Combination of decentralized waste drying and SSF techniques for household biowaste minimization and ethanol production

Combination of decentralized waste drying and SSF techniques for household biowaste minimization and ethanol production

Waste Management 52 (2016) 353–359 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman Comb...

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Waste Management 52 (2016) 353–359

Contents lists available at ScienceDirect

Waste Management journal homepage: www.elsevier.com/locate/wasman

Combination of decentralized waste drying and SSF techniques for household biowaste minimization and ethanol production A. Sotiropoulos a,⇑, I. Vourka a, A. Erotokritou a, J. Novakovic a, V. Panaretou a, S. Vakalis b, T. Thanos a, K. Moustakas a, D. Malamis a a National Technical University of Athens, School of Chemical Engineering, Unit of Environmental Science and Technology, 9, Heroon Polytechniou Str., 15773 Zographou Campus, Athens, Greece b Free University of Bolzano, Faculty of Science and Technology, Piazza Università 5, 39100 Bolzano, Italy

a r t i c l e

i n f o

Article history: Received 14 December 2015 Revised 27 February 2016 Accepted 24 March 2016 Available online 12 April 2016 Keywords: Ethanol Biofuels Biowaste Waste management Drying Decentralized

a b s t r a c t The results of the demonstration of an innovative household biowaste management and treatment scheme established in two Greek Municipalities for the production of lignocellulosic ethanol using dehydrated household biowaste as a substrate, are presented within this research. This is the first time that biowaste drying was tested at a decentralized level for the production of ethanol using the Simultaneous Saccharification and Fermentation (SSF) process, at a pilot scale in Greece. The decentralized biowaste drying method proved that the household biowaste mass and volume reduction may reach 80% through the dehydration process used. The chemical characteristics related to lignocellulosic ethanol production have proved to differ substantially between seasons thus; special attention should be given to the process applied for ethanol production mainly regarding the enzyme quality and quantity used during the pretreatment stage. The maximum ethanol production achieved was 29.12 g/L, approximately 60% of the maximum theoretical yield based on the substrate’s sugar content. The use of the decentralized waste drying as an alternative approach for household biowaste minimization and the production of second generation ethanol is considered to be a promising approach for efficient biowaste management and treatment in the future. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction Waste management still remains a challenge for the growing world. From the total amount of Municipal Solid Waste (MSW) produced a 40–50% of it is considered to be biological waste. This percentage is higher in low and middle income countries according to the World Bank (2012). The main environmental threat from biowaste is the production of methane during their decomposition in landfills. It is estimated that landfills are the third most important source of methane emissions in the United States of America (USA) (World Bank, 2012). In the USA the strategy is to capture the landfill methane through the Landfill Methane Outreach Program (EPA, 2012). In the European Union (EU), the Landfill Directive (Directive 1999/31/EC) obliges Member States to reduce the amount of biodegradable municipal waste going to landfill by 35% of 1995 levels by 2016 (for some countries by 2020) which is expected to significantly reduce the problem. Moreover, Directive 2009/28/EC ⇑ Corresponding author. E-mail address: [email protected] (A. Sotiropoulos). http://dx.doi.org/10.1016/j.wasman.2016.03.047 0956-053X/Ó 2016 Elsevier Ltd. All rights reserved.

«on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/77/EC and 2003/30/EC» obliges member states to use renewable energy resources. The fact that there is an ongoing economic crisis in many EU countries while, the predominant method of waste management and treatment is still landfilling, constitutes a significant problem for reaching legally-binding targets set by the EU legislation. The fact also, that the EU has set a 7% cap on biofuels produced from food crops in transport fuels, obliges member states to use alternative resources in order to reach the targets set. The already existing technologies, in many cases, need further optimization while they are unable to treat biowaste due to the fact that the raw material will biodegrade, loosing critical substances, if not treated ontime. Moreover, many biowaste treatment processes used today, are considered to be complicated and problematic and need to be further optimized. European policy focuses on actions taken towards resource efficiency, circular economy and climate change adaptation and mitigation. A concrete strategy on circular economy and resource efficiency has not been elaborated up until now, while targets set by the European Commission (EC) policy in regard to the drastic

