Sustainable energy for a winery through biogas production and its utilization: A Chilean case study

Sustainable Energy Technologies and Assessments 37 (2020) 100640

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Sustainable energy for a winery through biogas production and its utilization: A Chilean case study

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S. Montalvoa, J. Martineza, A. Castilloa, C. Huiliñira, , R. Borjab, Verónica Garcíac, Ricardo Salazard a

Environmental Biotechnology Laboratory, Department of Chemical Engineering, Universidad de Santiago de Chile, Alameda 3363, Central Station, Santiago, Chile Instituto de la Grasa (CSIC), Campus Universitario Pablo de Olavide – Edificio 46, Ctra.de Utrera, km 1, 41013 Sevilla, Spain c Department of Food Science and Technology, Universidad de Santiago de Chile (USACH), Santiago, Chile d Department of Materials Chemistry, Environmental Electrochemical Laboratory, (LEQMA), Faculty of Chemistry and Biology, Universidad de Santiago de Chile, Alameda 3363, Central Station, Santiago, Chile b

A R T I C LE I N FO

A B S T R A C T

Keywords: CO2 emissions Energy Kinetic study Methane production Vineyard residues

The anaerobic digestion of organic residues generated from the wine production process was evaluated. Organic residues namely the stalks, pomace, vine shoots and waste-activated sludge (WAS) from the liquid waste treatment plant and wine lees were used as substrates. A physical and chemical characterization of the solid residues was carried out, demonstrating that the different residues had favorable properties for methane production, although most had acidic characteristics. It was concluded that the highest methane yields (LCH4/kg VS) were achieved in the digesters operating with wine lees and WAS from the aerobic treatment plant with values of 876 ± 45 and 690 ± 25 L CH4/kg VS for day 57 of the batch process. By contrast, the wine shoots gave the lowest methane yield achieving values of 93 ± 5 and 150 ± 6 L CH4/kg VS on days 30 and 57, respectively. An energy balance was made for the use of biogas in a wine production plant, observing that the amount of biogas generated was sufficient to supply all the necessary energy used by the production plant. An environmental analysis was also carried out focused on the emission of greenhouse gases.

Introduction The worldwide production of wine is a large and heavily industrialized market. It is a timed, multi-stage process which produces a large amount of organic and inorganic waste. The processing of grapes into wine and its main relevant co-products (distilled beverages) is a process characterized by the generation of waste streams at the major steps involved, including agricultural practices such as pruning and exfoliation (branches and leaves), winemaking (skins, seeds, stems, lees) and distillation (solid and liquid residues) [1,2]. Winery wastewater is a major waste stream resulting from a number of activities which include tank, floor and equipment washing, barrel cleaning, wine and product loss, bottling facilities, filtration units, and rainwater captured in the wastewater management system [3]. Aerobic treatment systems are commonly used for the treatment of winery wastewater, because of their high efficiency and ease of use. Conventional activated sludge (CAS) treatments achieve removals of even up to 98% for COD (influent value = 2000–9000 mg/l) [4,5], and 50% for BOD5 [6]. However, in the aerobic process, due to the growth of the

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biomass, a biological sludge known as waste activated sludge (WAS), is generated and must be stabilized. Chile is currently the fourth largest wine exporter after France, Spain and Italy. It should be noted that its total wine production in 2018 reached 1,289,896,983 L, 35.9% higher than the previous year [7]. Different studies have been carried out to recover the added-value compounds present in these wastes [8–11]. Despite these studies, many of which have yielded very good results from the process point of view, the application of methods for recovering compounds and by-products from wine residues on an industrial scale is still extremely limited due to: 1) many of these studies are very specific; 2) the natural variation in the composition of vineyard residues does not guarantee the obtaining of a by-product of homogenous and constant quality; 3) extraction methods and sometimes purification of the desired products are complicated and 4) in most cases the cost of these processes is high. Fossil fuels make the biggest contribution to global warming [12,13]. Therefore, to decrease the use of this type of fuels, biomass fuel has been given increased attention [12–15]. A study carried out in Spain highlights that the energy potential of the vineyards in this

Corresponding author. E-mail address: [email protected] (C. Huiliñir).

https://doi.org/10.1016/j.seta.2020.100640 Received 21 July 2019; Received in revised form 4 December 2019; Accepted 14 January 2020 2213-1388/ © 2020 Elsevier Ltd. All rights reserved.

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show the results of vineyard residues and WAS composting processes [21–23]. The sludge generated in the treatment plant entails a very high cost due to its provision in a sanitary landfill. In this work, based on the characterization of vineyard residues namely: wine lees, stalks, pomace, wine shoots and waste activated sludge (WAS) from a winery wastewater aerobic treatment plant, the biochemical methane production (BMP) of these different individual wastes and their combinations was determined to estimate the production of methane that can be obtained in the vineyard under study. To the best of our knowledge a study comparing methane productions of the different wastes generated in a vineyard and winery has not been reported previously. With these results, a biogas production plant was designed to meet the energy needs of the entire production process. Finally, another objective of this work was to assess the impact of the implementation of the anaerobic digestion process on greenhouse gases emissions.

