Treatment of mezcal vinasses: A review

Biomethane Production from Sugarcane Vinasse in a Circular Economy: Developments and Innovations

Sugarcane ethanol production generates about 360 billion liters of vinasse, a liquid effluent with an average chemical oxygen demand of 46,000 mg/L. Vinasse still contains about 11% of the original energy from sugarcane juice, but this chemical energy is diluted. This residue, usually discarded or applied in fertigation, is a suitable substrate for anaerobic digestion (AD). Although the technology is not yet widespread—only 3% of bioethanol plants used it in Brazil in the past, most discontinuing the process—the research continues. With a biomethane potential ranging from 215 to 324 L of methane produced by kilogram of organic matter in vinasse, AD could improve the energy output of sugarcane biorefineries. At the same time, the residual digestate could still be used as an agricultural amendment or for microalgal production for further stream valorization. This review presents the current technology for ethanol production from sugarcane and describes the state of the art in vinasse AD, including technological trends, through a recent patent evaluation. It also appraises the integration of vinasse AD in an ideal sugarcane biorefinery approach. It finally discusses bottlenecks and presents possible directions for technology development and widespread adoption of this simple yet powerful approach for bioresource recovery.

Resistance evaluation of Canna indica, Cyperus papyrus, Iris sibirica, and Typha latifolia to phytotoxic characteristics of diluted tequila vinasses in wetland microcosms

Tequila vinasse has a high contaminating capacity due to its physicochemical characteristics. Efficient and low-cost alternative treatments are required to reduce and control the environmental impacts caused by raw vinasse discharges, mainly from micro and small factories. One option is wetland technologies in which vegetation plays an important role in the proper functioning of the system; thus, the species to be used must be properly selected based on their resistance and tolerance to the toxic effects of vinasse. Therefore, this study aims to evaluate the resistance of four macrophyte species to tequila vinasse in wetland microcosms that is, Canna indica, Cyperus papyrus, Iris sibirica, and Typha latifolia which were exposed to 5, 7, 10, 12, and 15% of vinasse diluted with domestic wastewater. The control parameters (relative content, evapotranspiration, pH, electrical conductivity, and apparent color) showed that the plants in general developed stress symptoms. However, statistical analysis revealed a significant difference (p < 0.05) between plant species and vinasse treatments, further evidencing that I. sibirica is the species with the greatest potential to be used as emergent vegetation in treatment wetlands for the purification of tequila vinasse.

Agro-industrial wastewater in a circular economy: Characteristics, impacts and applications for bioenergy and biochemicals

The generation of agroindustrial byproducts is rising fast worldwide. The slaughter of animals, the production of bioethanol, and the processing of oil palm, cassava, and milk are industrial activities that, in 2019, generated huge amounts of wastewaters, around 2448, 1650, 256, 85, and 0.143 billion liters, respectively. Thus, it is urgent to reduce the environmental impact of these effluents through new integrated processes applying biorefinery and circular economy concepts to produce energy or new products. This review provides the characteristics of some of the most important agro-industrial wastes, including their physicochemical composition, worldwide average production, and possible environmental impacts. In addition, some alternatives for reusing these materials are addressed, focusing mainly on energy savings and the possibilities of generating value-added products. Finally, this review considers recent research and technological innovations and perspectives for the future.

Regulation of Hydrogen Peroxide Dosage in a Heterogeneous Photo-Fenton Process

In this work, a classical linear control approach for the peroxide (H2O2) dosage in a photo-Fenton process is presented as a suitable solution for improving the efficiency in the treatment of recalcitrant organic compounds that cannot be degraded by classical wastewater treatment processes like anaerobic digestion. Experiments were carried out to degrade Lignin, Melanoidin, and Gallic acid, which are typical recalcitrant organic compounds present in some kinds of effluents such as vinasses from the Tequila and Cachaça industries. Experiments were carried in Open-Loop mode for obtaining the degradation model for the three compounds in the form of a Transfer Function, and in Closed-Loop mode for controlling the concentration of each compound. First-order Transfer Functions were obtained using the reaction curve method, and then, based on these models, the parameters of Proportional Integral controllers were calculated using the direct synthesis method. In the Closed-Loop experiments, the Total Organic Carbon removal was 39% for lignin, 7% for melanoidin, and 29% for Gallic acid, which were greater than those obtained in the Open-Loop experiments.