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reduction of greenhouse gases (GHGs), that play an important role in the negative impacts of climate change, have not been defined per sector. Decentralized household biowaste drying for the production of fully dehydrated lingo-cellulosic biomass out of household biowaste and the subsequent production of second generation of ethanol, by using its carbohydrate content with the use of the SSF process (Sun and Cheng, 2002) constitutes a waste management and treatment option that has never been tested at any scale in the past. The SSF process involves the simultaneous batch acid hydrolysis and fermentation of the lignocellulosic substrate, while it can also operate as a fed-batch process which is considered to provide substantial benefits to the whole environmental and economic viability of the process. The process is used for the treatment of different types of lignocellulosic materials (Olofsson et al., 2008) such as agricultural products and waste. The already existing processes use raw household biowaste material and their efficiency remains low, due to lack of stability in the substrate used on the one hand, and microbial activity that intercepts the enzyme activity during the fermentation process on the other hand, thus they do not operate at full scale worldwide (Sotiropoulos et al., 2015). The fact that the mass and volume of the raw material is significantly reduced with relatively low energy consumption (0.9 kW h/kgwet substrate) along with the fact that the carbohydrate content of the dehydrated material is preserved (Sotiropoulos et al., 2015), while the ethanol yield produced seems to be satisfying when compared to bibliography, constitutes a most promising and concrete, regarding its results, option for household biowaste management and treatment.

2. Materials and methods 2.1. Description of the case study areas The Municipalities in which the innovative household biowaste (dried at decentralized level) to ethanol waste management scheme was established and implemented were PapagosCholargos and Aspropyrgos Municipalities. Both of the Municipalities belong to the Attica region in Greece. The total amount of Municipal Solid Waste (MSW) generated in Papagos-Cholargos Municipality in 2014 was 17,986 t year 1 (392.3 kg cap 1 year) this quantity is less by approximately 8% than the one recorded by Sotiropoulos et al. (2015), which could be accredited to the ongoing economic crisis in Greece which has contributed to the significant reduction of MSW produced by the civilians (civilians throw less). In Aspropyrgos Municipality the quantity of MSW produced for 2014 was 16,114 t year 1 (534.3 kg cap 1 year). In both Municipalities, the MSW generated are sent to the landfill of Ano-Liosia in Attica region, while a recycling system which includes the source separation of packaging waste using 610 blue bins for the case of Papagos-Cholargos and 450 for the case of Aspropyrgos Municipality (in both case the capacity is 1.100 L) has been established at a small scale. The collected recyclables in both cases, are transferred to the Mechanical Biological Treatment (MBT) plant of Ano-Liosia in Attica, in order to be recycled. Both of the Municipalities did not produce biofuels at any scale at the time this research started. The selection of the participating households was performed on a voluntary basis by providing the necessary publicity and awareness raising campaigns in both Municipalities. In total 82 residencies (251 civilians) participated the demonstration of this innovative waste management scheme while more than 160 residencies showed willingness to participate to this research.

2.2. Training of the participating households/implementation of the innovative household biowaste to ethanol management scheme Training seminars in the Municipalities and door to door for the civilians were implemented. The seminars main target was for the participating civilians, to provide pure substrate, for the bioconversion process of the dehydrated material, to take place. The seminars included: (a) introduction of the civilians in source separation techniques, (b) information on the environmental and socioeconomic benefits of the proposed household biowaste management scheme for both Municipalities, (c) presentation of the source separation guide to the civilians, and (d) presentation of the data that should be recorded during the implementation of the pilot program. For the implementation of the innovative household biowaste management and treatment scheme, the following equipment was distributed to the participating householders: (1) a 23 L commercialized kitchen waste bin that was placed in the householders’ kitchens for the collection of their biowaste, (2) a 120 L brown bin for the collection of the source separated household biowaste outside the participating households and (3) a source separation manual with guidelines for the proper separation of the generated household biowaste. The waste material that should be disposed in the waste bins were: Kitchen waste which included all waste produced in kitchens in every form (cooked and uncooked) such as: pasta, rice, flour, cereals, meat, fish and bones, dairy, fruits and vegetables, including kitchen paper waste and garden waste in order to achieve higher cellulose content to our substrate. The source separated household biowaste were transferred at the National Technical University of Athens (NTUA) facilities by the Municipalities waste authorities, 3 times per week for a period of 12 months (1 year) in order to be further treated. The waste were manually sorted by the research staff in order to define its purity levels while, it was further treated with the use of a commercialized biomass dryer in order to reduce its mass and volume and simultaneously preserve the incoming substrate’s characteristics (Sotiropoulos et al., 2015). The main parts of the drying method used can be seen in Fig. 1: The waste drying system used was a drum dryer with an agitation system used for crushing and pulverizing the material to 1–2 mm diameter. The specific model used was GC-100 of GAIA Corporation. The drying temperature was 175 °C while the dryer operated for an 8 h period in order to completely dehydrate 50 kg of wet substrate. Two trials were performed on a daily basis (16 h operation). The final dry product, having approximately 1–2 mm diameter was further enzymatically treated with the use of a pilot scale bioconversion facility installed at the NTUA premises. The main parts of the facility used for the bioconversion process are illustrated in Fig. 2: The waste management scheme and its full operation is described in the Waste2bio project DVD film (Waste2bio Project DVD film, 2015)