country is 282 ktoe/year [16]. Although biomass combustion generates fewer negative effects than fossil fuels, the thermal oxidation of vineyard waste also produces gases and particulate matter with serious polluting and toxic potential. Further, the operation of the incinerators used for combustion requires a very careful operation. Finally, in this operation, bottom ash is generated that must be disposed onto land. Anaerobic digestion (AD) processes with low moisture content, termed dry digestion (DD), have garnered wide interest in order to capitalize on higher organic loading rates, lower consumption of energy for heating, smaller digester footprints and production of less wastewater [17]. AD is the most commonly applied treatment for the stabilization of WAS [18], in this way it is possible to obtain energy and a by-product called digestate that is used as fertilizer and irrigation water. For this reason, vineyard residues and WAS have been used for biogas production [1,19,20]. In addition, AD of organic wastes is basically of three types. AD carried out at a temperature range of 45–60 °C is referred to as ‘thermophilic’, whereas that carried out at a temperature range of 20–45 °C is known as ‘mesophilic’, which is the most used process. The AD of organic matter at low temperatures (< 20 °C) is known as ‘psychrophilic’ digestion. Most reactors operate at either mesophilic or thermophilic temperatures, with optima at 35 and 55 °C, respectively. The feasibility of revaluing organic waste generated in the production of wines from a winery which produces 127,907,534 million red and white wines annually, located in the central zone of Chile was evaluated as a case study through the application of the joint anaerobic digestion of vineyard waste, WAS from winery wastewater treatment plants and wine lees [21,22]. Fig. 1 shows a schematic diagram of the winery production system and the generation of the different wastes. Nowadays, in this winery, the vine shoots are arranged in the same field as “soil amended”, causing their acidification. The pomace, seeds and wine lees are sold at a very low price to a company which extracts the by-products from these residues and sells them to the same company, such as tannins, tartaric acid and others. Only a small part of this waste is subjected to the composting process, giving a value to the waste, converting it into a by-product soil improver. Several studies

Material and methods Determination of the amount of waste generated The quantities generated from each type of waste used for biogas production were measured in situ during sampling and quantification carried out throughout one year considering both stages of harvest and no harvest.

Substrates and inoculum The substrates for all the anaerobic digestion assays were stalks, pomace, vine shoots, wine lees and WAS. The inoculum for anaerobic assays was obtained from a sludge anaerobic reactor operated in “La Farfana”, a municipal wastewater treatment plant which is operated by Aguas Andinas, located in Santiago de Chile. This anaerobic inoculum had a specific methanogenic activity of 0.34 g CH4-COD/(g VSS·L), which is considered a high value [24].

Fig. 1. Schematic diagram of the winery production system. 2

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values were determined. Statistical processing and analysis of data were carried out using the Minitab 8 software. An analysis of variance (ANOVA) was made, and a comparison of confidence intervals for mean values was made with a confidence level of 95%. As previously mentioned in Section 2.3, three experimental runs were performed with the aim of assessing the influence of the residue characteristics and their variations in reactor behavior and performance. However, considering that the results obtained in the experimental runs have variations in the order of 3–5%, in some cases only data corresponding to one experimental run will be shown, each one having been performed in duplicate. Each analysis was also performed, at least in duplicate, which allows for the statistical validation of these results.

Experimental design and set up For the BMP (Biochemical Methane Potential) assays, each anaerobic reactor was operated with 232 mL of anaerobic inoculum (5000 mgVSS/L) and with a waste mass between 175 and 248 g (concentration of total solids in the reactors of 60,000 and 120000 mg/l depending on the residue to be evaluated). Finally, they were diluted with distilled water up to 500 mL. The reactors of 500 mL capacity were placed in a thermoregulated bath at 35 ± 2 °C, a batch process which lasted 57 days. All the reactors were sealed and the headspace of each flask was flushed with nitrogen at the beginning of the assay. The produced biogas was passed through a 3% NaOH solution to capture CO2, and the remaining gas was assumed to be methane. This system for measuring methane production is commonly used in these kinds of experiments [25]. Three reactors with the same volume of inoculum (232 mL) and diluted with distilled water up to 500 mL but without substrate addition were used as blank controls. The methane production due to biomass decay and the possible presence of residual substrate in the inoculum was subtracted by performing these blank controls. Therefore, the methane produced by the blank controls was subtracted from the reactors with substrate. Due to the importance of maintaining the homogeneity of the sludge within the reactors, they were subjected to a moderate manual stirring several times per day for several seconds. Methane production was monitored daily throughout the process. Three experimental runs were carried out with the same operational conditions but with samples taken at different times. The experiments were carried out in the laboratories of the Chemical Engineering Department of the University of Santiago de Chile. Each run was performed in duplicate with a total of 112 discontinuous digesters, with 8 different substrates: Reactor 1: Anaerobic inoculum + Stalks; Reactor 2: Anaerobic inoculum + Pomace; Reactor 3: Anaerobic inoculum + vine shoots; Reactor 4: Anaerobic inoculum + Lees of wine; Reactor 5: Anaerobic inoculum + WAS; Reactor 6: Anaerobic inoculum + Mixture of Lees of wine and vine shoots 1:1; Reactor 7: Anaerobic inoculum + Mixture of wine Lees, pomace, stalks 1:1:1; and Reactor 8: Anaerobic inoculum + Mixture of wine Lees, pomace, stalks, vine shoots and sludge 1:1:1:1:1