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.

Chlorella vulgaris growth on anaerobically digested sugarcane vinasse: influence of turbidity

This paper shows the influence of turbidity (in Nephelometric Turbidity Units - NTU), chemical oxygen demand (COD) and aeration (CO2 supply) on the productivity and growth rate and lipid content of microalgae (a mixed culture predominantly composed of Chlorella vulgaris), using anaerobically digested vinasse as a culture medium. The microalgae can be cultivated in anaerobically digested vinasse, at turbidity and chemical oxygen demand of 690 NTU and 2.5 gCOD L -1, respectively, according to the modified Gompertz model, and removal of turbidity by filtration did not influence the microalgae productivity (≈ 77 mg L1 d1). Furthermore, aeration increased the productivity up to 139 mg L1 d1, with a biomass dry weight of 2.7 g L-1. Finally, a maximum lipid content of 265 mg L -1 was obtained, while a nitrogen removal of 98% was recorded for all conditions. Thus, the combination of anaerobic digestion followed by the use of the digestate for the cultivation of microalgae may be an efficient way to treat large quantities of this residue, in turn yielding large amounts of microalgae biomass, which can be transformed into fertilizer and biofuel.

Efficacy of polyextremophilic Aeribacillus pallidus on bioprocessing of beet vinasse derived from ethanol industries

This work aimed to evaluate the applicability of Aeribacillus pallidus for the aerobic treatment of the concentrated beet vinasse with high chemical oxygen demand (COD 685 g.L^-1) that is defined as an environmental pollutant. This bacterium is a polyextremophilic strain and grow aerobically up to 7.5% vinasse at high temperature (50 °C). In the bioreactor and under controlled conditions, A. pallidus reduced the soluble COD content of 5% vinasse up to 27% during 48 h and utilized glucose and glycerol, completely. Furthermore, a reduction of manganese, copper, aluminum, and nickel concentrations was observed in the treated vinasse with A. pallidus. The obtained results make this strain as an appropriate alternative to be used for the aerobic bioprocessing of the vinasse.

Sequential degradation of raw vinasse by a laccase enzyme producing fungus Pleurotus sajor-caju and its ATPS purification

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Vinasse degradation and laccase production by Pleurotus sajor-caju were performed;

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Laccase activity induction by copper sulfate and ethanol in raw vinasse as substrate was confirmed;

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Fermentation time to maximum laccase activity was reduced to just 3 days when cooper sulfate was used as inducer;

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The use of laccase inducers does not interfere with decolorization and turbidity removal;

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Aqueous two-phase systems reached 2.88-fold in laccase purification, with recovery of ∼ 99.9% to upper phase (PEG-rich phase).

This study evaluated simultaneously the raw vinasse degradation, an effluent from the sugar-alcohol industry, the laccase production by Pleurotus sajor-caju and its purification using aqueous two-phase systems (ATPS). To improve laccase production, different concentrations of inducers (ethanol and CuSO₄) were added. The higher laccase production promoted an increase of 4-fold using 0.4 mM of CuSO₄ as inducer, with maximum enzymatic activity of 539.3 U/L on the 3^rd day of fermentation. The final treated vinasse had a decolorization of 92% and turbidity removal of 99% using CuSO₄. Moreover, the produced laccase was then purified by ATPS in a single purification step, reaching 2.9-fold and recovered ≈ 99,9 %, in the top phase (PEG-rich phase) using 12 wt% of PEG 1500 + 20 wt% of citrate buffer + enzyme broth + water, at 25 °C. Thus, an integrated process of vinasse degradation, laccase production and purification with potential industrial application was proposed.

