Preparation Of Biochar-Based Microbial Immobilization Body And Its Ability To Remove Inorganic Nitrogen From Water

The object of this study was to explore NH₄⁺-N and NO₃^--N removal ability of biochar-immobilized heterotrophic nitrifying bacteria and aerobic denitrifying bacteria from water.Based on the isolation and identification of Pseudomonas sp.Strain-???heterotrophic nitrifying bacterium?and Pseudomonas aeruginosa Strain-I?aerobic denitrifying bacterium?,the microbial immobilization body were prepared by using original and HNO₃/Mg²⁺/NaOH/NaOH+Mg²⁺modified rice husk-derived biochars?designated as OBC/HBC/NBC/NMBC?with the adsorption and entrapment methods,respectively.Then the removal kinetics of NH₄⁺-N and NO₃^--N by the microbial immobilization body and the growth kinetics of Pseudomonas sp.Strain-??and Pseudomonas aeruginosa Strain-I were explored.The removal of inorganic nitrogen?NH₄⁺-N/NO₃^--N?in water by the biochar-based microbial immobilization body has a good effect.In 100 mg?L^-1NH₄⁺-N solution,the maximum removal rate of the biochar-based microbial immobilization body can reach 90.93%.In 100 mg?L^-1 NO₃^--N solution,the maximum removal rate of biochar based microbial immobilizers was 91.49%.Ricehuskbiocharwasmodifiedbyfourmethods(HNO₃/Mg²⁺/NaOH/NaOH+Mg²⁺modification)to improve its adsorption effect on NH₄⁺-N/NO₃^--N and its fixation effect on microorganisms.The most obvious improvement of biochar properties is the modification by NaOH+Mg²⁺.NaOH+Mg²⁺modification increased the pH and pH_pzc of the rice husk-derived biochar by 1.42 and 2.36,respectively.The specific surface area and total pore volume of NMBC were 3.56 and 3.20 times higher than that of OBC,total acid oxygen-containing functional groups decreased 0.207 mmol?g^-1,total basic oxygen-containing functional groups increased 0.530 mmol?g^-1,and the amount of biomass attached to the surface of NMBC increased by 333.05 nmol P?g^-1?Pseudomonas sp.Strain-???compared with OBC.Preparation of biochar-based heterotrophic nitrification immobilization body and its ability to remove NH₄⁺-N from water,the results indicated that Pseudomonas sp.Strain-??possesses the ability of heterotrophic nitrification,and NH₄⁺-N and total nitrogen removal rates?mass fraction?reached 80.24%and 21.35%in 72 h respectively with the initial NH₄⁺-N mass concentration of116.18 mg?L^-1.NaOH+Mg²⁺modification strengthened removal ability of the rice husk-derived biochar or biochar-based microbial immobilization body.The initial concentration of NH₄⁺-N was 100 mg?L^-1,the removal rate promote from15.37%?OBC?to 20.43%?NMBC?,the microbial immobilization body with the adsorption methods promote from 28.47%?prepared by OBC?to 58.35%?prepared by NMBC?.In the initial NH₄⁺-N concentration of 100 mg?L^-1,200 mg?L^-1 and 300mg?L^-1 conditions,within 48 hours to explore the unmodified and modified biochar microbial immobilization body removal of NH₄⁺-N dynamics results show that the NaOH+Mg²⁺modified biochar base microbial immobilization body's ability to remove the water NH₄⁺-N,strongest and unmodified biochar base microbial immobilization body's ability to remove the water NH₄⁺-N the weakest.Nitrification immobilization body showed that adsorption method was better than embedding method.The initial concentration of NH₄⁺-N was 100mg?L^-1,the microbial immobilization body with the adsorption methods with NMBC?NMBC-adsorption?the removal rate was 90.93%in 48 h,the maximum removal rate was 15.20 mg??L?h?^-1;the entrapment methods with NMBC?NMBC-entrapment?the removal rate was 79.32%in 48 h,the maximum removal rate was 11.37 mg??L?h?