Design of the biogas production system. For the dimensioning on an industrial scale of the biogas production system and its use of electrical and thermal energy from harvest and winery wastes, calculations were made starting from the amount of residue generated in the different agricultural and industrial processes, taking into account each one of the necessary units of the system starting from the residue transporting operation. Environmental considerations. Considerations of environmental character must prevail when developing any project, which is why as part of this case study an analysis on this aspect was included, based mainly on the category of greenhouse gases, which is the main factor in the case of biogas production [29]. Amount of waste generated Vine shoots The grape harvest is carried out from June to February, and in those months two prunings are done during the months of June-July and January-February. These prunings generate the vine shoots residue, which is composed of the branches of the wine plant and its leaves. 5 kg of vine shoots are generated per wine plant, and there are 4000 wine shoots per hectare in the 6000 ha of the vineyard, so that each stage of harvesting produces 120,000 tons of wine shoots amounting to 240,000 tons of waste from that agricultural activity per year [11].

Chemical and statistical analyses The residues were characterized by measuring the following parameters: Chemical Oxygen Demand (COD), total solids (TS), total Kjeldahl nitrogen (TKN), total phosphorus (TP), volatile solids (VS), total suspended solids (SS), volatile suspended solids (VSS), pH and density (ρ), which were determined according to Standard Methods [26]. In the case of the solid residue, the measurements of the parameters COD and pH were carried out by means of a dilution of the waste with distilled water in a 1:1 ratio. Phenolic compounds (SP) were determined through a high performance liquid chromatograph (HPLC) attached to an aligned photodiode detector (DAD). The equipment used in this study is a liquid chromatograph Merk-Hitachi model L-4200 UV–Vis Detector with internal pump, and a thermostat column holder. The column used was a Novapack C18, of 300 mm length and 3.9 mm of internal diameter [27]. The determination of metal concentrations was performed using a Perkin Elmer Optima 3000 ICP according to standard protocols based on official methods of the US-EPA [28]. Biogas was analyzed using a gas chromatographer CG Clarus Perkin Elmer 680, equipped with a thermal conductivity detector TCD with argon as carrier gas. The temperatures of the column and detector were 120 and 160 °C, respectively, and the model of the packed column was TDX-1 (2 m long and a 3 mm inner diameter). Na, K and Fe were measured by inductively coupled plasma - atomic emission spectrometry (Optima 7000DV, Perkin Elmer). The pH evolution during the anaerobic assays was carried out using the following procedure: two times a week, two digesters working under the same conditions were taken out of operation and the pH

Stalks Stalks are generated during the de-stemming of the grape fences. This operation is carried out in the harvest yard. In total there are 2,265 tons per year, generated from stalks. This waste is generated from March to June, coinciding with the grape reception time but the majority occurs in April, which is the month with the highest rates of harvest and production [11]. Pomace The pomace and seeds are generated in two stages of the process in the winery (see Fig. 1). For white grapes, after going through the pressing process, the pomace is removed from the process in trucks to the composting field. In the case of red grapes, the pomace is also generated in the pressing process, but this is loaded together with the juice into the vat and fermented together. This operation is carried out to color the wines. Once the fermentation is finished, the pomace and seeds are generated as residues, which are removed manually from the vats. In total there are 13,971 tons of pomace generated annually. Wine lees Unlike other wastes, this residue is generated throughout the year. However, its generation peak period is during the harvest months. The 3

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Table 1 Main characteristics of residues that were anaerobically digested in the BMP tests. Parameter

Stalks

Wine lees

Pomace

Vine shoots

WAS

M1

M2

M3

pH COD (g/L) TS (g/L) VS (g/L) VS (%) SS (g/L) VSS (mg/L) TKN (mg/kg) SP (mg/kg) TP (mg/kg) Na (mg/kg) K (mg/kg) Fe (mg/kg) Density (kg/L)

4.6–5.0 – – – 24.3–28 – – 11.0–11.5 16.8–19.2 0.90–0.92 416 30 128 0.91

3.6–4.0 – – – 11.5–15.2 – – 798–810 7.7–8.3 4.6–5.3 249 72.8 357 1.0

3.8–4.2 – – – 40.0–47.4 – – 18–24 1.2–1.8 1.45–1.83 391 11.9 370 0.85

3.7–4.5 – – – 23.8–27.1 – – 525–535 20.6–23.0 86.8–91.2 637 43 157 1.05

6.2 – 6.7 10.5–11.5 9.6–10.0 7.8–8.2 1–2 7.4–8.0 5.6–6.2 41.6–43.0 1.1–1.5 9.1–12.7 2732 20.7 3128 0.95