2-Phenylethanol and 2-phenylethylacetate production by nonconventional yeasts using tequila vinasses as a substrate

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Yeast species influenced the de novo synthesis of 2-phenylethylacetate.

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Inhibitory compounds showed a strong influence on cell growth and 2-phenylethylacetate production for the evaluated yeasts.

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More than a 50 % reduction in the chemical and biochemical oxygen demand was achieved by yeast fermentation.

Vinasses from the tequila industry are wastewaters with highly elevated organic loads. Therefore, to obtain value-added products by yeast fermentations, such as 2-phenylethanol (2-PE) and 2-phenylethylacetate (2-PEA), could be interesting for industrial applications from tequila vinasses. In this study, four yeasts species (Wickerhamomyces anomalus, Candida glabrata, Candida utilis, and Candida parapsilosis) were evaluated with two different chemically defined media and tequila vinasses. Differences in the aroma compounds production were observed depending on the medium and yeast species used. In tequila vinasses, the highest concentration (65 mg/L) of 2-PEA was reached by C. glabrata, the inhibitory compounds decreased biomass production and synthesis of 2-PEA, and biochemical and chemical oxygen demands were reduced by more than 50 %. Tequila vinasses were suitable for the production of 2-phenylethylacetate by the shikimate pathway. A metabolic network was developed to obtain a guideline to improve 2-PE and 2-PEA production using flux balance analysis (FBA).

Arthrospira maxima OF15 biomass cultivation at laboratory and pilot scale from sugarcane vinasse for potential biological new peptides production

An environmental friendly process was developed to produce Arthrospira maxima's biomass from sugarcane vinasse, which was generated in a bioethanol production chain, at laboratory and pilot scale. Peptides fractions were than obtained from enzymatically hydrolyzed biomass. High microalgae biomass productivities were reached (0.150 g L^-1 day^-1) coupled with a significant reduction of BOD and COD (89.2 and 81%, respectively). Three peptide fractions were obtained from microalgae biomass through single or sequential enzymatic hydrolysis. Antioxidant, antimicrobial, anti-inflammatory, and/or anti-collagenase activities of biopetides' fractions were observed. The PHS showed multi-biological activities. The three peptides fractions could be potential candidates for different applications in pharmaceutical, cosmetic and food industry.

Identification and Quantification of Volatile Compounds Found in Vinasses from Two Different Processes of Tequila Production

Vinasses are the main byproducts of ethanol distillation and distilled beverages worldwide and are generated in substantial volumes. Tequila vinasses (TVs) could be used as a feedstock for biohydrogen production through a dark fermentative (DF) process due to their high content of organic matter. However, TV components have not been previously assayed in order to evaluate if they may dark ferment. This work aimed to identify and quantify volatile compounds (VC) in TV and determine if the VC profile depends upon the type of production process (whether the stems were initially cooked or not). TVs were sampled from 3 agave stems with a not-cooking (NC) process, and 3 agave stems with a cooking (C) process, and volatile compounds were determined by gas chromatography coupled with mass spectrometry (GC–MS). A total of 111 volatile compounds were identified, the TV from the cooking process (C) showed the higher presence of furanic compounds (furfural and 5-(hydroxymethyl) furfural) and organic acids (acetic acid and butyric acid), which have been reported as potential inhibitors for DF. To our knowledge, this is the first description of the VC composition from TVs. This study could serve as a base for further investigations related to vinasses from diverse sources.

