Sweet Sorghum Stalks Research Articles

Sorghum bicolor L. Stalk Stiffness Is Marginally Affected by Time of Day under Field Conditions

This study sought to better understand how time of day (ToD) or turgor pressure might affect the flexural stiffness of sweet sorghum stalks and potentially regulate stalk lodging resistance. Stalk flexural stiffness measured across a 48 h period in 2019 showed a significant diurnal association with leaf water potential and stalk flexural stiffness. While the correlation between stalk flexural stiffness and this proxy for internal turgor status was statistically significant, it only accounted for roughly 2% of the overall variance in stiffness. Given that turgor status is a dynamic rather than fixed physiological variable like the cellular structure, these data suggest that internal turgor plays a small yet significant role in influencing the flexural stiffness of fully mature stalks prior to a stalk lodging event. The association was assessed at earlier developmental stages across three distinct cultivars and found not to be significant. Panicle weight and stalk basal weight, but not stalk Brix or water content, were found to be better predictors of stalk flexural stiffness than either ToD or turgor status. Observation across three cultivars and four distinct developmental stages ranging from the vegetative to the hard-dough stages suggests that stalk flexural stiffness changes significantly as a function of time. However, neither ToD nor turgor status appear to meaningfully contribute to observed variations in stalk flexural stiffness in either individual stalks or across larger populations. As turgor status was not found to meaningfully influence stalk strength or flexural stiffness at any developmental time point examined in any of the three sweet sorghum cultivars under study, turgor pressure likely offers only inconsequential contributions to the biomechanics underlying sweet sorghum stalk lodging resistance.

Hydrogen and Fatty Acid Production by Dark Fermentation of Sweet Sorghum Stalks as an Efficient Pre-treatment for Energy Recovery Before Their Bioconversion into Methane

Hydrogen and Fatty Acid Production by Dark Fermentation of Sweet Sorghum Stalks as an Efficient Pre-treatment for Energy Recovery Before Their Bioconversion into Methane

Development of sustainable biomass residues for biofuels applications

A comprehensive understanding of physiochemical properties, thermal degradation behavior and chemical composition is significant for biomass residues before their thermochemical conversion for energy production. In this investigation, teff straw (TS), coffee husk (CH), corn cob (CC), and sweet sorghum stalk (SSS) residues were characterized to assess their potential applications as value-added bioenergy and chemical products. The thermal degradation behavior of CC, CH, TS and SSS samples is calculated using four different heating rates. The activation energy values ranged from 81.919 to 262.238 and 85.737–212.349 kJ mol−1 and were generated by the KAS and FWO models and aided in understanding the biomass conversion process into bio-products. The cellulose, hemicellulose, and lignin contents of CC, CH, TS, and SSS were found to be in the ranges of 31.56–41.15%, 23.9–32.02%, and 19.85–25.07%, respectively. The calorific values of the residues ranged from 17.3 to 19.7 MJ/kg, comparable to crude biomass. Scanning electron micrographs revealed agglomerated, irregular, and rough textures, with parallel lines providing nutrient and water transport pathways in all biomass samples. Energy Dispersive X-ray spectra and X-ray diffraction analysis indicated the presence of high carbonaceous material and crystalline nature. FTIR analysis identified prominent band peaks at specific wave numbers. Based on these findings, it can be concluded that these residues hold potential as energy sources for various applications, such as the textile, plastics, paints, automobile, and food additive industries.

Bagasse Yield and Quality Traits of Silage Made From Juice-Extracted Sweet Sorghum

This study was conducted to investigate possible use of juice-extracted sweet sorghum stalks (bagasse) as a quality roughage source through silage making. A total of 21 different sweet sorghum (Sorghum bicolor var. saccharatum (L.) Mohlenbr.) genotypes supplied from different sources were used as the primary material of the study. Field experiments were conducted in a randomized blocks design with 4 replications on the experimental fields of Eastern Mediterranean Agricultural Research Institute under 2nd crop conditions during the growing seasons of 2016 and 2017 years. Plants were harvested for bioethanol production at milk-dough stage of panicle grains. Plant leaves and panicles were stripped and remaining stalks were extracted through squeezing. Juice-extracted stalks (bagasse) were ensilaged for 60 days and quality traits were analyzed at the end of silage period. As the average of two years, bagasse yields varied between 42.6-113.9 t ha-1, silage DM yields varied between 11.6-40.0 t ha-1. In addition, crude protein (CP) content, acid detergent lignin (ADL), neutral detergent fiber (NDF) and acid detergent fiber (ADF) values varied between 29.79 - 50.84 g/kg DM, between 49.3 - 91.4 g/kg DM, between 525.1-694.8 g/kg DM and between 351.2-486.8 g/kg DM, respectively. It was concluded based on present findings that silages made from juice-extracted stalks of sweet sorghum grown under 2nd crop conditions of Cukurova region could be used as quality roughage source for livestock. Keywords: Bagasse yield; Genotype; Silage quality; Sweet sorghum