4.6–5.0 36–38 – – 18–21 –

4.5–4.9 20–24 – – 34–38 –

4.8–5.2 11.5–13.5 – – 19–23 –

670–690 – 200–250 – – – 0.89

285–290 – 90–120 – – – 0.90

310–340 – 110–140 – – – 0.93

the clusters. The VS/TS and VSS/SS ratios in the WAS were 0.8 and 0.76, respectively, which indicated that these sludges were of essentially organic characteristics. High levels of nitrogen and phosphorus stood out in wine lees and in wine shoots. The stalk was the residue that had the least amount of these nutrients. For phosphorus levels, the vine shoot had the largest amount, due to the assimilation of this nutrient. The WAS from the treatment plant had a lower content, as when most of the time phosphorus must be added for the growth of the active sludge. The same was true for the wine lees, due to the formation and precipitation of iron phosphate. Potassium was found in the wine lees in greater quantity due to the formation and precipitation of potassium bitartrate in the winemaking process. Large amounts of Fe and Na were observed in the WAS because the active sludge assimilated them. Polyphenols were present in greater quantity in the stalks and in the vine shoots. By disposing of the stalks and shoot residues into the soil, the polyphenols came into contact with the soil's crust and caused acidification of the medium, an inhibition of seed germination and immobilization of nitrogen, bringing direct negative consequences for agriculture. With respect to the density of the wastes, shown in Table 1, it can be said that all are not far from the water density of 1 kg/L. The values for all the parameters of the substrate mixtures M1, M2 and M3 corresponded to the contribution made by each of the substrates individually.

month of March stands out for the bulk of the generation; in this month the first wines to leave are the whites, which generate a greater amount of wine with respect to the red wines. This residue is composed of wine solids. They are generated when the wines are filtered. 1,743 tonnes of spent wine lees are generated per year [10]. WAs Winery wastewater generated in the wine industry is treated in a conventional activated sludge process where the excess biomass which grows in the biological reactor, which is known as WAS, is purged and removed from the system. Two months stand out, February, which is the month of the least production, since it is the period of maintenance in the winery and winery treatment plant, and April, which is the maximum production due to the greater activity of the biomass in what refers to BOD5. In total there are 114,429 m3 of WAS per year, corresponding to 108,707 kg of WAS (0.95 kg/m3 density) [6]. Substrates and inoculum characteristics Table 1 shows the main physical and chemical characteristics of the substrates used in the BMP assays. In each of the three experimental runs, samples of waste taken at different times were used. The following mixtures of the different substrates tested were also assayed. Mixture 1(M1): Anaerobic inoculum, wine lees and vine shoots; Mixture 2 (M2): Anaerobic inoculum, wine lees, stalks and pomace; Mixture 3(M3): Anaerobic inoculum, wine lees, pomace, stalk, vine shoots and WAS.

Biochemical methane potential (BMP) assays Results and discussion As was previously mentioned, three experimental runs with the same conditions were carried out with the purpose of observing to what extent the variations in the characteristics of the residues affected the behavior of the digesters. The results of methane production showed variations in the order of only 3–5%, so the results of only one experimental run will be shown in Fig. 2. The methane generation yield in LCH4/kg VS of residue was calculated based on the mass of initial volatile solids present in the residue or mixture of residues to be evaluated. Fig. 2 shows the comparison of these methane yields. The best performance was that of the WAS, up to 30 days of reaction, however, later, the performance of the wine lees was better. The worst yield obtained was that of the wine shoots, which is related to its woody nature, with a high content of lignocellulosic matter, difficult to biodegrade by anaerobic microorganisms. According to Fig. 2, the digestion of the WAS had a yield (up to 30 days) of 443 ± 20 L CH4/kg VS, very similar to that of the wine lees (416 ± 15 L CH4/kg VS). In addition, methane values of 690 ± 25 and 876 ± 45 L CH4/kg VS were achieved for WAS and wine lees, respectively, for day 57 of the batch process. The waste mixtures also had yields close to those reported in the literature with values between

As can be seen in Table 1, the pH of the vineyard residues and the sludge in general was shown in acid tendency with values of around 4 pH units. In the case of WAS, the pH was closer to the neutral, basically due to the operating conditions of the aerobic reactor of the wastewater treatment plant. The pH of the wine lees was the most acidic reaching 3.8 pH units on average. The low pH is a problem when disposing waste in the field, as it causes soil acidification with the consequent damage to the plantation. Due to the low pH of the residues and their mixtures at the beginning of the process, it was necessary to raise the pH to 7 in all laboratory digesters, which was done by adding a sodium hydroxide solution. The lowest percentage of volatile solids was in the WAS (wet base) due to its high water content. However, this organic matter was in a more available form for later biological conversions than the one that contained untreated solid waste. Among the substrates tested, the one with the greatest amount of organic material, base % VS, was the pomace due to its origin since this was the residue that remained after the extracted grape juice containing the residue, which was very rich in sugars and constituted the skin of the grape, the seeds and the ends of 4

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Fig. 2. Cumulative methane yields for the 8 conditions (residues and mixture of residues) tested.

but to provide anaerobic microorganisms that shortened the start-up period of the reactors. In addition to having a good specific methanogenic activity of 0.34 g CH4-COD/g VSS·L, the inoculum also showed a convenient distribution of solid concentration according to the following proportions: The VS were around 50% (w/w), this meant that the inoculum had a high proportion of organic matter. On the other hand, the VSS represented 64% of the SS and 87% of the VS, which was a sign of a major quantity of biomass in the total solids.