Combined treatment of mezcal vinasses by ozonation and activated sludge

In Mexico, mezcal production generates huge amounts of vinasses (MV) that cause negative environmental impacts. Thus, MV treatment is necessary before discharge to water bodies. Although there is no information for mezcal vinasses, similar effluents have been treated by biological processes (i.e. anaerobic and aerobic) usually complemented by oxidative chemical pretreatments (ozonation) and physico-chemical methods. In this work MV were first ozonated and followed by batch aerobic biological degradation. In the ozonation stage, organic matter removals were 4.5-11 % as COD, whereas the removal of aromatic compounds and phenols were 16-32 % and 48-83 % respectively. In the aerobic post-treatment, COD depletions up to 85 % were achieved; removals in ozone pre-treated vinasses were higher (80 to 85 %) than that of raw vinasse (69 %). It seems that ozonation preferentially attacked the recalcitrant fraction of organic matter present in the vinasses and increased its aerobic biodegradability.

Carbohydrate based polymeric materials as slow release electron donors for sulphate removal from wastewater

Many industrial sulphate rich wastewaters are deficient in electron donors to achieve complete sulphate removal. Therefore, pure and expensive chemicals are supplied externally. In this study, carbohydrate based polymers (CBP) as potato (2 and 5 mm³), filter paper (2 and 5 mm²) and crab shell (2 and 4 mm Ø) were tested as slow release electron donors (SRED) for biological sulphate reduction at 30 °C and initial pH of 7.0. Using the CBP as SRED, sulphate reduction was carried out at different rates: filter paper 0.065-0.050 > potato 0.022-0.034 > crab shell 0.006-0.009 mg SO₄^2-.mg VSS^-1d^-1. These were also affected by the hydrolysis-fermentation rates: potato 0.087-0.070 > filter paper 0.039-0.047 > crab shell 0.011-0.028 mg COD_S.mg VSS^-1d^-1, respectively. Additionally, the sulphate removal efficiencies using filter paper (cellulose, > 98%), potato (starch, > 82%) and crab shell (chitin, > 32%) were achieved only when using CBP as SRED and in the absence of other easily available electron donors. This study showed that the natural characteristics of the CBP limited the hydrolysis-fermentation step and, therefore, the sulphate reduction rates.

Microalgae-activated sludge treatment of molasses wastewater in sequencing batch photo-bioreactor

The aim of this work was the examination of the treatment potential of molasses wastewater, by the utilization of activated sludge and microalgae. The systems used included a sequencing batch bioreactor and a similar photo-bioreactor, favoring microalgae growth. The microalgae treatment of molasses wastewater mixture resulted in a considerable reduction in the total nitrogen content. A reduction in the ammonium and nitrate content was observed in the photo-bioreactor, while the effluent's total nitrogen consisted mainly of 50% organic nitrogen. The transformation of the nitrogen forms in the photo-bioreactor was attributed to microalgae activity, resulting in the production of a better quality effluent. Lower COD removal was observed for the photo-bioreactor than the control, which however increased, by the replacement of the anoxic phase by a long aeration period. The mechanism of nitrogen removal included both the denitrification process during the anoxic stage and the microalgae activities, as the replacement of the anoxic stage resulted in low total nitrogen removal capacities. A decrease in the photobioreactor performance was observed after 35 days of operation due to biofilm formation on the light tube surface, while the operation at higher temperature accelerated microalgae growth, resulting thus in the early failure of the photoreactor.

Enhancement of the performance of a combined microalgae-activated sludge system for the treatment of high strength molasses wastewater

The treatment of molasses wastewater, by a combined microalgae-activated sludge process, for the simultaneous organics and total nitrogen reduction, was examined. Further enhancement of the performance of the combined process was accomplished, by means of biofilm carriers or electrocoagulation. A LED light tube was immersed into the reactor tank aiming to enhance the growth of photosynthetic microalgae, while in a similar unit, biofilm carriers were added to the system, representing a moving bed bioreactor. Exposure of the activated sludge biocommunity to light source, resulted in the growth of microalgae and photoreactors exhibited higher removal rates of total nitrogen and nitrates. However, operation at longer times resulted in low effluent quality due to the presence of microalgae cells as a result of high growth rates, and potential light shading effect. Nevertheless, the moving bed system was more beneficial than the single photoreactor, as biofilm carriers provided a self cleaning capacity of the light source, reducing the effect of microalgae deposition. Advanced treatment of the biological effluents, by electrocoagulation, increased even more the process efficiency: the combined photobioreactor and electrocoagulation process resulted in about 78% COD removal and more than 35% total nitrogen removal in the effluent, where nitrates represented almost the single form of total nitrogen.

