European Biomass Conference and Exhibition 2017 ...

25th European Biomass Conference and Exhibition, 12-15 June 2017, Stockholm, Sweden

COMPARATIVE STUDY CONCERNING ANAEROBIC FERMENTATION OF DEGRADED CEREALS A. E. CIOABLĂ1, I. IONEL1*, G.A. DUMITREL2, M. D. VASILESCU1 POLITEHNICA Timişoara, Faculty for Mechanical Engineering 300222, 1 Mihai Viteazu Blv., Timisoara, Romania, Tel. 0040 256 403 748, [email protected], [email protected], [email protected] 2University POLITEHNICA Timişoara, Faculty of Industrial Chemistry and Environmental Engineering, 300223, 6 Vasile Parvan Blv., Timisoara, Romania, [email protected] 1University

ABSTRACT: The present work underlines the possibility of using two types of degraded cereal materials, with and without waste waters, in order to establish the influence of these additions. The paper focuses on the parallel experiments conducted in order to determine the main process parameters for two different batches containing degraded cereals, one containing residual water and the other containing normal tap water. The scope is to depict the main parameters’ values during the process and establish the general influence of waste water over degraded cereal materials. Keywords: anaerobic digestion, agricultural residues, wastewater, biogas, cereal

1

INTRODUCTION

increase considerably. Due to the continuous development of human society, wastewater has become more and more difficult to manage. By discharging, without treatment, into the surface water, the environment is polluted and the human health is seriously threatened. Anaerobic digestion is a cost effective alternative for wastewater management [16]. In this context, the aim of the present study was to determine the biogas potential of two degraded cereal materials, used in the anaerobic digestion process, alone or in combination with waste water from a beer factory.

According to International Renewable Energy Agency (IRENA), the worldwide renewable capacity recorded in 2015 the highest annual growth rate from history (8.3%), reaching a global value of 1985 GW [1]. The value represented almost one-fourth of the global electric generating capacity. This increase was related to the problems that society is currently facing: resource depletion, pollution increase, need for energy security and demonstrates that the efforts to eliminate these dangers are starting to work [2-4]. In this context, the anaerobic digestion process has become more and more studied because the biogas formed is an important source of renewable energy. During anaerobic digestion, in the absence of oxygen, the organic material undergoes chemical and biological transformations that have been divided into four stages: hydrolysis of proteins, carbohydrates and lipids; acidogenesis of amino acids, sugars, fatty acids and alcohols; acetogenesis with formation of acetic acid, hydrogen and carbon dioxide and methanogenesis with methane and carbon dioxide formation [5]. The ratelimiting step for a solid organic substrate is hydrolysis, but it changes to methanogenesis for a soluble organic substrate [6]. The product of digestion process, called biogas, is formed from a mixture of gases: mainly methane (40 – 75%), carbon dioxide (25 – 55 %) and small quantities of other gases (hydrogen sulfide, ammonia, nitrogen, oxygen and hydrogen) [7]. It can be further used for electricity and heat production or, as transport fuel. The by-product, called digestate, can replace the industrial fertilizers, having the qualities of a good soil conditioner [8-10]. In order to understand the influence of raw material composition on the efficiency of the anaerobic digestion process, over time, a high number of agricultural and industrial residues has been tested: organic domestic, garden and agro-industrial wastes, crop residues, manure, wastewater sludges, energy crops [11-13]. The results have led to the idea of simultaneous digestion of a mixture formed of two or more substrates. This method was called co-digestion. The advantages of this method are: the potential toxic compounds from the substrate are diluted, so their effect on the digestion process is diminished; the nutrients from the substrate are better balanced; the microorganisms are multiple and act simultaneously [14,15]. Through co-digestion it is expected that both the amount of biogas produced and its methane content will

2

EXPERIMENTAL PART

2.1 Description of pilot plant The pilot plant used for the anaerobic digestion process is presented in Fig. 1. It is functional mounted in the Multifunctional Laboratory of the Faculty for Mechanical Engineering, Politehnica University Timisoara, according two Patents (17-18) hold.

