Although it is primarily grown as food, corn also represents a very good raw material for the production of biogas due to the favourable starch and fibre ratio that is the basis of its structure. In addition, an important fact is that there are large arable or potentially arable areas in our country that are triturated with different pollutants, so that the production of plant crops for dietary purposes on these surfaces is not possible.
The aim of this paper was to determine the biometric potential of various varieties of corn grain in laboratory conditions through a series of experimental measurements. The obtained results are based on the assessment of the possibility of applying energy plantations of corn grown on contaminated arable or recultivated surfaces in the production of biogas

Mirnesa Zohorović

Samra Halilović

Vedran Stuhli

Zoran Iličković

English

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S. Halilović, V. Stuhli, M. Zohorović, Z. Iličković, “Determination of the biomethanic potential of corn grain”, Technologica Acta, vol. 11, no. 1, pp. 1–4, 2018. 1 ISSN 1840-0426 (P); ISSN 2232-7588 (E) http://tf.untz.ba/technologica-acta DETERMINATION OF THE BIOMETHANIC POTENTIAL OF CORN GRAIN ORIGINAL SCIENTIFIC PAPER Samra Halilović1*, Vedran Stuhli2, Mirnesa Zohorović2, Zoran Iličković2   RECEIVED 2017-12-16 ACCEPTED 2018-05-18 1Institute for Chemical Engineering, Tuzla, Bosnia and Herzegovina 2Faculty of Technology, University of Tuzla, Tuzla, Bosnia and Herzegovina * samra.halilovic95@gmail.com  ABSTRACT: Although it is primarily grown as food, corn also represents a very good raw material for the pro-duction of biogas due to the favourable starch and fibre ratio that is the basis of its structure. In addition, an im-portant fact is that there are large arable or potentially arable areas in our country that are triturated with dif-ferent pollutants, so that the production of plant crops for dietary purposes on these surfaces is not possible. The aim of this paper was to determine the biometric potential of various varieties of corn grain in laboratory conditions through a series of experimental measurements. The obtained results are based on the assessment of the possibility of applying energy plantations of corn grown on contaminated arable or recultivated surfaces in the production of biogas.  KEYWORDS: corn, biomethane potential, sludge, anaerobic digestion, biogas  INTRODUCTION  Owing to increased energy consumption and re-duction of fossil fuels in the world, systems have re-cently been developed in order to meet renewable energy needs, which is the cause of development of new technological processes of energy production. In addition, renewable energy sources form part of the European fight against climate change, while at the same time increasing the number of employees con-tributes to economic growth and development of the whole region [1], [2], [3].  At the global level of biomass energy production, very high potential has been estimated that can be unambiguously linked to the potential of biogas. Ex-isting estimates are made on the basis of different assumptions, but all the results indicate the use of a very small part of that potential. The European Bio-mass Association (AEBIOM) estimates that biomass energy can increase from 72 Mtoe in 2004 to 220 Mtoe in 2020 (1 Mtoe = 11.63 TWh) [4].  Biogas plants using agricultural raw materials are one of the most important examples of anaerobic di-gestion in the world. Compared to other biofuels, anaerobic digestion biogas is an important priority in European transport and energy guidelines, and is of increasing importance because it offers many envi-ronmental benefits and an additional source of in-come for farmers [5].  