Research On Advanced Dephosphorization From Municipal Sewage By Porous Calcium Silicate

As a growing problem, eutrophication has aroused extensive attention. The StateEnvironmental Protection Administration promulgated the “Pollutant Emission Standards ofMunicipal Wastewater Treatment Plant”, which sets strict demand in the phosphorusconcentration of the emission, claiming that the effluent concentration of phosphorus should beless than0.5mg/L, limited by the discharging standard in National Level A. Those municipalwastewater treatment plants, which do not have the function of phosphorus removal, need to berenovated. This paper aims to develop new efficient materials for phosphorus adsorption, whichmay provide an effective solution for further phosphorus removal from municipal sewage onthe basis of microporous calcium silicate and application in removal of phosphorus fromwastewater. Porous calcium silicate filter material were used to do experiment of removingphosphorus form simulating phosphorus-containing wastewater and the effluent of thesecondary sedimentation tank in order to investigate capability of phosphorus removal underdifferent influence factors. Moreover, isotherms, thermodynamics, dynamics of adsorption,fractionation of phosphorus forms and characterization of the media are used to analyse themechanism of phosphorus removal. The results showed that:1Compared to the traditional adsorption material, like limestone, water-granulatedslag and ceramisite etc., porous calcium silicate filter material has higher phosphorus removalefficiency. In process of treating low concentration (2~10mg/L) simulation wastewater, theeffluent concentration of phosphorus is less than0.5mg/L under porous calcium silicate filterdosage of10g/L, water temperature of25, pH of7.0to9.0, particle diameter of4.0to14.0mesh, and reaction time of2h. At the same time, using intermittent feeding mode to conduct thefilter stability evaluation by feeding100mL effluent of the2L secondary sedimentation tank atone time, the effluent phosphorus concentration is less than0.4mg/L. Additionally, the result oforthogonal experiment showed that the effect of influent concentration has the most influenceon phosphorus removal, followed by the particle size, dosage, reaction time, reactiontemperature, and pH value last.2As the slower the adsorption rate is or the higher the packing is, the higher thephosphorus removal efficiency gets, and the penetration curve of type S is more flat, thepenetration time is longer. The lower the ingoing phosphorus concentration is, the higher the effective use of time of the adsorption bed is. The BDST curve can well describe the process ofthe adsorption of phosphorus by media under different filtration velocity and height of media.3Langmuir equation can well reflect the isothermal adsorption characteristics ofdifferent sizes and different temperature conditions. The pseudo-second order kinetic equationcan well reflect the adsorption kinetic model of different initial phosphorus concentration andtemperature. Adsorption rate of main control stage was related to particle size, powder (20-100mesh) for particle diffusion, granular (4-14orders) as film diffusion. Thermodynamicinvestigations showed that the adsorption process is an endothermic, spontaneous chemical andphysical adsorption coexist process. Under activation energy Ea46.261kJ/mol and three kindsof temperature (298K,308K,318K), the average adsorption energy were more than8kJ/mol,which further illustrated chemical reaction was playing a leading role in the process ofadsorption of phosphorus.