Study Of Removal Of Dissolved Phosphorus And Heavy Metal Ions From Stormwater Runoff By Bioretention Media

As one of the essentialcomponents in the construction process of"sponge city",stormwater bioretention has become an important facility to manage rainwater runoff in developed countries.The water treatment residuals?WTRs?are generated during the process of purifying raw water.WTRs have large potential of adsorbing pollutants so that they can be used as alternative bioretention media.In this thesis,effectsof dosage and pH on adsorption of dissolved phosphorus by the five selected media,bentonite,kaolin,natural zeolite,fly ash and WTRs,were investigated.The adsorption characteristics of dissolved phosphorus and heavy metals including Pb²⁺,Cu²⁺,Cd²⁺,Zn²⁺by WTRs were investigatedby analyzing adsorption isotherms,adsorptionkinetic models and adsorption thermodynamic model.The different WTRs samples were characterized by FTIR,SEM,and BET to understand their nature characteristic and construction.The research contents and results are listed as follows:?1?The adsorptionremoval rates of phosphorus in control solution and artificial stormwater by five kinds of media increased with dose.The WTRs had the best removal effect on phosphorus adsorption,and when the dosage was one gram,the removal rate of phosphorus reached 99%.The removal rates of phosphorus by bentonite,kaolin and natural zeolite were easily influenced by interfering ions in artificial stormwater,while fly ash and WTRs were less affected.Bentonite and kaolin had better adsorption effect under neutral condition,natural zeolite and WTRshad better adsorption effect under acidic condition,and fly ash had better adsorption effect under alkaline condition.?2?The adsorptionremoval rates of heavy metal ions by WTRsincreased with increase of dose and pH value.?3?With increase of initial concentrations of phosphorus and heavy metal ions,the removal rates decreased while the amount of phosphorus and heavy metal ions adsorped by WTRs increased.It was found that the Langmuir,Freundlich and Tempkin isothermswell fit the experimental results.The theoretical maximum adsorption capacity?q_m?of phosphorus by WRTs was7.82 mg/g,and the order of the theoretical maximum adsorption capacity?q_m?of heavy metal ions was Pb²⁺>Cd²⁺>Cu²⁺>Zn²⁺at both 20?and30?.?4?The pseudo-second-order kinetic model can precisely describe the adsorption process of phosphorus and heavy metal ions.The fitting results of W-M kineticmodel showed that the adsorption processes of phosphorus and heavy metal ions were controlled by both liquid film diffusion and intragranular diffusion.Elovich model fitting results showed that the adsorption of phosphorus and heavy metal ions by WTRs was a heterogeneous diffusion process.The results of adsorption thermodynamics test showed that the temperature increase was beneficial for phosphorus and heavy metal adsorption,and the adsorption process was aspontaneous,endothermic and entropy-increasing reaction.?5?Results of characteriaction showed that WTRs mainly contained hydroxyl and amide groups,and the peaks of both two groups became weakened after adsorption.The surface of WTRs was rough and there were many cracks of different sizes.There were pore structures of different depths in the cracks.The specific surface area is 36.69m²/g,the total pore volume is 0.06234 cm³/g,and the adsorption average pore width is 6.79 nm.