Maize is the most dominant crop for biogas pro-duction. It is cultivated all over the world, and the breeding area is very broad, resulting from the varie-ty of corn utilization and abilities that can thrive on various soils and in various climatic conditions. Corn crops are the third world crops, after wheat and rice. All parts of corn can be used either as food or for industrial processing [6].   MATERIAL AND METHODS  The basic substrate was chopped corn grain (di-ameter 0.5-1 mm) of two varieties, hybrid maize NS 444 Ultra and a homemade Bosanac variety. For the purpose of achieving the production of biogas as an inoculum, sludge from the treatment plant for com-munal waste water in Živinice was used.  For the purposes of this paper, a laboratory reac-tor system for anaerobic digestion of organic matter with glass eudiometric pipes (manufacturers Šurlan-Medulin), mounted on glass bottles of 500 ml were used. Provision of anaerobic conditions was per-formed by sparging of nitrogen in order to displace the air from the reactor, while providing the required constant temperature of the reactor system at 35°C ± 2°C was carried out by heating in a water bath with circulating water (Figure 1). Using the eudiometric pipes, the production of biogas is simple to read off, because produced gas pushes the liquid level down, while the fluid goes back into the storage bottle.  The pressure and temperature of the ambient air were measured on the set pressure hydrometers or eudiometric tubes, whose values were used to convert the volume of the resulting biogas to normal condi-tions. Mixing of the substrate was realized mechani-cally using a magnetic stirrer. 2  S. Halilović, V. Stuhli, M. Zohorović, Z. Iličković, “Determination of the biomethanic potential of corn grain”, Technologica Acta, vol. 11, no. 1, pp. 1–4 ISSN 1840-0426 (P); ISSN 2232-7588 (E) http://tf.untz.ba/technologica-acta    Figure 1. Laboratory reactor system: a. system layout; b. reactor block scheme   Measuring the volume of biogas produced in the reactor was performed in accordance with DIN 38 414 [7], and a gas composition analysis was per-formed on a gas chromatograph "PERKIN ELMER", equipped with the software package "Arnel". Helium was used as a gas carrier (flow rate 34 ml / min). A mixture of gases was used to calibrate the device which consists of CO, CO2, CH4 and O2 (Messer, Germany). The gas chromatograph has two columns: 70 HayeSep N 60/80, 1/800 SF (maximum tempera-ture 150°C) and 90 Molecular Sieve 1345-1360, 1/800 SF (maximum temperature 375°C). Conditions governing the furnace chromatograph are: initial temperature 60°C, total retention time 12 min, maxi-mum temperature 150°C.  Because of the inhibition of anaerobic substrate degradation due to a sudden increase in the concen-tration of volatile fatty acids at the beginning of the process, which was reflected in a decrease of pH be-low 4, it was necessary to buffer the substrate by combining two bicarbonate buffers. By adding 150 mg of NaHCO3 and 170 mg of KHCO3 in relation to 1 g of total organic volatile matter [8] in the sub-strate, the optimum pH range was obtained.  To determine the necessary parameters in the substrates, the methods described below were used.  Determination of dry and volatile organic matter was performed according to Method 2540-B and 2540 Solid-Solid E. Standard Methods for the Exam-ination of Water and Wastewater [9]. Electrometric measurement of pH was carried out by direct meas-urement, with the pH meter METTLER TOLEDO FE 20/EL 20. Prior to each measurement, an internal control was performed with certified reference mate-rials of pH- value 4.01; 7.01; 10.01.  The nitrogen content by Kjeldahl was determined according to Method 4500-Norg B. Standard Methods for the Examination of Water and Wastewater 20nd edition. APHA, Washington, DC [10]. The method consists of three stages: digestion at a temperature of 340°C (boiling point of H2SO4) in the presence of concentrated sulfuric acid and selenium Kjeldahl cat-alyst; distillation in the presence of NaOH where dis-tillate accepts in the solution of boric acid, and titra-tion with 0.1 M HCl in the presence of indicator bromocresol green. Determination was made on Kjeldahl apparatus Gerhardt. To determine the chem-ical oxygen demand, the standard method was used according to the ISO 6060:2000 [11].  