Study On Phosphorus Removal Effect In Rapid Infiltration Column Of Steel Slag And Cinder Mixture

Rapid infiltration column of steel slag and cinder mixture is a new sewagetreatment process, based on China's increasingly severe eutrophication, shortage ofland resources, and other issues, for the purpose of developing a highly efficientphosphorus removal and new environment-friendly sewage treatment process. Rapidinfiltration column of steel slag and cinder mixture is the second part of the two-stepearthworms-strengthen rapid infiltration process, with excellent phosphorus removaleffect. To a certain extent, this process could solve effluent TP concentrationremaining higher water problem in sewage treatment process. Phosphorus adsorptioncapacities, dynamic adsorption performance, and pH effects on phosphorus adsorptioneffect of steel slag and cinder are analyzed by phosphorus static adsorptionexperiments. Sewage phosphorus removal effect, phosphorus migration andtransformation in column, and column life period are studied by analyzing TPconcentration in influent and effluent, content of different phosphorus in filling, andrunning stability of rapid infiltration column. This study provides technical parametersand operating date for two-step earthworms strengthen rapid infiltration processdeveloping to pilot scale.(1) Phosphorus adsorption capacities of modified steel slag and cinderrespectively are 2.411 mg/g and 0.410 mg/g, higher than unmodified steel slag andcinder (1.391 mg/g, 0.240 mg/g). Modified steel slag can shorten the time to reachsaturation adsorption. The greater the concentration of phosphate, the more the timeshortens. 20 mg／L phosphorus solution shortens 4 h, and 40 mg/L phosphorus solutionshortens 10 h, and 60 mg/L phosphorus solution shortens 12 h. Steel slag and cinderboth have rapid and low phosphate adsorption process, but the reaction of dissolvedphosphorus turning into precipitation phosphorus results in phosphorus removal rateclose tol00 %, which exists in the steel slag slow adsorption process. Phosphorusremoval rate of cinder is only about 40%. Steel slag and cinder rich in iron andaluminum ion, so they have similar rule on pH. In acidic solution, phosphate removalrates both are the fastest, followed by a neutral solution, alkaline slowly. To sum up,steel slag is superior to cinder in phosphorus removal effect. Hydrochloric acidmodification can improve the phosphorus adsorption capacity of steel slag and cinder.(2) Exploratory experiments show that rapid infiltration column of steel slag and cinder has excellent phosphorus removal effect. Rapid infiltration column effluent TPwere not detected at hydraulic loading of 0.5 m/d. When the hydraulic load increasedto 1 m/d, effluent TP concentration is about 0.2~0.4 mg/L. Hydraulic load hasnegative effect on the removal of TE Steel slag and cinder stratified is inferior tomixed-loading in TP removal effect. Stratified column is easy to harden, with shortercycle operation. Surface-filled sand rapid infiltration plugged easier than fillingceramic.(3) Rapid infiltration column of steel slag and cinder mixture experiments showthat the TP removal effects of 1# (steel slag: cinder = 1:1.5) and 3# (steel slag: cinder= 1: 5) rapid infiltration column are better. The effluent TP concentrations of them areless than 1 mg/L, which can meet I-B criteria specified in Discharge Standard ofPollutants for Municipal Wastewater Treatment Plant (GB 18918-2002). The TPremoval effects of 2# (steel slag: cinder = 1:3) is worst among the three columns, TPconcentration of which has been close to 1.5 mg/L in the later. When hydraulic loadincrease from 1 m/d to 4 m/d, effluent TP concentrations change a little. In thishydraulic load range, hydraulic load has a little effect on the removal of TP, soenhancing system' hydraulic load is feasible. Though continuous inlet water andraising filler height can both increase the removal rate of phosphorus, with effluent TPconcentration less than 1 mg/L.(4) In the different rapid infiltration column, contents of different sedimentphosphorus and TP show increasing trends along depth of column. Content of organicphosphorus shows a downward trend along depth of column. Steel slag and cinderloading ratio and hydraulic loading of system Fe-P are both direct proportional to TPcontent. Continuous operation and height increase both have positive effect on TPconcentration. At each sample point, Fe-P content is the largest (1.2 to 2.7 mg/kg),followed by Ca-P (0.92 to 1.08 mg/kg), A1-P (0.49 to 0.61 mg/kg), O- P (0.39 ~ 0.60mg/kg), organic phosphorus (0.22 to 0.38 mg/kg). The relation ship between Fe-Pcontent and TP content is significantly correlated. TP content in rapid infiltrationcolumn the more, TP removal effect of the column is the good.(5) After more than 130 days' operation, effluent TP average concentrations of3# and 4# rapid infiltration columns respective are 1.05 mg/L and 1.65 mg/L.Phosphorus adsorption capacities of both rapid infiltration columns gradually close tothe theoretical adsorption, adsorption capacities of which are both decreased. Thephosphorus adsorption capacity of 4# rapid infiltration column decreases more than that of 3# column, which match to its poor effluent quality.(6) The theory phosphorus adsorption capacity of 3# rapid infiltration column(4.64 g) is less than 4# rapid infiltration column (13.29 g), but the actual phosphorusadsorption of the former (9.85 g) is more than the latter (7.28 g), and the former'effluent quality is better than the latter's, too. The effective utilization of steel slag isone of the important factors of phosphorus removal effects, so we deduce steel slageffective utilization rate of 3# rapid infiltration is far greater that of 4# rapidinfiltration column.To sum up, choosing steel slag and cinder as rapid infiltration column filler canbring full play into phosphorus slag outstanding characteristics and maintain loweffluent TP concentration of rapid infiltration column. Rapid infiltration column ofsteel slag and cinder mixture has many advantages, such as, high hydraulic loading,long running cycle, strong anti-clogging characteristic, adsorbted and precipitatedphosphorus hardly released into the environment, less pollution to the environment.Research objectives are achieved primarily. However, the insufficiencies in this studyrequire further studies and improve.