Optimization of Bioethanol Production after Enzymatic Treatment of Sweet Sorghum Stalks

Optimization of Bioethanol Production after Enzymatic Treatment of Sweet Sorghum Stalks

Preparation of microcrystalline cellulose from agricultural residues and their application as polylactic acid/microcrystalline cellulose composite films for the preservation of Lanzhou lily

Microcrystalline celluloses were isolated from four agricultural residues, including sweet sorghum stalk, Jerusalem artichoke stalk, grains stillage, and Chinese herb residue, and characterized in terms of physicochemical and structural properties. The obtained microcrystalline celluloses were composited with polylactic acid as a packing film for the preservation of Lanzhou lily. All the agricultural residues-derived microcrystalline celluloses were in cellulose Iβ structure with high purity and good thermal stability. Microcrystalline celluloses from sweet sorghum stalk had a higher degree of polymerization (327) and crystallinity (70.52 %) than others. The preservation effect of lily bulbs packaged by films were significantly improved indicated by the lessened weight loss rate and the meliorative hardness and whiteness, which ascribe to the repressed oxidation reactions. Polylactic acid/microcrystalline cellulose composite films prepared from sweet sorghum straw have been proved the most effective. This work could offer a value-added outlet for agricultural residues to produce microcrystalline celluloses-based biocompatible films for preservation of Lanzhou lily.

Physicochemical analysis and intermediate pyrolysis of Bambara Groundnut Shell (BGS), Sweet Sorghum Stalk (SSS), and Shea Nutshell (SNS)

ABSTRACT The current work focused on the intermediate pyrolysis of Bambara Groundnut Shells (BGS-G1), Sweet Sorghum Stalk (SSS), and Shea Nutshells (SNS). These feedstocks are readily available as wastes or by-products from industrial and agricultural activities. The thermo-gravimetric analysis of the biomass samples exhibited decomposition and devolatilization potentials in the temperature range of 110–650°C. The kinetic modelling resulted in the activation energy of BGS G1 being the lowest as 20.43 kJ/mol and SNS as the highest 24.89 kJ/mol among the three biomass samples. Intermediate pyrolysis was conducted in a vertical tube reactor at a temperature of 600°C, with nitrogen flow at 10 ml/min and heating rate ≥ 33.0℃/min. The yield of pyrolysis bio-oil was 38.0 ± 6.4, 44.2 ± 6, and 39.7 ± 5.2 wt.% for BGS-G1, SSS, and SNS, respectively. The HHV of bio-oil varied as 23.7 ± 1.8, 23.8 ± 1.8, to 26.5 ± 2.0 MJ/kg for BGS-G1 SSS and SNS respectively. The biochar recorded the lowest HHV for BGS-G1 as 18.8 ± 1.2 MJ/kg and the highest for SNS as 26.4 ± 1.8 MJ/kg. The FTIR of bio-oil revealed significant functional groups, and GC-MS (Gas Chromatography and Mass Spectrometry) analysis categorized the compounds in bio-oils as ketones, furans, phenolics, acids, phenols and benzene derivatives. The physicochemical analysis of the feedstocks and the products (bio-oil and biochar) showed their potential for bioenergy and biochemical (green chemicals) production.

Biomass and Dry Matter Yield Potential of Some Early Sweet Sorghum (Sorghum bicolor var. saccharatum (L.) Mohlenbr.) Genotypes

