Cassava Stillage Research Articles

Economic viability of two-stage biohydrogen and biomethane production from cassava stillage residue focusing on solids content and pretreatment

Biohythane (a mixture of hydrogen and methane) may play a significant role in a future decarbonised energy system. The production of biohythane can be achieved by sequential dark hydrogen fermentation and anaerobic digestion. However, the technology readiness level of biohythane can be limited by many process constraints negatively affecting its commercial feasibility. Here, a pilot experiment on fermentative hythane production from cassava stillage residue (CSR) incorporating dilute acid pretreatment and enzymolysis was undertaken. The production of hydrogen and methane was 72.0 ± 10.7 and 295.4 ± 28.5 mL/g volatile solid, respectively. Different scenarios for techno-economic analysis were developed in terms of the dried/wet form of CSR and total solids content during fermentation. Results suggested that hythane from CSR was not economically feasible with a high production cost (1.39–2.33 €/m3). There was a trade-off relationship between the increase in methane yield through pretreatment and the associated cost.

Semi-continuous feeding combined with traditional domestication improved anaerobic performance during treatment of cassava stillage

The effects of feeding pattern were studied during anaerobic digestion of cassava stillage. Continuous feeding and semi-continuous feeding, were adopted in two internal circulation (IC) reactors (A and B, respectively). The reactors showed different performance in the anaerobic digestion process. The maximum difference, was observed for the soluble chemical oxygen demand (SCOD) removal rate and the biogas production, which were 23.2% and 95.7 L/2 d higher in reactor B than reactor A, respectively. The overall VFAs level of reactor A was higher than that of reactor B. Microbial community analyses indicated that the abundances of dominant bacteria and methanogens became higher in the reactor B than in reactor A as the digestion process progressed. Hence, semi-continuous feeding showed superior performance than continuous feeding for SCOD removal rate, biogas production, and the relative abundances of methanogens in the case of high OLR.

Simultaneous carbon and nitrogen removal from anaerobic effluent of the cassava ethanol industry

This study investigated the simultaneous carbon and nitrogen removal from anaerobic effluent of cassava stillage using a lab-scale integrated system consisting of an upflow anaerobic sludge blanket (UASB) reactor and an activated sludge (AS) process. Simultaneous denitrification and methanogenesis (SDM) was observed in the UASB with nitrate recirculation. Compared with the blank reactor without recirculation, the overall chemical oxygen demand (COD) removal efficiencies in the combined system with nitrate recirculation were similar (80-90%), while the TN removal efficiencies were significantly improved from 4.7% to 71.0%. Additionally, the anaerobic COD removal efficiencies increased from 21% to 40% as the recirculation ratio decreased from 3 to 1. Although the influent nitrate concentrations fluctuated (60-140mgN/L), the nitrate removal efficiencies could be maintained at about 97% under different recirculation conditions. With the decreasing recirculation ratio from 3 to 1, the CH4 content in biogas improved from 2% to 40% while the N2 content reduced from 95.8% to 50.6%. The 16S rDNA sequencing results indicated that bacteria diversity in anaerobic SDM granular sludge was much higher than archaea. The effect of recirculation ratios on the bacterial and archaeal communities in SDM granular sludge could be further confirmed by the relative abundance of denitrifying bacteria.

Advances in modifying lignin structures for largely enhancing high-lignin biomass saccharification

Traditional chemical treatments require high energy and concentrated agents to decrease high-lignin biomass recalcitrance during lignin removal. A low-cost and environment-friendly method via modifying the lignin structure without lignin degradation overcomes lignin barrier in wood-feeding termites. In this study, thermal hydroxyl radicals in the biomimetic system performed in high-lignin cassava stillage residues did not reduce total lignin level but altered the lignin monostructure. The major β-O-4′ remained conserved, whereas hydroxylation and modification of selective intermonomer side-chain linkages occurred in the treated lignin. The treatment can enhance enzymatic saccharification with cellulose conversion of cassava stillage residues at 97%, twice higher than that of the control. In addition, the modified lignin exhibited low invalid adsorption capacity into commercial cellulases, thereby improving the performance of cellulosic feedstock. Modifying the lignin structure, instead of removing lignin, provides new insights for development of novel treatments for high-lignin biomass.

