Process for treating vinasse by means of accelerated evaporation

Abstract

The invention relates to a process for treating vinasse, which comprises the following steps: providing crude vinasse; stabilising the crude vinasse at a pH of 6-7; coagulating and flocculating the stabilised vinasse by applying a chemical coagulant at the outlet of a pump that supplies a stabilisation tank and, at the same time, applying a chemical flocculant at the inlet of the flow entering the stabilisation tank, thereby obtaining an aqueous phase and a solid phase (sludge); extruding the solid phase of the previous step using a conventional press; sending the extruded solids to a drying bed for disposal; capturing the aqueous phase in a watertight reservoir; and carrying out accelerated evaporation of the aqueous phase of the previous step by fragmenting the liquid residue using evaporators that reduce the particle size to 20-50 µm.

Description

[0001] PROCESS FOR THE TREATMENT OF VINASEED, BY ACCELERATED EVAPORATION

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to the technical field of Physics and Chemistry, because it provides a process for the treatment of vinasse, by accelerated evaporation.

[0004] BACKGROUND OF THE INVENTION

[0005] Tequila vinasse is defined as a liquid residue composed of non-volatile substances that is generated and remains at the bottom of the still during the distillation of fermented agave must in the tequila production process. Fusel oil, which is composed of a mixture of higher alcohol vapors (those with more than two carbon atoms, primarily amyl alcohol), is also included. Fusel oil is a clear, transparent fluid known in tequila slang as "flemasas," obtained during rectification or the second distillation (López-López & Contreras Ramos, 2015). Physically, vinasse is a reddish-brown, cloudy liquid due to its high suspended solids content, with a characteristic caramel-alcohol odor reminiscent of cooked agave (López-López & Contreras Ramos, 2015).The vinasse contains agave fibers that were not retained during the juice filtration stage, exhausted yeast cells, residual sugars, acids, esters, higher alcohols, substances that give the caramel color, etc. (López-López & Contreras Ramos, 2015; Rodríguez-Félix et al., 2018). Although these effluents are not classified as hazardous waste, they are categorized as complex wastewater whose organic load makes it one of the main pollutants that has altered the ecosystem of the Santiago-Guadalajara River (de Anda et al., 2022; Zurita et al., 2022).The lack of both financing and availability of technology are reasons why many of the tequila producing companies do not have formal wastewater treatment systems (WWTPs), with the exception of some large and medium-sized companies which have expensive facilities for the purification of vinasse through combined physicochemical and biological processes (López-López et al., 2010).

[0006] Small and medium-sized producers in Jalisco lack efficient and accessible technologies for treating the problem of vinasse (stillage) from tequila production. The tequila industry in Jalisco faces the challenge of complying with the recently updated Mexican Official Standard NOM-001-SEMARNAT-2021 regarding its industrial discharges. Conventional treatment methods, mostly based on anaerobic, aerobic, or a combination of both biological processes, are not only inaccessible to small and medium-sized producers but are also failing to resolve the pollution problem generated by tequila vinasse. A new treatment method is proposed, based on a primary treatment using a physicochemical process that aims to lower the temperature, stabilize the pH, and reduce the suspended solids load in the vinasse.This primary treatment is followed by a spraying process that forms microdroplets, promoting the accelerated evaporation of the aqueous phase of the vinasse. The aqueous fraction of the vinasse is incorporated into the hydrological cycle as microdroplets of water vapor. This process does not generate polluting discharges into water bodies and is environmentally friendly; energy costs are minimal, as are the production costs per cubic meter of treated vinasse.

