estimated theoretically by means of stoichiometric calculations, using the Dulong hypothesis, based on the calorific values of the elementary components of a fuel. The substitutability of a combustible gas is defined when two gases are compared in terms of heat production, at the same pressure, or when they have the same Wobbe number. By knowledge of the interchangeability of gases, makes up the replacement of one fuel by another in a given case. Since the proportion of methane in the biogas obtained from the treatment of CWP, its variation occurs according to the levels of biodegradable organic matter present in this liquid effluent and the type of treatment systems used. Dinsdale et al. (1997), treating wastewater from soluble coffee using UASB bench, obtained biogas with an average percentage of methane of 62.3%. Campos et al. (2010), in laboratory tests with wastewater from anaerobic digestion of coffee wastewater, found 56% to 63% methane in biogas. Clarke and Macrae (1987) report that it is possible to produce 0.067 m3 biogas.kg-1 of coffee pulp, with approximate 70% of methane and 30% of carbon dioxide by anaerobic processes, with 90% efficiency in removal of organic matter. Bruno and Oliveira (2008) used an anaerobic system of two separate phases for biogas production from coffee pulp juice and found a methane percentage ranging from 69 to 89% in the reactor 1 and from 52 to 73% in the reactor 2. Received: 18/12/11 Accepted: 06/06/12 571 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 This study aimed at determining the concentration of methane in the biogas from the anaerobic treatment of wastewater from coffee wet process (CWP) using gas chromatography analysis. Biogas analysis was collected from a UASB reactor operated at mesophilic temperature. As already mentioned the quality of biogas varies depending on the physical-chemical characteristics of the effluent, and thus we evaluated the interference of these factors on the concentration of biogas. In this research were also performed theoretical calculations of the lower calorific value or net calorific value (NCV), and higher calorific value or Gross calorific value (GCV), also the interchangeability of biogas via the Wobbe number. MATERIAL AND METHODS Sampling of biogas The biogas used for the analysis was assembled from an experiment in the Laboratory of Water Analysis of Engineering Department (DEG) at the Federal University of Lavras (UFLA), where the liquid effluent originated from wet coffee process, underwent anaerobic treatment. The treatment system consisted of a acidification and equalization tank (AET), an upflow anaerobic sludge blanket (UASB), a facultative aerated pond (FAP), an equalization tank, a gas tank, two metering pumps and a heating system. The equalization tank had the function of maintaining the level of biogas in the UASB. The gas produced by the three-phase separator (TPS), passed through the equalization tank and was subsequently sent to the gas tank, which had the task of accumulating the biogas. Silicone hoses were used to conduct the biogas, since they are flexible and allow a good seal. The biogas sampling was withdrawn in the output of the three-phase separator of the UASB reactor, using collection device and an apparatus consisting of two points and a vacuum tube. The apparatus of two nozzles was mounted with a hypodermic needle and an intravenous catheter 40/12 16, glued to the ends in opposite directions, with which it is pierced with one end in the silicone hose and with the other end to the vacuum tube. The vacuum tube was used brand BD Vacuntainer®, siliconized glass, without additive, nominal volume of 10 mL. The collection of biogas was performed until the pressure inside the tube would stabilize the pressure in the reactor. The tube was weighed before and after collection, to certify the presence of biogas inside. Characterization of gas chromatography For the analysis of methane concentration in biogas was used gas-solid chromatography (GSC). Analyses were performed at the Central Analytical Chemistry and Exploration (CAPQ), Department of Chemistry (DC), Federal University of Lavras (UFLA). The flow chart of the system used can be seen in Figure 1. Figure 1. Flow chart of gas chromatography A gas chromatograph Varian