2.3. Evaluation of the waste management scheme Extended physicochemical characterization of the source separated household biowaste was performed by measuring a wide variety of parameters, related to the assessment of the effectiveness of the waste management scheme and the bioconversion process used. The assessment of the innovative waste management scheme was implemented through the evaluation of the following parameters:

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Raw material placed inside the waste dryer

355

Dried material at the end of the process

Fig. 1. Commercialized decentralized waste dryer schematic diagram.

Fig. 2. Pilot scale bioconversion facility.

 The purity level of the incoming household biowaste was determined through optical sorting of the incoming biowaste. The sorting took place, each time the waste were delivered at the NTUA facilities.  Incoming biowaste mass was measured prior and after the drying process with the use of a digital scale.  Incoming biowaste volume was measured before and after the drying process by calculating the volume of the initial substrate and the final dry product in a graduated cylinder container used for the purposes of the research.  The energy consumption for the drying of the feedstock material at decentralized level, was recorded through direct measurements with the use of an energy meter (Sotiropoulos et al., 2015).  pH was measured based on EPA Method 9045D using a pH meter (Mettler Toledo MPC 227 pH/Conductivity Meter).  The remaining water content of the collected biomass was determined after drying the collected samples at 105 °C for approximately 24 h.  The determination of structural carbohydrates, and lipids was performed using HPLC based on Sluiter et al. (2004).  The determination of total reduced sugars, glucose content and ethanol was performed using the method described by Dogaris et al. (2009).

 The fermentation of the thermally pretreated material was held in the 200 L bioconversion facility, in which a quantity of dried waste was placed in a concentration of 30% (w/v). Followed the pH was adjusted to 5.0 (common optimum pH for the enzymes used). The appropriate quantity of enzymes was added so that the activity of a-amylase (Liquozyme DS SC) to be approximately 0.049 and 5.1 U/g of starch, (Spirizyme Fuel) 5.0 U/g of starch, mix 5:1 (v/v), CelluclastÒ 1.5 L and Novozyme 188, Ò Cellic CTec2, and so that the total cellulase activity in any case to be 10 g FPU/cellulose.  The material was further treated hydrothermally in three stages. More specifically, 30 min at 85 °C with Liquozyme DS SC, then 30 min at 65 °C with Spirizyme Fuel and 6 h with CelluclastÒ 1.5 L, Novozyme 188 and ÒCellic CTec2 at 50 °C. Finally, after adding 15 mg/g of dry yeast from LEAF technologies, the fermentation process took place until there was no more CO2 coming out of the lab reactor. It should be stressed that specific samples with the chemical properties recorded in Table 4, was used for the fermentation process in order to be able to obtain concrete results.  Crude protein in the substrate and the fermentation residue was estimated using Kjeldahl’s method as described in AOAC methods (1995). 3. Results and discussion 3.1. Results in regard to the waste management scheme efficiency The optical inspection of the incoming raw material (household biowaste) revealed that the purity level reached 100% since the presence of non-biodegradable materials was barely equal to 0.001%. This was achieved through proper training of the participating householders and the fact that the civilians did not have to separate their waste in a complicated way, rejecting certain categories of biowaste from the total amount they placed inside their waste bins (e.g. cooked from uncooked kitchen waste, paper towels, bones, acidic biowaste, etc.). The civilians threw all the quantity of the kitchen and garden waste produced. According to Favoino (2003), the purity level of source separated biowaste in Italy reached 98–99% while Gibbs and Hogg (2007) reported that