Novel process combining anaerobic-aerobic digestion and ion exchange resin for full recycling of cassava stillage in ethanol fermentation

A novel cleaner ethanol production process has been developed. Thin stillage is treated initially by anaerobic digestion followed by aerobic digestion and then further treated by chloride anion exchange resin. This allows the fully-digested and resin-treated stillage to be completely recycled for use as process water in the next ethanol fermentation batch, which eliminates wastewater discharges and minimizes consumption of fresh water. The method was evaluated at the laboratory scale. Process parameters were very similar to those found using tap water. Maximal ethanol production rate in the fully-recycled stillage was 0.9g/L/h, which was similar to the 0.9g/L/h found with the tap water control. The consumption of fresh water was reduced from 4.1L/L (fresh water/ethanol) to zero. Compared with anaerobically-aerobically digested stillage which had not been treated with resin, the fermentation time was reduced by 28% (from 72h to 52h) and reached the level achieved with tap water. This novel process can assist in sustainable development of the ethanol industry.

Biochemical characterization of a novel feruloyl esterase from Penicillium piceum and its application in biomass bioconversion

A putative feruloyl esterase (FAE) was successfully cloned from the genomic DNA of Penicillium piceum and expressed in E. coli. The deduced internal amino acid sequence of the novel FAE was found to have 56% sequence identity with FAE from Aspergillius flavus and was designated as PpFAE. PpFAE contained the conserved region flanking the characteristic G-X-S-X-G motif of a serine esterase, suggesting a FAE function for the protein. Substrate specificity profiling revealed that PpFAE was a type C FAE. The optimum temperature and pH for PpFAE were 70°C and 3.0, respectively. PpFAE was very stable under a pH range of 3.0–5.0 (>96% of maximum enzymatic activity) and displayed thermostability with thermal denaturing half-lives of 220min at 70°C and 150min at 60°C. Supplementation with low doses of PpFAE (120μg/g substrate) increased glucose yields released from corn stover, wheat bran, corn cob, and cassava stillage residues by 68.8%, 38.6%, 15.6%, and 20.0%, respectively. Supplementation with PpFAE could break down the intermolecular ester bonds that cross-link lignin with hemicellulose, effectively increasing the Xyl/Ara ratio and decreasing hydrogen bond intensity of the crude biomass.

Cassava stillage and its anaerobic fermentation liquid as external carbon sources in biological nutrient removal

The aim of this study was to investigate the effects of one kind of food industry effluent, cassava stillage and its anaerobic fermentation liquid, on biological nutrient removal (BNR) from municipal wastewater in anaerobic-anoxic-aerobic sequencing batch reactors (SBRs). Experiments were carried out with cassava stillage supernatant and its anaerobic fermentation liquid, and one pure compound (sodium acetate) served as an external carbon source. Cyclic studies indicated that the cassava by-products not only affected the transformation of nitrogen, phosphorus, poly-β-hydroxyalkanoates (PHAs), and glycogen in the BNR process, but also resulted in higher removal efficiencies for phosphorus and nitrogen compared with sodium acetate. Furthermore, assays for phosphorus accumulating organisms (PAOs) and denitrifying phosphorus accumulating organisms (DPAOs) demonstrated that the proportion of DPAOs to PAOs reached 62.6% (Day 86) and 61.8% (Day 65) when using cassava stillage and its anaerobic fermentation liquid, respectively, as the external carbon source. In addition, the nitrate utilization rates (NURs) of the cassava by-products were in the range of 5.49-5.99 g N/(kg MLVSS⋅h) (MLVSS is mixed liquor volatile suspended solids) and 6.63-6.81 g N/(kg MLVSS⋅h), respectively. The improvement in BNR performance and the reduction in the amount of cassava stillage to be treated in-situ make cassava stillage and its anaerobic fermentation liquid attractive alternatives to sodium acetate as external carbon sources for BNR processes.