Sweet sorghum plant is a warm season annual crop. It can be used for animal feeding in the one-cut agricultural system. Sweet sorghum is grown for the purpose of fresh and dry grass and for silage production. Biomass of sweet sorghum is nutritive due to sweet sorghum stalk contains 15-20% sugar. The study aimed to determine biomass, dry matter yield and some agricultural characteristics of some early sweet sorghum genotypes. Research was carried out during the second crop-growing season of 2016 at the Eyyubiye campus of experimental area of the Harran University in Sanliurfa, Turkiye. The experiment was designed as complete randomized blocks design with four replicates. This study utilized 12 early sweet sorghum genotypes as crop material. The experiment investigated some yield characteristics such as cluster formation period, plant height, stalk diameter, stalk ratio, leaf ratio, cluster ratio, dry matter yield and biomass yield. Results showed significant differences between the genotypes for tested characteristics (P≤0.01). Cluster formation period values ranged from 54.25 to 69.00 day, plant height from 252.25 to 340.75 cm, stalk diameter from 19.15 to 25.60 mm, stalk ratio from 75.72% to 86.75%. Leaf ratio values varied between 8.83% and 15.98%, cluster ratio between 4.40% and 10.31%. Dry matter yield values were between 2918.12 and 8456.25 kg da-1, biomass yield values between 9283.5 and 18400.0 kg da-1. Findings revealed that UNLY-hybrid-4, Rox Orange, Blue Ribben, and Colman sweet sorghum cultivars gave higher values than others in terms of plant height, dry matter yield and biomass yield.

Preparation of Composite Reinforced Agent Based on Sweet Sorghum Stalk Fiber through Alkali Pressure Steam Treated Method

Increasing global concern to environmental issues and sustainability related to preservation of non-renewable natural resources has encouraged research to develop new environmental friendly materials and products based on renewable natural resources. Sorghum fiber has potential to be a composite reinforcement because it has a good mechanical properties, environmental friendly and inexpensive. The preparation process of sorghum fiber is needed to improve its compatibility with polypropylene (PP). Thermal alkalization is the method used in conducting fiber preparation. In this study, alkalization-thermal treatment with 0%, 5% and 10% NaOH and pressurized steam for 1 and 3 minutes was carried out to change the hydrophobicity of sorghum fiber. The most optimum result was obtained at 5% NaOH concentration with 3 minutes pressure-soaking, showing cleaner and fibrillated morphology based on FESEM testing. It was less lignin and hemicellulose content as indicated by FTIR testing result, better hydrophobicity as indicated through Sessil Drop testing result that showed contact angle of 120.9◦, as well as significant increase in crystallinity index of 6.3% as indicated through X-Ray Diffraction (XRD) test result. The increase in the hydrophobicity of the modified sorghum fiber indicated the increase of the natural fiber compatibility with polymer matrix.

Pilot-scale fermentation of 300 t/a total solvents from sweet sorghum stalk juice

Solvent production from non-grain crops as the substrate via microbial fermentation has been projected to replace highly polluting and unsustainable chemical production methods in fossil oil refinery. Although a promising process pilot-scale studies, the prerequisite for production at industrial scale, are rare. This study reports a complete pilot test process using sweet sorghum stalk juice as feedstock, including the acquisition of sweet sorghum stalk juice, laboratory screening of suitable strains, optimization of industrial conditions, and a pilot-scale test at Yuanxing Bioenergy Co., ltd., China. Strain CIBT S0031 (Clostridium saccharobutylicum DSM13864) performed exceptionally in sweet sorghum stalk juice fermentation compared to other solventogenic clostridia tested. Furthermore, a simple and reliable non-anaerobic inoculation method applicable to extensive industrial solvent fermentation was developed. The optimal minimal medium was adapted for pilot scale fermentation, containing only sweet sorghum stalk juice diluted with industrial water, 1.5 g/L ammonium sulfate, and 1 g/L calcium carbonate. The solvent titers of single batch fermentation (2.36 m3), fed-batch (2.28 m3), and semi-continuous fermentation (7.14 m3) reached 16.5 g/L, 19.29 g/L, and 18.39 g/L, respectively, which replicated the laboratory results at the ton-scale. In the multi-stage process for continuous fermentation (total of 48.3 m3, chained with one breeding tank and three fermenters of 16 m3), 800 kg of solvents was produced with a yield of 0.45 g /g, comparable to corn-based fermentation. This study verified the effectiveness of the tested strain and the pilot process, thus laying a solid foundation for the large-scale production of solvents from a non-grain crop.

