Characterization And Composting Of Different Modified Kiwifruit Branch Biochar

With the improvement of China’s agricultural subsidy policy and the mechanism to promote agriculture through science and technology,the kiwifruit industry in agricultural production has gradually expanded,while also increasing the production of kiwifruit branches.However,how to deal with the increasing number of kiwifruit branches is an important issue for sustainable agricultural development.Biochar,as an energy utilization measure for waste,has proven to be a promising adsorbent and composting additive for its unique structure and excellent physicochemical properties.At present,relatively few experimental studies have been conducted on the resource utilization of kiwifruit branches,especially in terms of modified kiwifruit branch biochar and its composting effectiveness.In this study,modified biochar was prepared from kiwifruit branches by using three methods:alkali modification,acid modification,and oxidation modification to obtain NaOH-modified（KB-NaOH）,KOH-modified（KB-KOH）,HNO₃-modified（KB-HNO₃）and FeCl₃-modified（KB-FeCl₃）kiwifruit branch biochar,and unmodified kiwifruit branch biochar（KB-un modified）were used as a control.Their characterization properties and adsorption capacity were analyzed by measuring the relevant indexes of modified biochar and fitting isothermal adsorption and adsorption kinetic curves in order to clarify the optimal modification methods for biochar preparation.In addition,a study was conducted to clarify the changes of modified biochar on the composting properties during the mixed composting process by mixing modified biochar with cattle manure digestate and pig manure in different ratios with five treatments of CK,D1,D2,D3 and D4,i.e.,pig manure:cattle manure digestate:biochar（mass ratio）of 100:0:0,100:0:2.5,75:25:2.5,50:50:2.5 and 25:75:2.5,respectively,to analyze and optimize the mixed composting method of digestate.The main results of this study are as follows:（1）The determination and analysis of the characterization properties showed that the modified kiwifruit branch biochar increased the electrical conductivity,ash content,specific surface area,and pore volume while decreasing the average pore size compared to unmodified kiwifruit branch biochar.KB-NaOH and KB-KOH increased the pH value of biochar,while KB-HNO₃ and KB-FeCl₃ showed the opposite results.In addition,KB-NaOH,KB-KOH,KB-HNO₃,and KB-FeCl₃ treatments all significantly increased the absorption peaks at 2920 cm^-1 and 2850 cm^-1 compared with KB-unmodified treatment,indicating that the modified biochar increased the surface methylene.The KB-NaOH and KB-KOH treatments increased the absorption peak at873 cm^-1 compared to the other three treatments,indicating an increase in hypomethylation on the surface of the alkaline modified biochar.（2）Experiments on isothermal adsorption and adsorption kinetics of kiwifruit branch biochar were carried out to verify its adsorption capacity for nitrogen（ammonium nitrogen-ammonium chloride:NH₄⁺-N,urea-organic nitrogen:TN）,phosphorus（potassium dihydrogen phosphate:TP）,and reducing substances（glucose:RDS）.In the isothermal adsorption process of kiwifruit branch biochar,the correlation coefficient R² of the model fitting parameters showed that the Freundlich model was more suitable to describe the changing trends of kiwifruit branch biochar adsorption capacity than the Langmuir model.The adsorption capacities of kiwifruit branch biochar for NH₄⁺-N,TN,TP,and RDS followed KB-KOH>KB-NaOH>KB-FeCl₃>KB-HNO₃>KB-unmodified,KB-KOH>KB-FeCl₃>KB-NaOH>KB-HNO₃>KB-unmodified,KB-FeCl₃>KB-KOH>KB-HNO₃>KB-NaOH>KB-unmodified,and KB-NaOH>KB-KOH>KB-FeCl₃>KB-HNO₃>KB-unmodified,respectively.In the adsorption kinetics process of kiwifruit branch biochar,the pseudo-second-order kinetic equation model was more suitable for describing the adsorption kinetic process of kiwifruit branch biochar than the pseudo-first-order kinetic equation model.The adsorption capacities of kiwifruit branch biochar for NH₄⁺-N,TN,TP,and RDS followed KB-KOH>KB-NaOH>KB-FeCl₃>KB-HNO₃>KB-unmodified、KB-KOH>KB-NaOH>KB-FeCl₃>KB-HNO₃>KB-unmodified、KB-FeCl3>KB-KOH>KB-NaOH>KB-HNO3>KB-unmodified,and KB-NaOH>KB-KOH>KB-FeCl₃>KB-HNO₃>KB-unmodified,respectively.In general,the fitting results of biochar adsorption isotherm curve and adsorption kinetic curve showed that KB-NaOH and KB-KOH treatments could better improve the adsorption capacity and adsorption capacity of kiwifruit branch biochar surface than other treatments.（3）Pig manure,cattle manure digestate,and NaOH modified kiwifruit branch biochar were mixed in different proportions,and the relevant properties of the compost during the mixed composting process were determined to show that the addition of modified biochar could promote the decomposition of organic matter in the compost and improve their physicochemical properties.The D2,D3 and D4 treatments can not only ensure the excellent conditions of temperature,moisture,pH value,and EC during the composting process compared with CK,but also can rapidly corrode the compost and meet the requirements of organic fertilizers.In addition,the D2 treatment performed better than the D3 and D4 treatments,which could complete the compost more efficiently,and was suitable for popularization and application in agricultural development.