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in Great Britain the purity levels of household biowaste reached 95% using one bin for a certain number of households. Finally, Sotiropoulos et al. (2015) reports that using the household waste drying technique the purity level of the incoming biomass reached 99.9%. The quantity of household biowaste that was sourced separated and transferred at the NTUA facilities for further treatment with the use of the decentralized waste drying system, along with the mass of the dried waste and the system’s energy consumption, is recorded in Table 1. More than 260 trials of the waste drying process were performed in total. The average energy consumption of the decentralized waste dryer was recorded equal to 0.91 kW h kg 1 while it ranged between 0.91 and 0.92 kW h kg 1. The energy consumption is significantly lower than the energy consumption of the household waste drying method which has been recorded equal to 1.87 kW h kg 1 (Ranged between 0.56 and 3.41 kW h kg 1) by Sotiropoulos et al. (2015). The mean household biowaste mass reduction was also recorded equal to 78% w/w approximately, which is higher than the one recorded during the implementation of the household waste drying method, as described by Sotiropoulos et al. (2015). This differentiation can be seen in Fig. 3. It should be stressed that decentralized waste drying involves the drying of waste at a decentralized facility while domestic waste drying involves the drying of waste inside the households with the use of a domestic waste dryer (drying at source). From the results, it was recorded that the raw material composition did not have significant effect to the decentralized waste drying process in addition to domestic waste drying technique where the quality of the incoming material was recorded to have significant effect in the material mass reduction as recorded by Sotiropoulos et al. (2015). The fact that the material was pulverized during the dehydration process when using the decentralized waste drying method while for the case of domestic waste drying the material is just being dehydrated and not pulverized, is considered to have contributed to this observation. The volume reduction of the biowaste was recorded equal to 83.25% (values ranged between 74.53% and 87.17%). This differentiation can be attributed to the differentiation of the incoming waste material which differs substantially between seasons in regard to its initial moisture content, size and shape, etc. The values of pH and moisture content of the dehydrated household biomass per season are presented in Table 2. It should be stressed that the moisture content of the dehydrated material reached 3.61% w/w ranging from 2.44 to 5.53% w/w. The pH values were recorded to be rather stable throughout the year, which can be attributed to the absence of water inside the waste material and the homogenization during the drying process. According to Sundberg et al. (2011), the pH of household waste collected for composting, ranged between 4.7 and 6.1. Malamis et al. (2015), reported that the pH of source segregated household

Table 1 Parameters recorded throughout the waste management scheme demonstration phase. Parameter

Value

Unit of measurement

Wet biowaste mass (person month 1) 251 civilians biowaste mass (month 1) Wet biowaste mass of 251 civilians for 12 months Dried biowaste mass of 251 civilians for 12 months Total energy consumption of the commercialized waste dryer

4.8 1204.8 14457.6

kg kg kg

5783.6

kg

13156.42

KW h

90 78.37

80

Mass Reduction (%w/w)

356

67.44

70 60 50 40 30 20 10 0

Decentralised Waste Drying

Waste Drying

Fig. 3. Comparison of mass reduction between decentralized waste drying and domestic waste drying methods.

Table 2 Seasonal variation of the values of pH and moisture content (% w/w) of the raw household biomass. Seasons

pH

SDTV

Water Content (% w/w)

SDTV

Spring Summer Autumn Winter

5.41 5.55 5.55 5.44

0.06 0.04 0.1 0.12

92 86 73 70

0.01 0.04 0.32 0.56

biowaste ranged between 5.09 and 5.31, while Fernández et al. (2015), reported pH of communal biowaste equal to 4.98. Variations of the raw material water content have also been recorded since this varied from 70% to 92% w/w. The fact that the material’s water content was significantly higher during the summer period than in the winter, is attributed to the civilians’ waste production habits. The results of the determination of the starch, cellulose and glucose content of the dried biowaste material are presented in Table 3. As can be seen in Table 3, the starch content varied significantly between seasons between 3.86% and 10.12% w/w and was found to be less during summertime when compared to the rest of the seasons, since the participating civilians seemed to throw (not consume) waste with less starch content. Results on the seasonal variation of household biowaste starch content have not been recorded up until now. Αdditional data on household biowaste starch content has been recorded equal to 34.8% w/w by Zhang et al. (2011) while Moon et al. (2008) reported high starch content at 30.1% w/w. It should be stressed that such high values were not recorded throughout the research duration in regard to household biowaste which could be attributed to the differentiation of the civilians’ waste habits. The cellulose content of the dehydrated waste was higher during spring and autumn since, according to the optical observations conducted, during these seasons, the presence of cuttings (leaves and woody biomass) from gardens was higher, contributing to the raise of incoming cellulose since these type of waste have significantly high cellulose content, enriching the waste samples. In

Table 3 Seasonal variation of starch, cellulose, glucose (% w/w) content of the dried household biowaste. Seasons

Starch (% w/w)

SDTV

Cellulose (% w/w)

