| Allicin is an organic sulfide found in garlic that has a broad spectrum of antibacterial effects.The garlic production and consumption in China are second to none in the world.During the processing and consuming,garlic will produce a great amount of Allicin and degrade the waste from its product.The waste from the catering process and the waste activated sludge formed by the wastewater which from the garlic processing enterprise who use the biological method,both have high concentration Allicin and its degradation product.Meanwhile,along with the urbanization,food waste and waste activated sludge become an environmental problem for the city manager who must be faced.Many scholars and engineering practice have favored the use of anaerobic digestion technology for the safe reduction and resource disposal of the food waste and sludge.When considering the allicin and its degradation product as contaminants,they exist in food waste combined with the waste activated sludge anaerobic co-digestion system,there have few literatures researched the effects and mechanism of this system when resource product generates.The sequential batch reactor is used in this study,a series of experiment was run under 35±1℃and p H=7.0±0.2 conditions,the effect of Allicin and its degradation on the production of resources produced in the anaerobic digestion system which was constructed by the reaction substrate of food waste,waste activated sludge and food waste combined with waste activated sludge were studied.At the same time,the feasibility of controlling the production of resource products in the anaerobic co-digestion system of food waste containing allicin combined with waste activated sludge was investigated by various pretreatment methods.Economic benefit analysis is used to evaluate the potential of each pretreatment method in engineering application.Firstly,the differences between volatile short-chain fatty acids（VFAs）,hydrogen and methane formed from different food waste component were investigated in this study.Different doses and form of allicin were added to the system to investigate the influence of allicin on the formation of VFAs,hydrogen and methane.The results showed that the yield of VFAs,hydrogen and methane were significantly different in the anaerobic digestion of food waste from different sources.Besides,although allicin formed by fresh garlic with a certain dose can inhibit the yield of VFAs,hydrogen and methane in the anaerobic digestion system of food waste,its correlation is poor.By investigating the effects of allicin on the hydrolysis,acidification and methanation of organics in the anaerobic digestion system of food waste,and the relative activity of functional enzymes,the mechanism of inhibiting the production of VFAs,hydrogen and methane by the anaerobic digestion of food waste was preliminarily revealed.The results showed that the dissolution and hydrolysis of organic matter were promoted when a certain dose of allicin was present in food waste.However,allicin promoted the accumulation of propionic acid in VFAs components and significantly inhibited the accumulation of acetic acid and butyric acid.At the same time,the“acetic acid nutrient type”and“hydrogen nutrient type”methane production and metabolism pathways were significantly inhibited.Also,the relative activity of methane-producing enzymes F420 and Co M in the anaerobic digestion system of food waste containing garlic was only 0.08-1.04%.After that,three kinds of allicin degradation products were selected in this study,are respectively diallyl sulfide（DAS）,diallyl disulfide（DADS）and diallyl trisulfide（DATS）,and the effects of adding different doses of allicin degradation products to waste activated sludge on the production of resource products by anaerobic digestion of waste activated sludge were discussed.By analyzing the yield of VFAs,hydrogen and methane in the system,the degradation rules of the substrates in each stage of anaerobic digestion and the cell integrity.The mechanism of the inhibition of allicin degradation products on VFAs,hydrogen and methane formation in the anaerobic digestion process of waste activated sludge was preliminarily explored.The results showed that the degradation rate of allicin in the waste activated sludge methanation stage was significantly inhibited,and the degradation rates of sodium acetate in the high-dose（2.0ml）DAS,DADS and DATS groups were only 7.93±2.11%,7.74±2.02%and 7.70±2.02%,respectively.Allicin degradation products had a negative effect on cell integrity in the anaerobic digestion system of the waste activated sludge.The concentrations of LDH and DNA in the reactor of each high-dose（2.0ml）were 111.67±5.03%,112.77±3.68%and 118.13±2.61%of the CK group,respectively.Subsequently,based on the above research results,this study investigated the effect and mechanism of allicin and its degradation products on the anaerobic co-digestion system of food waste combined with waste activated sludge.Effects of allicin and its degradation products on the production of resource products in the anaerobic co-digestion system of food waste combined with waste activated sludge,the influence of the system of dissolving,hydrolysis of organic matter and releasing regularity of nitrogen,phosphorus and COD in the balance between the system input and output,the release behavior of sulfur dioxide,functional enzyme activity,cell integrity and the system of microbial community succession law,all reveal the function that allicin and its degradation products inhibit the production of VFAs,hydrogen and methane by anaerobic co-digestion of food waste combined with waste activated sludge.The results showed that allicin and its degradation products significantly inhibited the formation of VFAs,hydrogen and methane in the anaerobic co-digestion system of food waste combined with waste activated sludge,with the maximum inhibition rates of 50.48%,68.66%and 92.29%,respectively.Besides,the presence of allicin and its degradation products significantly increased the proportion of propionic acid in VFAs components,with the maximum proportion reaching 46.57±3.73%.However,compared with the inhibition effect of the anaerobic digestion system,the yield of VFAs,hydrogen and methane in the anaerobic co-digestion system all increased to some extent.Allicin and its degradation products caused COD in the anaerobic co-digestion system flow into hydrogen sulfide.Moreover,the microbial community in the reactor under the stress of allicin and its degradation products evolved towards the sulfide reduction system and the microbial community structure capable of competing with the systemFinally,this study investigated the effects of various pretreatment methods on the recovery of methane production in the anaerobic digestion system of food waste combined with waste activated sludge containing allicin and its degradation products.The experimental results show that thermal pretreatment,alkali pretreatment and combined thermal-alkali pretreatment can effectively improve the methane production rate.However,the electromagnetic field stimulation technology has no obvious effect on the methane production rate of the system,but it has a certain effect on the methane production rate of the anaerobic co-digestion system without allicin and its degradation products.Through the analysis of economic benefit,the combined thermal-alkali pretreatment is the most suitable pretreatment technology for the anaerobic co-digestion system of food waste with garlic and waste activated sludge.By exploring the effect of allicin on the anaerobic co-digestion process of food waste combined with waste activated sludge,this study revealed the mechanism of action of allicin in inhibiting the production of VFAs,hydrogen and methane in the system.The effect of allicin on the anaerobic co-digestion of food waste combined with waste activated sludge by various pretreatment techniques was investigated.It provides the necessary theoretical support for the fine control of the application of food waste combined with waste activated sludge anaerobic co-digestion engineering. |
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