| The hydrolysis stage in anaerobic digestion process can be divided into three acid-producing types:butyric acid type,propionic acid type and ethanol type.This study proposed a novel semi-continuous two-phase anaerobic digestion system characterized by methanogenesis-from-alcoholization by inoculating yeast in the hydrolysis acidification stage.The new system could alleviate acidification and improve the performance and stability of anaerobic digestion system and this paper has carried out detailed research on this system and clarified the regulation mechanism.Anaerobic digestion technology is one of the widely used food waste recycling technologies.Due to the high content of easily degradable organic matter in food waste,acidification is likely to occur in the anaerobic digestion system.In order to solve these problems,this study proposed a novel semi-continuous two-phase anaerobic digestion system characterized by methanogenesis-from-alcoholization,which could alleviate acidification and improve the performance and stability of anaerobic digestion system.This paper has carried out detailed research on this system and clarified the regulation mechanism.In batch anaerobic digestion,the hydrolysis and acidification efficiency of the food waste was enhanced after the ethanol pre-fermentation.Compared with the control group,the concentrations of ethanol,acetic acid and total volatile fatty acid(TVFA)in the substrate were increased by 4.5,4.9 and 1.4 times respectively.From the change of the ratio of ethanol to the total amount of hydrolytic acidification products,it could be known that the substrate was more converted to ethanol,which reduced the formation of organic acids such as propionic acid,thereby improving the stability of the anaerobic digestion system.In addition,during methane fermentation,ethanol as to a slow release matrix can be gradually converted into acetic acid which was easily utilized by methanogens.In semi-continuous single-phase anaerobic digestion,the pre-fermentation group after 24 h ethanol pre-fermentation could maintain a high substrate degradation efficiency and stable pH value.Moreover,the highest organic loading rate of the system reached 5.0 gVS/(L-d),and the average methane yield reached 391.3 mL/g VS,which was 6.4%higher than the control group.When the ammonia nitrogen concentration in the system reached 2485 mg/L,ammonia nitrogen inhibition occurred,which led to the accumulation of TVFA.After the TVFA concentration exceeded 2500 mg/L,the pH of the system was significantly reduced by acid inhibition,and system turned to be unstable.The first phase of the novel enhanced ethanol-type semi-continuous two-phase anaerobic digestion system was characterized by the simultaneous production of ethanol and organic acids.The HRT of the system was 2 d,and the digestale of the methanogenic phase was firstly centrifuged and then the supernatant was recirculated.Compared with the traditional digestate recirculation two-phase anaerobic system,in the novel system,the maximum organic loading rate was increased from 5.0 gVS/(L·d)to 6.0 gVS/(L·d).So that the effective volume of the system was reduced by 21.4%while the average volume methane production rate was increased by 33.5%.The TVFA/total alkalinity(TA)ratio can be used as an early warning indicator for system operation:TVFA/TA<0.4,the system runs stably;0.4<TVFA/TA<0.6,the system has a tendency to be unstable;TVFA/TA>0.6,the system will be completely acidified and unstable.This study provided an effective method for the regulation and stable operation of anaerobic digestion of food waste.At the same time,it also provided a new way to reduce the volume of system equipment while obtained higher methane yield. |
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