Research On The Methane Yield From Eggplant Stalk By Pretreatments And Anaerobic Digestion

As one of the most popular agricultural products in China,eggplant lefts a large amount of stalk wastes after harvesting every year.Most of these eggplant stalk(ES)wastes are directly burned,which is not only a waste of potential resources,but also causes serious environmental pollution.Anaerobic digestion(AD)is a technology of transforming waste resources into renewable energy,and the process is efficient and clean,which has a very broad application prospect.Because of rich organic matter,ES can be used as a raw material in AD process.Therefore,this study's objectives were to effectively utilize the waste resources of ES in AD process.Firstly,response surface methodology(RSM)was used to explore the effects of the feed to inoculum ratio(F/I)and the organic loading(OL)on methane yield of ES under different temperatures,and then determined the optimal F/I and OL.The result showed that OL was the key factor affecting the methane yield of ES.The highest cumulative methane yield(CMY)was inferred at an F/I of 3.0 and OL of 35.0 g VS/L by RSM under 37? or 55?.They were 110.3 mL/g VS and 121.3 mL/g VS,respectively,which were far from the theoretical maximum methane potential(320.0 mL/g VS).Due to the natural resistance of lignocelluloses to enzymatic hydrolysis,it was important to pretreat ES.Secondly,the effects of 10 different pretreatments,including acid(H2SO4 and H3PO4),alkaline(NaOH,KOH and Ca(OH)2),alkali hydrogen peroxide(AHP,adjusted pH by three alkalines),microwave,and ultrasonic pretreatments on the compositional and structural alteration of ES were studied to enhance hydrolysis.Then,the effects of 4 well-performing pretreatments on the methane yield were studied under the optimal digestion condition.Furthermore,the effects of pretreating ES with the black liquor and decreasing alkali in pretreatment on the methane yield of ES were explored to save the resources of reagents and water.The result showed that NaOH,KOH,and AHP(adjusted pH by NaOH and KOH)pretreatments performed well on the compositional and structural alteration of ES.Under the optimal digestion condition,the highest CMY of 262.2 mL/g VS and the biodegradability of 81.8%were obtained after 1.5%AHP(adjusted pH by KOH to 11.5)pretreatment.The methane yield can't be effectively improved after pretreating ES with the black liquor or decreasing alkali in pretreatment.Compared to the untreated ES,the highest CMYs of them increased by 156.5%and 70.2%,respectively,except for 1.5%AHP(adjusted pH by KOH to 11.5)pretreatment.Finally,for maximum methane yield of ES,anaerobic co-digestion was carried out using AHP pretreated eggplant stalk(PES)and three types of manure(pig manure(PM),chicken manure and cow dung)in varying proportions to investigate their influence on methanation performance.The result showed that the CMY increased with PES and PM.At PES:PM ratios of 1:1,1:2,and 1:4(volatile solid,VS basis),the CMYs were 283.4 mL/g VS,338.8 mL/g VS,and 359.2 mL/g VS,respectively.Compared to the CMY of ES alone(60.4 mL/g VS),they increased by 369.2%,460.9%,and 494.7%,respectively.This study not only provided an efficient systematic research of ES in AD process,but also enlarged the scale of industrial utilization with reliable basis.