Utilization of vinasses as soil amendment: consequences and perspectives

Vinasses are a residual liquid generated after the production of beverages, such as mezcal and tequila, from agave (Agave L.), sugarcane (Saccharum officinarum L.) or sugar beet (Beta vulgaris L.). These effluents have specific characteristics such as an acidic pH (from 3.9 to 5.1), a high chemical oxygen demand (50,000-95,000 mg L(-1)) and biological oxygen demand content (18,900-78,300 mg L(-1)), a high total solids content (79,000 and 37,500 mg L(-1)), high total volatile solids 79,000 and 82,222 mg L(-1), and K(+) (10-345 g L(-1)) content. Vinasses are most commonly discarded onto soil. Irrigation of soil with vinasses, however, may induce physical, chemical and biochemical changes and affect crop yields. Emission of greenhouse gases (GHG), such as carbon dioxide, nitrous oxide and methane, might increase from soils irrigated with vinasses. An estimation of GHG emission from soil irrigated with vinasses is given and discussed in this review.

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

In recent years, anaerobic digestion has been recognized as a suitable alternative for tequila vinasses treatment due to its high energy recovery and chemical oxygen demand (COD) removal efficiency. However, key factors such as the lack of suitable monitoring schemes and the presence of load disturbances, which may induce unstable operating conditions in continuous systems, have limited its application at full scale. Therefore, the aim of this work was to evaluate the anaerobic sequencing batch reactor (AnSBR) configuration in order to provide a low cost and easy operation alternative for the treatment of these complex effluents. In particular, the AnSBR was evaluated under different pH-temperature combinations: 7 and 32 °C; 7 and 38 °C; 8 and 32 °C and 8 and 38 °C. Results showed that the AnSBR configuration was able to achieve high COD removal efficiencies (around 85%) for all the tested conditions, while the highest methane yield was obtained at pH 7 and 38 °C (0.29 L/g COD added). Furthermore, high robustness was found in all the AnSBR experiments. Therefore, the full-scale application of the AnSBR technology for the treatment of tequila vinasses is quite encouraging, in particular for small and medium size tequila industries that operate under seasonal conditions.

Post-treatment of molasses wastewater by electrocoagulation and process optimization through response surface analysis

Molasses wastewater is a high strength effluent of food industry such as distilleries, sugar and yeast production plants etc. It is characterized by a dark brown color and exhibits a high content in substances of recalcitrant nature such as melanoidins. In this study, electrocoagulation (EC) was studied as a post treatment step for biologically treated molasses wastewater with high nitrogen content obtained from a baker's yeast industry. Iron and copper electrodes were used in various forms; the influence and interaction of current density, molasses wastewater dilution, and reaction time, on COD, color, ammonium and nitrate removal rates and operating cost were studied and optimized through Box Behnken's response surface analysis. Reaction time varied from 0.5 to 4 h, current density varied from 5 to 40 mA/cm(2) and dilution from 0 to 90% (v/v expressed as water concentration). pH, conductivity and temperature measurements were also carried out during each experiment. From preliminary experiments, it was concluded that the application of aeration and sample dilution, considerably influenced the kinetics of the process. The obtained results showed that COD removal varied between 10 and 54%, corresponding to an operation cost ranging from 0.2 to 33 euro/kg COD removed. Significant removal rates were obtained for nitrogen as nitrate and ammonium (i.e. 70% ammonium removal). A linear relation of COD and ammonium to the design parameters was observed, while operation cost and nitrate removal responded in a curvilinear function. A low ratio of electrode surface to treated volume was used, associated to a low investment cost; in addition, iron wastes could be utilized as low cost electrodes i.e. iron fillings from lathes, aiming to a low operation cost due to electrodes replacement. In general, electrocoagulation proved to be an effective and low cost process for biologically treated molasses-wastewater treatment for additional removal of COD and nitrogen content and color reduction. Treated effluent samples with good quality were produced by EC, with COD, NH4-N and NO3-N concentrations of 180, 52 and 2 mg/l respectively. Response surface analysis revealed that optimized conditions could be established under moderate molasses wastewater dilution, (e.g. 45%), at 3.5 h treatment time and 33 mA/cm(2) current density.

