Study On Enhanced Phosphorus Recovery Efficiency Of Dewatered Sludge By Persulfate Synergistic Superparamagnetic Nanoadsorbent

Phosphorus plays an important role in the growth and metabolism of plants and animals.The recovery and utilization of phosphorus is particularly important due to the sharp decrease of phosphate rock reserves,the increase in the cost of phosphate fertilizers and the serious eutrophication of water body.The surplus sludge of the sewage treatment plant is an important gathering place for phosphorus pollutants.Recovering phosphorus from municipal dewatered sludge can not only alleviate the pressure on phosphorus resources,but avoid eutrophication of water body.The effect of potassium persulfate dissolving phosphorus from dewatered sludge was studied.The superparamagnetic nanocomposites loaded with Lanthanum(La)and Cerium(Ce)were used to remove phosphate,and the adsorption desorption law and mechanism were explored.La-MHs,La-LDHs,Ce-MHs and Ce-LDHs spherical superparamagnetic nanocomposites were prepared and characterized.The results of SEM and XRD were as follows:The particle size of the nanocomposites are 30-80nm,with regular shape,uniform distribution and strong adsorption capacity.The crystallinity decreased and the specific surface area increased after La and Ce were loaded on the composites.The effects of K₂S₂O₈dosage,temperature and time on TP dissolution from dewatered sludge were investigated.The results showed that most of phosphorus in dewatered sludge could be dissolved into supernatant in the form of PO₄^3-when 20 g K₂S₂O₈was added to each gram of sludge for 180 min at 120?;Most of the organic matter in the supernatant including metabolites and humic acid has been removed except a small amount of protein;The Cl^-,NO₃^-,SO₄^2-,PO₄^3-in the dewatered sludge were dissolved into the supernatant by K₂S₂O₈and the content of heavy metal elements was increased to varying degrees.In this paper,the effects of adsorption time,material dosage,coexisting anions and different loading metals on phosphate adsorption were investigated.The adsorption equilibrium time was about 30min,and the adsorption capacities of La-MH,Ce-MH,Ce-LDH,and La-LDH were 41.18 mg/g,38.59 mg/g,37.39 mg/g,35.15 mg/g,respectively;With the increase of material dosage,the adsorption capacity decreased,but the adsorption efficiency increased;The Cl^-,NO₃^-,SO₄^2-,PO₄^3-in the system reduced the adsorption capacity to a certain extent,but the ionic concentration had little effect on the adsorption capacity;The adsorption capacity and efficiency of the hydrous metal oxide(MHs)material were better than LDH material,The adsorption capacity of La-MH composite showed superior adsorption capacity than the other composites;The desorption rate of the composite decreased with the increase of desorption cycles.After 8 adsorption desorption cycles,the desorption rate of the composite ranged from 56.52%to 93.48%and could be reused.After dynamics fitting,It was found that the pseudo-second order kinetic equation model could better describe the adsorption process of materials;The adsorption between the composite material and PO₄^3-was achieved through ion exchange/shared electron interaction.It was found that the adsorption process was"Three-stage"by Weber Morris model fitting,and the adsorption rate was affected by internal and external diffusion;The fitting results of the adsorption isotherm model showed that the Freundlich adsorption isotherm model could better describe the isotherm adsorption process of phosphate on the composite material-multi-molecular layer adsorption.This study confirmed that the persulfate digestion coupled with superparamagnetic nanomaterial adsorption process can effectively recover the phosphorus from dewatered sludge,which was in line with the pollutant treatment concept of"resource conversion and energy recovery"in future water treatment plants.If the treatment cost can be further reduced and the biotoxicity of the nanoparticle material can be confirmed,the material will have a broader application prospect in the transfer and reuse of phosphorus resources.