Investigation of the heat release rate and particle generation during fixed bed gasification of sweet sorghum stalk

Sweet sorghum (SS) is an agricultural crop that is produced commercially in Nigeria. The crop has a high biowaste energy in its stalk, which is an attractive source of bioenergy in rural areas where it is produced. The residue–to-produce ratio (RPR) of the crop is 1.25 kg of biowaste for 1 kg of SS produced. The solid residue that results from the crop can be subjected to gasification to produce combustible gases: carbon monoxide (CO), hydrocarbon gases (total hydrocarbons) and hydrogen. The combustible gases can be piped into a burner for heat or into a Compression Ignition (CI) engine for electricity generation. This will enhance energy security as well as energy equity in rural areas in Nigeria and sub-saharan African countries where the crop is also produced. This research was aimed at optimising the gasification of SS stalk residue to maximise the yield of combustible gases from the first stage of the process. The restricted ventilation cone calorimeter method was used to gasify SS stalks on a laboratory scale. The test was carried out at air flow rates per exposed flat surface area of 9, 11.2, 12.9, 14.3, 15.5, 16.3, and 19.2 g/s·m2 respectively, which controls the gasification rate or power output. The speciation of the gases that evolved from the gasification of the biomass samples was carried out by an FTIR that was calibrated for 60 species. Current uses of biomass residues in open fire heating generates toxic fine particulate emissions and this work aimed to show that this was not a greater problem with gasification. A dynamic electrical mobility particle spectrometer (DMS500) was used to measure the particulate size distribution and concentration, as an efficient gasifier should not be generating major yields of soot, which would be a problem for a downstream reciprocating engine. The optimum equivalence ratio (Ф) for the best energy transfer to the gaseous products was 2.1, which was similar to previous work on pine using this equipment where the optimum equivalence ratio was 2.8. The hot gases efficiency at the optimum Ф was 81%, which compares well to that of 78% for pine.

The Effect of Hydrolysis Time with Trichoderma Reesei on Soluble Sugar Concentration in Sweet Sorghum Stalk Pulp and Alcohol Concentration of Its Fermentation Results

It has been done a study on the use of Trichoderma reesei in the hydrolysis of sweet sorghum stalk pulp continued to fermentation by Saccharomyces cerevisiae to produce bioethanol. The purpose of this study was to examine the effect of hydrolysis time by T. reesei on the sugar content of sweet sorghum stalk pulp and the ethanol concentration obtained after its fermentation using Saccharomyces cerevisiae. The sweet sorghum stalks were cut into small pieces, blended until crushed, incubated with T. reesei at various times. and then fermented using S. cerevisiae for 24 hours after the incubation period was complete. The results showed that the soluble sugar concentration in the sweet sorghum stalk pulp increased after the incubation, which occurred from the 8th to the 24th hour. Furthermore, it continued to decrease until the longest incubation time. The alcohol concentration produced after the fermentation period changed according to the pattern of changes in sugar concentration in the substrate. These results suggest that to increase bioethanol production from sweet sorghum stalk, it will be better to incubate the pulp of stalk first with T. reesei for approximately 24 hours before fermented with S. cerevisiae.

Carbon footprint analysis of sweet sorghum-based bioethanol production in the potential saline - Alkali land of northwest China

Available saline-alkali land could be used to plant bioenergy crops for biofuel stocks, retaining productive land for food crops. Sweet sorghum is a promising candidate for bioethanol production due to its ability to tolerate environmental stresses. This study estimated the available saline-alkali land for sweet sorghum planting in northwest China using a multi-factorial analysis, quantified its bioethanol potential, and assessed the carbon footprint of sweet sorghum stalk (SSS)-based bioethanol production on this land using a life cycle assessment. The results revealed 9.33 × 105 ha saline-alkali land available for sweet sorghum planting, or 11.47% of the total saline-alkali land in the study area, with a potential yield of 6.87 × 107 t sweet sorghum stalk, producing 4.29 × 106 t bioethanol. The carbon footprint of SSS-based bioethanol production ranged from 2.21 to 2.25 t CO2 eq t−1 bioethanol across selected districts. Sweet sorghum cultivation accounted for most of the carbon footprint in each district (40.18–45.30%). Compared to gasoline, the carbon footprint for pure bioethanol (E100) made from SSS in the selected districts declined by 33.42–49.94% with or without reusing the bagasse co-product. The carbon footprint of E10 (10% bioethanol from SSS and 90% gasoline) declined by 2.68–4.49%. Thus, it is possible to cultivate sweet sorghum on the selected saline-alkali land in northwest China for bioethanol production. However, future studies are needed to (1) improve sweet sorghum genotypes and identify optimal agronomic management for feedstock, (2) advance technologies for bioethanol production, (3) develop bioethanol-tolerant yeast and bacteria strains, and (4) stimulate policy support for growers and industrialists to accelerate cleaner production.

Isolation and Identification of Polyphenols From Fresh Sweet Sorghum Stems and Their Antibacterial Mechanism Against Foodborne Pathogens.

