Biogas production in an anaerobic sequencing batch reactor by using tequila vinasses: effect of pH and temperature

Microbial granules on reactors performance during organic butyrate digestion: clean production

This critical review for anaerobic degradation of complex organic compounds like butyrate using reactors has been enormously applied for biogas production. Biogas production rate has a great impact on: reactor granulation methanogenesis, nutrient content, shear velocity, organic loading and loss of nutrients taking place in the reactor continuously. Various technologies have been applied to closed anaerobic reactors to improve biogas production and treatment efficiency. Recent reviews showed that the application of closed anaerobic reactors can accelerate the degradation of organics like volatile fatty acid-butyrate and affect microbial biofilm formation by increasing the number of methanogens and increase methane production 16.5 L-1 CH4 L-1 POME-1. The closed anaerobic reactors with stable microbial biofilm and established organic load were responsible for the improvement of the reactor and methane production. The technology mentioned in this review can be used to monitor biogas concentration, which directly correlates to organic concentrations. This review attempts to evaluate interactions among the: degradation of organics, closed anaerobic reactors system, and microbial granules. This article provides a useful picture for the improvement of the degradation of organic butyrate for COD removal, biogas and methane production in an anaerobic closed reactor.

Energy generation from bioelectrochemical techniques: Concepts, reactor configurations and modeling approaches

The process industries play a significant role in boosting the economy of any nation. However, poor management in several industries has been posing worrisome threats to an environment that was previously immaculate. As a result, the untreated waste and wastewater discarded by many industries contain abundant organic matter and other toxic chemicals. It is more likely that they disrupt the proper functioning of the water bodies by perturbing the sustenance of many species of flora and fauna occupying the different trophic levels. The simultaneous threats to human health and the environment, as well as the global energy problem, have encouraged a number of nations to work on the development of renewable energy sources. Hence, bioelectrochemical systems (BESs) have attracted the attention of several stakeholders throughout the world on many counts. The bioelectricity generated from BESs has been recognized as a clean fuel. Besides, this technology has advantages such as the direct conversion of substrate to electricity, and efficient operation at ambient and even low temperatures. An overview of the BESs, its important operating parameters, bioremediation of industrial waste and wastewaters, biodegradation kinetics, and artificial neural network (ANN) modeling to describe substrate removal/elimination and energy production of the BESs are discussed. When considering the potential for use in the industrial sector, certain technical issues of BES design and the principal microorganisms/biocatalysts involved in the degradation of waste are also highlighted in this review.

Decarbonising distilled spirits: An assessment of the potential associated with anaerobic digestion of by-products at nine operational distilleries

This work aims to assess the potential biogas resource of by-products from the production of distilled spirits at 9 operational distilleries in 7 countries. An additional objective was the calculation of the energy resource and Scope 1 greenhouse gas (GHG) emission savings from the use of 21 by-products from the distilleries as a feedstock for anaerobic digestion (AD). To present a holistic perspective on the integration of AD with distilleries, an overview of additional criteria to be considered was provided. The biochemical methane potential (BMP) of the by-products associated with a selection of distilled spirits was experimentally determined. The BMP ranged from 161 L methane per kg volatile solid (LCH₄/kgVS) to 589 LCH₄/kgVS with an average value of 332 LCH₄/kgVS. Biogas could reduce distillery fossil fuel demand by 49% when produced from un-processed by-products, by 66% when produced from a mixture of separated by-products, by 16% when produced from concentrated by-products and by 13% when produced from liquid by-products. The average Scope 1 GHG emission saving when using un-processed by-products was 52%, a mix of separated by-products allowed for a reduction of 66%, liquid by-products achieved an average reduction of 14%, and the use of concentrated by-products reduced GHG emissions by 17% on average. When evaluating which distilleries are "of most interest" for the integration of AD, other criteria to be considered include: by-product properties, the size of the AD facility required, the quantity of digestate produced, and the location of the distilleries in terms of both land availability to construct the AD facility and the proximity to land on which to spread digestate.

