Ammonium And Phosphate Removal And Recovery From Wastewater Using Magnetic Mg-loaded Chinese Herbal Medicine Residues And Its Resource Utilization Performance

Excessive ammonium（NH₄⁺）and phosphate(PO₄^3-)in aquatic environments can cause serious eutrophication.Agricultural waste is an efficient adsorbent for nutrients removal and has good potential for comprehensive utilisation of resources.In this study,two raw Chinese medicinal herbal residues（CMHRs）(Rhizoma Typhonium Gigantei（ZB）and Radix Glycyrrhizae Preparata（ZG）were used to prepare magnetic Mg-loaded Chinese medicinal herbal residues（FM-CMHRs）(Rhizoma Typhonium Gigantei（FM-ZB）and magnetic Mg-loaded Radix Glycyrrhizae Preparata（FM-ZG）by co-precipitation.These four adsorbents were implemented to simultaneously remove NH₄⁺and PO₄^3-from water.Parameters such as adsorbent dosage,solution pH,contact time and initial concentration that influenced the adsorption process onto adsorbents,along with removal mechanism,adsorbents reusability and effects of adsorbed-Chinese medicine residue on soil nutrients and plant growth.The results are as follows.（1）The microstructure of ZB was irregular with numerous spherical particles,while ZG displayed an uneven flaky structure with few rough grooves.After modification,Mg O and Fe₃O₄ were successfully loaded on two CHMRs,and FM-CHMRs exhibited larger specific surface and rougher structure with massive spherical particles.In addition,the S_BETof FM-ZB and FM-ZG were 45.72-and 28.10-times larger than that of ZB and ZG.Two FM-CHMRs could be readily separated and recovered under an external magnetic field.（2）The nutrients adsorption was significantly influenced by dosage,pH,contact time and initial concentration.NH₄⁺adsorption capacity increased first and then decreased with the increase of pH,while the adsorption capacity of PO₄^3-decreased significantly.The adsorption of NH₄⁺and PO₄^3-increased significantly with increasing reaction time and initial concentration,and tends to be flat.The presence of Na⁺,K⁺and Ca²⁺form competitive adsorption with NH₄⁺,and the presence of Ca²⁺improves the adsorption of PO₄^3-.Compared with CK,the presence of anions reduced PO₄^3-adsorption capacity,and SO₄^2-significantly decreased the adsorption of PO₄^3-by 21.39%to 30.81%.（3）The adsorption of NH₄⁺and PO₄^3-by CMHRs were well described by the pseudo-second-order and intra-particle diffusion models,respectively.Those by FM-CMHRs were fitted best with pseudo-second-order model.The Langmuir isotherm model is the best fit model for the adsorption equilibrium data,suggesting monolayer adsorption of NH₄⁺and PO₄^3-by the four adsorbents.The theoretical maximum adsorption capacity by ZB was 190.40 N mg g^-1 and435.29 P mg g^-1.In addition,the maximum adsorption capacity recorded by ZG was 209.20 N mg g^-1 and 451.78 P mg g^-1.The maximum adsorption capacity of FM-ZB was 591.51 N mg g^-1and 551.97 P mg g^-1,while the maximum adsorption capacity of FM-ZG was 615.57 N mg g^-1and 635.35 P mg g^-1(pH,8.0;dosage,0.2 g L^-1;initial concentration,60 mg L^-1;and contact time,180 min,for both the herbal residues).（4）FTIR and XPS analysis showed that hydroxyl,carboxyl,Mg²⁺,Fe²⁺and Fe³⁺were the main functional groups and ions during the adsorption process.NH₄⁺and PO₄^3-are mainly adsorbed by intra-particle diffusion,electrostatic attraction,ion exchange,complexation and ligand exchange,and FM-CMHRs adsorbed PO₄^3-by surface precipitation.（5）The adsorption capacity of NH₄⁺and PO₄^3-from swine wastewater by CMHRs was228.45-252.72 mg g^-1 and 52.53-57.44 mg g^-1,respectively.And those by FM-CMHRs were435.82-455.50 mg g^-1 and 104.76-120.54 mg g^-1,respectively.The adsorption capacity of the CMHRs decreased significantly after the 2 cycles,which was less than 50%of the initial adsorption capacity.By contrast,FM-ZB and FM-ZG still maintained more than 70%of the primal NH₄⁺and PO₄^3-adsorption capacities from swine wastewater after 4 adsorption-desorption cycles.Therefore,FM-CHMRs exhibited great reusability and practical performance for simultaneously removal of NH₄⁺and PO₄^3-from wastewater.According to the economic analysis results,FM-CHMRs is more economical than CHMRs due to higher adsorption capacity,better recycling and magnetic recovery performance.（6）Application of the adsorbed-adsorbents can increase soil fertility and promote plant growth.The contents of soil organic matter,available N and available P were significantly higher than those of CK.The contents of Fe and Mg,which are essential elements for plant growth,were also increased in FM-CMHRs and FM-CMHRs-NP treatments.CMHRs-NP and FM-CMHRs-NP have positive effect on the growth of Alfalfa,the plant fresh weight and plant height were significantly increased by 20.71-23.74%and 27.03%-32.74%,respectively.Compared with CK,adsorbed-adsorbents can significantly improve vitamin C,chlorophyll,soluble protein and soluble sugar content of alfalfa.