Research On Organic Fertilizer Preparation By Co-Hydrothermal Treatment Of Kitchen Waste Anaerobic Digestion Biogas Residue And Straw And Its Application

Anaerobic digestion biogas residue of kitchen waste is not only a typical waste biomass,but also a secondary resource of great development and application value.In order to achieve better reduction,harmless and resource utilization of anaerobic digestion biogas residue of kitchen waste,this study discussed the feasibility of using waste biomass straw conditioning anaerobic digestion biogas residue catalytic hydrothermal preparation of organic fertilizer,and the physicochemical properties of biogas residue and its derived hydrochar were characterized in various aspects.Then the feasibility of preparing slow release fertilizer by adsorption of nitrogen and phosphorus from hydrothermal solution by zeolite was evaluated from the perspective of resource recovery.Finally,the safety and reliability of hydrochar as humic acid organic fertilizer were verified by a number of microbial tests and heavy metal tests,and the improvement effect of hydrochar on the growth and development of crops and soil physical and chemical properties in barren red soil was verified by pot experiment.The main conclusions were as follows:（1）The best preparation conditions of hydrochar humic acid organic fertilizer:the best hydrothermal reaction temperature of biogas residue hydrochar fertilizer preparation was 240℃,the best residence time was 6 h.The hydrochar prepared under the hydrothermal reaction condition has higher organic matter（22.86wt%）,humic acid content（16.25wt%）and solid recovery of nitrogen and phosphorus resources.The optimum mass ratio of biogas residue and straw was 2:1,and the content of organic matter,humic acid and total nutrient of the co-hydrochar prepared according to this ratio was 44.3wt%,18.1wt%and 4.23wt%.The addition of metal salt catalysts such as Fe Cl₃could accelerated the progress of hydrothermal humation of organic matter,and increase the contents of humic acid and total nutrient in hydrochar（humic acid:27.8wt%,total nutrient:5.04wt%）.All indexes of hydrochar obtained could meet the index requirements of organic fertilizer.（2）Physical and chemical properties of hydrochar humic acid organic fertilizer:elemental analysis results showed that hydrothermal process promoted the hydrolysis of organic matter in raw materials,resulting in the reduction of O content in hydrochar,the increase of C and H content,and the decrease of O/C ratio.The pore structure analysis results showed that the addition of Fe Cl₃catalyst changed the micropore structure and specific surface area of the hydrochar,and a large number of carbon microspheres appeared on the surface of the hydrochar.The results of functional group analysis showed that the types and quantities of functional groups on the surface of biogas residue changed significantly in the process of hydrothermal treatment,the number of hydroxyl groups decreased,and the number of carboxyl groups,aliphatic groups and aromatic groups increased substantially.O in hydrochar mostly existed in the form of C-O bond and C=O bond,while C mostly existed in the form of C-C bond,C-H bond and C=O.The results of crystal structure analysis showed that hydrothermal process could promoted the dehydration reaction of monohydrate calcite in biogas residue,and increased the content of silica.（3）Confirmed the feasibility of adsorption of zeolite to recover nitrogen and phosphorus in hydrothermal solution:The zeolite with the dosage of 50 g/L had a good adsorption effect on ammonia nitrogen（removal rate of 60.9%）and K⁺（removal rate of 78.1%）in the hydrothermal solution.It also had a certain adsorption and removal effect on COD_Cr,humic acid and dissolved protein in the hydrothermal solution,but the adsorption effect on dissolved polysaccharide and phosphorus in the hydrothermal solution was not good.The adsorbed zeolite could be mixed with hydrochar at the ratio of 1:4 to prepare mixed organic fertilizer with slow release properties.（4）Microorganism test and heavy metal test verified the safety and reliability of hydrochar as an organic fertilizer.The hydrochar prepared in this study could meet the requirements of microbial safety test such as seed germination rate,fecal Escherichia coli count and ascaris egg mortality in the standard of biological organic fertilizer,but couldn’t meet the requirements of the number of effective viable bacteria.However,this defect could be solved by inoculation with a high content of microbial microbial agent.All the heavy metal indexes of hydrochar could meet the index requirements of organic fertilizer.（5）Hydrochar significantly improved the growth and development of crops and soil physical and chemical properties in the poor red soil:the application of hydrochar on the poor red soil could promote the growth and development of lettuce and other crops,alleviate soil acidification,enhance soil water retention,and increase the total nutrient content and EC value in the soil（increased by 62.4%）.