As a C4 energy crop widely planted all over the world, sweet sorghum is mainly used in sugar making and brewing. Fresh sweet sorghum stalks contain many natural ingredients that have antioxidant properties and can significantly inhibit the growth of foodborne pathogens. In this study, the polyphenols in sweet sorghum were extracted by acid ethanol and ion precipitation, and the types of polyphenols were determined by HPLC-MS. The polyphenol content in fresh sweet sorghum stalks was 5.77 mg/g after process optimization with 18 types of phenolic acids identified. The extract had a total antioxidant capacity of 9.4 μmol Trolox/mL. Polyphenol extract of sweet sorghum displayed antibacterial activity against Staphylococcus aureus, Escherichia coli, Listeria spp., and Salmonella spp. The extract increased the conductivity of cell suspensions by destroying the membrane structure, resulting in leakage of cell electrolytes. Changes in bacterial morphology and internal structure were indicated. The data describe an optimized process to extract polyphenols from sweet sorghum stalks and the methodology to identify the major components within the extract. The data provide a novel option for the comprehensive utilization of fresh sweet sorghum stalks.

Evaluation of Cell Wall Chemistry of Della and Its Mutant Sweet Sorghum Stalks.

The cell wall compositional (lignin and polysaccharides) variation of two sweet sorghum varieties, Della (D) and its variant REDforGREEN (RG), was evaluated at internodes (IN) and nodes (N) using high-performance liquid chromatography (HPLC), pyrolysis-gas chromatography-mass spectrometry (Py-GCMS), X-ray diffraction (XRD), and two-dimensional (2D) 1H-13C nuclear magnetic resonance (NMR). The stalks were grown in 2018 (D1 and RG1) and 2019 (D2 and RG2) seasons. In RG1, Klason lignin reductions by 16-44 and 2-26% were detected in IN and N, respectively. The analyses also revealed that lignin from the sorghum stalks was enriched in guaiacyl units and the syringyl/guaiacyl ratio was increased in RG1 and RG2, respectively, by 96% and more than 2-fold at IN and 61 and 23% at N. The glucan content was reduced by 23-27% for RG1 and by 17-22% for RG2 at internodes. Structural variations due to changes in both cellulose- and hemicellulose-based sugars were detected. The nonacylated and γ-acylated β-O-4 linkages were the main interunit linkages detected in lignin. These results indicate compositional variation of stalks due to the RG variation, and the growing season could influence their mechanical and lodging behavior.

Studying the process of extracting sugary substances from the stalks of sweet sorghum in the technology of making food syrups

The need to intensify the process of extracting sugar substances from sweet sorghum stalks in order to improve the quality and yield of the target product has been substantiated. Existing techniques of sugar substance extraction used in sweet sorghum processing technologies have been analyzed. The application of a combined technique for extracting sugary substances has been proposed implying the production of pressed and diffusion juice. The results of optimizing the press technique of juice extraction from sorghum stalks are given. The equations of material balance of products and sugars have been built, depending on such factors as the degree of pressing, the initial content of solids and sugars in the stalks. A procedure for calculating the yield of pressed juice, cake, and the content of total sugars has been devised, according to which the preliminary pressing of the stalks ensures the extraction of juice in the range of 25‒35 %, the yield of the pressed cake is 75‒65 % on average, with a sugar content exceeding 60 %. It has been experimentally established that the use of the anti-current process of extraction of sugar substances from the pressed cake ensures their complete extraction from raw materials. The rational parameters for this process have been defined. At a temperature of 66–70 °C and a duration of 20 minutes, it is possible to obtain an extract whose content of solids is 13.0 %, total sugars ‒ 11.10 %, and whose purity is 85.38 %. The research was carried out in order to intensify the extraction of sugar substances from sweet sorghum plant raw materials, to improve the technical level of the extraction process, and implement the devised method under industrial conditions. Further implementation of these results in the food industry could make it possible to establish the production of a wide range of sugar-containing products, both organically and as a natural substitute for sugar in food products.

Biotransformation of hydroquinone into α-arbutin by transglucosylation activity of a metagenomic amylosucrase.

