High-efficient Anaerobic Digestion Of Vinegar Residue

As the major by-product of vinegar production industry,large amount of vinegar residue?VR?was produced owning to the increasing demand of vinegar and highly developed vinegar production industry in China.With the increase of population,the demand of vinegar become larger and larger,thus total 3 million tons of VR were produced every year.VR is mainly composed by bran,rice chaff,and other filling materials which are rich in lignocellulose structure.VR caused serious environmental pollution owing to the high acidity and moisture content,while traditional treatment methods like landfill and incineration often caused secondary pollution,and it is also a waste of bioresources.Anaerobic digestion could convert organic waste into renewable energy rapidly,steadily,and environmental friendly.There is no report showing that VR has been applied in AD industry successfully at present.Therefore,in order to treat the large number of VR in a short period of time and utilize it as a resource in future industrial application,this study carried out a series of anaerobic digestion research on VR.Firstly,this study applied central composite design of response surface methodology to investigate the influences of feed to inoculum ratio,organic loading,and initial pH on methane production and the interaction between them.The maximum cumulative methane yield of 203.91 mL gVS^-1 and biodegradability of 46.99%were obtained at feed to inoculum ratio of 0.5,organic loading of 31.49 gVS L^-1,and initial pH of 7.29,which was considered as the best condition.Additionally,a significant interaction was found between feed to inoculum ratio and organic loading,which showed a possibility of using high F/I?more than 1.5?and organic loading(more than 40 gVS L^-1)in future industrial application.Secondly,10 kinds of different pretreatment methods were applied to treat VR in order to make a comparison among these pretreatment methods and seek for the optimal method as well as the conditions which achieved the maximum methane production.Results showed that acid pretreatment removed the most of hemicellulose in VR and alkaline pretreatment showed the strongest delignification.The crystal style of cellulose in VR presented an intermediate form between cellulose I and II.All the pretreatment methods could only swell cellulose and alkaline pretreatment showed the stronger swelling effect,which could transfer cellulose crystal style into I structure during the regeneration process.Additionally,alkaline pretreatment improved the methane production more effectively.Specifically,3%NaOH,5%KOH,and 4%A-H₂O₂ obtained high cumulative methane yield of 308.79,289.86,and 294.32 mL gVS^-1,respectively,which have very significant improvements?p<0.01?compared with untreated VR(194.04 mL gVS^-1).In addition,specific methane yield?SMY?and volumetric methane yield?VMY?were compared between liquid state anaerobic digestion?LS-AD?and solid state anaerobic digestion?SS-AD?of VR according to the different loading TS.LS-AD obtained the maximum cumulative SMY value of 194.82 mL gVS^-1 at TS10%,while performed not well in cumulative VMY.SS-AD performed better in cumulative VMY especially for TS20%,which not only gained the maximum value of 23.53 L_methaneL_{work volume}^-1,but also achieved a relative high cumulative SMY of 174.32 mL gVS^-1.Moreover,it only cost 16 days to gain more than 80%of methane production and achieved high methane production rate,indicating the digestion time might be greatly reduced.Besides,combined pretreatment of alkali and microwave were applied to improve methane production of VR under SS-AD condition.Results showed that combined pretreatment destroed the lignocellulose structure and exposed degradable carbohydrates more effectively.Combined pretreatment removed more lignin than single pretreatment,while the delignification might be inhibited by the first step.The swelling effect of combined pretreatment was also stronger than single pretreatment,which could transfer cellulose crystal style into I structure during the regeneration process.NaOH and KOH single pretreatment were found not proper to be applied in SS-AD,while the combined pretreatment could buffer the inhibition of Na+ and K+,and decrease the TAN values during the digestion process,thus making the digestion system more appropriate for methanation.This study provided precious theoretical basis for the future utilizing of vinegar residue waste and valuable reference for industrial real application,which reduce its pollution as well as improving its conversion into renewable energy more effectively and faster.