evaluation of maturity and fertilizer capacity of compost derived from ...

Density-pressure relationship in densification of swine solidfractionAbstractNiccolò Pampuro 1 *, Alessio Facello 1 , Eugenio Cavallo 11 Institute for Agricultural and Earth Moving Machines (IMAMOTER), Italian NationalResearch Council (CNR), Strada delle Cacce, 73 – 10135 Torino, Italy* Corresponding author. E-mail: n.pampuro@ima.to.cnr.itIn accordance to European Regulation (91/676/CEE), which limits the amount of nitrogenavailable for distribution on agricultural lands that fall in nitrate vulnerable zones (NVZ),livestock farms have to find alternative solution for manure management. In order to avoidwater pollution several technologies have been developed and one of these is solid-liquidseparation allowing to obtain a solid fraction and a clarified liquid.As a consequence of low bulk density, the solid fraction is very difficult to handle, transportand store. One possible solution to these problems is densification of biomass materials intopellets, briquettes or cubes. Two techniques are used for size enlargement of particulatematerials: tumble agglomeration and pressure agglomeration.This paper reports the results of a first investigation on physical behavior of swine solidfraction during pressure agglomeration in a cylindrical die.The investigation was carried out using a hydraulic press prototype equipped with measuringsensors to record the variables influencing the densification process.Two different types of materials have been used: swine solid fraction derived frommechanical separation and compost obtained by mixing the first material with wood chips.The initial bulk density values (ρ 0 ) were 250 kg . m -3 and 450 kg . m -3 for the first and the secondmaterial respectively.Seven levels of compaction pressure between 20 MPa and 80 MPa and two applicationtimes for each pressure level (10 and 40 s) were considered.During the pressure agglomeration the density increase was distinctly nonlinear and differentin the two materials. At the upper limit of this pressure range the density was about 1337kg . m -3 and 1129 kg . m -3 for swine solid fraction and compost respectively.The tests carried out showed that, although there were significant differences between thefinal density values obtained at different pressure levels, the densification process efficiencydecreased with increasing applied pressure.Key words: densification, pressure agglomeration, hydraulic press, swine solid fraction.1. IntroductionThe main problem of livestock waste, in particular pig slurry, is the concentration of itsproduction in specific geographic areas. In Italy 70% of the national livestock asset isconcentrated in 5 regions in the north part of the country. In these areas, slurry managementmainly consists of spreading it in agricultural lands after pond storage. The excessive amountof pig slurry spread on soil has contributed to nitrate water pollution both in surface and inground waters, especially in areas classified as vulnerable zones to nitrate in accordancewith European Regulation (91/676/CEE).In order to avoid water pollution several technologies have been developed. One of these isthe solid-liquid separation, which allows to obtain a solid fraction and a clarified liquid.As a consequence of low bulk density, the solid fraction is very difficult to handle, transportand store. One possible solution to these problems is densification of biomass materials intopellets, briquettes or cubes. Densification increases the biomass bulk density from an initialbulk density of 40-200 kg . m -3 to a final one of more than 800 kg . m -3 (Mani et al., 2003;1

Temperature inside the heaps at 0.4 m, 0.8 m and 1.2 m high above the floor andenvironmental temperature were continuously recorded. The decision to turn the compostingpiles was based on the temperature of the decomposing material. When the temperature oftwo of the three probes in the decomposing material was over 60°C, the pile was turned(Caceres et al., 2006).Optimal humidity (between 50-60%) of windrows was maintained spreading water duringturning operations by a rain distribution system placed under the covering (Bernal et al.,1998).At the end of the composting process, the initial bulk density values (ρ 0 ) were 450 kg . m -3 and250 kg . m -3 for WCC and SSFC respectively.2.3. Statistical analysisIn the densification test one way analysis of variance (ANOVA) was performed to comparefinal density values. Bonferroni’s test was used for testing significant statistical differencesamong samples at a probably (P) of 0.05. All statistical analyses were done with SPSSsoftware.The values reported in Table 2 and in Table 3 were the means of five replicates.3. Results and discussionThe relationship of compressed density versus compressive pressure for WCC and SSFC isshown in figure 2.FIGURE 2: Relationship between density (theoretical values and experimental data) andapplied pressure on WCC and SSFCIn the range of pressure up to 10 MPa the density increase was linear. Compressed densityat the limit of this pressure range was about 800 kg . m -3 and 700 kg . m -3 for WCC and SSFCrespectively. The second phase of compression included pressure from about 10 MPa toabout 80 MPa. The density increase in this pressure range was distinctly nonlinear anddifferent for WCC and SSFC. At the upper limit of this pressure range the density was about1300 kg . m -3 and 1200 kg . m -3 for WCC and SSFC respectively.3