Effects of sulfide on the integration of denitrification with anaerobic digestion

The effects of sulfide on the integration of denitrification with anaerobic digestion using anaerobic effluents of cassava stillage as carbon source were investigated. Batch tests indicated that nitrate reduction efficiencies decreased from 96.5% to 15.8% as sulfide/nitrate (S/NO3(-)-N) ratios increased from 0.27 to 1.60. At low S/NO3(-)-N ratios (0.27-1.08) anaerobic acidogenesis was accelerated. Nitrate was reduced to nitrite via sulfur-based autotrophic denitrification, after which the formed nitrite and residual nitrate were converted to N2 via heterotrophic denitrification. Increases in the S/NO3(-)-N ratio (1.60) caused a shift (76.3%) in the nitrate reduction pathway from denitrification to dissimilatory nitrate reduction to ammonia (DNRA). Sulfide concentrations (S/NO3(-)-N ratio of 1.60) suppressed not only heterotrophic denitrification but also acidogenesis. The potentially toxic effect of sulfide on acid production was mitigated by its rapid oxidation to sulfur, allowing the recovery of acidogenesis.

A green and efficient method for preparing acetylated cassava stillage residue and the production of all-plant fibre composites

Cassava stillage residue (CSR), a kind of agro-industrial plant fibres , was directly acetylated and converted into thermoplastic material by mechanical activation-assisted solid phase reaction (MASPR) in a stirring ball mill without the use of organic solvent and additives. As combining mechanical activation and chemical modification in the same equipment, the destruction of hydrogen bonds and crystalline structure of CSR induced by intense milling improved the reactivity of CSR, leading to the effective acetylation of CSR. After acetylation by MASPR, the modified CSRs possessed thermoplasticity, ascribing to the introduction of acetyl groups and the destruction of high crystallinity structure of cellulose. The self-reinforced all-plant fibre composites (APFC) were successfully produced with the modified CSRs as both matrix and reinforcement by hot pressing technology. The direct acetylation of CSR and successful production of APFC suggested that MASPR was a simple, efficient and environmentally friendly method for chemical modification of agro-industrial lignocellulose biomass.

Mechanical and interfacial properties of poly(vinyl chloride) based composites reinforced by cassava stillage residue with different surface treatments

Abstract Cassava stillage residue (CSR), a kind of agro-industrial plant fiber, was modified by coupling agent (CA), mechanical activation (MA), and MA-assisted CA (MACA) surface treatments, respectively. The untreated and different surface treated CSRs were used to prepare plant fibers/polymer composites (PFPC) with poly(vinyl chloride) (PVC) as polymer matrix, and the properties of these CSR/PVC composites were compared. Surface treated CSR/PVC composites possessed better mechanical properties, water resistance and dimensional stability compared with the untreated CSR/PVC composite, attributing to the improvement of interfacial properties between CSR and PVC matrix. MACA-treated CSR was the best reinforcement among four types of CSRs (untreated, MA-treated, CA-treated, and MACA-treated CSRs) because MACA treatment led to the significant improvement of dispersion, interfacial adhesion and compatibility between CSR and PVC. MACA treatment could be considered as an effective and green method for enhancing reinforcement efficiency of plant fibers and the properties of PFPC.

Nitrate reduction pathway in an anaerobic acidification reactor and its effect on acid fermentation

This study investigated the performance of a reactor in which denitrification was integrated into the anaerobic acidogenic process. Industrial wastewater cassava stillage was used as the carbon source, and the nitrate reduction pathway and its effects on acid fermentation were examined. Results from batch and semi-continuous tests showed that the presence of nitrate did not inhibit anaerobic acidification but altered the distribution of volatile fatty acid (VFA) species. Nitrate reduction was attributable to denitrification and to dissimilatory nitrate reduction to ammonia (DNRA). The ratio of DNRA to denitrification was proportional to the ratio of [Formula: see text] . After 130 days of semi-continuous operation, denitrification removal efficiency accounted for about 60% at a [Formula: see text] of 50. The proportional distribution of VFAs was acetate, followed by propionate and then butyrate. The polymerase chain reaction-denaturing gradient gel electrophoresis results confirmed the contributions of denitrification and DNRA in the nitrate-amended reactor and showed that the addition of nitrate enriched the structure of the bacterial community, but did not suppress the activity of acid-producing bacteria.

