| Summary: | 碩士 === 逢甲大學 === 綠色能源科技碩士學位學程 === 107 === The uncontrolled discharge of large amounts of food waste (FW) causes severe environmental pollution in many countries. However, FW has a high energy potential of being converted into bioenergy. Within different possible treatment routes, anaerobic digestion of FW into biogas, is a proven and effective solution for FW treatment and valorization. Hydrogen and methane are the potential alternative energy carriers with autonomous extensive and viable importance. The mixture of hydrogen and methane is hythane and it gains attention due to its advantages as a valuable fuel. Furthermore, biohythane is a better transportation fuel than compressed natural gas in terms of high range of flammability, reducing ignition temperature as well as time, low nitrous oxide (NOx) emissions and improving engine performance without specific modification.
On the one hand, considering their complementary properties, co-production of a mixture of hydrogen and methane in the form of biohythane in two-stage anaerobic digestion process is gaining more interest than their individual production due to its advantages of hydraulic retention time (HRT), high energy recovery, high chemical oxygen demand (COD) removal, higher hydrogen and methane yields, and reducing carbon dioxide in biogas. On the other hand, such anaerobic biohythane productions using two separated bioreactors require more processes and cost for storing and mixing hydrogen and methane.
The present study dealt with the potential biohythane production in a two-compartment (lower, hydrogenesis; upper, methanogenesis) reactor (TCR) via a single-stage anaerobic fermentation at mesophilic temperature. Two main conditions were tested (1) the effect of various HRTs of 10, 7, 5, 3 and 2 d using FW as a substrate (40 g COD/L), (2) the effect of various substrate concentrations of 10, 20, 40 and 80 g COD/L at a constant HRT of 2 days.
In investigating the effects of HRTs on biohythane potential experiments, HRT 2 d resulted in peak hydrogen and methane production rates with values of 714 and 254 mL/L-d, respectively and had contents of hydrogen 8.6% and methane 48.0% in the produced gas. At this HRT, Clostridium sensu stricto 2 and Methanosaeta were dominant species in H2 and CH4 compartments, respectively. Moreover, substrate concentrations (SCs) were significantly correlated with biogas production. At SC 10 g COD/L, almost no hydrogen production was observed during steady-state while at an optimal SC of 40 g COD/L, higher hydrogen production was obtained than at 80 g COD/L, approximately fourfold compared to 20 g COD/L. There was insignificance in increasing hydrogen production when SC was changed from 40 to 80 g COD/L; furthermore, the methane production was negatively affected due to high SC.
The novelty of this work is creating a two-compartment reactor for single-stage anaerobic biohythane fermentation. However, there are a variety of improvements needs applying in TCR to enhance biohythane productivity as well as organic removal efficiency.
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