RESULTS AND DISCUSSION  The anaerobic digestion experiment of two grain varieties and waste sludge from municipal wastewater treatment plants was carried out at meso-philic conditions (36 ± 1°C). When experimenting with the mixture of corn grain substrate and waste sludge, experimental data [12] were used as a blank test waste sludge was used without additives (Table 1).   Table 1. Composition of the cosubstrate in the formed blends (2&3) and the blank test (1) Test  sludge mas% Bosanac mas % NS 444 Ultra mas % H2O mas % 1 100 0 0 0 2 49.67 0.33 0 50 3 49.64 0 0.36 50  The values of the physico-chemical parameters of the treadmill are shown in the Table 2.  Table 2. Physico-chemical characteristics of the cosubstrates used at the beginning of the experiment  Parameter Unit 1 2 3 TS % 5.05 2.83 2.84 VS % 3.36 1.96 1.99 VS/TS - 0.66 0.69 0.70 pH - 6.41 6.21 6.09 COD g/kg 48.6 102.58 117.96 TKN g/kg 2.80 2.20 2.00 TS – total solids; VS – volatile solids; COD - chemical oxygen demand; TKN - total Kjeldahl nitrogen   The ratio of VS / TS to the blank test sample (1) and the formed coagulates (2 and 3) approx. 0.7 the condition of the presence of sufficient quantity of organic matter in the reactors is satisfied. The content of dry matter in reactors 2 and 3 is lower than the content of dry matter in the control sample (1).  The optimum ratio of organic matter and nitrogen in the ratio of 30:1 in this case is expressed through HPK:TKN and ranges from 17:1 in the control sam-S. Halilović, V. Stuhli, M. Zohorović, Z. Iličković, “Determination of the biomethanic potential of corn grain”, Technologica Acta, vol. 11, no. 1, pp. 1–4, 2018. 3 ISSN 1840-0426 (P); ISSN 2232-7588 (E) http://tf.untz.ba/technologica-acta ple up to 60:1 in reactor 3 (HPK reactor: TKN = 47:1). It is clear that substrates are not loaded with nutrients especially nitrogen.  The graphs show daily biogas production (Figure 2) and cumulative yield of biogas (Figure 3) in reac-tors 1, 2 and 3. On the biogas daily production dia-gram, discontinuous biogas production is observed.  010203040506070800 5 10 15 20 25 30daysml 123 Figure 2. Daily biogas production diagram  01002003004005006007008000 10 20 30daysml 123 Figure 3. Cumulative biogas yield   The cumulative yield of the biogas (Figure 3) confirms the adaptation phases and the beginning of hydrolysis in the first days of the process. The dia-gram clearly shows a significantly larger biogas pro-duction in reactors 2 and 3 compared to the con-trolled sample 1.  Table 3 gives characteristics of the digested resi-due (digestate) which remains after the experiment has been realized. If we compare the content of dry and volatile organic matter before and after the pro-cess, it is easy to conclude that a certain part of the matter has been transformed into gas products. Also, the value of HPK for all three samples is significantly lower in the digestate (Table 2) compared to HPK values in substrates prior to the decomposition pro-cess (Table 1). In addition, the lower value of TKN content in digestates can be noted with respect to the TKN values in the initial coagulants. Based on the proportion of methane in biogas and biogas produc-tion, a calculation of methane production was per-formed for all three analyzed cases (Figure 4).  