Preparation of a novel carbon-based solid acid from cassava stillage residue and its use for the esterification of free fatty acids in waste cooking oil

A novel carbon-based solid acid catalyst was prepared by the sulfonation of incompletely carbonized cassava stillage residue (CSR) with concentrated sulfuric acid, and employed to catalyze the esterification of methanol and free fatty acids (FFAs) in waste cooking oil (WCO). The effects of the carbonization and the sulfonation temperatures on the pore structure, acid density and catalytic activity of the CSR-derived catalysts were systematically investigated. Low temperature carbonization and high temperature sulfonation can cause the collapse of the carbon framework, while high temperature carbonization is not conducive to the attachment of SO3H groups on the surface. The catalyst showed high catalytic activity for esterification, and the acid value for WCO is reduced to below 2mg KOH/g after reaction. The activity of catalyst can be well maintained after five cycles. CSR can be considered a promising raw material for the production of a new eco-friendly solid acid catalyst.

Microbial Communities in Anaerobic Acidification-Denitrification and Methanogenesis Process for Cassava Stillage Treatment

This study investigated operational performance and microbial communities in the integrated acidification-denitrification bioreactor and the followed methanogenesis process. Industrial wastewater, cassava stillage (CS) was used as the carbon source amended with or without nitrate. The results showed that acidification and denitrification could occur simultaneously in a single acidification-denitrification reactor, and denitrificatoin did not suppress the acidogenic activity. Both denitrification and DNRA could contribute to nitrate reduction and proportions of them were about 60% and 40% respectively at the tested condition of COD/NO3-Nof 50. The introduction of nitrate into acidogenic phase did not have any effect on the followed methanogenic process. Microbial communities sampled from two systems were analyzed by culture-independent techniques based on PCR-DGGE. The relative abundance of acid-producing bacteria (primarily Parabacteroides distasonis and Chloroflexi) in the nitrate-amended reactor further confirmed that the addition of nitrate did not suppress the activity of acid-producing bacteria. Bacteria involved in denitrification and DNRA were also detected. The archaeal communities in methanogenic reactors of two systems showed no significant differences. And Methanoculleus and Methanolobus were the dominant bacteria in the culture.

Effect of Ionic Liquid Pretreatment on the Structure and Enzymatic Saccharification of Cassava Stillage Residues

Cassava stillage residue (CSR), the solid wastes generated from cassava-based bio-ethanol production, can be used to produce ethanol because of its high contents of cellulose. This study has focused on the pretreatment of CSR using the ionic liquid (IL) of 1-butyl-3-methyl imidazolium chloride ([Bmim]Cl). The changes in surface morphology, particle size and functional groups of pretreated CSR were examined by scanning electron microscopy (SEM), laser diffraction instrument and Fourier transform infrared (FTIR) spectroscopy. The results showed that [Bmim]Cl pretreatment could significantly damage the structure of cassava cellulose and increase the enzymatic saccharification rate.

VFAs Production Potential of Brewery Industry Wastewater and Starch Wastewater

The volatile fatty acids (VFAs) are kinds of effective external carbon source for enhanced biological nutrients removal. Volatile fatty acids (VFAs) production from anaerobic fermentation from cassava stillage (CS) wastewater, starch wastewater (SW) and the yellow wine wastewater (YWW) was conducted in batch tests. The VFAs production potential and the characteristics of the fermentative liquid were compared and discussed. Experimental results indicated that the cassava stillage wastewater and the starch wastewater were preferable feed for anaerobic VFAs fermentation. Acetic acid, propionic acid and butyric acid were the main components of the VFAs with respective percentage of 36.5%, 20% and 40% at the end of its fermentation.

Enhanced thermophilic fermentative hydrogen production from cassava stillage by chemical pretreatments

Acid and alkaline pretreatments for enhanced hydrogen production from cassava stillage were investigated in the present study. The result showed that acid pretreatment was suitable for enhancement of soluble carbohydrate while alkaline pretreatment stimulated more soluble total organic carbon production from cassava stillage. Acid pretreatment thereby has higher capacity to promote hydrogen production compared with alkaline pretreatment. Effects of pretreatment temperature, time and acid concentration on hydrogen production were also revealed by response surface methodology. The results showed that the increase of all factors increased the soluble carbohydrate production, whereas hydrogen production was inhibited when the factors exceeded their optimal values. The optimal conditions for hydrogen production were pretreatment temperature 89.5 °C, concentration 1.4% and time 69 min for the highest hydrogen production of 434 mL, 67% higher than raw cassava stillage.