Figure 1: Pilot plant anaerobic digestion system The investigated agricultural biomass is grounded in a mill and then fed into the tank (1), where the preparation of the biomass suspension is done. The pump (2) is used to introduce the suspension into the fermentation batch reactors (3). The right pH of the fermentation process is assured by inserting correction agent from the tank (4), when needed. During the anaerobic digestion process, the biogas is produced. It is passed through a filter (5) for H2S removal and a CO2 retention system (6). The purified gas is sent through the pipe (8) to the users. The digestate is

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downloaded at the base of the reactors (9). The solid fraction is air dried and sent to a compost deposit, for further use as a fertilizer. If necessary, the liquid fraction is neutralized in the system (10) and sent to the sewage network. The temperature in the reactors is controlled with the system (11). In order to obtain a homogenous suspension, the bubbling system (12), made by polypropylene pipes, is used. A small tank (13) for biogas collection is placed at the top of the reactors. The reactors are operated under mesophilic temperature conditions. 75 kg of dry biomass and 2000 L water are used to prepare the suspension for anaerobic digestion. Biogas production of each digester was measured daily by means of a gas counter. Methane (CH4) and carbon dioxide (CO2) compositions (v/v) were measured by using a Delta 1600 IV gas analyzer. Temperature and pH were also continuously measured: the temperature by means of J thermocouples connected to AD-025V2DS-C temperature controllers and pH by means of pH sensors, model HI 1210, connected to pH controllers, model BL 981411. The residence time of the batches in the digesters was 37 days.

Table I: Properties of biomasses used in the anaerobic digestion process

2.2 Chemical analysis Two agricultural biomasses: degraded corn and tworow barley were used for this study. The substrates were prepared with water (1) degraded corn + water: DC; (2) degraded two-row barley + water: DTB, and (3) degraded two-row barley with wastewater from a beer factory - BW (degraded corn + wastewater: BW-DC; degraded two-row barley + wastewater: BW-DTB). The samples collected were successively subjected to physical and chemical analyses. The laboratory analyses were made according to the following standards: - EN 14774 – Solid bio-fuels – Determination of moisture content – Oven dry method (parts 2 and 3) [19]; - EN 14775 - Solid bio-fuels - Determination of ash content [20]; - EN 14918 - Solid bio-fuels – Determination of calorific value [21]; - EN 15290 – Solid bio-fuels – Determination of major elements [22]; - EN 15297 – Solid bio-fuels – Determination of minor elements [23]; - EN 15104 – Solid bio-fuels – Determination of total content of carbon, hydrogen and nitrogen – Instrumental methods [24]; - EN 15148 – Solid bio-fuels – Determination of the content of volatile matter [25]. All analyses were performed in duplicate, for attesting them with best and concluding result.

From the table I it can be observed that the ash content for beer factory wastewater is high, not being suitable for being used in firing processes. The net calorific value is high for all the used materials, representing a good indicator that there is a large availability of energetic potential, useful in conversion processes. The C/N ratio is in the recommended domain for DC and DTB batches, but has very low values in case of the BW material, thus it is necessary to use it only in co fermentation with cereal biomass.

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Biomass Moisture content (db) (%) Ash content (db) (%) Gross calorific value (db) (J/g) Net calorific value (db) (J/g) Carbon content (%)

DC

DTB

BW

10

10.7

5

1.55

2.22

26.5

18400

18354

17200

16800

16763

16000

40.3

40.1

36.5

Hydrogen content (%)

6.6

6.5

5.5

Nitrogen content (%)

1.3

1.38

7.1

0.103

0.114

0.44

0.034

0.097

0.27

85.7

82.4

42.5

Sulphur content (db) (%) Chlorine content (db) (%) Volatile matter content (db) (%)

The pH variation in the digester is shown in Fig. 2.

RESULTS AND DISCUSSION Figure 2: pH variation for studied materials

To assess the potential use of considered raw materials in anaerobic digestion process, they were physic-chemical characterized: moisture content, ash content, gross and net calorific value, carbon content, nitrogen content, hydrogen content, sulphur content, chlorine content, volatile matter content. The values are presented in table I.