Arbutin is a naturally occurring glycosylated product of hydroquinone. With the ability to interrupt melanin biosynthesis in epidermal cells, it is a promising cosmetic ingredient. In this study, a novel amylosucrase, Asmet, identified from a thermal spring metagenome, has been characterized for arbutin biosynthesis. Asmet was able to catalyze transglucosylation of hydroquinone to arbutin, taking sucrose as glycosyl donor, in the temperature range of 20°C to 40°C and pH 5.0 to 6.0, with the relative activity of 80% or more. The presence of chloride salts of Li, K, and Na at 1mM concentration did not exhibit any notable effect on the enzyme's activity, unlike Cu, Ni, and Mn, which were observed to be detrimental. The hydroquinone (20mM) to sucrose ratio of 1:1 to 1:10 was appropriate for the catalytic biosynthesis of arbutin. The maximum hydroquinone to arbutin conversion of 70% was obtained in 24h of Asmet led catalysis, at 30°C and pH 6.0. Arbutin production was also demonstrated using low-cost feedstock, table sugar, muscovado, and sweet sorghum stalk extract, as a replacement for sucrose. Whole-cell catalysis of hydroquinone to arbutin transglucosylation was also established.

Silage Fermentation on Sweet Sorghum Whole Plant for Fen-Flavor Baijiu.

The technology for producing bioethanol from sweet sorghum stalks by solid-state fermentation has developed rapidly in recent years, and has many similarities with traditional Chinese liquor production. However, the product from sweet sorghum stalks was lacking in volatile flavors, and the level of harmful contents were uncertain, therefore it could not be sold as liquor. In this study, the protein, fat, and tannin in the clusters and leaves of sweet sorghum were utilized to increase the content of flavor compounds in the ethanol product through the anaerobic fermentation of Saccharomyces cerevisiae. Meanwhile, the silage fermentation method was used to extend the preservation time of the raw materials and to further enhance the flavors of Fen-flavor liquor, with ethyl acetate as the characteristic flavor. The effects of different feedstock groups on ethyl acetate, ethyl lactate, methanol, acetaldehyde, acetal, fusel oil, total acid, and total ester were evaluated by analyzing the chemical composition of different parts of sweet sorghum and determined by gas chromatograph. The effect of different fermentation periods on the volatile flavor of sweet sorghum Baijiu was evaluated. The yield of the characteristic volatile flavor was increased by the extension of the fermentation time. Sweet sorghum Baijiu with a high ester content can be used as a flavoring liquor, blended with liquor with a shorter fermentation period to prepare the finished Fen-flavor Baijiu, conforming to the Chinese national standard for sale.

Sweet sorghum stalks extract has antimicrobial activity

Biochemicals production from the energy crop, sweet sorghum [Sorghum bicolor (L.) Moench], has attracted wide attention. However, utilization of sweet sorghum for phenolic compounds production has not yet been reported. To improve comprehensive utilization of sweet sorghum, a strategy combining acidic ethanol extraction and ion precipitation was developed to extract highly active phenolic compounds from sweet sorghum fresh stalks, which increased the final total phenolic content to 276.79 mg gallic acid equivalents/g dried extract. The sweet sorghum phenolic compounds extract was rich in gallic, gentisic, trans-ferulic, caffeic, coumaric, chlorogenic, and p-hydroxybenzoic acids, showing strong antioxidant properties. Evaluation of cell membrane integrity and biomacromolecules (protein and nucleic acid) leakage revealed that the sweet sorghum phenolic compounds extract had significant bacteriostatic activity against Staphylococcus aureus CMCC26003 and Escherichia coli CMCC44102, suggesting potential antimicrobial effects. This study provided a novel strategy for comprehensive utilization of sweet sorghum.

Dark Fermentation of Sweet Sorghum Stalks, Cheese Whey and Cow Manure Mixture: Effect of pH, Pretreatment and Organic Load

The aim of this study was to determine the optimal conditions for dark fermentation using agro-industrial liquid wastewaters mixed with sweet sorghum stalks (i.e., 55% sorghum, 40% cheese whey, and 5% liquid cow manure). Batch experiments were performed to investigate the effect of controlled pH (5.0, 5.5, 6.0, 6.5) on the production of bio-hydrogen and volatile fatty acids. According to the obtained results, the maximum hydrogen yield of 0.52 mol H2/mol eq. glucose was measured at pH 5.5 accompanied by the highest volatile fatty acids production, whereas similar hydrogen productivity was also observed at pH 6.0 and 6.5. The use of heat-treated anaerobic sludge as inoculum had a positive impact on bio-hydrogen production, exhibiting an increased yield of 1.09 mol H2/mol eq. glucose. On the other hand, the pretreated (ensiled) sorghum, instead of a fresh one, led to a lower hydrogen production, while the organic load decrease did not affect the process performance. In all experiments, the main fermentation end-products were volatile fatty acids (i.e., acetic, propionic, butyric), ethanol and lactic acid.