Table 3. Final results of batch anaerobic digestion after experi-ment Parameter Unit 1 2 3 TS % 2.79 2.22 2.19 VS % 1.36 1.26 1.09 pH - 7.57 7.44 7.47 HPK g/kg 14.43 15.12 10.47 TKN g/kg 1.06 1.35 1.15 V biogas ml 208.2 612.84 685.75 V methane ml 64.77 366.05 411.38 W methane % 31.11 59.73 59.99 spec. gas yield ml CH4/gVS 14.49 466.90 524.72  0501001502002503003504004500 5 10 15 20 25 30daysml123 Figure 4 Cumulative yield of methane   Similarly to the case of cumulative production of biogas and methane production from cobblestone 2 and 3, it is considerably higher than methane produc-tion of controlled sample 1. In addition, the share of methane in biogas in samples 2 and 3 is almost iden-tical and is close to 60 % while the share in the bio-gas of the sample is almost twice as small.  CONCLUSIONS  Based on the physical-chemical analysis of waste sludge from the municipal wastewater treatment plant and the maize hybrid cultivar “NS 444 Ultra”, as well as the preserved Bosanac variety, all three types of substrates represent potential biogas raw materials owing to very favourable VS content and HPK repre-senting the amount of organic matter from which me-thane is obtained, and a favourable ratio of the mac-ronutrient expressed through the ratio HPK: TKN. 4  S. Halilović, V. Stuhli, M. Zohorović, Z. Iličković, “Determination of the biomethanic potential of corn grain”, Technologica Acta, vol. 11, no. 1, pp. 1–4 ISSN 1840-0426 (P); ISSN 2232-7588 (E) http://tf.untz.ba/technologica-acta  By comparing the content of dry and volatile or-ganic matter before and after the process, it is easy to conclude that a certain part of matter has been trans-formed into gas products. Also, the value of HPK and TKN for all three samples is significantly lower at the end of the process compared to the HPK and TKN values in the substrates prior to the decomposi-tion process, which is particularly relevant for the 2 and 3 blends. Methane production from both sub-strates 2 and 3 is considerably larger in comparison to the methane production of the controlled sample 1. In addition, the proportion of methane in the biogas in samples 2 and 3 is almost identical and is close to 60 % while the biogas fraction of the blank test sam-ple is almost twice as small.  The specific production of methane produced from the sands and grains of hybrid maize NS 444 Ultra is 524.72 ml of CH4/gVS, while the sludge and the Bosanac grain is 466.90 ml of CH4/gVS.  REFERENCES [1] T. Amon, B. Amon, V. Kryvoruchko, W. Zollitsch, K. May-er, L. Gruber, "Biogas production from maize and dairy cat-tle manure-Influence of biomass composition on the me-thane yield”, Agriculture, Ecosystems and Environment, pp. 173-182, 2007.  [2] P. Balsari, P. Bonfanti, E. Bozza, F. Sangiorgi, "Evaluation of the influence of animal feeding on the performances of a biogas installation (mathematical model)", Proceedings of the 3rd International Symposium “Anaerobic Digestion, Boston, 1983.  [3] P. Vindiš, P. Muršec, C. Rozman, F. Cus, "A multi-criteria assessment of energy crops for biogas production", Journal of Mechanical Engineering, 2009. [4] Z. Osman, "Projekt biolinskog postrojenja", Diplomski rad, 2015.  [5] T. Al Seadi, D. Rutz, H. Prassl, M. Kottner, T. Finsterwal-der, S. Volk, R. Janssen, Priručnik za bioplin, Intelligent Energy Europe, 2008. [6] D. Čakija, "Proizvodnja silažnog kukuruza na OPG-u Čakija za potrebe bio-plinskog postrojenja bioplinara Ogranica, Gregurovec" Diplomski rad, 2-5, 2016.  [7] DIN 38 414-S1-1986-11 (1986): Analyses of Water, Drink-ing Water, Waste Water, Sludge, Sediments and Residues.   [8] A. Flor, L. Arroja, I. Capela, "Anaerobic co-digestion of organic fraction of municipal solid waste and waste activat-ed sludge at different ratios", Proceedings Sardinia 2003, Ninth International Waste Management and Landfill Sym-posium S. Margherita di Pula, Cagliari, Italy, 2003. [9] Method 2540-B and 2540 Solid-Solid E. Standard Methods for the Examination of Water and Wastewater. [10] Method 4500-Norg B. Standard Methods for the Examination of Water and Wastewater 20nd edition. APHA, Washington, DC, 1998. [11] BAS ISO 6060 Određivanje hemijske potrošnje kisika, 2000.   

Determination of the biomethanic potential of corn grain

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