Chrompack PC-3800 coupled to a microcomputer was applied in this research. For carrier gas and make-up gas was used nitrogen. The column used was a column Restek Rt-Q-PLOT, 0.53 mm internal diameter (id) and 15 m long, built in fused silica, having as the solid phase-divinyl benzene (DVB), 20 µm film thickness (df). For sample injection, a gas-tight syringe type, brand SGE 1MR-GT, 1 mL, with divisions of 0.02 mL was used. The flame ionization detector (FID) was used, powered by hydrogen and synthetic air. The software used was the Varian Star 4.5 # 1, Burger, (2004). The nitrogen passed through filters to remove possible contamination by ambient air and humidity. The filters used were a Chrompack 17 971 and 17 970. Calibration of the method of analysis Gas N2 Detector – “FID” computer sample injection Gases H2 and Air column 572 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 The chromatographic method of analysis used was calibrated using a standard methane having the following characteristics: methane 2.5 Cil G, 99.50% mol / mol of purity, of White Martins. The sample of the pattern of methane gas was transferred from the cylinder to a reservoir sampler rubber, and was subsequently collected using a gas-tight syringe. A vacuum pump was used to expel completely the rubber tank before filling with methane, to ensure the absence of any contaminant. A calibration curve was performed for each day of analysis. Calibration curves utilized were linear equations of the of methane standard concentrations (mg L-1) for the area obtained in the chromatogram, according to Equation 1. Y = ax + b Equation (1) Where: Y= methane concentration (mg L-1); a = angular coefficient; x = area; b = interception point on the y-axis. In determining the standard of methane concentration (Y) in each standard volume injected, the following calculations were used (ABBOTT; VAN NESS, 1992): a) through Equation 2, known as the equation of ideal gas, the number of moles (n) for each test portion has been determined: P.V = n. R. T Equation (2) Where: Po = atmospheric pressure at STP (101,325.0 Pa); M = average molar mass of air (0.02890 kg mol-1); g = gravitational constant (9.80665 m s-2); z = altitude site (922.12 m); R = universal gas constant (8.3144126 J K-1mol-1); T = temperature (K). The pressure has been corrected using the barometric formula, according to Equation Where: P = local conditions pressure(Pa); Po = atmospheric pressure at standard temperature and pressure (101325.0 Pa); Mar= average molar mass of air (0.02890 kg mol -1); g = gravitational constant (9,80665 m s-2); z = local elevation (922,12 m); R = universal gas constant (8,3144126 J K-1mol-1); T = temperature (K). The temperature was measured using a mercury thermometer, range -10 to 110oC, with divisions of 1oC, according to the method 2559 B (APHA, 2005). The local altitude of 922.12 m, was determined through March 3045U IBGE, located in front of the building UFLA (IBGE, 2005). a) From Equation 4, the mass of methane in taking the test pattern was calculated: M = n. M Equation (4) where, m = mass of methane (g); n = number of moles (moles); M = molecular weight of methane (16.0430 g). b) From Equation 5, the concentration of methane in taking the test pattern was calculated: where, C = concentration of methane (mg L-1); m = mass of methane (mg); V = volume of test-taking pattern (mL). Calculations of the concentration of methane in biogas The concentration of methane in biogas was obtained by analysis of samples, in triplicate, intest- taking volume corresponding to 0.3 mL. It was used to calculate the concentration of methane, the following motion of calculations: a) from the area in the chromatogram obtained, the concentration (C1) of methane in mg L -1 through the linear equation of the calibration method (Equation 1) was calculated; b) from C1, was calculated the C2 concentration by volume of methane per volume of biogas (L CH4 – L biogas-1), using Equation 2 (the ideal gas equation); c) from C2, the C3 concentration in methane percentage in biogas was calculated, using Equation 6: C3 = C2 . 