Implications of stillage land disposal: a critical review on the impacts of fertigation

Stillage is the main wastewater from ethanol production, generated specifically in the step of distillation. Regardless the feedstock, stillage contains high concentrations of organic matter, potassium and sulfates, as well as acidic and corrosive characteristics. Currently almost the entire volume of stillage generated in Brazilian distilleries is directed to the fertigation of sugarcane fields, due to its fertilizer character. However, the polluting potential of stillage characterizes its land disposal as problematic, considering probable negative impacts on the soil structure and water resources in case of excessive dosages. Since the literature lacks critical content describing clearly the cons related to the reuse of stillage in agriculture in the long-term, this review aimed to assess the real polluting potential of stillage, and the implications of its land disposal and/or discharge into water bodies. Evidence from the literature indicate that the main obstacles to reuse stillage in natura include risks of soil salinization; clogging of pores, reduction in the microbial activity and the significant depletion of dissolved oxygen concentrations in water bodies; contamination per nitrates and eutrophication; soil structure destabilization due to high concentrations of potassium and sodium; and, possible acidification of soil and water resources, considering the low pH of stillage (∼4,5). Toxic metals, such as cadmium, lead, copper, chromium and nickel, were also identified in concentrations above the recommended limits in stillage samples, increasing risks to human health (e.g. carcinogenic potential) and to crops (e.g. productivity loss). In short, although some studies report benefits from the land application of stillage, its treatment prior to disposal is essential to make fertigation an environmentally suitable practice.

Conversion of yellow wine lees into high-protein yeast culture by solid-state fermentation

This study is focussed on the possibility of producing a yeast culture with yellow wine lees as a substrate by solid-state fermentation (SSF). Results showed that a yeast count of 1.58 × 10⁹ CFU/g was achieved by signal factor and orthogonal experiments. After fermentation, the starch content in the yeast culture reduced from 32.2% ± 0.5% to 7.5% ± 0.2%, and the contents of crude protein and peptide increased from 36.1% ± 0.8% to 48.0% ± 1.0% and 3.9% ± 0.2% to 7.2% ± 0.4%, respectively. Additionally, large amounts of short peptides and free amino acids were detected by fast protein liquid chromatography (FPLC). These results suggest that yellow wine lees are a suitable substrate for the production of yeast cultures. It can serve as a growth-promoting factor and help reduce the shortage of protein feed in the animal industry. This research provides a potential way for the utilization of agro-industrial residues.

Biohydrogen, biomethane and bioelectricity as crucial components of biorefinery of organic wastes: a review