The initial pH for DTB, DC and BW-DTB was in the range 8.5 – 9. A difference was recorded for the BW-DC, which showed an initial pH of 7.1 and maintained this value throughout the entire digestion process. The process of BW-DTB digestion started at a pH equal to 9. It decreased in the second days of fermentation to 6.9. For the next 20 day, the pH remained around this value. Then it started to slowly increased, at the end of the study reaching a value equal to 8. The pH during the digestion of DC and DTB was very unstable, as the conversion of acids molecules into biogas

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is marked by the increase of pH.. The decrease of pH is due to the hydrolysis of the degradable part of organic wastes. Even is the pH was relatively difficult to control, mainly due to the fact that the materials presents a low value of buffer in terms of maintaining a stable pH during time, the final values, obtained by using either a lime based suspension or caustic soda reached in due time the optimum values, corresponding with the neutral and recommended pH regime meaning values of (6.5 – 7.5). In the final stages of the process, all the studied material reached the neutral pH domain, but the time variation of pH shows that part of the materials are better suited for this type of anaerobe process. Fig. 3 shows the amount of methane produced over time, for the four substrates investigated.

Figure 4: Methane content in biogas

Figure 3: Cumulative biogas production Figure 5: Carbone dioxide content in biogas In the case of BW-DTB and BW-DC, the generation of biogas started in the second day of the process. This demonstrates that the degradation of organic matter started almost immediately. Biogas production for BW-DC showed a rapid increase in the first 10 days, and then diminished, seeming to end on day 30. In the case of the BW-DTB substrate, biogas production has been steadily increasing over the entire digestion period. For the other two substrates a lag time of 10 days and 6 days was recorded for DC and DTB, respectively. These delays can be due to the improper conditions of digestion (not enough microorganisms to degrade the organic matter or the fermentation conditions are not suitable for the existing bacteria). The biogas production was constantly increasing during the digestion process, the evolution from figure 3 suggesting that the digestion process should be continued. The highest amount of biogas was obtained for the codigestion situations: 20.4 m3 for BW-DC, 14.9 for BWDTB, while the production of biogas for DTB was 7.4 m3 and for DC, 1.7 m3. Fig. 4 and 5 show the methane and carbon dioxide variation in time, for all the batches investigated.

In Fig. 4 it can be seen that the biogas from the codigestion of BW-DC and BW-DTB delivered a high content of methane, already from the first days of the process. The methane content gradually increased during digestion of DC and DTB. The maximum methane percentage was reached after 16 days. The increase of methane concentration in biogas leads to the decrease in carbon dioxide concentration. The resulted digestate was characterized from physicchemical point of view, the results being presented in table II. Table II: Characteristics of the residues from anaerobic digestion process (data for db – dry basis) Digestate from anaerobic digestion of: Moisture content (%) Ash content (db) (%) Carbon content (%) Hydrogen content (%) Nitrogen content (%) Sulphur content (%) Chlorine content (%) Volatile matter content (%)

BW- BWDC DTB 3.04 0.75 2 2.5 47.3 56.9 4.11 3.24 32.3 27.4 47.1 48.7 4.2 3 6.64 7.16 1.69 1.09 1.20 1.12 0.180 0.131 0.062 0.081 0.004 0.011 0.308 0.273 40.6 59.1 76.4 81.2 DC

DTB

From table II one observes, by comparison to the analysis before the process, that the ash content for DC and

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DTB is very high – the main reason for this behavior being the fact that for those materials the pH correction was accomplished with the help of a lime based suspension, which contained high calcium quantities and increased the mineral part of the materials, making them unsuitable for further combustion or co –combustion processes. Because of this aspect, the next determinations have been achieved using a caustic soda based suspension, which had no major influence over the ash content for the BW-DC and BWDTB batches. Sulphur and chlorine content for all the batches was low, and from this point of view there were no issues relative to the risk of damaging the burners inside the combustion equipment, if the biogas produced is designated for further combustion or co-combustion processes.

