Study On The Effect Of Organics On Phosphate Removal By Resin-Based Hydrated Ferric Oxide

Resin-based HFO（Hydrated ferric oxide）composites were widely used in the field of phosphorus removal.Recently,the current research was mainly focused on styrene resin-based HFO composite adsorbents for phosphorus removal.However,acrylic resin-based HFO composite adsorbents were less studied.Especially,the effect of type of solvent in the preparation and organic matter on acrylic resin-based HFO composite adsorbents for phosphorus removal was still unclear.In this study,HFO particles were loaded into acrylic acid macroporous strong base anion exchange resin D213 by"Fe³⁺loading-Na OH in situ precipitation-heat treatment",and composite adsorbents with different loading amounts were prepared by changing loading phase solvent.Based on the material properties and adsorption performance,the best solvent for the preparation of HFO-D213 was selected.Subsequently,the effects of different molecular weight organics（Humic acid,HA;Tannic acid,TA;Gallic acid,GA）on the structural properties and phosphorus removal performance of HFO-D213 were analyzed,and the mechanism of organics on phosphorus removal was revealed.Then,HA,TA and GA were used to investigate the anti-organic contamination performance of HFO-D213.The feasibility of reusing HFO-D213for treating secondary effluent was verified,and it provided a theoretical basis for its application in advanced phosphorus removal from wastewater.The main findings were as follows:（1）Six composite adsorbents were prepared by dissolving Fe Cl₃ in different solvents at the loading stage,and the HFO loading（6.3%to 12.9%）tended to increase with the increase of ethanol.Among them,the composite adsorbents prepared by ethanol and methanol had the largest HFO load（approximately 12.5%）.The HFO were all amorphous nanoparticles and the HFO was distributed in the U-shape,and the closer to the inner part of the resin,the less HFO were loaded.Additionally,the phosphate adsorption capacity increased with increasing HFO loading,and the maximum was approximately 11.5 mg/g for the composite adsorbents prepared with ethanol and methanol.The composite adsorbents reached adsorption equilibrium at 240 min,and internal diffusion was not the only rate-controlling step.Furthermore,the composite adsorbent adsorbed best at p H 6～8.The degree of influence of inorganic anions on phosphorus removal was SO₄^2->Cl^->NO₃^-.The phosphorus removal rates were maintained at 99%in 3 consecutive cycles,and the composite adsorbent was efficiently eluted using 5%Na OH+5%Na Cl with an elution rate of about 100%.Based on the comprehensive material properties and adsorption properties,and the characteristics of low price and low toxicity,ethanol was determined as the best solvent in the loading stage,and prepared composite adsorbent HFO-D213 was used for subsequent research.（2）The adsorption of different molecular weight organics（HA,TA,GA）roughened the surface of HFO-D213,but the crystalline shape and distribution of the HFO did not change and remained as amorphous HFO with U-shaped distribution.When the concentration of organic matter（HA,TA,GA,in DOC）increased from 5 mg/L to 200 mg/L,the phosphorus removal rate of HFO-D213 decreased and the minimum rates were 80%,33%and 22%,respectively.The degree of influence was GA>TA>HA.After adding 20 mg/L organics,the maximum phosphate adsorption capacity of HFO-D213 decreased,especially after adding GA,the maximum phosphate adsorption capacity was only 26.4 mg/g,which was significantly lower than that of the blank group（40.1 mg/g）.Additionally,the organics significantly prolonged the equilibrium time of phosphorus removal,and the equilibrium time was 360 min,420 min and 420 min,respectively.The optimal p H was 6～9,5～7.5 and 7.5～9,respectively.The preadsorbed organic matter had a significant effect on phosphorus removal with the degree of influence being GA>TA>HA.FT-IR,XPS,SEM-EDX analysis showed that organics and phosphate mainly competed for the active site of the quaternary ammonium group of the D213.（3）Based on the static adsorption and elution experiments of phosphorus and organic matter（HA,TA,GA）binary solution,the phosphorus removal rates of HFO-213 were stable at 95%,80%and 90%in 5 cycles,respectively.The phosphorus elution rates of 5%Na OH+5%Na Cl were maintained at 99%,and the organics elution rate were higher than 80%.When HFO-D213treated the simulated secondary effluent,the phosphorus removal rate was stable at 80%for 5cycles,and the phosphorus elution effect was highly efficient,with all elution rates close to 100%.Subsequently,when HFO-D213 treated the actual secondary effluent,the phosphorus removal rates were maintained at 75%within 20 static adsorption elution cycles,and the elution rates were all close to 99%.Furthermore,when HFO-D213 fixed bed treated secondary effluent,the effluent total phosphorus concentration of 0.3 mg/L was set as the penetration point,and the overwater volumes of 3 cycles were 780 BV,540 BV and 480 BV,respectively.The phosphorus elution rates of 20 BV eluent（5%Na OH+5%Na Cl）were 90%,99%and 99%,respectively.Additionally,the HFO loading did not change significantly and the material performance was stable and good.