100 Equation (6) where, C3 = concentration of methane (%); C2 = concentration of methane (L CH4 - L biogas -1). Theoretical calculations of the calorific values of biogas 573 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 The theoretical calculations of the lower calorific value or net calorific value (NCV), and higher calorific value or gross calorific value (GCV), were performed by means of the Dulong hypothesis, according to the following motion calculations: a) the elemental composition of methane (CH4), defines the percentage of carbon (C) and hydrogen (H2) in the formula; b) using the calorific values of elementary C and H2, defined the lower and higher calorific values of methane; c) the result of the concentration of methane in the biogas, defined the lower and higher calorific values of biogas. The gas calorific value is the amount of heat released in complete combustion of one unit mass of fuel. The lower or net calorific value (NCV) is the amount of heat released in combustion minus the amount lost to vaporization of water in the process (RUSSOMANO, 1987). The calculations of the calorific values of biogas, the following values were considered: - Atomic weight: carbon, 12.01115 g; hydrogen, 1.00797 g; - Methane molecular weight: 16.04303 g; - Calorific elementary: carbon, 8133 kcal kg-1, hydrogen, 34.500 kcal kg-1; - Loss of heat by the vaporization of water: 539.74 kcal kg-1 water (RUSSOMANO, 1987). Calculations of the interchangeability of biogas The interchangeability of biogas was obtained in relation to natural gas, piped gas (city gas) and LPG (liquefied petroleum gas), using the number of Wobbe (W) according to Equation 7. where: W = number of Wobbe (kcal m-3); GCV = gross calorific value (kcal m-3); ρ = density of gas. Physico-chemical analysis of coffee wastewater The frequency and methodology used for the physical and chemical parameters analyzed in the coffee wastewater for correlation with the quality of biogas are presented in Table 1. Table1. Physico-chemical parameters, output frequency analysis and methodologies used for monitoring the quality of coffee wastewater Physical-Chemical Parameters Frequency Referencies pH Daily APHA, AWWA, WPCF (2005) Total (TA), partial (PA) and intermediated alkalinity (IA) 3 x week Ripley et al. (1986), Jenkins et. al (1983) Chemical Oxygen Demand (COD) 3 x week APHA, AWWA, WPCF (2005) Biochemical Oxygen Demand (BOD5) Weekly APHA, AWWA, WPCF (2005). Wincley methodology Total (TS), Fix (FS) and Volatile (VS) Solids Weekly APHA, AWWA, WPCF (2005) Total Kjeldahl nitrogen (TKN) 2 x month APHA, AWWA, WPCF (2005) Total phosphorus (P) 2 x month APHA, AWWA, WPCF (2005) Total acidity (AVT) 3 x week Potenciometric method (NaOH 0,02N) Phenolic compounds 2 x month Méthod 5550B- APHA, AWWA, WPCF (2005). Using extraction with methanol, standardized curve with tartaric acid and read in spectrophotometer. The operational parameters applied and system performance studied are presented in the Prado and Campos (2008); Prado and Campos (2010) and Campos et al. (2010). The theoretical metanogênica activity (TMA) presented in the results and discussion was calculated using the concepts and methodology presented in Silva et al. (2011a) and Silva et al. (2011b). Statistics For calculations, the Sisvar software, version 4.6 (Build 63) and the software Excel for 574 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 Windows XP was used. The data entered in Excel files were converted into dBase IV and processed by Sisvar for statistical analysis: - Measures of location: mean (x), maximum (max) min (minimum); - Measures of variability: standard deviation (s) and coefficient of variation (cv); - Measures of comparison and decision making: analysis of variance (ANOVA) and means were compared by the test of Student-Newman-Keuls (SNK). RESULTS AND DISCUSSION Results of the calibration method Sampling for biogas analysis was performed during 86 days with intervals of two days. The total samples analysis performed was 41. The values obtained can be seen in Tables 1, 2 and 3. From the data in Table 3, was obtained the linear equation, y = 0.0000089167x - 0.595738807. Table 1. Parameters of the chromatography Chromatography Parameter Value Column temperature (oC) 50 Run time (min) 4 Injector temperature (oC) 220 Split rate in the injector 10 Detector temperature (oC) 250 Detector range (g sec-1 ) 1 x 10-12 Linear velocity of gases (cm.s-1) 51 Flow of N2 in the column (mL min -1) 6,2 