Research On The Methane Performance From Potato Stems And Tomato Stems By Anaerobic Digestion

With the increase of population and improvement of diet structure,the demand for vegetables is increasing.As the fourth largest food crop and one of the three most traded vegetables in the world,the annual production of potatoes and tomatoes is more than 300 million tons and 180 million tons,respectively.Potatoes and tomatoes are typically herbaceous plants,which will produce a large number of stems and branches during the growing and harvesting process.Due to the high water content and organic matter content,improper management of these fresh stems will not only pollute the environment seriously,but also waste a lot of natural resources.With the increasingly serious global environmental problems and the growing demand for energy,it is necessary to explore an environmental and cost-effictive waste treatment method.Anaerobic digestion（AD）can convert organic waste into biomethane through microorganisms,which is widely used in the energy-based treatment of vegetable waste.Therefore,in this study,the anaerobic performance of fresh potato stems（PS）and tomato stems（TS）was systematically investigated.Firstly,to improve the hydrolysis performance and methane yield,the raw materials were pretreated by acid（H₂SO₄,HCl）,alkaline（Na OH,KOH,Ca（OH）₂,alkali hydrogen peroxide（AHP））,microwave and reflux methane soaking.The results showed that 1.5%AHP pretreatment was the most effective for enhancing AD performance of potato and tomato stems.The CMY of 160.63 m L/g VS and 149.65 m L/g VS,and the biodegradation rates（B_d）are 52.51%and 50.46%,which were 63.09%and 77.08%higher than unpretreated potato and tomato stems,respectively.The structural analysis showed that 1.5%AHP pretreatment could effectively destroy the lignocellulose structure of potato and tomato stems,and remove lignin to reduce the barrier effect of lignin on cellulose and hemicellulose.Secondly,to further enhance the cumulative methane production of potato and tomato stems after 1.5%AHP pretreatment,the organic load（OL）and feed to inoculum ratio（F/I ration）during AD process were optimized by response surface methodology（RSM）.The results showed that the key factor of PS was the OL,and the highest CMY was 198.42 m L/g VS when the OL and F/I ratio were 30 g VS/L and 1.0,respectively.Both the OL and F/I ratio significantly affected the AD performance of TS,and the highest CMY was 199.04 m L/g VS when the OL and F/I ratio were 30 g VS/L and2.5,respectively.Finally,to balance the nutrient imbalance of the single-substrate for AD,and maximize the CMY of potato and tomato stems.Potato and tomato stems after 1.5%AHP pretreatment were co-digested with chicken manure（CM）and pig manure（PM）under the optimal OL and F/I ratio,respectively.The results showed that CMY of both potato and tomato stems could be effectively enhanced by adding both CM and PM.The highest SEI of PS and CM or PM was obtained at the ratio of 1:1,and the CMY was 215.39 m L/g VS and 216.72 m L/g VS,respectively.The highest SEI of TS and CM was obtained at the ratio of 3:1,and the CMY is 170.95 m L/g VS;the highest SEI of TS and PM was obtained at the ratio of 1:3,and the CMY is 185.43 m L/g VS.Overall,the co-digestion with PM was more effective than that with CM.This study maximized the cumulative methane production from potato and tomato stems by pretreatment,optimizing experimental parameters and co-digestion with animal manure.And providing a theoretical basis and data support for their future large-scale anaerobic digestion.