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Hydrolysis could be rate-limiting for the dark fermentative H 2 production from cassava starch (CS) due to its semicrystalline nature. Therefore, the effects of CS extrusion and enzymatic hydrolysis on improving dark fermentation (DF) were studied. Preliminary DF experiments were conducted to investigate the effects of inoculum (sludge) heat-pretreatment, which increased H 2 production from untreated-CS by over 154%. Likewise, 15 g/L starch was considered best for H 2 production. Extruded-CS presented a maximum H 2 yield of 1.58 mol H 2 /mol glucose with a 76% reduction in the fermentation adaptive phase and 43% increase in maximum H 2 productivity compared to untreated-CS. Meanwhile, extruded-CS hydrolysate presented a maximum H 2 yield of 1.8 mol H 2 /mol glucose with a 63% reduction in the fermentation adaptive phase and 18% increase in H 2 productivity. A comprehensive assessment of the H 2 yield, process time, production rate, and process simplification revealed extruded-CS as the most promising feedstock under the evaluated conditions. [Display omitted] • Heat pretreatment of sludge improved H 2 production from cassava starch by over 154%. • Extrusion pretreatment of cassava starch reduced the adaptive fermentation phase by 76%. • Extrusion pretreatment of cassava starch improved maximum H 2 productivity by 43%. • With extrusion pretreatment, the overall process productivity reached 110.13 NmLH 2 /L/h. [ABSTRACT FROM AUTHOR]

The enzymatic hydrolysis of native starch lacks efficiency because starch is mostly confined in semi-crystalline granules. To address the challenges associated with gelatinization and render native cassava starch (CS) amenable to enzymatic hydrolysis (enzyme cocktail from Aspergillus awamori and Trichoderma reesei), dry-extrusion pretreatment of CS mixed with sugarcane bagasse (SB) was studied. Results showed that among the CS:SB mass ratios studied (1:1; 1:0.5 and 1:0.25), extruded CS:SB (1:0.25) gave the highest 3-hour glucose yield (71.5%) after enzymatic hydrolysis. Extrusion reduced CS:SB (1:0.25) crystallinity by 78% and increased the intensity of all major FTIR absorption bands by 67–202%. The optimum 3-hour glucose yield from extruded CS:SB (1:0.25) hydrolysis was 74.1%, which was 330% higher than from untreated CS. The water absorption and solubility indices of the treated biomass increased by 145% and 12,640%, respectively under the optimum conditions, aiding the hydrolysis process. The dry extrudates were easy to manipulate and store. [Display omitted] [ABSTRACT FROM AUTHOR]

Anaerobic digestion has been widely applied for waste treatment, renewable energy generation and biofertilizer production. The biogas potential in Brazil is sizable, but the state of Rio de Janeiro is largely dependent on fossil fuels, and there is a lack of biogas potential assessments in the state. Thus, this study evaluated biomethane, electricity and biofertilizer potentials in the region. Three different scenarios of biomass supply were considered for four major biowaste streams: sewage sludge; cattle manure; sugarcane processing waste; and food waste. Biomethane generation from the assessed sources could reach 0.6–1.3 billion Nm3 year−1, corresponding to 1,768–3,961 GWh year−1 of electricity and 1.6–3.3 million Mg year−1 of biofertilizer. Cattle manure was responsible for 73–84% of the projected biomethane production, presenting an opportunity to reduce the significant emissions from livestock farming. The estimated biofertilizer production could meet the demands of the state, and the produced electricity could offset up to 10% of the demand. The gas grid could facilitate the distribution of upgraded biomethane, and 10–22% of the natural gas demand could be met. The findings of this work highlight the high potential for biogas generation in Rio de Janeiro, which is up to seven times larger than the current production. [ABSTRACT FROM AUTHOR]