[0007] The environmental impact of vinasse

[0008] The organic load contained in vinasse, measured as Biochemical Oxygen Demand (BOD), ranges from 16,000 to 36,000 mg BOD / L, the Chemical Oxygen Demand (COD) is between 41,000 and 68,000 mg COD / L, and total solids are between 26,000 and 67,000 mg TS / L, making vinasse a highly polluting waste product (López-López & Contreras Ramos, 2015). According to the National Chamber of the Tequila Industry, 271 million liters of tequila were produced in 2017, and 527 million liters were produced in 2021 (CNIT, 2022). Considering that for every liter of tequila, between 10 and 12 L of vinasse are generated, it is estimated that in the year 2021 approximately 5,270 million L of vinasse were produced.This amount has the pollution potential equivalent to that generated by the raw municipal wastewater of an urban concentration with an approximate population of between 4 and 8 million inhabitants depending on the level of concentration of organic matter present in the vinasse.

[0009] Composition of vinasse

[0010] Despite significant efforts to improve national wastewater discharge standards, approximately 80% of vinasse continues to be discharged directly into water bodies (rivers, streams, lakes, reservoirs) and municipal sewer systems, or directly onto the ground without adequate treatment (López-López et al., 2010; Zurita et al., 2022). This common practice causes varying degrees of degradation in the receiving water bodies due to the low pH, high temperature, and high organic load of these effluents. Furthermore, evidence of soil and groundwater contamination has been reported in the literature (Zurita et al., 2022). A summary of the physicochemical characteristics of the vinasse generated from the traditional tequila production process (100% agave) is shown in Table 1 (López-López et al., 2010), which have a pH of 3.4-4.5.

[0011] The study by Rodríguez-Félix et al. (2018) determined the differences in the composition of volatile organic compounds (VOCs) in tequila vinasse depending on whether the production process involves cooking the agave leaves before fermentation. This study identified more than 100 VOCs, including organic acids, esters, alcohols, aldehydes, alkanes, furan compounds, ketones, phenols, and pyrans. Table 1. Physicochemical characteristics of tequila vinasse.

[0012] < < < < <

[0013]

[0014] In the study by Rodríguez-Félix et al. (2018), it was found that the volatile compound profile was similar in vinasse obtained from processes involving cooking the agave leaves and vinasse obtained when the leaves are not cooked prior to fermentation. However, some differences in the concentration of volatile compounds were observed, suggesting that the cooking process influences the resulting vinasse composition. For example, the cooking process increases the content of furanic compounds and organic acids. Tequila vinasse obtained from an uncooked process showed a higher presence of phenolic compounds.The detailed description of the composition of vinasse aims to support the development of treatment technologies based on biological processes, since these processes, whether aerobic or anaerobic, face the challenge of decomposing VOCs classified as recalcitrant, that is, where conventional biological processes cannot degrade the organic matter.

[0015] Technologies for the treatment of vinasse

[0016] The conventional processes for treating tequila vinasse, for example, that are most commonly used in the industry are mentioned below (López-López et al., 2010).

[0017] Pretreatment

[0018] The pretreatment or conditioning of vinasse consists of lowering the temperature and raising the pH from 3.5 to 6-7. The common practice for lowering the temperature from 90 to 40 °C is to transport the vinasse to storage tanks or ponds under ambient conditions. pH neutralization of the vinasse is carried out in the same receiving tanks and, in some cases, in lagoons, using calcium hydroxide Ca(OH)2. Pretreatment is a common practice in both small-scale (laboratory) and large-scale (industrial) systems (López-López et al., 2010).

[0019] Treatment

[0020]

[0021] Sedimentation lagoons

[0022] They are very useful on an industrial scale for storage and have also been used to remove settleable solids present in vinasse (SS). However, when more than 80% of the SS is removed, the concentration of organic matter remains above 90%. Most of the lagoons used in tequila production facilities are not technically designed for this purpose, so there is a constant risk of soil and subsoil contamination (López-López et al., 2010).

[0023] Dissolved air flotation

[0024] This technology has rarely been applied to the treatment of vinasse on an industrial scale, but in the cases where it has been used, a polymer has been added to accelerate the separation of suspended solids (SS) before or after biological treatment. With this method, there is a higher SS removal rate of over 80%; however, dissolved solids (DS) and biological oxygen demand (BOD) are not significantly reduced (López-López et al., 2010).