^-1.The accumulation of NO₂^--N/NO₃^--N occurred during the biodegradation of NH₄⁺-N by immobilization body,and the accumulative amount of entrapment immobilization body increased significantly compared with adsorption immobilization body.Moreover,the growth kinetics of Pseudomonas sp.Strain-??immobilized by NaOH+Mg²⁺modified biochar during NH₄⁺-N biodegradation was simulated by Monod and Andrews models.The result showed that the microbial immobilization body prepared by adsorption method was more favorable for Pseudomonas sp.Strain-??growth by using NH₄⁺-N compared with the entrapment method.The process of Pseudomonas sp.Strain-??growth using NH₄⁺-N was investigated fitting Andrews model,the parameters with the adsorption and entrapment methods were:?_max?maximum specific growth rate?0.287 h^-1 and 0.258 h^-1;K_s?half-satruration constant?103.26 mg?L^-1 and 117.96mg?L^-1;K_s1?inhibition constant?342.88 mg?L^-1 and 285.19 mg?L^-1.Preparation of biochar-based aerobic denitrification immobilization body and its ability to remove NO₃^--N from water,the results indicated that Pseudomonas aeruginosa Strain-I possesses the ability of aerobic denitrification,and NO₃^--N and total nitrogen removal rates?mass fraction?reached 100%and53.92%in 72 h respectively with the initial NO₃^--N mass concentration of 69.25mg?L^-1.NaOH+Mg²⁺modification increased the amount of biomass attached to the surface of NMBC increased by 309.14 nmol P?g^-1?Pseudomonas aeruginosa Strain-I?compared with OBC.NaOH+Mg²⁺modification strengthened removal ability of the rice husk-derived biochar or biochar-based microbial immobilization body.The initial concentration of NO₃^--N was 100 mg?L^-1,the removal rate promote from0.16%?OBC?to 12.63%?NMBC?,the microbial immobilization body with the adsorption methods promote from 22.34?prepared by OBC?to 44.44%?prepared by NMBC?.In the initial NO₃^--N concentration of 100 mg?L^-1,200mg?L^-1 and 300 mg?L^-1 conditions,within 48 hours to explore the unmodified and modified biochar microbial immobilization body removal of NO₃^--N dynamics results show that the NaOH+Mg²⁺modified biochar base microbial immobilization body's ability to remove the water NO₃^--N,strongest and unmodified biochar base microbial immobilization body's ability to remove the water NO₃^--N the weakest.Denitrification immobilization body showed that adsorption method was better than embedding method.The initial concentration of NO₃^--N was 100mg?L^-1,the microbial immobilization body with the adsorption methods with NMBC?NMBC-adsorption?the removal rate was 91.49%in 48 h,the maximum removal rate was 12.78 mg??L?h?^-1;the entrapment methods with NMBC?NMBC-entrapment?the removal rate was 90.63%in 48 h,the maximum removal rate was 9.08 mg??L?h?^-1.Moreover,the growth kinetics of Pseudomonas aeruginosa Strain-I immobilized by NaOH+Mg²⁺modified biochar during NO₃^--N biodegradation was simulated by Monod and Andrews models.The result showed that the microbial immobilization body prepared by adsorption method was more favorable for Pseudomonas aeruginosa Strain-I growth by using NO₃^--N compared with the entrapment method.The process of Pseudomonas aeruginosa Strain-I growth using NO₃^--N,the parameters with the adsorption and entrapment methods were:?_max 0.204 h^-1 and 0.199 h^-1;K_s 71.78 mg?L^-1 and82.53 mg?L^-1;K_s1 413.12 mg?L^-1 and 398.01 mg?L^-1.This study will be helpful for understanding the influence of biochar modification on the enhancement of microbial immobilization body characteristics and the effect of immobilization method on bacteria growth,and will provide a theoretical reference for the engineering application of biochar-based microbial immobilization body in water treatment.