Performance of an anaerobic sequencing batch reactor operating under high organic loading in treatment of biodiesel wastewater

Studies reporting the performance of anaerobic sequencing batch reactor (AnSBR) operating with high organic loadings are scarce. This study aimed to contribute to the technical and scientific literature by reporting the experience obtained when biodiesel wastewater was treated in an AnSBR applying organic loading rates (OLR) above those commonly used in batch reactor projects. For this, physicochemical and chromatographic analysis of the effluent were carried out. Further, the biomass was assessed chemically and morphologically, along with bacterial diversity characteristics. Supported by these analyses, the system performance was discussed in terms of COD remotion efficiency and buffering capacity. The AnSBR reached 10% of COD removal at the steady-state, which caused the biomass defragmentation and facilitated washout. This suggests that the startup and operation of AnSBR under optimized conditions with an average applied OLR of 11.3 gCOD L-1 d-1 worked as a pressure for the microbiota selection, stimulating the production of total volatile acids, which promoted system reduction efficiency and souring. In this context, food/microorganism ratios above 1.0 gCOD gTVS -1 d-1 can favor acidogenic activity, and total volatile acids/bicarbonate alkalinity concentration ratios above 1.9 may indicate acidification. The addition of support material for immobilizing/increasing biomass retention and/or operation under two-stage may be interesting alternatives for increasing AnSBR efficiencies under high OLRs.

Graphical abstract

New insights into microbial interactions and putative competitive mechanisms during the hydrogen production from tequila vinasses

This study aimed to characterize the prokaryotic community and putative microbial interactions involved in hydrogen (H₂) production during the dark fermentation (DF) process, applying principal components analysis (PCA) to correlate changes in operational, physicochemical, and biological variables. For this purpose, a continuous stirred-tank reactor-type digester fed with tequila vinasses was operated at 24, 18, and 12 h of hydraulic retention times (HRTs) to apply organic loading rates of 20, 36, and 54 g-COD L^-1 d^-1, corresponding to stages I, II, and III, respectively. Results indicated high population dynamics for Archaea during the DF process toward a decrease in total sequences from 6299 to 99. Concerning the Bacteria community, lactic acid bacteria (LAB) were dominant reaching a relative abundance of 57.67%, while dominant H₂-producing bacteria (HPB) decreased from 25.76% to 21.06% during stage III. Putative competitive exclusion mechanisms such as competition for substrates, bacteriocins production, and micronutrient depletion carried out by Archaea and non-H₂-producing bacteria (non-HPB), especially LAB, could negatively impact the dominance of HPB such as Ethanoligenens harbinense and Clostridium tyrobutyricum. As a consequence, low maximal volumetric H₂ production rate (672 mL-H₂ L^-1 d^-1) and yield (3.88 mol-H₂ assimilated sugars^-1) were obtained. The global scenario obtained by PCA correlations suggested that C. tyrobutyricum positively impacted H₂ molar yield through butyrate fermentation using the butyryl-CoA:acetate CoA transferase pathway, while the most abundant HPB E. harbinense decreased its relative abundance at the shortest HRT toward the dominance of non-HPB. This study provides new insights into the microbial interactions and helps to better understand the DF performance for H₂ production using tequila vinasses as substrate. KEY POINTS: • E. harbinense and C. tyrobutyricum were responsible for H₂ production. • Clostridiales used acetate and butyrate fermentations for H₂ production. • LAB won the competition for sugars against Clostridiales during DF. • Putative bacteriocins production and micronutrients depletion could favor LAB.

Acclimation of microorganisms for an efficient production of volatile fatty acids and biogas from mezcal vinasses in a dark fermentation process

Mezcal is an alcoholic artisanal drink made from agave plants in Mexico. Its production causes the generation of wastewater called vinasses, which are highly polluting residues due to its concentration of organic matter as chemical oxygen demand (COD) (35,000-122,000 mg/L) and acidity (pH < 4). Due to their organic content, these residues can be used in dark fermentation to obtain biogas, which is rich in hydrogen. In this work, the acclimation of inoculum by means of a dark fermentation process, in the presence of toxic compounds from mezcal vinasses was studied. The strategy of increasing the initial concentration of vinasse in each treatment cycle in a sequencing batch reactor (SBR) reactor was applied. It was possible to obtain a maximum biogas production of 984 ± 187 mL/L, from vinasses (18,367 ± 1,200 mg COD/L), with an organic matter removal efficiency of 20 ± 1%. A maximum generation of volatile fatty acids (VFA) of 980 ± 538 mg/L equivalent to a production of 74 ± 21% of the influent concentration and removal rate of organic matter of 1,125 ± 234 mg COD/L d^-1 equivalent to a removal efficiency of 20 ± 4% was obtained from vinasses with a concentration of 19,648 ± 1,702 mg COD/L.

