Study On The Performance Of Agricultural Waste Modified Biochar For Phosphorus Removal From Circulating Cooling Sewage

In recent years,China’s rapid industrial development,cooling water volume increased sharply.In order to improve its utilization rate,organophosphorus scale inhibitor is added to circulating cooling water,so the effluent water contains high phosphorus,how to effectively deal with the sewage of circulating cooling water system has become a hot topic.China is a largely agricultural country,the environmental problems brought by the disposal of agricultural waste are widely concerned,while the crisis of water pollution also brings us a lot of trouble.Thus,the treatment method of"waste contral by waste"provides us with a better choice.The modified biochar adsorbent was made from plant-derived biomass（wheat straw,corn straw,and peanut shell powder）to study the best preparation conditions and the performance of the adsorbent on phosphorus removal from wastewater before and after modification;the effects of environmental factors on phosphorus removal were studied;the performance and mechanism of the adsorbent on phosphorus treatment in wastewater were analyzed by adsorption kinetic model,isothermal adsorption model,adsorption thermodynamics and characterization.The main conclusions were as follows:（1）The wheat straw biocar materials（WS-2Mg/Ce-600）modified by magnesium chloride and cerium chloride were prepared by optimizing the preparation conditions,and the best adsorption effect for HEDP was obtained at the dosage of 2.5 g/L,p H=6,and the initial HEDP concentration of 10 mg/L.The reaction was equilibrated after2880 min,and the coexisting anions did not affect the adsorption;The model fitting results were more consistented with the proposed secondary kinetic equations and Freundlich model,and the reaction process was a chemical reaction-driven multilayer adsorption.SEM showed that the modified wheat straw had a lamellar structure and particulate matter attached to the surface;XRD results showed that the diffraction peaks of Mg and Ce oxides or hydroxides appeared before the reaction,and they all decreased after the reaction,and the reaction mechanism is chemical precipitation.（2）Magnesium chloride modified wheat straw biochar（WS-0.1Mg-600）was prepared by optimizing the preparation conditions,and the best adsorption of PO₄^3-was achieved at the dosage of 1.25 g/L,p H=7,and the initial PO₄^3-concentration of 10 mg/L.The adsorption equilibrium was reached after 1440 min of reaction;the coexisting anions inhibited the adsorption of PO₄^3-by WS-0.1Mg-600,and the order of influence was CO₃^2->Cl^->SO₄^2->F^-.The model fitting results were more consistented with the proposed secondary dynamics and Langmuir model.SEM revealed that granular materials was attached to the surface,and the main elements were C,O,Mg,and Cl,of which the weight percentage of Mg was 5.79%;XRD results showed that the oxides or hydroxide diffraction peaks of magnesium on the surface of the biochar changed before and after the reaction,presumably because the Mg O or Mg（OH）₂loaded on WS-0.1Mg-600 reacted with phosphorus in water to form new substances.（3）The wheat straw biocar materials（WS-3Mg/Ce-600）modified by magnesium chloride and cerium chloride were prepared by optimizing the preparation conditions,and the best capacity was obtained at the dosage of 2.5 g/L.The adsorption capacity of TP was 7.76±0.2 mg/g,and the removal rate was 94.76±0.39%.The adsorption results were under the Pseudo second order Kinetics and Langmuir model,the phosphorus removal was exothermic and spontaneous.SEM showed thatof granular materials was attached to the surface,and the main elements were C,O,Mg,Ce,Cl,of which the weight percentages of Mg were 5.21%and cerium were 1.26%;XRD results showed that Mg,Ce oxide or hydroxide peak appeared before the reaction,which indicated that they were successfully loaded on the surface of biological carbon,while the change of diffraction peak after the reaction indicated that they formed a new material with phosphorus in water,thus,the removal rate of total phosphorus by the adsorbent is increased.FTIR showed that the surface contained chemical bonds such as O-H,C=C,M-O（M=Mg or Ce）,M-O-P（M=Mg or Ce）,and O-P,which contributed to the removal of TP.XPS showed that WS-3Mg/Ce-600 adsorption process,the proportion of M-O content increaseed while the proportion of M-OH content decreaseed,and the reaction mechanism is the exchange of ligands between the hydroxyl groups on the material surface and the phosphorus in the wastewater.The innovation of this thesis is to prepare modified biochar from agricultural wastes as raw material to treat TP in circulating cooling wastewater.The preparation conditions were optimized through experimental research to improve its performance on phosphorus removal,and the mechanism of adsorption was studied.It provides reference for rational and efficient treatment of phosphorus in circulating cooling wastewater.