[4] [5] [6]

[7] [8] [9]

[10]

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CONCLUSIONS [12]

The studies carried on focusing on the use of cereal biomass in anaerobic digestion plants for biogas production have led to the following conclusions: - Degraded agricultural cereals are a suitable raw material for the anaerobic digestion process; - The use of a digestion substrate consisting of the biomass mix with residual water from a bear factory increases considerably the amount of biogas obtained from anaerobic digestion, but also the methane content; - The most effective substrate for anaerobic digestion was found to be BW-DC, followed by BW-DTB, DTB and DC; - The digestate composition as resulted from experiments illustrates that it can be successfully used as fertilizer in agriculture.

[13]

[14] [15] [16]

[17]

[18] 5

ACKNOWLEDGEMENTS

This work was supported also by a grant financed by the Romanian National Authority for Scientific Research and Innovation, CNCS – UEFISCDI, project number PNII-RU-TE-2014-4-1043.

[19]

[20] [21]

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REFERENCES [22]

[1]

[2] [3]

International Renewable Energy Agency – IRENA, Renewable Energy Capacity Statistics, (2016), pp. 56, http://www.irena.org/menu/ index.aspx?mnu=Subcat&PriMenuID=36&CatID= 141&SubcatID=1719 (accessed in May 5, 2017). F. Umbach, Energy Policy, 38(3), (2010), pp. 1229– 40. L. Hughes, Y. P. Lipscy, Annu. Rev. Polit. Sci., 16 (1), (2013), pag. 449–69.

[23] [24]

[25]

883

A. P. Mathews, Procedia Comput. Sci., 32, (2014), pag. 731-737. B. Demirel, P. Scherer, Rev. Environ. Sci. Bio., 7, (2008), pag.173–190. J. Ma, C. Frear, Z.Wang, L. Yu, Q. Zhao, X. Li, S. Chen, Bioresour. Technol., 134, (2013), pag. 391– 395. R. Kadam, N.L. Panwar, Renew. Sustainable Energy Rev., 78, (2017), pag. 892 – 903. R. Nkoa, Agron. Sustainable Dev., 34 (2), (2014), pag. 473-492. F. Monlau, C. Sambusiti, E. Ficara, A. Aboulkas, A. Barakata, H. Carrère, Energy Environ. Sci., 8, (2015), pag. 2600-2621. T. Al Seadi, C. Lukehurst, Quality management of digestate from biogas plants used as fertiliser, IEA Bioenergy, (2012), pag. 40. R. A. Labatut, L. T. Angenent, N. R. Scott, Bioresour. Technol., 102, (2011), pag. 2255–2264. V.N. Nkemka, M. Murto, Bioresour. Technol. 128, (2013), pag. 164–172. H. Bouallagui, H. Lahdheb, E. Ben Romdan, B. Rachdi, M. Hamdi, J. Environ. Manage., 90, (2009), pag. 1844–1849. R. M. Jingura, R. Matengaifa, Renew. Sustainable Energy Rev.,13, (2009), pag. 1116–1120. R. Karray, F. Karray, S. Loukil, N. Mhiri, S. Sayadi, Waste Manage., 61, (2017), pag. 171–178. J.B. van Lier, N. Mahmoud, G. Zeeman, Anaerobic wastewater treatment in Biological Wastewater Treatment: Principles, Modeling and Design, IWA Publishing, London, UK, (2008), pag. 401 – 442. Barboni, V., Ionel, I., et comp. Process and installation for producing biogas from municipal biodegradable wastes with co2 retention, Patent Number: RO125718-A0; RO125718-B1, 2010. Savu, A., Ionel I., et comp. Process and installation for obtaining biogas from biomass waste, Patent Number: RO 122047/28.11.2008. European Standard EN 14774, Solid bio-fuels – Determination of moisture content – Oven dry method, (2009). European Standard EN 14775, Solid bio-fuels Determination of ash content, (2009). European Standard EN 14918, Solid biofuels – Determination of calorific value, (2010). European Standard EN 15290, Solid bio-fuels – Determination of major elements, (2011). European Standard EN 15297, Solid bio-fuels – Determination of minor elements (2011). European Standard EN 15104, Solid bio-fuels – Determination of total content of carbon, hydrogen and nitrogen – Instrumental methods, (2011). European Standard 15148, Solid bi-ofuels – Determination of the content of volatile matter, (2010).