Study of a coupled adsorption/electro-oxidation process as a tertiary treatment for tequila industry wastewater

Vinasse wastewater from tequila industry that has been conventionally treated is usually characterized by a chemical oxygen demand (COD) above 150 mg L^-1, which is the maximum content permitted for discharge by Mexican Regulation. In order to increase the wastewater quality, different processes were applied, and from the experimental results, the advantages and limitations were analyzed. In this way, although Fenton experiments showed acceptable COD removal efficiencies (79-90%), operation as well as cost limit its adoption as a viable technology. Therefore, additional experiments explored electro-Fenton (EF) as well as adsorption coupled to EF in a tubular reactor. The corresponding data revealed that there was no additional increase in COD removal performance probably due to the low oxygen solubility in the electrolytic solution and the high pH that prevents the existence of Fe²⁺ ions necessary for the Fenton mixture. In view of these results, when an activated carbon (AC) filter was coupled to polarization at current densities between 0.5 and 2 mA cm^-2, removal efficiencies from 71 to 81%, corresponding to final COD of 78 to 33 mg L^-1, were achieved. Also, the adsorbent surface was continuously regenerated, promoting a more efficient adsorption and a longer service life for the AC filter. In this case, by using a current density of 0.5 mA cm^-2, COD was reduced to sufficiently small values for discharge into natural water bodies, maintaining low energy consumption and therefore acceptable operation costs.

Enhanced methane production and organic matter removal from tequila vinasses by anaerobic digestion assisted via bioelectrochemical power-to-gas

In this study, showed a strategy to generate methane and remove organic matter removal from tequila vinasses through of anaerobic digestion assisted via bioelectrochemical power to-gas. Specific methanogenic activity (SMA) assays in batch mode were tested and a single-stage bioelectrochemical upflow anaerobic sludge blanket reactor (UASB) was evaluated to generate methane during tequila vinasses treatment. The results showed that the methane production in the bioelectrochemical UASB reactor applied at low voltage of 0.5 V and under HRT of 7 d was higher than the in the conventional UASB reactor. The specific methane production rate in bioelectrochemical UASB reactor was up to 2.9 NL CH₄/L d, with a maximum methane yield of 0.32 NL CH₄/g COD_removed. Similar COD removals were observed in the bioelectrochemical UASB reactor and conventional reactors (92-93%). High carbon dioxide reduction and hydrogen production were observed in the bioelectrochemical UASB reactor.

Tequila Still Distillation Fractioned Residual Streams for Use in Biorefinery

Tequila vinasses is a mixture made from up to six still distillation two-stage process residual effluents. First stage fractions: residual must (60%), heads (0.9%) and tails (20.0%); second stage fractions: non-evaporated (8.0%), heads (0.1%) and tails (1.0%); the result is a more complex effluent for its treatment or biorefining. The objectives of this study were to: (a) characterize the five still distillation volatile streams in the Tequila 100% Agave processing; compounds: methanol, ethanol, acetaldehyde, ethyl acetate, sec-butanol, n-propanol, iso-butanol, n-butanol, iso-amyl, n-amyl, and ethyl lactate were detected by gas chromatography; calculated chemical oxygen demand from chemical composition had very high values (53,760–1,239,220 mg/L); measurement of pH (3.24–4.80), color (38.6 UC Pt-Co max), turbidity (46.1 max), electrical conductivity (3.30–172.20 μS/cm), and solid content (0 mg/L) was also made; (b) report an energy analysis (2.02 × 109 KWh) and CO2 production (429 × 106 kg) in the Tequila industry during 2019; (c) up to date residues (365.2 × 106 kg agave bagasse, 1146.1 × 106 kg agave leaves and 3300.0 × 106 L agave vinasse) in 2019; (d) economic analysis, current tequila vinasses treatment price is 16.00 USD/m3 but could reach a considerable fraction value if is bio-refined, a break down component analysis reach for five volatile streams $51.23–$140.00 USD/m3.

Potential Utilisation of Dark-Fermented Palm Oil Mill Effluent in Continuous Production of Biomethane by Self-Granulated Mixed Culture

Two-stage anaerobic digestion of palm oil mill effluent (POME) is a promising method for converting the waste from the largest agricultural industry in Southeast Asia into a clean and sustainable energy. This study investigates the degradation of acid-rich effluent from the dark fermentation stage for the production of biomethane (BioCH4) in a 30-L continuous stirred-tank reactor (CSTR). The continuous methanogenic process was operated with varied HRTs (10 - 1 day) and OLRs (4.6-40.6 gCOD/L.d-1) under thermophilic conditions. Methanothermobacter sp. was the dominant thermophilic archaea that was responsible for the production rate of 4.3 LCH4/LPOME.d-1 and methane yield of 256.77 LCH4kgCOD at HRT of 2 d, which is the lowest HRT reported in the literature. The process was able to digest 85% and 64% of the initial POME's COD and TSS, respectively. The formation of methane producing granules (MPG) played a pivotal role in sustaining the efficient and productive anaerobic system. We report herein that the anaerobic digestion was not only beneficial in reducing the contaminants in the liquid effluent, but generating BioCH4 gas with a positive net energy gain of 7.6 kJ/gCOD.