SDTV

Glucose (% w/w)

SDTV

Spring Summer Autumn Winter

9.77 3.86 8.70 10.12

1.05 0.16 0.91 0.72

13.95 6.44 26.34 12.44

3.06 0.69 3.30 2.51

0.52 1.39 2.25 3.01

0.03 0.09 0.44 0.13

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to cold months (Autumn, Winter). This may be attributed to the fact that glucose in easily consumed by microbes during the warm months due to elevated temperatures and high microbial activity thus, based on Sotiropoulos et al. (2015), the glucose is partially consumed by microbes before it reaches the decentralized waste drying facility. On the other hand, during the cold months, the microbial activity is expected to be significantly smaller due to lower temperatures. It should be stressed that the water content of the material is also expected to have played an important role to this variation. Other researchers have recorded the quantity of glucose presented in their food waste samples. Matsakas et al. (2014) have recorded glucose content of 4.39% w/w while Sotiropoulos et al. (2015) have recorded glucose content of 2.2% w/w before the biodegradation takes place. The raise of microbial activity and the number of bacterial cells and fungi produced, contributing to the reduction of glucose and the biodegradation of the biowaste material, has been recorded by Mayrhofer et al. (2006). The fact that there is a significant seasonal variation to the dehydrated substrates’ chemical characteristics, in regard to its starch, cellulose and glucose content, is considered to have direct effect to the bioconversion process since, the molecules which are able to produce soluble sugars differ, thus affecting the overall bioconversion process efficiency at a negative or positive manner. This could be surpassed by combining the dried household biowaste mass with an additional waste mass such as waste paper thus, producing a substrate with stable carbohydrate content which would be beneficial for the whole waste management scheme. Finally, the protein of the original substrate was determined equal to 12% w/w while the protein in the fermentation residue was determined equal to 25% which is attributed to the enzymes

Table 4 Household biowaste initial characteristics related to the bioconversion process. Parameter

Value g/100 g dry-solid

STDV

Water-soluble Total reducing sugars Glucose Sucrose Fructose Cellulose Starch

35.99 14.11 3.46 3.47 4.38 11.21 6.67

0.08 0.35 0.10 0.68 0.09 0.22 0.46

Table 5 SSF process under different conditions. Amylolytic enzymes

Cellulolytic enzymes

Liquozyme SC DS (U/g starch)

Spirizyme Fuel (U/g starch)

Celluclast 1.5 L/Novozyme 188 (5/1 V/V) (FPU/g cellulose)

Cellic CTec2 (FPU/g cellulose)

0.049 5.1 0.049 5.1

5.00 5.00 5.00 5.00

10 10 – –

– – 10 10

this case also, the seasonal variation of cellulose content in household biowaste has never been recorded. Based of bibliography, the cellulose content of various food waste has been recorded by Sotiropoulos et al. (2015) and was equal to 17.2% while Matsakas et al. (2014) recorded cellulose content of 18.2% w/w. Yan et al. (2012) reported rather low cellulose content 1.98% w/w. The glucose content of the dried material varied significantly between seasons. More specifically, during the warm months (spring, summer), the glucose content was less when compared Table 6 Results of bioethanol production for the dried household biowaste using the SSF process.

a b

Enzyme load

Ethanol production (g/L)

Productivity ethanol (g/L h)

% Maximum theoretical yielda

% Maximum theoretical yieldb

Liquozyme Liquozyme Liquozyme Liquozyme

28.90 29.12 27.21 27.67

1.39 3.01 2.54 2.80

170.01 176.28 159.66 162.42

62.35 63.72 58.55 59.57

(0.053)/Spirizyme (5.06)/Celluclast/Novozyme (10 FPU/g Cellulose) (5.1)/Spirizyme (5.00)/Celluclast/Novozyme (10 FPU/g Cellulose) (0.049)/Spirizyme (5.00)/Cellic (10 FPU/g Cellulose) (5.1)/Spirizyme (5.00)/Cellic (10 FPU/g Cellulose)

Based on the maximum theoretical yield of ethanol from the bioconversion of non-structural sugars. Based on the maximum theoretical ethanol yield from the bioconversion of non-structural sugars and cellulose (Yethanol/sugar = 0.504).