300 and 350 LCH4/kg VS [30]). The vine shoots had the worst methane yield, reaching a value of only 93 ± 5 and 150 ± 6 L CH4/kg VS on days 30 and 57, respectively, because the shoot is woody in nature and contains a high content of lignocellulosic matter, difficult to biodegrade by anaerobic microorganisms [31]. Because this matter (vine shoot) is a substrate that is difficult to biodegrade, less methane is generated. The pomace and the stalks also obtained low yields between 115 and 170 LCH4/kg VS. The trends remained similar until the final days of the experiment. In the case of the mixtures with favorable conditions, the development of microorganisms and their metabolism was faster and remained high for longer, compared to the their development in an environment with a single substrate. The best development and microbial metabolism resulted in high production and high biogas yield. It is important to note that the pH started to drop from the beginning of the process in all reactors reaching the 6.6 value at days 7–12 due to the formation of volatile fatty acids (VFA). However, it started to rise again and reached a stable value at around 7.2 for days 17–22. This coincided with the behavior of the methane production observed in Fig. 2, where during the first days there was little methane generation (VFA formation stage) and subsequently there was an accelerated stage of methane formation from the days 17–22. In others studies the BMP had been calculated mainly from pomace, obtaining values in the range of 76 and 231 mL CH4/g VS [17,32–35]. This variation in the BMP values was related to the different conditions in which these studies were developed, influencing, fundamentally, the quality of the anaerobic inoculum used and, of course, the composition and concentration of the different compounds present in the grapes, which in turn, depended on the type of soil where the grapes were grown, the fruit strain, the climate where the crop was grown and other natural variables in the environment. However, as can be observed in Fig. 2 the methane productivity in this case study for the pomace was about 280 LCH4/kg VS on average, which is only a little higher than the values reported in the referenced studies. The anaerobic inoculum had the following characteristics: pH 6.5; COD 8.5 g/L; TS 10.6 g/L; VS 6 g/L; SS 8.5 g/L and VSS 4 g/L. This pH contributed to slightly raising the value of this parameter in the reactors because the pH of all the residues, except for WAS, was close to 4 which was harmful for the anaerobic process. The COD, although it was lower than those of all the mixtures, was convenient in this case because its function was not to supply organic matter for the methane production,

Kinetic study The modified Gompertz kinetic model is a sigmoid function that is used as a mathematical model for a time series, where growth is the slowest at the beginning and at the end of a given time period [36]. It is one of the best functions for predicting biogas production in batchmode anaerobic digestion processes. Many researchers have studied the application of first-order and second-order kinetic models, and other models, and found that the modified Gompertz model has one of the best fits to data pertaining to biogas or methane production as a function of time under anaerobic processes conducted in batch mode. In addition, the modified Gompertz model was calibrated and examined using extensive experimental data [36,37]. In the modified Gompertz model, the cumulative methane production is related to the digestion time through the following equation:

B = Bm·exp[−exp[(Rm ·e / Bm)·(λ − t ) + 1]]

(1)

where: B is the cumulative methane production at time t (mL CH4/g VSadded), Bm is the maximum methane production or methane yield potential (mL CH4/g VSadded), Rm is the maximum methane production rate (mL CH4/(g VSadded·d)), λ is the lag time (d), t is the digestion time (d) at which the cumulative methane production is calculated, and e is the exp(1) = 2.7183. The parameters Bm, Rm, and λ were calculated for each of the runs using the non-linear regression approach with SigmaPlot 11.0 software. Table 2 shows the values of the parameters obtained from the modified Gompertz model for the eight substrates assayed. Additionally, the determination coefficient (R2) and standard error of estimate (SEE) were determined to evaluate the goodness-of-fit. The high values for R2 and low values for SEE validated the application of the modified Gompertz equation to the obtained experimental data. 5

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Main parameters for the design of the biogas production system

Table 2 Kinetic parameters derived from the application of the Modified Gompertz model to the BMP assays of the different wine wastes.* REACTOR

Bm (L CH4/kg VS)

Rm (L CH4/(kg VS·d))

ʎ (d)

R2

*S.E.E.

R1 R2 R3 R4 R5 R6 R7 R8

371 ± 5 449 ± 13 201 ± 4 1022 ± 9 695 ± 8 611 ± 8 638 ± 6 838 ± 7

10.1 ± 0.1 8.5 ± 0.1 4.6 ± 0.1 23.4 ± 0.1 19.9 ± 0.4 15.1 ± 0.2 15.6 ± 0.2 19.1 ± 0.1

13.7 ± 0.2 17.0 ± 0.2 10.7 ± 0.3 12.5 ± 0.1 8.2 ± 0.3 11.9 ± 0.2 10.8 ± 0.0 11.7 ± 0.1