[0025] Physicochemical processes

[0026] This is the most widely used physicochemical process at pilot and industrial scales for treating tequila vinasse. It uses Al2(SÜ4)3 as a coagulant and a polymer as a flocculant. At an industrial scale, it is used to remove suspended solids and colloidal solids with efficiencies of 20 to 30% (López-López et al., 2010). The use of polyacrylamide as a flocculant to reduce the concentration of solids and the organic load in vinasse has also been reported (Íñiguez-Covarrubias & Peraza-Luna, 2007). More recently, Ferral-Pérez (2015) reported that the use of biopolymers such as chitosan substantially improves the coagulation-flocculation process of tequila vinasse.

[0027] Biological processes

[0028] Anaerobic digestion

[0029] The biological process has been used for the treatment of tequila vinasse at laboratory, pilot, and industrial scales due to its technical and economic advantages over aerobic processes. An anaerobic digester is capable of removing 90 to 95% of the organic matter from tequila vinasse in the form of COD; in addition, the proposed system can produce methane-rich biogas (López-López et al., 2010; López-López & Contreras-Ramos, 2015; Moguel-Castañeda et al., 2020).

[0030] Acidogenesis for hydrogen production

[0031] There is a growing interest in the production of hydrogen (H2) from organic waste through biological processes. This is primarily due to its high energy content as H2, and its use for energy production generates only water and heat as byproducts. Very few reports exist on the use of vinasse for hydrogen production, and all of these are at the laboratory level and employ a truncated version of anaerobic digestion, yielding gaseous H2 and CO2 as final products. The aforementioned studies have demonstrated significant potential for H2 production from tequila vinasse, as well as for optimizing fermentation conditions to scale up this process (López-López et al., 2010; Serrano-Meza et al., 2022).

[0032] Use of microalgae

[0033] To add value to tequila vinasse, microalgae-yeast biomass was produced on vinasse diluted with tequila process water (the first rinse water from agave syrup production). In batch experiments, a vinasse concentration of 10% v / v resulted in the highest biomass productivity, pH, and microalgae growth compared to 20% and 30% v / v. The system is a novel and promising technology for treating tequila wastewater while producing settleable materials (Barcia et al., 2020).

[0034] Advanced processes

[0035] Ozone is a strong oxidant widely used in drinking water purification and wastewater treatment. This oxidizing agent has been used to degrade colors, phenols, pesticides, and alcoholic vinasse as pre- and post-treatments in biological processes. In addition to ozone, oxidation with chlorine, UV radiation, and hydrogen peroxide has been reported with high color removal rates and moderate COD removal, although the latter has increased (97%) with the use of TiO2 as a photocatalyst (López-López et al., 2010). For the reduction of phenols contained in vinasse, laboratory results have been published using a coagulation-flocculation process coupled with heterogeneous photocatalysis using titanium dioxide nanoparticles (Arreola et al., 2020).

[0036] Full-scale processes for the treatment of vinasse

[0037] Figure 1 of the publication by López-López et al., 2010, presents a schematic summary of the most common industrial systems used for treating tequila vinasse. Due to industry confidentiality, the treatment systems presented in Figure 1 were designated Case A, B, C, D, and E (López-López et al., 2010).

[0038] US patent document 10138150B1 discloses a method for treating vinasse to generate usable water, comprising the following steps: obtaining a quantity of vinasse; reacting the vinasse with persulfate to form an oxidized mixture; reacting the oxidized mixture with peroxide to form a peroxide-treated mixture; adjusting the pH of the vinasse to a value above approximately pH 6, and more preferably in the range of approximately pH 6 to approximately pH 7, to form a pH-adjusted mixture; reacting the pH-adjusted mixture with an inorganic coagulant and a low molecular weight cationic polymer to form solid particles; and removing the solid particles to produce a liquid fraction. The method may further comprise vacuum distillation of the liquid fraction to generate a distillate fraction.The method may further comprise evaporating the liquid fraction to produce an evaporative fraction. The method may further comprise reacting the vinasse with ferrous iron ions before reacting it with persulfate. In other embodiments, ferrous iron ions are added to the vinasse to achieve a concentration of approximately 1 to 25 mg / L. In some cases, the oxidized mixture may be reacted with peroxide for approximately 2 to 4 hours. In other cases, the vinasse may be at a temperature above 65°C. In still other cases, the vinasse may be at an acidic pH, such as a pH below 5. In other cases, the inorganic coagulant may comprise an aluminum-based inorganic coagulant. In some embodiments, the aluminum-based inorganic coagulant is aluminum chlorohydrate. In some cases, the polymer may comprise epi-dma {poly(dimethylamine-co-epichlorohydrine)}.

