How to Comprehensively Utilize the Discarded Fresh Tobacco Leaf？

Xiqing LIU，Weiping FENG ，Zhifu XU，Dongyang HU，Zairan DENG，Wenyu LI，

1.Hengyang Branch of Hunan Tobacco Company，Hengyang 421600，China；2.Qidong County Branch of Hunan Tobacco Company，Qidong 421600，China

1 Introduction

In recent years，with the increasing growing area of tobacco leaf in Qidong County of Hunan Province，frequent occurrence of tobacco plant diseases and implementation of guideline＂optimizing tobacco structure and destroying some underdeveloped leaves in the upper part and malnourished leaves in the lower part＂issued by the State Tobacco Monopoly Administration，the amount of discarded fresh tobacco leaves is increasing in the tobacco field.Studies have shown that in the tobacco harvest process，it will produce approximately 5%of secondary tobacco leaves［1］.In production，influenced by the traditional extensive agricultural production patterns and habits，tobacco growers arbitrarily throw away the discarded fresh tobacco leaf，which not only wastes available resources and pollutes environment，but also deviates from the current idea of clean，efficient and sustainable agriculture［2－3］.In addition，the improperly discarded fresh tobacco leaf is bound to become a beneficial parasitic place for a variety of pests，which will become an important transmission source of pests and diseases in tobacco fields in the coming year.Therefore，the effective treatment and rational utilization of discarded fresh tobacco leaf has a practical necessity.Based on modern tobacco demands on green，environmental protection and sustainable development，as well as actual situation of biog as production facility in some villages of local tobacco area，this paper selects Longwan Village of Fengshiyan Town as the experimental site and explores the rational way of discarded fresh tobacco leaf biog as fermentation.

2 Materials and methods

2.1 MaterialsThe experiment is set in Longwan Village，Fengshiyan Town，Qidong County，Hengyang City.The tobacco growing area of this village is about46.67 ha，and the discarded fresh tobacco leaves are produced by this village.The biog as digester for experiment，built in 2010，ishydraulic，with the volume of 8 m3.

2.2 M ethods

2.2.1 Contrast experiment of discarded fresh tobacco leaf pretreatment.Treatment1：500 kg of discarded fresh tobacco leaves without being crushed are mixed with cow dung in 1：2 proportion to be directly placed into biog as digester.Treatment 2：500kg of discarded fresh tobacco leaves are crushed and cut into 8－10 cm sections，and mixed with cow dung in 1：2 proportion to be directly put into the biog as digester.Treatment 3：500kg of discarded fresh tobacco leaves are pulverized and cut into 8－10 cm sections，and mixed with cow dung in 1：2 proportion and water to be wetted and retted for 3d；after the tobacco leaves get brown and are initially rotted，they are put into biog as fermentation tank.Indicator recording：Comparative observation and recording are performed on biog as occurrence and biog as residue crusting.The gas production rate，gas production，dynamic pH changes of biog as slurry and crusting amount of biog as residue are regarded as the recording indicators.

2.2.2 Contrast experiment of inoculum selection.Treatment 1：Cow dung is as the mixing material.Treatment 2：Pig manure is as the mixing material.Treatment 3：Chicken manure is as the mixing material.500kg of preliminarily crushed discarded fresh tobacco leaves are mixed with the dung of three kinds of livestock in 1：2 proportion to go through preliminary retting and fermentation for 3d and they are put into biog as digester.Then the gas production rate，gas production and dynamic pH changes are observed and recorded.

3 Results and analysis

3.1 Comparative analysis of discarded fresh tobacco leaf pretreatment

3.1.1 Comparative analysis of gas production and gas production rate.In terms of gas production，there is a small difference between Treatment2 and 3，and the continuousburn time is117 and 121 h，respectively；the continuous burn time of Treatment 1 is shortest，only 80 h.In terms of gas production rate，it is highest in Treatment3.On the second day after material input，it begins to produce gas；on the third day after material input，the amount of bio gas has reached the combustible standards.For Treatment2，on the third day after material input，it begins to produce gas，but it is not combustible until the sixth day.In Treatment3，the gas production is slowest，and the biog as can not reach the combustible level until the eighth day.

3.1.2 pH changes.Fig.1 shows that after the material is put into biog as digester under three treatments，pH decreases apparently，but there is a big difference in the decline rate.In Treatment3，on the second day after material input，pH decreases to a minimum，and then increases slowly.In Treatment 1 and 2，on the sixth day，pH decreases to a minimum.There is the biggest drop in Treatment2，and pH is only 3.5 on the sixth day，showing obvious acidification.

3.1.3 Biogas residue crusting.After the biog as fermentation，biog as slurry is cleared.By comparing the three treatments，the crusting is most unobvious in Treatment 3；there is obvious crusting in Treatment 1，thus affecting the biog as production；the crusting amount is small in Treatment2.