0.9989 0.9984 0.9980 0.9997 0.9984 0.9991 0.9995 0.9997

5.74 5.13 3.90 7.30 13.70 8.06 6.53 5.69

Calculation of the biogas needed to produce in the anaerobic system The biogas production system is designed based on the results obtained in anaerobic digestion tests at the laboratory level and the results of methane generation yields. The fundamental parameter to be analysed in order to define the sizing of the system is the electrical and thermal energy consumed in the winery, since it is intended to replace the energy consumption from the central interconnected system, by energy produced from the anaerobic digestion system. The total consumption of electrical energy was 9,709,171 kwh/ year, with the months of highest and lowest consumption being January (774,240 kwh/month) and April (932,818 kwh/month), respectively. 15% of this consumption corresponds to the winery wastewater treatment plant. The electricity consumption in the anaerobic treatment plant is 6% of the electrical energy produced. There is a safety factor of 2%, and therefore, the energy that the anaerobic plant should produce is 10,553,447 kwh/year. Another consumption in the winery industry is thermal energy. Boilers are used to generate steam in their internal processes. This consumption is determined with the consumption data of natural gas and the calorific value of this gas. The month of lowest and highest consumptions are February (33.93 m3/month) and April (70.23 m3/ month), respectively, with a total natural gas consumption of 631.7 m3/ year. The calorific value of this gas is 10.8 kwh/m3. Therefore, 6844 kw of thermal energy are consumed per year. To meet the need for electrical and thermal energy in the winery from the biogas that is produced, it is necessary to take into account the following: generation index 6 kwh/m3 biogas [42], overall efficiency of the conversion of biogas to electricity, 32–45% [43] (in this study 40% was chosen), overall efficiency of the conversion of biogas to heat, 50%. Therefore, considering these efficiencies, an electrical energy generation index of 2.4 kwh/m3 biogas and a thermal energy generation index of 3.0 kwh/ m3 biogas would be obtained. With these values, the amount of biogas needed to produce and cover all the energy needs of the winery is 4,397,270 m3 per year.

*SEE: Standard Error of Estimate. R1: stalks; R2: pomace; R3: wine shoots; R4: Lees of wine; R5: WAS; R6: lees of wine + wine shoots; R7: lees + pomace + stalks; R8: lees + pomace + stalks + shoots + WAS. *References: [36,37].

The longest lag phases (minimum time to produce methane) of 17.0 and 13.7 days were predicted for pomace and stalks, respectively; while the shortest values were found for wine shoots and lees. This difference is a consequence of the complex structure of pomace and stalks, which contain mainly non-starch polysaccharides and other difficult-to-biodegrade compounds, such as phenols and alkylphenols [38]. Although these compounds are digestible in anaerobic digestion processes, their complex structures make their transformation into volatile fatty acids (VFA) difficult, requiring more time than that necessary for easily degradable compounds, which contributes to the higher duration of the lag phase [39]. The maximum methane production rate, Rm, values obtained in the present work were lower than those reported by [40] in the batch anaerobic digestion of vinasse (beet molasses) (40 L CH4/(kg VS·d)) and sugar beet pulp silage (SBPS) (49 L CH4/(kg VS·d)) as well as in different mixtures SBPS-vinasse (3:1, 1:1, 1:3), with values ranging from 42 to 67 L CH4/(kg VS·d). On the other hand, Syaichurrozi et al. [41] reported values for Rm of 15.2 L CH4/(kg VS·d) in the anaerobic fermentation of vinasse (cane molasses), when urea was added into vinasse to adjust the COD/N ratio to 600/7. This Rm value was within the range of values achieved in the present work for stalks and pomace. In addition, Da Ros et al. [38]) achieved values for Rm of 8 L CH4/ (kg VS·d)) in the thermophilic (55 °C) batch anaerobic digestion of grape stalks, a value very similar to that obtained in the present work (10.1 L CH4/(kg VS·d)). By contrast, for grape marc and wine lees, Rm values of 19 and 110 L CH4/(kg VS·d)) were achieved at thermophilic temperature, which were 2 and 5 times higher than those obtained in the present work at mesophilic temperature [38]. Again, the low Rm values found for grape stalks can be attributed to the high contents of lignine, cellulose and hemicellulose present in this waste [38].

Calculation of the biogas produced from vineyard waste, wine lees and WAS Taking into account the results presented in Table 1 (Section 3.1), the amount of waste generated, and the methane yield values presented in Fig. 2, Table 3 is created. To calculate the amount of biogas generated, a methane content of 62.5% was used, which was obtained from the biogas analyses carried out. For the selection of the quantities of each residue to be used for the production of biogas, the following criteria were applied: - First take the total amount of wine lees that have the highest biogas yield – this does not satisfy the total energy demand for the industry. - Calculate the potential of biogas production with the entire amount of waste in the same ratio of the M3 mixture, which had the highest biogas yield after the wine lees. The total energy demand for the industry is not still satisfied. - Therefore, to meet the total energy demand of the industry, all

Table 3 Biogas contributed by each residue. Parameter 3

m CH4/kg VS)* m3 biogas/kg VS) Total availability (kg/y) VS %** Total VS (kg/y) Biogas produced (m3/y)

WAS

Wine lees

Pomace

Stalks

Vine shoots

0.3488 0.55808 108,699,000 1.52 1,652,225 922,074

0.416 0.6656 1,743,218 13 230,976 153,738

0.1155 0.1848 13,971,437 43.71 6,106,915 1,128,558

0.1697 0.27152 2,265,007 26.13 591,846 160,698

0.0931 0.14896 54,570,410 25 13,642,602 2,032,202

*Value reached for day 30 of the batch process. ** Wet base. 6

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generated is 502 m3/h, the volume of air to be applied vs the volume of biogas generated is 4%. Therefore, the air flow required is 20.1 m3/h. A 3.5 kw power blower is chosen that delivers an air flow of 35 m3/h, and the equipment must operate with restricted flow with valves. For the design, two blowers are considered, one operating and another stand by. The co-generation process consists of an internal combustion engine powered by the biogas generated in the digestion and previously purified [47]. The motor drive induces movement in the generator, producing electrical energy. This passes to a substation and is then distributed to the same anaerobic treatment plant and to all the facilities of the cellar. The combustion gases are expelled at temperatures above 800 °C. This heat is collected in a heat exchanger, which can produce steam or hot water that must be sufficient to raise the temperature of the substrate mixture and satisfy the thermal energy demand of the cellar. Taking into account that the annual need in the cellar is 10,553,447 kwh/year, the capacity of the cogeneration unit (CCUe) will be:

