Effect Of Agricultural Waste-Based Biochar On Anaerobic Fermentation And Its Heavy Metals

Currently anaerobic fermentation has become the main way of rural biogas development.As anaerobic fermentation gas production is the use of organic matter under anaerobic conditions through the action of methanogenic bacteria to decompose organic matter,methane release process.Therefore,it not only improves energy utilization and reduces greenhouse gas emissions,but also provides clean fuel for agricultural production.However,anaerobic fermentation produces a large amount of methane containing heavy metal ions,and such substances will bring a great impact on the ecological environment.Biochar is a carbon-containing material with cellulose,lignin and other main components,and the cellulose and lignin in it can be cracked to obtain biochar.Biochar is a new type of adsorbent,biochar has a large specific surface area and rich pores,has strong adsorption performance,and can adsorb a variety of metal ions.At the same time,biochar also has certain chemical stability.In recent years,the adsorption of heavy metal ions with biochar has attracted widespread attention.Among the many adsorption materials,biomass has a wide range of sources,low price and strong degradability.In this study,different agricultural waste-based biochars were prepared from corn stalks,rice husks,tea residue and bamboo chips,and experiments were carried out on the multi-anaerobic fermentation system,in order to explore the role and mechanism of agricultural waste-based biochar in the migration and transformation of heavy metals in the multi-anaerobic fermentation process.Biochar as a carbon containing material has a large specific surface area and can adsorb heavy metal ions.In this paper,different agricultural wastes(corn straw,rice husk,tea pomace and bamboo chips)were used as the base materials to prepare biochar under the same conditions,while the optimal process conditions in the multiple anaerobic fermentation with rice straw,aquatic plants,kitchen waste and pig manure as the fermentation substrates were screened to investigate the effects of different agricultural waste-based biochar on the gas production rate and heavy metals in the multiple anaerobic fermentation process.The following main conclusions were obtained from the study:(1)The structural properties and physicochemical properties of biochar prepared from different agricultural wastes under the same temperature conditions are different.Because the ash content affects the yield,the yield of bamboo char is higher than that of rice husk-based biochar;while the ash content is related to the specific surface area of biochar,so the specific surface area of bamboo char is larger than that of corn strawbased biochar.(2)In the test of screening the anaerobic fermentation of multi-feedstock mixture,the best process parameters of multi-fermentation anaerobic fermentation were obtained by appropriate experimental methods based on the daily and cumulative gas production of anaerobic fermentation: substrate ratio(rice straw: aquatic plants: kitchen waste: pig manure = 1:1:1:1),temperature of 30℃,C/N value of 30,and TS of 15%(3)The addition of all four agricultural waste-based biochar significantly improved the gas production and cumulative gas production of multiple anaerobic fermentation.Maize straw-based biochar and tea residue-based biochar increased the daily gas production by 25-50% compared with the group without biochar addition,while the cumulative gas production in the experimental groups with rice husk-based biochar and tea residue-based biochar addition increased by 18-25% compared with the experimental group without biochar addition.(4)Agricultural waste-based biochar had better adsorption capacity and passivation effect on heavy metals Cr,Cu and Zn.Among them,the adsorption capacity of tea residue-based biochar was stronger than that of other agricultural waste-based biochar,which reduced the contents of heavy metals Cr,Cu and Zn in the biogas liquor by 91.95%,88.78% and 92.27%,respectively.The passivation rates of the effective state of heavy metals Cr,Cu and Zn in the digestate increased by 91.95%,89.86% and91.99%,respectively.