[0039] With the aim of contributing to the solution of the problems that the state of the art suffers, a process for the treatment of vinasse was developed, by means of accelerated evaporation, whose characteristic details and advantages are clearly shown in the following detailed description, figures and examples, which are accompanied for the sole purpose of demonstrating its conception and some preferred embodiments of the present invention.

[0040] BRIEF DESCRIPTION OF THE FIGURES

[0041] Figure 1 is a block diagram of the accelerated evaporation vinasse treatment process of the present invention.

[0042] DETAILED DESCRIPTION OF THE INVENTION

[0043] The object of the present invention is a process for the treatment of vinasse, by accelerated evaporation, which comprises the following stages:

[0044] i) supplying raw vinasse from the production of spirits, where such vinasse is commonly acidic, around a pH of 3;

[0045] ii) stabilize the raw vinasse at a pH of 6 and 7, with an aqueous suspension of calcium hydroxide, in a ratio of 28.57% Ca(OH)2 to 71.43% raw vinasse, and stirring at 360 rpm to lower the temperature of the vinasse from 90 to 40°C;

[0046] iii) coagulate-flocculate the stabilized vinasse by applying a chemical coagulant to the outlet of the pump that feeds the stabilization tank and at the same time applying a chemical flocculant to the inlet of the flow entering the stabilization tank, where said coagulant and flocculant agents are applied in a proportion of 80:20, for a reaction time for the formation of clots and flocs of around 20 s in the case of the coagulant and 2 s for the flocculant, in order to favor the sedimentation of non-settleable colloidal matter or increase the rate of sedimentation by the formation of floc; and as a result, an aqueous phase and a solid phase (sludge) are obtained;

[0047] iv) extruding the solid phase from the previous stage, through a conventional press comprising a filter element consisting of two types of rings: a fixed ring and a movable ring; and a screw that pushes a filter element and transfers and pressurizes the solid phase (sludge); wherein the spaces between the rings and the screw passage are designed to gradually narrow towards the outlet direction of the formed sludge cake, and the internal pressure of the filter element increases due to the volume compression effect, which thickens and dehydrates the sludge; the conventional press operates continuously with a rotation of 30 rpm and a pressure of 100 kPa;

[0048] v) send the solids separated from the previous stage to a drying bed for disposal, or something similar;

[0049] vi) to capture the aqueous phase that originated in stages iii) and iv), in an impermeable reservoir to prevent the aqueous phase from seeping into the soil; and

[0050] vi i) accelerate evaporation of the aqueous phase from the previous stage, by fragmenting liquid waste through evaporators that reduce the particle size to the order of 20 to 50 p.

[0051] Coagulating and flocculant agents can be chemical additives. Examples of coagulant chemical additives include aluminum hydroxide (Al₂(SO₄)₂), ferric chloride (FeCl₂), and potassium alum dodecahydrate (KAI(SO₄)₂·12H₂O), and their possible combinations. Some examples of flocculant chemical additives are VTA Nanofloc A644 (VTA®), hydroxypropyl methylcellulose (HPMC), hydroxyethyl cellulose (C₂HeO₂)ₓ (HEC), Aqualyx® (NaHS₂O₃·2H₂O), and their possible combinations. Hybrid coagulant / flocculant agents, such as Hepafloc K100® and Zeoturb®, have also been developed and can be used.

