Preparation Of Two New Types Of Constructed Wetland Substrates And Experimental Study On Enhanced Phosphorus Removal

Eutrophication is the most serious water environmental problem in the world today.Phosphorus is considered to be the main controlling factor causing eutrophication of water bodies.Reducing the concentration of phosphorus in water is one of the effective measures to control eutrophication of water bodies.Constructed wetland technology（CWs）has attracted wide attention because of its low operating cost,good effluent quality,and landscape effects.Among them,the interception,adsorption and precipitation of matrix fillers are the main ways to remove phosphorus in constructed wetlands.Traditional natural raw materials and composite materials synthesized from raw materials are currently widely used matrix materials,such as gravel,bentonite,ceramsite,etc.The disadvantages of these materials are expensive and poor in processing effects.In addition,most of the materials are in powder form,which will cause clogging and running with water.In order to solve the above problems,this research has successfully developed two new types of constructed wetland substrates-drinking water treatment sludge composite substrate（DWTSCS）/new iron-carbon-loaded substrate（NICLS）.The DWTSCS prepared in this paper is based on drinking water treatment sludge as the main raw material,bentonite,zeolite,and fly ash as additives,and cement as the binder.On the basis of orthogonal experiment and mixture design method,the best quality ratio of raw materials in DWTSCS was determined,and the final non-burning DWTSCS was obtained.Perform SEM,EDS,XPS,XRD analysis on the prepared DWTSCS.The effects of initial phosphorus concentration,p H,adsorption time,adsorption temperature,competing ions and humic acid on the phosphorus removal performance of DWTSCS were analyzed.Explore the isotherm adsorption characteristics,adsorption kinetics and thermodynamic behavior of DWTSCS to phosphate.The effect of DWTSCS on the dynamic adsorption of phosphorus removal under the conditions of different inlet water flow rates and different initial phosphorus concentrations in the inlet water was studied.Finally,the phosphorus in the saturated DWTSCS was extracted in stages.The results show that:（1）The optimal weight ratio of DWTSCS:cement22.32%,DWTS 51.62%,bentonite 13.03%,zeolite 4.34%,fly ash 8.69%.（2）Increasing the initial concentration of phosphorus,increasing the temperature,and increasing the p H of the solution are conducive to the adsorption of phosphate by DWTSCS.The addition of coexisting ions CO₃^2-and humic acid will hinder the adsorption of phosphate by DWTSCS.The adsorption behavior of phosphorus conforms to the quasi-second-order kinetic model（R²>0.95）and the adsorption process can be simulated using Langmuir and Freundlich models（R_F>0.95 and R_L>0.95）.The maximum adsorption capacity of DWTSCS for phosphorus measured by Langmuir is 40 mg/g.The adsorption of phosphate by DWTSCS is a spontaneous endothermic reaction.（3）In the dynamic test,the inlet water flow rate and the initial phosphorus concentration of the inlet water are inversely proportional to the breakthrough time of adsorption.The Thomas model（R²>0.95）and Yoon-Nelson model（R²>0.95）can well fit the effect of DWTSCS on phosphorus under different conditions.Adsorption effect.DWTSCS adsorbs saturated phosphorus mainly in the form of Ca-P and Al-P.The NICLS in this article uses zeolite as aggregate,iron carbon powder as raw material,hydroxycellulose as thickener,and water-based polyurethane as binder.Use single factor design method to optimize materials,determine the best ratio of raw materials,and get the final new NICLS.SEM,EDS,XRD analysis of the prepared NICLS were carried out,and the effects of initial phosphorus concentration,p H,reaction time,and reaction temperature on the phosphorus removal performance of NICLS were analyzed.The effect of dynamic phosphorus removal by NICLS under different initial phosphorus concentration conditions of influent was explored.The results showed that:（1）The optimal synthesis conditions of NICLS were 1g hydroxycellulose,activated carbon was wood activated carbon,activated carbon particle size was 200-60 mesh,and Fe/C ratio was 1:1.（2）The iron-carbon powder is successfully loaded on the zeolite,and the surface of NICLS is rough and has a relatively large specific surface area.（3）Decreasing the p H of the solution,increasing the temperature and increasing the initial phosphorus concentration are beneficial to the removal of phosphate by NICLS,and the reaction equilibrium time is about 24 h.（4）In the dynamic test,the initial phosphorus concentration of the influent is inversely proportional to the time to saturation.