The empirical Bailey’s model (Bailey et al., 1986) was fitted to the experimental results. Thismodel, modified to meet the conditions of swine solid fraction compression, assumed thefollowing form:where:ρ = compressed density (kg . m -3 );ρ 0 = initial bulk density (kg . m -3 );p = compression pressure (MPa);A, B, C = model parameters.Values of model parameters are presented in Table 1.TABLE 1: Values of empirical model parametersMaterialA [kg∙m -3 ]ParametersB [kg∙m -3 ∙MPa -1 ] C [Mpa -1 ]WCC 420 6.289 0.149SSFC 562 4.717 0.137The tests performed showed that the density material increase diminished when the pressureapplied was augmented. Indeed moving from 20 MPa to 30 MPa the increase was 11%,while passing from 70 MPa to 80 MPa the increase was reduced to 1.4% as shown in figure3. It is therefore possible to affirm that the efficiency of the densification process decreaseswith increasing pressure applied on the material.FIGURE 3: Average increase in density refers to pressure increaseAverage values of final density obtained with the test are showed in Tables 2 and 3.The data highlighted significant differences between the two materials, the two timing ofpressure application and the seven levels of applied pressure.TABLE 2: Average density values (kg . m -3 ) of WCC and SSFC materials obtained usingdifferent pressure levels (20, 30, 40, 50, 60, 70 and 80 MPa)MaterialPressure [MPa]20 30 40 50 60 70 80PWCC 964.19 a 1047.69 b 1136.56 c 1211.89 d 1255.44 e 1288.65 f 1337.66 g ***SSFC 868.72 a 961.60 b 1042.23 c 1059.96 d 1100.84 e 1140.65 f 1129.15 g ****** Significant at the 0.01 levels of probabilitya, b, c, d, e, f, g mean values for materials with different letters differ significantly (P

TABLE 3: Average density values (kg . m -3 ) of WCC and SSFC materials obtained with twotimeapplication of pressure (10 and 40 s)4. ConclusionsMaterialTime [s]10 40WCC 1167.35 1187.53 ***SSFC 1028.38 1058.24 ****** Significant at the 0.01 levels of probabilityAlthough significant differences were found between the final density values obtained atdifferent pressure levels, the densification process efficiency decreased with increasingapplied pressure.Further tests will be carried out with the aim of verifying the maximum pressure beyondwhich the increase in density of WCC and SSFC is not significant.In order to verify the influence of the pressure application time on the final density will beconsidered different times.The economic and energetic evaluation of the process will be analysed.5. AcknowledgementsThis work was carried out within the framework of the “FITRAREF” project, funded by theItalian Ministry of Agriculture and Forestry (Call OIGA, 2009), under the scientific direction ofDr. Eugenio Cavallo (CNR-IMAMOTER). Authors also acknowledge Mr. Giuseppe Palettoand Mr. Guarino Benvegnù (CNR-IMAMOTER) for the technical support.ReferencesBailey, A. C., Johnson, C. E., & Shafer, R. L. (1986). A model for agricultural soil compaction.Journal of Agricultural Engineering Research, 33 (4), 257-262.Bernal, M. P., Paredes, C., Sanchez-Monedero, M. A., & Cegarra, J. (1998). Maturity andstability parameters of composts prepared with a wide range of organic waste. BioresourceTechnology, 63, 91-99.Caceres, F., Flotats, X., & Marfa, O. (2006). Changes in the chemical and physiochemicalproperties of the solid fraction of cattle slurry during composting using different aerationstrategies. Waste Management, 26, 1081-1091.Council Directive 91/676/CEE concerning water pollution caused by nitrates from agriculturalsources.Kaliyan, N. & Vance Morey, R. (2009). Factors affecting strength and durability of densifiedbiomass products. Biomass and Bioenergy, 33, 337-359.Mani, S., Tabil, L.G. & Sokhansanj, S. (2003). An overview of compaction of biomass grinds.Powder Handling and Processing, 15, 160-168.McMullen, J., Fasina, O.O., Wood, C.W. & Feng, Y. (2005). Storage and handlingcharacteristics of pellets from poultry litter. Applied Engineering in Agriculture, 21, 645-651.Obernberger, I. & Thek, G. (2004). Physical characterisation and chemical composition ofdensified biomass fuels with regard to their combustion behaviour. Biomass and Bioenergy,27, 653-669.Pietsch, W. (2002). Agglomeration processes – phenomena, technologies, equipment.Weinheim: Wiley-VCH.P5