[0052] It should be clarified that the reservoir where the aqueous phase recovered in stages iii) and iv) is captured may have dimensions according to the vinasse treatment capacity to be treated.

[0053] A further embodiment of the vinasse treatment process of the present invention involves installing the evaporators on a structure with floats in the reservoir where the aqueous phase (pretreated vinasse) is collected. The floats are fixed in place to prevent them from being displaced by the wind.

[0054] In summary, the proposed vinasse treatment technology is based on a pretreatment process to lower the temperature from 90 to 40°C and stabilize the pH between 6 and 7. This is followed by the addition of a coagulant such as Al₂(SO₄)₂, which acts synergistically with a polymer flocculant to separate as many suspended solids as possible. The vinasse then undergoes an extrusion process to separate the solid from the liquid fraction. Finally, the liquid fraction is pumped to a spray system in an open area where a turbine rotating at 18,000 rpm atomizes the water to form microdroplets between 20 and 50 µm. Once released, the microdroplets are rapidly evaporated by solar radiation.The non-aqueous fraction of the vinasse is collected in a geomembrane-lined pile, where it is subsequently removed for disposal as non-hazardous solid waste. This technology (process) provides an alternative treatment for vinasse from the tequila industry and is equally applicable to vinasse generated in the production of other alcoholic beverages through fermentation and distillation from various agave plants or plants with high sugar content, such as mezcal, sotol, bacanora, and raicilla, among others. It also allows for the treatment of vinasse generated in the ethyl alcohol production industry from sugarcane.To date, the liquid waste generated during the production of alcoholic compounds obtained through fermentation and distillation has posed a serious problem for the environment, particularly for water bodies and soil. Existing treatment processes are costly and complex, and in most cases, fail to comply with the environmental standard NOM-001-SEMARNAT-2021. This has led to many streams, rivers, lakes, and reservoirs gradually becoming receptacles for the clandestine disposal of this waste (Zurita et al., 2022). Regarding soil, it has been documented that vinasse applied directly to the soil has altered its chemical composition, accelerating salinization (Christofoletti et al., 2013; Moran-Salazar et al., 2016).

[0055] EXAMPLES

[0056] The following example is included only to illustrate the concept, technical advantages, and some preferred embodiments of the invention; therefore, this example should not be considered as limiting the scope of protection of said invention.

[0057] Example 1. Process for the treatment of raw vinasse from a tequila distillery.

[0058] i) In a conventional pretreatment tank, raw vinasse from a tequila distillation process was collected, where said vinasse had a pH of 3. ii) In the same pretreatment tank, the pH of the raw vinasse was stabilized to a value between 6 and 7, with an aqueous suspension of calcium hydroxide, in a ratio of 400 g of Ca(OH)2 / Kg of raw vinasse, and it was stirred at 360 rpm, to decrease the temperature of the vinasse from 90 to 40°C. iii) Even after the vinasse was stabilized in the pretreatment tank, it was coagulated and flocculated by applying aluminum hydroxide (Al2(SO4)s) as a coagulant at the outlet of the pump feeding the stabilization tank and hydroxypropyl methylcellulose (HPMC) as a flocculant at the inlet of the flow entering the stabilization tank. Approximately 20 mg / L of coagulant and 5 mg / L of flocculant were added.The reaction time was approximately 20 seconds for the coagulants and 2 seconds for the flocculants, with clots and flocs forming rapidly. Mechanical agitation was not required, as the turbulence necessary for good mixing was achieved by the flow rate at the stabilization tank. As a result, two phases were obtained: an aqueous phase and a solid phase (sludge). The solid phase (sludge) from the previous stage was then extruded using a conventional press. This press was structured with a filter element consisting of two types of rings: a fixed ring and a moving ring. A screw pushes the filter element, transferring and pressurizing the solid phase (sludge).The spaces between the rings and the screw pitch were designed to gradually narrow towards the mud cake outlet direction and the internal pressure of the filter element increases due to the volume compression effect, which thickens and dehydrates the mud (Volute™, n.d.; GN, 2023); this equipment operated continuously with a rotation of 30 rpm and a pressure of 100 kPa.