Total flow in the column (mL min-1) 72,4 Total pression of N2 (psi) 85 Pressure of H2 (psi) 60 Pressure of synthetic air (psi) 85 Pressure in the column (psi) 1,2 Table 2. Environmental Parameters Table 3. Parameters of stander curve. The pressure values set to the N2, H2 and synthetic air were regulated to maintain the flow within specification: for N2, flow rates from 0.5 to 10 mL m-1 column and 20-25 mL m-1 as make-up gas, for the H2 flow rate of 35 to 40 mL m -1 and the synthetic air, flow rate 350-400 mL m-1. Analysis results of methane The analysis results in average concentrations of methane can be seen in Table 4. Environmental Parameters Value Environmental temperature (K) 293.95 High (m) 922.12 Column pressure (atm.) 0.899 Parâmetros da curva padrão Stand volume (mL) Concentration (mg L-1) Chromatogram area 0.060 3.5679247277 453,182 0.100 5.9465412128 723,841 0.140 8.3251576979 1,053,060 0.180 10.7037741830 1,271,816 0.220 13.0823906681 1,496,392 0.300 17.8396236383 2,071,600 575 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 The average concentration in percentage had a minimum value of 48.60%, a maximum value of 68.14% and an average of 57.19%. The standard deviation (s) was 4.41%, demonstrating a low variability around the mean. The treatment process was divided into periods and sub-periods depending on the pH and alkalinity, the addition of NaOH in the CWP was according to Table 5. A sampling of the biogas was also divided into periods and sub-periods, followed by the same criterion. In Tables 6 and 7 are the analysis of variance and comparison of the average concentrations of methane by the test of Student- Newman-Keuls (SNK) for the periods and sub- periods. Table 4. Average concentrations of methane Average concentrations of methane Sample (mg L-1) (LCH4 L -1biogas) (%) 1 384.17 0.645 64.47 2 372.00 0.624 62.43 3 382.67 0.650 65.04 4 349.65 0.594 59.43 5 351.56 0.598 59.61 6 312.19 0.531 53.35 7 319.23 0.541 54.09 8 343.01 0.581 58.12 9 345.32 0.587 58.69 10 330.32 0.560 55.97 11 330.73 0.562 56.21 12 338.59 0.575 57.55 13 331.66 0.562 56.20 14 335.38 0.568 56.83 15 308.01 0.514 51.41 16 310.57 0.518 51.84 17 376.42 0.628 62.83 18 369.86 0.617 61.73 19 367.96 0.614 61.42 20 408.25 0.681 68.14 21 339.25 0.571 57.14 22 361.79 0.609 60.94 23 309.70 0.522 52.16 24 343.21 0.578 57.81 25 316.55 0.528 52.84 26 352.04 0.588 58.76 27 333.40 0.556 55.65 28 335.53 0.563 56.35 29 346.96 0.583 58.26 30 372.72 0,626 62.59 31 347.42 0.583 58.34 32 353.38 0.594 59.43 33 337.83 0.566 56.56 34 344.86 0.579 57.91 35 337.14 0.564 56.44 36 290.32 0.486 48.60 37 290.40 0.486 48.62 38 314.47 0.526 52.65 39 299.66 0.502 50.17 40 332.63 0.557 55.69 41 314.29 0.526 52.62 576 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 Table 5. Division of periods and sub-periods of treatment of (CWP) Period Sub-period Total of days Addition of NaOH NaOH (%) Local of addition IV A 21 yes 10.0 AET IV B 27 no ----- ----- V A 14 no ----- ----- V B 18 yes 10.0 AET VI A 06 yes 10.0 AET VI B 15 yes 2.5 UASB, with pump Table 6. Analysis of variance of the concentration of methane during periods and sub-periods FV GL SQ QM Fc Periods and sub-periods 5 1,120.55 224.11 19.52* Experimental error 117 1,343.16 11.48 Total 122 2,463.71 CV = 5.92%; FV: Varying sources examined in the analysis of variance; GL: degrees of freedom; SQ: Sum of squares; QM: Mean Square; Fc: calculated value for the test statistic F. Table 7. Average concentrations of methane in the periods and sub-periods Period and sub-period Methane (%) IV-A 63.98 a IV-B 57.22 b V-A 55.14 b V-B 62.03 a VI-A 55.39 b VI-B 55.33 b Means followed by the same letter do not differ by SNK test at 5% probability. It can be observed the significant differences at 5% probability in methane concentration between periods. The highest values of average concentrations of methane were obtained in periods IV-A and VB, which are significantly different from the results of other periods. The low CV shows a good precision in the analysis. One can compare the average concentrations of methane in the periods and sub-periods with the mean values of pollutant removal efficiencies and analysis obtained during the treatment of ARC, according to Tables 8, 9, 10, 11, 12 and 13. The coefficient of simple correlation (r) was 0.399 for CH4/COD; to CH4/BOD5 was 0.163 and for CH4 / N, was -0.633, for CH4 / P was -0.386 and for CH4/compounds phenolic were - 0.321. The values obtained show a low correlation. The correlation CH4/N showed the greatest value, however, still down 0.80 and its negative sign indicates that the variation of methane concentration is opposite to the variation of removal efficiency in the reactor. The simple correlation coefficient (r) for CH4 / N, was 0.158 and for CH4 / P was -0.404 and for CH4/ phenolic compounds, was -0.549. The low values obtained for correlations with N and P, show a low correlation between the concentration of methane with concentrations of N and P. For the correlation with the phenolic compounds, it appears that there is a negative correlation median, indicating that the methane concentration increases in the opposite direction to the concentration of phenolics. The variation in concentration of phenolic compounds in the CWP caused negative interference in methane concentration, as these compounds are toxic to bacteria, interfering with the metabolism of them. The removal efficiencies of COD, BOD5, N and P in all periods, showed no significant correlations in the variation of the concentration of methane in the biogas from the CWP. Considering the I-UASB, the simple correlation coefficient (r) for CH4/pH was 0.504 and for CH4/temp, was 0.673, indicating the existence of a positive correlation median, where the concentration of methane is correlated with the increase of pH and temperature. Whereas E-UASB, the simple correlation coefficient (r) for CH4/pH was 0.355 and for 577 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 CH4/temp, was 0.619, indicating the existence of a positive correlation with respect to the median temperature, which increased methane concentration is correlated with the increasing of temperature. For pH, the correlation was very low. The simple correlation coefficient (r) was 0.317 for CH4/PA; for CH4/IA was -0.344, for CH4/TA was -0.090, for CH4/IA/PA was -0.623 and, for CH4/AVT , was -0.743, indicating low correlation with respect to PA, IA and TA. There is a negative median correlation coefficient of methane with the IA/PA and the acidity, which increases the concentration of methane, is related to the decrease of IA/PA and acidity. The simple correlation coefficient (r) was - 0.182 for CH4/PA; to CH4/IA was -0.313, for CH4/TA was -0.253, for CH4/IA/PA was -0.336 and for CH4 /acidity, was -0.433, indicating low correlations with the variables in E-UASB and methane concentration. Table 8. Methane (%) and pollutants removal efficiency (%) in the UASB reactor Period and sub-period CH4 COD BOD N P Phenolic compounds IV-A 63.98 76.09 75.50 -23.35 15.76 19.54 IV-B 57.22 82.17 86.63 32.51 -7.43 22.04 V-A 55.14 72.04 73.99 -0.79 37.16 -3.75 V-B 62.03 77.21 78.17 1.89 20.66 1.78 VI-A 55.39 70.54 71.95 --- 27.38 --- VI-B 55.33 74.43 73.25 13.37 30.43 27.75 Table 9. Methane (%) and nitrogen, phosphorus and phenolic compounds (mg L-1) in the influent (I-UASB) Period e sub-period CH4 N P Phenolic compounds IV-A 63.98 19.27 186.17 84.55 IV-B 57.22 23.43 200.83 49.78 V-A 55.14 19.00 351.17 158.86 V-B 62.03 18.43 239.58 100.81 -A 55.39 * 162.50 * VI-B 55.33 14.52 162.92 381.80 * There was no analysis in this sub-period. Table 10. Methane (%) and pH and temperature (°C) in the influent (I-UASB) and effluent (E-UASB) Period and sub- period CH4 pH I-UASB Temp I-UASB pH E-UASB Temp E-UASB IV-A 63.98 6.93 26.47 7.34 26.59 IV-B 57.22 5.35 25.01 6.73 24.78 V-A 55.14 4.79 23.34 6.29 22.10 V-B 62.03 6.34 23.22 6.97 21.46 VI-A 55.39 6.50 22.50 7.34 20.90 VI-B 55.33 6.56 22.82 7.19 20.31 Table 11. Methane (%) Ripley and acidity and alkalinity (mg L-1 of CaCO3) in the I-UASB Period and sub-period CH4 PA IA TA IA/PA AVT IV-A 63.98 431.30 485.87 917.17 1.3 118.01 IV-B 57.22 0.00 492.16 492.16 ∞ 209.14 V-A 55.14 36.47 308.88 345.35 3.8 248.71 V-B 62.03 175.31 576.86 752.17 3.6 101.75 VI-A 55.39 340.07 917.35 1,257.42 2.7 168.39 VI-B 55.33 356.03 1,005.11 1,361.15 3.8 154.55 578 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 Table 12. Methane (%) Ripley and acidity and alkalinity (mg LCaCO3 -1) in E-UASB Period and sub-period CH4 PA IA TA IA/PA AVT IV-A 63.98 752.16 321.04 1,073.20 0,4 