Table 4 Costs of the operating units and equipment of biogas plant and their energy consumption ($USD dollars). Operation units*

Investment costs

Maintenance costs (monthly)

Operational costs (monthly)

Fuel or Necessary Power

1

$172966

$3653

$9756

2 3 4 5 6 7 8 9 10

$159559 $155714 $111499 $98042 $146102 $1477440 $317196 $12496 $911218

$1057 $1845 $2115 $1922 $1845 $4464 $4998 $1250 –

$3845 – – – – $17109 – – –

5000 L of Diesel/ monthly – – – – – 113.6 Kw 1410 Kw – –

*1-Tractors, dredger and vineyard residue storage hopper. 2-Equipment to weigh the vineyard residues with its foundations. 3-Trench receptor of vineyard residues with endless screws elevators. 4-Crusher and conveyor belt. 5-Mixer of vineyard residues, wine lees and WAS, screw pumps and WAS collector. 6-Heat exchanger. 7-Anaerobic digesters, mixer, torch, blower, purge pumps. 8-Cogeneration unit and transfer substation. 9-Biogas treatment (silica gel unit). 10-Various items (sludge storage, foundations, valves and piping, electric engineering, instrumentation and control, detail engineering, urbanization, environmental studies). **The costs are included in operational costs.

CCUe =

KgVS y KgVS

d

365 y ·4

-

(2)

This OLR is selected because with this volume of digester it is possible to operate with a high hydraulic retention time (HRTD) of 30 days according to:

HRTD =

15222 m3 497

ton m3 ·1 ton d

= 1205 kw (4)

-Tractors, dredger and vineyard residue storage hopper (1) Equipment to weigh the vineyard residues with its foundations (2) -Trench receptor of vineyard residues with screw elevators (3) Crusher and conveyor belt (4) Mixer of vineyard residues, wine lees and WAS, screw pumps and WAS collector (5) Heat exchanger (6) Anaerobic digesters, mixer, torch, blower, purge pumps (7) Co-generation unit and transfer substation (8) Biogas treatment (silica gel unit) (9) Various items (sludge storage, foundations, valves and piping, electric engineering, instrumentation and control, detailed engineering, urbanization, environmental studies) (10)

Table 4 shows the investment, maintenance and operational costs of the aforementioned operating units and equipment and their energy consumption. Operational costs include the cost of labor for operation and maintenance. Taking into account the data in Table 4, we can calculate the general expenses of the investment, which would be in USD 3,562,232, and to which would have to be added the installation of the site, general expenses and incidental costs. The design of the biogas production system is made to replace the electric energy consumption of the cellar, which for the 9,709,171 kwh/y of consumption, considering the rate of the zone that is of USD 0.087 the kwh. would represent an annual cost of USD 840,217. For the total natural gas used in the wine production annually, 631,732 L, and a rate for the area of USD 0.58 per liter, the cost would be USD 364,461. Other income to be considered:

= 15222 m3

m3d

h

The complete system for biogas production begins with the collection of wastes and has the following operational units and equipment:

Main characteristics of the most important operational units of the system The most important units of the biogas production system are the anaerobic digester, the biogas treatment devices and the cogeneration equipment. The volume of the anaerobic digester (VD) is calculated based on the organic volumetric loading rate (OLR), which according to bibliography, can be between 2 and 4 kg VS/m3·d and based on a residence time of 30 days [44,45]. In this way, the volume of the digester would be:

22224565

d

365 y ·24 d

System for biogas production

residues will be used except those from the vine shoots, which is the residue with the lowest biogas yield, of which only the amount needed to complete the total biogas production requirements will be used.

VD =

10, 553, 447kwh/y

= 30.1 d (3)

For the design of the system, two digestion units are considered. Therefore, each unit will have a volume of 7601 m3. They will be fed with half the flow each, 10.4ton/h, operated in parallel. Both reactors will be mechanically mixed and a mixing power is estimated at 7 w/m3 digester. To eliminate the humidity, a silica gel unit will be used in the biogas network. The silica gel can be recovered at high temperatures. The removal of H2S will be carried out by biological desulfurization with direct air injection into the reactor. This procedure has been applied successfully on an industrial scale [46]. The flow of biogas to be

- Savings of 80% polymer consumption for the dehydration of WAS since it is fully demonstrated that in the anaerobic digestion a smaller amount of biomass is produced since the growth yield of anaerobic microorganisms is much lower than those of aerobic ones. For this concept a saving of USD 29,597 per year will be obtained. - Elimination of the WAS disposal which currently goes to a sanitary landfill, obtaining a savings of USD 134,487 per year. - The soil of the vineyard is fertilized with nitrogen through urea and 7

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S. Montalvo, et al.

