چكيده لاتين
Hydrogen and butanol, two sustainable, clean and renewable energy carriers, are biologically obtained from dark fermentation and acetone-butanol-ethanol fermentation processes, respectively. These processes face major challenges such as primary carbon sources and energy investment on return. In order to solve these challenges, four scenarios were defined and implemented in this study. In the first scenario, prunings were co-processed with degradable fraction of municipal solid waste (MSW) in two pH operating conditions and three substrate concentration levels, without any pretreatment for the substrate. The inoculum was first pretreated with heat shock pretreatment under different conditions to obtain the highest biohydrogen yield and then used for further analysis of dark fermentation. The highest biohydrogen production of 84.06 ± 6.7 mL/g VS was obtained by dark fermentation of 20 g/L composite substrate under initially neutral conditions. Fermentation of individual substrates resulted in 40.9, 0.2, 0.1, and 0.2 mL/g VS of MSW, pine, mulberry, and cypress, respectively, 85% lower than dark fermentation with composite substrate. Changes in compositions during dark fermentation were determined. In addition, the modified Gompertz model (MGM) and modified Logistic model (MLM) were well-fitted on kinetic data. In the second scenario, a multi-step approach including "starchy dark fermentation", " intermediary autogenous acidic pretreatment " and "lignocellulosic dark fermentation" for biohydrogen production synergistically caused converting of organic waste to biohydrogen. In the first stage, 72-78% of starch was consumed and 494-2274 ml of biohydrogen was obtained per 100 grams of waste. The second stage involved improving the structure of lignocellulose-rich solids through the application of volatile fatty acid-rich liquor generated in the first stage for pretretament. The third stage produced 119-3154 ml of biohydrogen from 100 g of waste. Under optimal conditions, the three-step process produced a total of 5228 mL of hydrogen from 100 g of untreated substrate, which was 2.4 times more than the one-step dark fermentation. In the third scenario, the dark fermentation process was used as a biological pretreatment for ABE fermentation. The maximum amount of biohydrogen production was 246.72 ml/g belong to composite substrate. Also, pretreatment increase the yield of glucose between 52% (for the cypress sample) and 83% (for the composite substrate). Subsequently, the amount of butanol increased so that the highest amount of ABE production was seen in the case of composite substrate, which was equivalent to 65% increase. Finally, in the fourth scenario, following the efforts to integration of ABE fermentation and dark fermentation, the liquid obtained from the dark fermentation process were added in three different volumes to the ABE fermentation environment, leading to an increase from 2.4-4.2 to 5.7-4.2 g/liter, 0.45-0.41 to 0.8-0.71 g/liter and 1.5 to about 3 g/liter, in butanol, ethanol and the ratio of butanol to acetone, respectively.