76.36 IV-B 57.22 604.88 286.98 891.86 0,5 92.13 V-A 55.14 317.88 256.16 574.04 1,2 113.84 V-B 62.03 460.89 315.44 776.34 0,7 50.18 VI-A 55.39 1,048.76 366.39 1,415.15 0,4 49.39 VI-B 55.33 922.67 675.00 1,597.67 0,8 100.01 Table 13. Methane (%) and lateral solids (mg L-1) in the UASB Período e sub-period CH4 TS TFS TVS IV-A 63.98 26,729 10,646 16,083 IV-B 57.22 32,467 10,600 21,777 V-A 55.14 48,927 14,952 33,975 V-B 62.03 44,228 12,971 31,257 VI-A 55.39 * * * VI-B 55.33 50,021 12,863 37,157 * There was no analysis in this sub-period. The pH, acidity and alkalinity are directly related (Pereira et al. 2009). It was found that the highest concentrations of methane in the biogas were obtained during periods when the pH was as close to neutrality (7.00) and the acidity was lower, resulting in a ratio IA/PA minor. It is evident, therefore, the importance of adding NaOH to increase the alkalinity PA, contributing to a lower value of IA/PA. The alkalinity is due to PA that ensures the bicarbonate buffer in the reactor, a condition of utmost importance to maintaining good microbial activity in the reactor, with a satisfactory production of methane. The simple correlation coefficient (r) was - 0.660 for CH4/ST; to CH4/STF was -0.520 and, for CH4/TVS; was -0.667, indicating medians, negative correlations, in which the concentration of methane was opposed to the increase of biomass in reactor. The values of the concentration of methane and theoretical methanogenic activity (TMA) of biomass, can be seen in Table 14. Table 14. Methane (%) and TMA (m3CH4 kg -1TVS d-1) in the UASB Period e sub-period CH4 TMA IV-A 63.98 0.051 IV-B 57.22 0.073 V-A 55.14 0.061 V-B 62.03 0.049 VI-A 55.39 0.099 VI-B 55.33 0.167 The simple correlation coefficient (r) for CH4/TMA was -0.601, indicating a negative correlation median, where the concentration of methane was opposed to the increase in TMA. This demonstrates that the increase of methane production did not necessarily imply increasing the percentage of this component in biogas, which occurred concomitant increase of other components of biogas, like CO2, H2S and other gases. One must consider that: - During periods IV-A and V-B, it was obtained the highest values of methane concentration. During these periods, one can verify that with the addition of NaOH in the CWP, the pH in the I-UASB remained with values closer to neutrality, the ratio IA/PA was the lowest obtained in both influent and effluent of the UASB, and acidity had the lowest values; - During periods V-B and VI-B were also adding NaOH, but from the V period, due to the 579 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 increased loading, the pipes began clogging varying the flow. The temperature was maintained within the mesophilic range throughout the treatment process and there was a good removal efficiency of COD and BOD5 in all periods. The lowest concentration of methane were obtained from the VI period and may be related to the occurrence of low pH, high values IA/PA and frequent variations in discharge, resulting from blockage. In this period, the concentration of phenolic compounds in the CWP was higher than in previous periods, which may have interfered with the metabolism of anaerobic bacteria. Results of theoretical calculations of the calorific values For the calculations of lower calorific value or net calorific value (NCV), and higher calorific value or gross calorific value (GCV), it was considered the concentration of methane in the biogas from 68.14%, with a density of 0.61 kg.m-3. The values of GCV and NCV of the biogas can be seen in Table 15. Table 15. Calorific values of biogas Calorific values Kcal kg-1 Kcal m-3 kJ m-3 kWh m-3 GCV 10,051.41 6,131.36 25,654.23 7.11 NCV 9,315.85 5,682.67 23,776.86 6.59 It was considered: 1J = 0.2390 cal = 2.773 x 10-7 kWh. The values obtained are close to the reference values of mean of 23,380 kJ m-3 (6.5 kWh m-3) for the biogas from urban sewage, with 70% methane, and 21,610 kJ m-3 for biogas (CASSINI, 2003; STAFFORD et al. 1980). Calculation results of interchangeability For the calculations of interchangeability through the Wobbe number (W), considered the GCV of the gases. The values obtained are shown in Table 16. Table 16. Calculating the number of Wobbe Fuel GCV (kcal m-3) Density (kg m-3) W (kcal m-3) LPG 26,860 1.77 20,189.42 Natural gas 9,850 0.64 11,945.19 Pipe gas 4,700 0.57 6,225.17 CWP Biogas 6,131.36 0.61 7,850.65 The results have shown that it is not feasible, energetically, in the same proportion, the substitution of LPG or natural gas by biogas from the CWP, but is feasible with respect to piped gas. However, the biogas from the CWP can be used as additional gas in cases where using LPG and natural gas. The significant results of the NCV and GCV of the biogas, their interchangeability and the concentration of methane, demonstrating the feasibility of the treatment of CWP in UASB reactor and its energy use in agro-industrial properties of coffee. Biogas can be used in various stages of post- harvest processing of coffee as a supplementary energy source, using its thermal energy and the possibility of mixing it with another fuel gas for heating the air in the drying process of product. The increasing production and profitability of farms, need conserving energy. One of important actions that contribute to energy conservation would be developing ways to reduce losses in raw materials and energy utilization of waste, and thus an additional source of energy, such as the exploitation of biogas from CWP. One should also take into consideration that the treatment of CWP and the use of biogas contributes to the preservation of natural resources (soil and water) and the reduction of environmental pollution (soil, water and atmosphere), both by treatment of the CWP as by reducing the emission of methane into the atmosphere. In general, the results stood close to the values referenced in the literature, may be concluded that the production of biogas from the treatment of CWP in UASB reactor is a viable alternative to the use of residues from coffee processing, contributing to energy conservation and the preservation of natural resources. CONCLUSIONS The parameters that influence the changes in concentrations of methane in the biogas were temperature, pH, acidity and concentration of phenolic compounds in the CWP. Temperature variations with a magnitude of 8.9 at full term, 580 Anaerobic digestion... CAMPOS, C. M. M.; PRADO, M. A. C.; PEREIRA, E. L. Biosci. J., Uberlândia, v. 29, n. 3, p. 570-581, May/June 2013 correlated positively with the concentration of methane, which increased with increasing temperature, even if in all periods it was maintained within the mesophilic range. Should take into account also the negative interference of variations in flow, caused by blockage of the system and shock loads and wash- outs occurred during the increased concentrations of the flows. There is a need for operating the reactor with a systematic control of the parameters that are directly linked to biomass in the reactor, such as temperature, pH, alkalinity and acidity and other physical-chemical parameters of operation of the reactor, as the flow and loads, avoiding shock loads and scans so that they obtain best values of methane concentration. However, the results of methane concentration in biogas demonstrated to be close to the theoretical framework and are consistent. ACKNOWLEDGEMENTS The Study Group on Research and Technological Development of Liquid Effluents (PDTEL) thanks FAPEMIG and CNPq for financing the project and scholarships. Thanks are extended to Engineering Department of UFLA to allow the use of its laboratory in order to carry out the physical- chemical analysis. RESUMO: O metano é o principal constituinte do biogás, sendo o responsável pelo seu poder calorífico. Neste trabalho, são apresentadas as análises da concentração de metano no biogás produzido a partir do tratamento das águas residuárias do processamento por via úmida do café (ARC) em sistema de tratamento anaeróbio em escala de laboratório, sendo utilizado o café coco para a produção destas ARC. As análises foram realizadas por cromatografia gás-sólido (CGS), sendo o sistema composto de uma coluna Restek RT-Q-PLOT, tendo como fase fixa, o divinil-benzeno; do nitrogênio como fase móvel e um detector de ionização de chama (DIC). Os resultados da concentração de metano no biogás variaram de 48,60 a 68,14 %, sendo estas variações obtidas em função dos parâmetros do processo de tratamento. 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