Biogas Production From Vegetable Waste By Anaerobic Fermentation And Its Residue Application

With the rapid development of China’s economy,the continuous expansion of the scale of urbanization,the prosperity of the food industry and the increase of vegetables,the emission of vegetable waste is increasing day by day,and the proportion of vegetable waste in the city’s daily garbage is increasing.If the vegetable waste can not be treated in time,it will cause a serious harm to the ecological environment and the city appearance.Vegetable waste is mainly composed of waste vegetable stems and leaves from farmers’market,including cabbage,croissant,flat lotus,baby cabbage,etc.In view of the characteristics of vegetable waste in vegetable market,such as large water content,complex composition,easy to be rotten,easy to be decomposed by microorganisms,anaerobic fermentation can effectively treat vegetable waste and produce clean energy biogas.In this paper,we conducted a performance study on biogas production by anaerobic bacteria from vegetable waste,a pilot study on biogas production by semi-continuous fermentation of vegetable waste,and a study on the effect of biogas waste liquor from semi-continuous experiments on lettuce cultivation based on the previous study.The main tasks of this paper are as follows.（1）To explore the effect of the concentration of reactants and reaction temperature on the production of biogas by batch anaerobic fermentation in the mixture of vegetable waste（cabbage,croissant,lotus,baby cabbage）,inoculum and biogas slurry.Take the final gas production as a measurement index,and record the change values of TS,VS and p H before and after the reaction,and analyze the change law of the value.Through the comparison of multiple groups of tests,the best test conditions for daily gas production,cumulative gas production,pond capacity gas production rate and TS,VS removal rate are:the test temperature is 40°C,the fermentation concentration is 6%of the vegetable waste concentration,and the daily gas production is the most Fortunately,it is 1240 m L,the cumulative gas production is up to 3580 m L,the gas production rate of the tank volume is 0.477 m³·m^-3·d^-1,and the removal rates of TS and VS are 75.60%and 85.90%,respectively.The raw material gas production rate（TS,VS）was the highest under the test condition that the fermentation concentration is vegetable waste addition concentration 4%fermentation temperature 40°C,and the highest raw material TS gas production rate and raw material VS gas production rate are 0.544 L·g^-1 and0.638 L·g^-1.Based on the above data,it can be concluded that the optimal fermentation conditions for batch fermentation of anaerobic biogas from vegetable wastes are fermentation concentration 6%and fermentation temperature 40°C.（2）Explore the influencing factors and changing laws of semi-continuous anaerobic fermentation biogas production.The vegetable waste is used as the raw material for the experiment of biogas production by semi-continuous fermentation at different temperatures.The factors such as p H value,daily gas production,raw material VS gas production rate,methane content,organic load average VS gas production rate,tank capacity gas production rate and mechanical stirring are investigated.According to the comparison of actual data,the maximum daily biogas volume of the fermentation temperature of 40°C in the 8 L fermentation tank is 10.8 L,and the maximum gas production rate of the raw material（VS）at the fermentation temperature of 35°C is 1.2L·g^-1;10 L fermentation The maximum daily biogas production volume at the tank fermentation temperature of 35°C is 20 L,and the maximum gas production rate of the raw material（VS）at the fermentation temperature of 35°C is 1219.5 m L·g^-1.The maximum methane content at 35°C and 40°C is 70%and the maximum methane content at room temperature and 30°C is 58%and 62%,respectively.The p H of the feed varies from 6.3 to 9.15,and the p H of the discharge varies from 6.35 to 8.31.The maximum organic load VS average gas production rate is 0.91 L·g^-1 at a fermentation temperature of 35°C in a 10 L fermentor.When the fermentation temperature of the fermentor is 35°C,the gas production rate of the tank capacity is up to 1.865 m³·m^-3·d^-1.At a temperature of 35°C and an organic load of 2.5 kg VS·（m³·d）^-1,the biogas produced by semi-continuous fermentation is relatively good.（3）Determine the biogas slurry used to cultivate lettuce by analyzing the p H value of the batch anaerobic fermentation biogas slurry wastewater and the semi-continuous anaerobic fermentation discharge wastewater.Design multiple experimental groups of hydroponic lettuce to compare the effects of biogas slurry addition,biogas slurry concentration addition,and nutrient solution concentration on lettuce.By observing the biomass of lettuce twice a week and finally analyzing the reducing sugar and vitamin C indicators of lettuce,the optimal conditions for hydroponic biogas slurry were determined.According to the test data,the fresh weight of the semi-nutrient solution+5%biogas slurry cultivation method is 142.45 g,the number of leaves is 10,the plant height is 14 cm,the leaf width is 13.5 cm,and the root length is 22.00 cm,which is increased by 91.08%,42.86%,133.33%,152.34%,11.39%compared with the control group.The content of reducing sugar and vitamin C are the best cultivation method of semi-nutrient solution+5%biogas slurry,which can reach 5 mg·g^-1 and 0.17 mg·g^-1,respectively.Semi-nutrient solution+5%biogas slurry is the best method of fertilization.It is more suitable for hydroponic cultivation of lettuce.It has a significant effect on the growth of lettuce and has higher nutritional value.This study has a certain guiding role in anaerobic production of biogas from vegetable waste and hydroponic cultivation of vegetables with biogas slurry.