Enhanced fermentative hydrogen production from cassava stillage by co-digestion: The effects of different co-substrates

In this study, an efficient strategy to increase the hydrogen yield from cassava stillage (CS), by its co-digestion with organic wastes, was developed. The effects of different co-substrates on hydrogen yield were evaluated and compared, with increases obtained in all co-digestion reactors. The maximal hydrogen yield was achieved by CS co-digestion with cassava excess sludge (CES), which resulted in a 46% increase over the yield from CS alone. Improved hydrolysis and acidification performances, and thus increased hydrogen production, were additional benefits of co-digestion, especially with CES. Also, the presence of a co-substrate promoted butyrate over lactate generation. The most influential advantage of co-substrate addition was the enhanced pH buffering capacity, which correlated linearly with hydrogen yield (R2 = 0.98). Moreover, the co-substrates addition resulting in more favorable carbohydrate-COD/protein-COD ratio, C/N and C/P ratios, all of which also correlated linearly with hydrogen yield (R2 = 0.86, 0.71, and 0.75 respectively). Polymerase chain reaction–denaturing gradient gel electrophoresis analysis of the role of microorganisms indicated that the addition of even small amounts of co-substrate altered the bacterial communities within the reactors, enriching the proportion of hydrogen-producing bacteria. A species detected only in the co-digestion reactors was shown to be related to Clostridium cellulosi, which is an efficient hydrogen-producer, while some bacteria not involved in hydrogen production and present in the CS alone reactor were not detectable in any of the co-substrate-containing reactors.

Optimization of biohydrogen and methane recovery within a cassava ethanol wastewater/waste integrated management system

Thermophilic co-fermentation of cassava stillage (CS) and cassava excess sludge (CES) were investigated for hydrogen and methane production. The highest hydrogen yield (37.1ml/g-total-VS added) was obtained at VSCS/VSCES of 7:1, 17% higher than that with CS digestion alone. The CES recycle enhanced the substrate utilization and improved the buffer capacity. Further increase the CES fraction led to changed VFA distribution and more hydrogen consumption. FISH analysis revealed that both hydrogen producing bacteria and hydrogen consuming bacteria were enriched after CES recycled, and the acetobacteria percentage increased to 12.4% at VSCS/VSCES of 6:2. Relatively high efficient and stable hydrogen production was observed at VSCS/VSCES of 5:3 without pH adjusted and any pretreatment. The highest total energy yield, the highest COD and VS degradation were obtained at VSCS/VSCES of 7:1. GFC analysis indicated that the hydrolysis behavior was significantly improved by CES recycle at both hydrogen and methane production phase.

Effect of carbon source and COD/NO3−–N ratio on anaerobic simultaneous denitrification and methanogenesis for high-strength wastewater treatment

The effect of carbon source and COD/NO(3)(-)-N ratio on denitrification and methanogenesis in mixed methanogenic matrix was investigated in this study. Industrial wastewater, anaerobic treated cassava stillage (CS) and glucose synthetic wastewater were used as carbon sources respectively for comparison. Experimental results showed that denitrification was the main nitrate reduction pathway for all COD/NO(3)(-)-N ratios tested in two substrates. Simultaneous denitrification and methanogenesis occurred at COD/NO(3)(-)-N higher than 7 regardless of carbon sources. Incomplete denitrification was observed at COD/NO(3)(-)-N ratio below 7 in both the anaerobic effluent of CS and glucose-fed cultures due to the insufficient available organic carbon. The nature of carbon sources was observed to play a key role in the nitrate and organic carbon utilization rates. COD/NO(3)(-)-N ratio had a strong effect on the organic matter utilization pathways. Methanization consumed more organic matter than denitrification with further increase of COD/NO(3)(-)-N ratio above 7 in two substrates. Results of VFA variation suggested that propionate and butyrate were preferably utilized by the denitrifiers than acetate.

Microscopic structure and properties changes of cassava stillage residue pretreated by mechanical activation

This study has focused on the pretreatment of cassava stillage residue (CSR) by mechanical activation (MA) using a self-designed stirring ball mill. The changes in surface morphology, functional groups and crystalline structure of pretreated CSR were examined by using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) under reasonable conditions. The results showed that MA could significantly damage the crystal structure of CSR, resulting in the variation of surface morphology, the increase of amorphous region ratio and hydrogen bond energy, and the decrease in crystallinity and crystalline size. But no new functional groups generated during milling, and the crystal type of cellulose in CSR still belonged to cellulose I after MA.