3.2 Comparative analysis of inoculum selection

3.2.1 Gas production rate and gas production under each treatment.The results show that the production rate of biog as from biog as fermentation by mixing discarded fresh tobacco leaf with cow dung and pigmanure is the highest，and it begins to produce gas after material input and reaches the combustible level on the third day after the input.In terms of biog as amount，the continuous burn time of cow dung is 124 h，15h more than that of pigmanure；on the fourth day after the material input，chicken manure can reach the combustible level and the continuous burn time is 120 h.The rate of gas produced by mixing discarded fresh tobacco leaf and chicken manure for biog as fermentation is significantly slower than that of gas produced by mixing discarded fresh tobacco leaf and cow dung，and on the fourth day after the input，the gas produced can reach the combustible level，but the biog as duration is basically the same as that of cow dung.The rate of gas produced by mixing discarded fresh tobacco leaf and pigmanure for bio gas fermentation is significantly higher than that of gas produced by mixing discarded fresh tobacco leaf and chicken manure，but the gas production is the lowest.

3.2.2 pH changes.Fig.2 shows that the after material is put into fermentation tank，there is a significant acidification phenomenon，and it reaches the lowest level initially，and then rebounds slowly.The acidification is most significant in the treatment of mixing discarded fresh tobacco leaf with chicken manure，while the acidification in the treatment of mixing discarded fresh tobacco leaf with cow dung is roughly equal to that in the treatment of mixing discarded fresh tobacco leaf with pigmanure.

4 Conclusions and discussions

4.1 ConclusionsThe biog as fermentation is actually the metabolism and energy conversion process of a variety of methane bacteria，and the basic process can be divided into hydrolysis，acidogenic stagemethanogenic stage［4－5］.For the discarded fresh tobacco leaf，the hydrolysis is that in the action of fermentation bacteria，complex organic matter is under hydrolysis fermentation and the complex organic matter is converted into simple organic matter.At the acidogenic stage，in the action of acid-producing bacteria，simple organic matter is broken down into organic acid such as acetic acid and butyric acid.At the methanogenic stage，the product at the acidogenic stage continues to be broken down into methane and carbon dioxide.

4.1.1 Benefits of chopping discarded fresh tobacco leaf.The surface of discarded fresh tobacco leaf is covered with a layer of wax，so that it is not easily broken by methanemicrobes，and if it is directly put into the fermentation tank，there will be a large number of floating crusts.From the pretreatment experimental results about discarded fresh tobacco leaf，it is found that by chopping discarded fresh tobacco leaves，it can prevent fresh tobacco leaf from floating on the surface of biog as slurry and crusting after being put into fermentation tank，thus making the biog as production faster.

4.1.2 Retting fermentation of discarded fresh tobacco outside leaf tank.The process of biog as production by anaerobic fermentation of biog as material is completed by joint action of a variety of methane bacteria，and there is an acidification stage；the activity of methane bacteria is greatly influenced by pH.The retting of chopped discarded fresh tobacco leaves makes the hydrolysis and acidification occur outside biog as digester，which can reduce the degree of acidification of biog as slurry，and avoid the activity inhibiting of methane bacteria.In the process of retting，it allows the methane bacteria to grow and reproduce in a large number，so that the gas production is faster in biog as digester.In addition，the high temperature generated by humid retting can be up to 70℃，kill some bacteria and pests，and partially decompose the nicotin amide that can inhibit the activity of methane bacteria，which is conducive to biog as fermentation.

4.1.3 Cow dung as an ideal mixing material for biog as fermentation of discarded fresh tobacco leaf.After being ruminated，the cow dung is digested more fully，and mixing discarded fresh tobacco leaf with cow dung will cause slight acidification of biog as slurry，thus having a small effect on the activity of methane bacteria，which will help to quickly produce biog as.In addition，the cow dung itself is rich in methane bacteria，which will increase the number and types of methane bacteria in biog as slurry，more conducive to rapid generation of biog as.Chicken manure contains a lot of nitrogen，and it is acidic［6］.After being digested by chicken，there is still much energy，and it easily causes acidification after anaerobic fermentation.It does not contain methane bacteria，so there is a certain lag in biog as generation，but the biog as fermentation has long duration.

4.2 DiscussionsThe biog as slurry and biog as residues generated from anaerobic fermentation of discarded fresh tobacco leaf via biog as digester contain many kinds of trace elements such as N，P and K，and are ideal tobacco fertilizers having the features of both quick-acting fertilizer and slow-acting fertilizer.In addition，after biog as fertilizer is applied to the soil，it can increase the fertility of soil for planting tobacco，improve physical and chemical properties of soil，increase microbes in soil，significantly improve tobacco seedling's ability to resist frost and pest，and effectively reduce the occurrence of early flowering and pests.According to current statistics and reports as well as relevant experiments，it is found that the biog as fermentation broth can eliminate nearly 30 kinds of diseases for various crops such as grain crops，cash crops and vegetables，and it can partially replace pesticides［7－8］.Therefore，the study of returning biog as slurry to farmland and the effect of biog as slurry on tobacco growth will become an important research subject for people in the future.

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