Fig. 4. Ethanol production though time (j), glucose ( ) and total reducing sugars ( ) in SSF hydrothermally pretreated material batch process project. Combination of amylolytic and cellulolytic enzymes: (a) Liquozyme 0.049 U/g starch, Spirizyme 5.0 U/g starch, Celluclast/Novozyme (5/1 V/V) 10 FPU/g of cellulose. (b) Liquozyme 5.31 U/g of starch, Spirizyme 5.00 U/g starch, Celluclast/Novozyme (5/1 V/V) 10 FPU/g cellulose.

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Fig. 5. Ethanol production through time (j), glucose ( ) and total reducing sugars ( ) in SSF hydrothermally pretreated material batch process project. Combination amylolytic and cellulolytic enzymes: (a) Liquozyme 0.049 U/g starch, Spirizyme 5.00 U/g starch, Cellic CTec2 10 FPU/g of cellulose. (b) Liquozyme 5.1 U/g starch, Spirizyme 5.00 U/g starch, Cellic CTec 2 10 FPU/g cellulose.

used throughout the SSF process since the enzymes use are proteins. The fat content to the initial substrate was determined to be 6% while at the final residue it was 8%. 3.2. Bioconversion process results In Table 4 the content of soluble components and total polysaccharides of the dehydrated biomass material used during the bioconversion process are recorded. The quantity of amylolytic and cellulotic enzymes used for the SSF process is recorded in Table 5. In Table 6, the results of the production of dried household biowaste derived from 12 bioconversion trials using the SSF process are recorded. From Figs. 4 and 5 it is derived that the fermentation process has an increased rate during the first 13 h approximately. The rate slightly drops until the end of the process which is in 24 h time period. It should be noted that the glucose is minimized during the first 12 h. The maximum ethanol produced reached 29.12 g/L as reported in Table 6. Man et al. (2011), reported ethanol production of 24.17 g/L using Kluyveromyces marxianus on food waste. Moon et al. (2009), also performed a 3-h liquefaction process of food waste using both carbohydrases and amyloglucosidases and the ethanol production reached 29.1 g/L Wang et al. (2008) reported ethanol production of about 33.05 g/L of household waste (kitchen waste) which, the initial total sugar content was high though (63.88% w/w). Uncu and Cekmecelioglu (2011) reported 32.2 g/L ethanol production after 59 h of fermentation using food wastes treated with amylases while Walker et al. (2013), also used food waste with high starch content, but the produced ethanol was relatively low (8 g/L). 4. Conclusions Concluding, household biowaste mass and volume reduction may reach 80% using the decentralized drying method. Moreover, household biowaste, contain significant amounts of nonstructural sugars and structural polysaccharides (cellulose, starch, glucose) which differ substantially between seasons. The existence of such sugars give added value to the final dry biomass (dehydrated biowaste) thus, contributing to its use for the production of ethanol using this alternative resource. This differentiation

should be taken into consideration when designing a biowaste to ethanol waste management scheme in order to determine the enzymatic load that should be used. The fact that this differentiation exists, is expected to contribute to the ethanol yields produced using the SSF process producing high ethanol yields during certain periods and low ethanol yields during other periods in addition to first generation ethanol where this differentiation is not significant. Moreover, it should be added that the biomass qualitative characteristics may differ between different regions of the world thus; initial sampling should be implemented before starting a household biowaste to ethanol project in order to determine the produced biowaste characteristics. Finally, the results of the bioconversion of dehydrated household biowaste into ethanol revealed that the ethanol produced reached 29.12 g/L. It reached approximately 63% of the maximum theoretical yield, which means that the process could be further optimized. Thus, more trials should be performed regarding different quantities of the same enzymes and the elaboration of kinetic models for the dehydrated biowaste fermentation process. The production of ethanol is considered to be rather complicated since not only the substrates’ characteristics differ substantially between seasons but also, the quality and quantity of the enzymes used also differs substantially as a result of this differentiation. More research should be conducted in order to define the best way such a bioconversion facility should operate and also in regard to the economic viability of the waste management scheme. Acknowledgments This work has been elaborated in the framework of the LIFE + project entitled: Development and demonstration of an innovative method of converting waste into bioethanol, Waste2Bio, (LIFE 11 ENV/GR/000949, 2012–2016), which is co-financed by the European Commission. The authors would also like to thank Novozymes Corporation for generously providing the enzyme samples used for the operation of the bioconversion facility and Vekkos Recycling Solutions for providing the decentralised biomass dryer for the needs of this research and also LEAF technologies for generously providing the yeast. References AOAC, 1995. Official methods of analysis. In: Helirich, K. (Ed.), Association of Official Analytical Chemists, 16th ed. AOAC, Arlington, VA, USA.

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