Biohydrogen is a sustainable form of energy as it can be produced from organic waste through fermentation processes involving dark fermentation and photofermentation. Very often biohydrogen is included as a part of biorefinery approaches, which reclaim organic wastes that are abundant sources of renewable and low cost substrate that can be efficiently fermented by microorganisms. The aim of this work was to critically assess selected bioenergy alternatives from organic solid waste, such as biohydrogen and bioelectricity, to evaluate their relative advantages and disadvantages in the context of biorefineries, and finally to indicate the trends for future research and development. Biorefining is the sustainable processing of biomass into a spectrum of marketable products, which means: energy, materials, chemicals, food and feed. Dark fermentation of organic wastes could be the beach-head of complete biorefineries that generate biohydrogen as a first step and could significantly influence the future of solid waste management. Series systems show a better efficiency than one-stage process regarding substrate conversion to hydrogen and bioenergy. The dark fermentation also produces fermented by-products (fatty acids and solvents), so there is an opportunity for further combining with other processes that yield more bioenergy. Photoheterotrophic fermentation is one of them: photosynthetic heterotrophs, such as non-sulfur purple bacteria, can thrive on the simple organic substances produced in dark fermentation and light, to give more H2. Effluents from photoheterotrophic fermentation and digestates can be processed in microbial fuel cells for bioelectricity production and methanogenic digestion for methane generation, thus integrating a diverse block of bioenergies. Several digestates from bioenergies could be used for bioproducts generation, such as cellulolytic enzymes and saccharification processes, leading to ethanol fermentation (another bioenergy), thus completing the inverse cascade. Finally, biohydrogen, biomethane and bioelectricity could contribute to significant improvements for solid organic waste management in agricultural regions, as well as in urban areas.

The influence of total solids content and initial pH on batch biohydrogen production by solid substrate fermentation of agroindustrial wastes

Hydrogen is a valuable clean energy source, and its production by biological processes is attractive and environmentally sound and friendly. In México 5 million tons/yr of agroindustrial wastes are generated; these residues are rich in fermentable organic matter that can be used for hydrogen production. On the other hand, batch, intermittently vented, solid substrate fermentation of organic waste has attracted interest in the last 10 years. Thus the objective of our work was to determine the effect of initial total solids content and initial pH on H2 production in batch fermentation of a substrate that consisted of a mixture of sugarcane bagasse, pineapple peelings, and waste activated sludge. The experiment was a response surface based on 2(2) factorial with central and axial points with initial TS (15-35%) and initial pH (6.5-7.5) as factors. Fermentation was carried out at 35 °C, with intermittent venting of minireactors and periodic flushing with inert N2 gas. Up to 5 cycles of H2 production were observed; the best treatment in our work showed cumulative H2 productions (ca. 3 mmol H2/gds) with 18% and 6.65 initial TS and pH, respectively. There was a significant effect of TS on production of hydrogen, the latter decreased with initial TS increase from 18% onwards. Cumulative H2 productions achieved in this work were higher than those reported for organic fraction of municipal solid waste (OFMSW) and mixtures of OFMSW and fruit peels waste from fruit juice industry, using the same process. Specific energetic potential due to H2 in our work was attractive and fell in the high side of the range of reported results in the open literature. Batch dark fermentation of agrowastes as practiced in our work could be useful for future biorefineries that generate biohydrogen as a first step and could influence the management of this type of agricultural wastes in México and other countries and regions as well.

Sustainability of soil fertility and the use of lignocellulosic crop harvest residues for the production of biofuels: a literature review

Use of lignocellulosic crop harvest residues for liquid or gaseous biofuel production may impact soil quality, long-term soil fertility and the major determinants of the latter, stocks of soil organic carbon and nutrients. When soil organic carbon stocks of mineral cropland soils are to be maintained, there is scope for the removal of lignocellulosic harvest residues in several systems with much reduced tillage or no tillage. The scope for such removal might be increased when suitably treated residues from the conversion of harvest residues into biofuel are returned to cropland soils. For mineral cropland soils under conventional tillage, the scope for the production of liquid biofuels from harvest residues is likely to be less than in the case of no-till systems. When fertility of cropland soils is to be sustainable, nutrients present in suitably treated biofuel production residues have to be returned to these soils. Apparently, the actual return of carbon and nutrients present in residues of biofuel production from crop harvest residues to arable soils currently predominantly concerns the application of digestates of anaerobic digestion. The effects thereof on soil fertility and quality need further clarification. Further clarification about the effects on soil fertility and quality of chars and of co-products of lignocellulosic ethanol production is also needed.