[0059] v) The solids separated (sludge) from the previous stage were sent to a drying bed for disposal.

[0060] vi) The aqueous phase generated in steps iii) and iv) was collected in a reservoir 1 m deep and lined with a 1 mm thick polyethylene geomembrane to prevent seepage into the subsoil. vii) Finally, the aqueous phase was rapidly evaporated by fragmenting the liquid waste using sprinklers rotating at 18,000 rpm, reducing the particle size to approximately 20–50 µm (EK, 2022; e3Solutions, 2023; RWI, 2023). This size is similar to that of cloud droplets, which are < 100 µm (Berry, 1967; Breon et al., 2002; Houze, 2014). These evaporation systems have been successfully applied in the Mining, Energy, Food and Beverage, Bio and Pharmaceutical, Textile and Waste Management industries (EK, 2022).These evaporators were installed using floats in the reservoir where the aqueous phase (treated vinasse) was collected; and the floats were fixed to prevent their displacement by the wind.

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Claims

CLAIMS 1. A process for the treatment of vinasse, characterized in that it comprises the following steps: i) supplying raw stillage from the production of spirits, where such stillage is commonly acidic; i) stabilizing the pH of the raw stillage to a value between 6 and 7, with an aqueous suspension of calcium hydroxide, in a ratio of 28.57% Ca(OH)2 to 71.43% raw stillage, and stirring at 360 rpm to decrease the temperature of the stillage from 90 to 40°C; iii) coagulating-flocculating the stabilized vinasse by applying a chemical coagulant to the outlet of the pump feeding the stabilization tank and simultaneously applying a chemical flocculant to the inlet of the flow entering the stabilization tank, where said coagulant and flocculant agents are applied in a ratio of 80:20, for a reaction time for the formation of clots and flocs of around 20 s in the case of the coagulant and 2 s for the flocculant, to favor the sedimentation of non-settleable colloidal matter or increase the rate of sedimentation by the formation of floc; and as a result, an aqueous phase and a solid phase (sludge) are obtained; iv) extruding the solid phase from the previous stage, through a conventional press comprising a filter element consisting of two types of rings: a fixed ring and a movable ring; and a screw that pushes a filter element and transfers and pressurizes the solid phase (sludge); wherein the spaces between the rings and the pitch of the screw are designed to gradually narrow towards the outlet direction of the formed sludge cake, and the internal pressure of the filter element increases due to the volume compression effect, which thickens and dehydrates the solid phase (sludge); the conventional press operates continuously with a rotation of 30 rpm and a pressure of 100 kPa; v) send the solids separated from the previous stage to a drying bed for disposal; vi) to capture the aqueous phase that originated in stages iii) and iv), in an impermeable reservoir to prevent the aqueous phase from seeping into the soil; and vii) accelerate evaporation of the aqueous phase from the previous stage, by fragmenting liquid waste through evaporators that reduce the particle size to the order of 20 to 50 p instantaneously.

2. The process of claim 1, wherein the coagulant and flocculant agents are chemical additives.

3. The process according to claim 2, wherein the coagulant chemical additive is selected from the following group: aluminum hydroxide Al2(SO4)3, ferric chloride FeCh, potassium alum dodecahydrate KAI(SO4)2'12H2O, and combinations thereof; 4. The process according to claim 2, wherein the flocculant chemical additives are: Iron II Chloride (CAS No. 7758-94-3), Hydroxypropylmethylcellulose (HPMC), Hydroxyethylcellulose (C2HeO2)x (HEC), NaHSIO3·2H2O, and combinations thereof.

5. The process in accordance with claim 1, wherein the reservoir has dimensions according to the vinasse treatment capacity to be treated.

6. The process according to claim 1, wherein the evaporators are installed by means of floats in the reservoir where the aqueous phase is captured and floats are provided to fix them in place to prevent their displacement by the wind.

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