Among the sustainable and affordable energy options, biogas production by anaerobic digestion of vineyard wastes is a clean, simple technology and is less costly than comparable renewable technologies. Thus, for these industries biogas has a great potential in terms of wastes removal, job creation, reduced environmental impacts and providing clean and reliable energy to improve the quality of life.

with phosphorus from diammonium phosphate, which requires 900,000 kg of N and 52,500 kg of P per year. The 154 tons of sludge per day that will come out of the digesters will be subjected to dehydration and will have 2% nitrogen and 0.1% P, so the daily contribution of N will be 3.08 tons and phosphorus 0.154 tons., In this way 1,124,200 kg of N and 56,120 kg of P will be produced per year, which would guarantee the total replacement of the fertilizers, whose cost is USD 0.3/kg of N and USD 0.48/kg of P, which would represent an annual value for N of USD 282,191 and for P of USD 25,240.

Conclusions The characterization of the waste generated from the vineyard and in the production of wine shows that all of them have favorable characteristics for biogas generation, mainly due to its contents in organic matter and nutrients. The BMP tests show that all wastes have good potential for producing methane, the highest methane yields (LCH4/kg VS) were achieved in the digesters operating with wine lees and waste activated sludge (WAS) from the aerobic treatment plant with values of 876 ± 45 and 690 ± 25 L CH4/kg VS for day 57 of the batch process. It is shown that with the amount of wastes produced in this case it is possible to replace all the energy used in the winery if the vast majority is treated anaerobically. The implementation of the biogas production system has positive impacts on the environment, such as a significant reduction in the emission of greenhouse gases, a reduction in the probability of acidifying the soil in the area, a reduction in the risk of contamination of groundwater or the surface water resource, which considerably reduces problems for local agriculture. Another environmental benefit of the system proposed for the treatment of the residues of the evaluated vineyard, is that the digested sludge is an excellent soil amendment and its nutrient supply could replace all the chemical products added to the soil, reducing pollution of this type.

Adding all the costs that can be saved with the implementation of the biogas production system with electric and thermal energy generates an estimated total savings of USD 1,676,192 per year. Environmental considerations In Chile, the consumption of energy from the central interconnected system (SIC) has an emission factor (EF) of 181 g CO2/kwh, while the consumption of fuels such as liquefied natural gas (LNG), used in the cellar for thermal processes has an EF of 2.75 kg CO2/kg LNG. With this EF, it is possible to determine the amount of CO2 emitted into the atmosphere by wine production according to the energy concept. The use of pure biomass as fuel to generate electric and thermal energy has emissions which are considered neutral [48,49] in the sense that the CO2 emitted has been previously absorbed from the atmosphere by biomass. Therefore, an emission factor of 0 Ton CO2/m3 is applied. The biogas produced by the anaerobic digestion of organic waste (biomass) is considered to have an emission factor of 0 Ton CO2/ m3 of biogas, for the same concept. Because the project contemplates eliminating energy consumption from the SIC and eliminating the consumption of liquefied natural gas, all the CO2 produced by this process is considered a reduction in CO2 emissions [50]. In summary, the reduction of greenhouse gas emissions by the application of the biogas production system will be:

CRediT authorship contribution statement S. Montalvo: Conceptualization, Writing - original draft. J. Martinez: Investigation. A. Castillo: Project administration. C. Huiliñir: Conceptualization, Funding acquisition, Writing - review & editing. R. Borja: Writing - review & editing. Verónica García: Resources. Ricardo Salazar: Conceptualization, Resources.

- Reduction of emissions by biomass by the substitution of electric power generation:

Declaration of Competing Interest EF = 181 g CO2/kwh Electricity saved = 10,553,447 kwh/y Emissions savings = 181 × 10,553,447 = 1,910,173,907 g CO2/y or 1910 tons CO2/y

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements

- Reduction in emissions by biomass by substitution of thermal energy: EF = 2.75 kg CO2/kg LNG LNG saved = 632 m3/y; Density = 0.55 kg/L 0.55 × 1000 × 632 = 347,600 kg/y Emissions savings = 2.75 × 347,600 = 956 tons CO2/y

The authors would like to acknowledge the financial support provided by Universidad de Santiago de Chile under project DICYT 021811HC_DAS. This work is dedicated to the memory of our well esteemed and wonderful colleague Dr. Silvio Montalvo Martinez who recently passed away.

⇒

Appendix A. Supplementary data

- Reduction in emissions by transporting sludge to the landfill

Supplementary data to this article can be found online at https:// doi.org/10.1016/j.seta.2020.100640.

EF = 2.61 kg CO2/L diesel Fuel consumption = 28 L/d ⇒ 28 × 365 = 10220 L/y Emissions savings = 2.61 × 10220 × 10−3 = 27 tons CO2/y In total, 1,910 + 956 + 27 = 2893 tons CO2/y would be saved, but in the biogas production system there is an activity that generates fuel consumption, which is the collection and transportation of the vineyard wastes to the biogas production plant. The consumption of diesel for this concept will be 60,000 L per year so considering an emission factor of 2.61 kg CO2/L diesel the total emissions would be 157 tons CO2 per year. which would have to be subtracted from the tons of CO2 saved by the biogas production system. In this way, the true emission savings would be 2893–157 = 2736 tons CO2/y

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