Study On The Preparation And Adsorption Properties Of Pig Manure Biochar

With the development of large-scale and intensive pig farming,the emission of pig manure is increasing year by year.All the pig manure needs centralized treatment,and there is not enough land around the farms to absorb the increasing amount of pig manure.Untreated pig manure will pollute air,water and soil,and cause biological and pharmaceutical pollution.Therefore,the treatment,disposal and resource utilization of pig manure has become one of the important research fields of agricultural solid waste treatment and disposal.Pig manure contains high content of organic matter and rich nutrient components,but it also contains pollutants such as pathogenic microorganisms,heavy metals and antibiotics.Exploring an efficient and safe resource utilization technology of pig manure has become one of the hot spots in comprehensive treatment and utilization of pig manure.At present,pig manure can be converted into biochar through thermochemical treatment for comprehensive utilization in the field of pig manure and it has attracted extensive attention.In this study,the research of hydrothermal carbonization,liquefaction and pyrolysis of pig manure were studied in three aspects:（1）Microwave hydrothermal carbonization of pig manure;（2）Liquefaction of pig manure in ethanol-water mixture;（3）Co-pyrolysis of pig manure and algae.Firstly,the carbonization of pig manure by microwave heating was studied instead of traditional electric heating.The results showed that the appropriate reaction parameters for microwave hydrothermal carbonization of pig manure were as follows:the reaction temperature of 230℃,the reaction time of 30min,the solid-liquid ratio of 0.05 g/mL,the concentration of H₂SO₄of 0.4 mol/L,the dosage of CaO of 7.5 wt.%.Compared with raw material,the degree of carbonization and aromatization of biochar was enhanced,and the calorific value was from 18.2 MJ/kg to 21.5～23.4 MJ/kg.The addition of CaO increased pH from 6.8 to 7.6,and the introduction of H₂SO₄increased conductivity from 4.6 mS/cm to 8.3 mS/cm.Most of P（77.5%）was enriched in biochar,while more than half of K（54.0%）and N（66.6%）were transferred to process water.The introduction of H₂SO₄promotes the transfer of P to process water.The heavy metals in pig manure were mainly concentrated in biochar,and the introduction of H₂SO₄promoted the transfer of heavy metals to process water.In addition,compared with raw material,biochar has better thermal stability and surface porosity.Secondly,the ethanol-water mixed solvent system was introduced into the pig manure liquefaction process to prepare bio-oil and biochar,and the efficient liquefaction of pig manure based on ethanol-water mixed solvent was studied.The results showed that the appropriate reaction parameters were as follows:the reaction temperature of 280℃,the solid-liquid ratio of 0.1 g/mL,the ethanol-water mixture ratio of 50%,the reaction time of30 min.The biochar with and without KOH in ethanol-water mixture had high carbonization degree,strong aromatic and hydrophilic properties,while liquefied biochar an liquefied biochar from pure water or pure ethanol had higher calorific value.Compared with raw material,the pH of biochar increased to 7.3～7.8,and the electrical conductivity decreased to 0.8～3.4 mS/cm.The contents of TP and TK in biochar increased（except for TK in biochar from pure water）.After liquefaction,most heavy metals in pig manure were enriched in biochar,while the total heavy metals content in bio-oil was low.Compared with pig manure,the total contents of Cu,Zn,Cr and Ni of biochar increased（except the total content of Ni of biochar from pure ethanol）,the total contents of Pb and Cd of biochar decreased,and the leaching amount of six heavy metals decreased to a certain extent.Compared with pig manure,the thermal stability and surface porosity of biochar were enhanced,and the thermal stability of biochar with or without KOH in ethanol-water mixture was relatively stronger.Secondly,spirulina and Chlorella were introduced into the pyrolysis process of pig manure to prepare biochar,and the co-pyrolysis of pig manure and algae was studied.The results showed that the appropriate reaction parameters for the co-pyrolysis of pig manure and Spirulina/Chlorella were as follows:the reaction temperature of 600℃,the reaction time of 60 min,the mixing ratio of 50%.The introduction of Spirulina/Chlorella increased the content of volatile organic matter（VOM）and decreased the content of ash in biochar.The calorific value of biochar from pure pig manure is lower,but the carbonization degree is higher.Compared with t pig manure,the pH of biochar increased significantly,reaching9.23～10.54,and the electrical conductivity decreased（except for biochar from pure pig manure）.The content of TP and in the biochar increased while the content of TK decreased,and the contents of P and K in biochar fromSpirulina were higher than those from Chlorella.Compared with raw materials,the total amount of heavy metals in biochar increased（except Cd in biochar from pure pig manure and Zn in biochar from spirulina）.The leaching amount of heavy metals from biochar decreased compared with raw materials,and the introduction of algae also reduced the total amount of heavy metals in biochar.In addition,compared with pig manure,the thermal stability and porosity of biochar are enhanced.Finally,the application potential of pig manure biochar prepared from the above three thermochemical processes as adsorbents was discussed.The results showed that the liquefied biochar had the best adsorption capacity,with a maximum adsorption capacity of0.13 mg/g.And the maximum adsorption capacity of microwave hydrothermal biochar and pyrolytic carbon was 0.09 mg/g and 0.05 mg/g,respectively.It is suggested to apply an appropriate adsorption dose for biochar.The adsorption dose of pig manure hydrothermal biochar,liquefied biochar and pyrolytic biochar were 100 mg,80 mg and 200 mg,respectively.