Study On The Immobilization Of Powder And Its Phosphorus Removal Performance

At present,the urban sewage treatment capacity in China has reached 91% from Ministry of Housing and Urban-Rural Development,but the eutrophication is still serious,facing the pressure to improve the quality of the environment,upgrading and reconstruction is imminent,especially in the treatment of malodorous black river,requirements for phosphorus emissions will become more and more strict,the trend towards the implementation of IV class,and even III class water quality standards is becoming increasingly evident,in which case the development of phosphorus depth removal techniques is of great significance.The author combines the theory of chemical thermodynamics and kinetics,finding that in oder to meet the increasingly stringent environmental requirements,to further improve phosphorus removal effect of tail chemical process in sewage treatment plant,not only increase the cost of sewage treatment,but also improve the concentration of Al3+ or Fe3+ in tail water with the strictness of phosphorus removal requirements,and then enhance the ecological risk of tail water discharged from wastewater treatment plant.According to the principle of adsorption,phosphorus removal is though the adsorption of low concentration phosphorus on the solid surface.In the adsorption process,the ionic concentration of the aqueous solution is not raised,and the potential ecological risk is avoided apparently.However,though the literature and preliminary tests,the phosphorus removal capacity of large particle adsorption materials is usually lower,while the powder adsorption materials are easy to drain and difficult to recover in the process of water treatment.Therefore,this paper intends to screen out the powder materials with good adsorption phosphorus removal ability,then a new immobilized powder phosphorus removal material is constructed with excellent adsorption phosphorus removal effect through immobilization technology.The main contents are as follows: screening of powdered phosphorus removal materials with good phosphorus removal performance,studying on fixation method and influence factors of powdered phosphorus removal material.Finally,investigating phosphorus removal performance of immobilized materials,conclusions are as follows:(1)The adsorption properties of calcite,activated calcite,hydrated calcium silicate,acidic alumina,activated alumina and nano alumina were studied by sequencing batch experiment and continuous flow column experiment.The results showed that the calcium silicate hydrate(CSH)was the best material for the treatment of low concentration of phosphorus in wastewater,the removal rate of low concentration phosphorus(TP<2 mg/L)in the sequencing batch experiment was up to 100%,and in the continuous flow column can run longest running time,but the loss of powders was very obvious.(2)Studied on hydrated calcium silicate powder(CSH)immobilization methods,the research results showed polyvinyl alcohol immobilized mechanism can achieve the CSH powder immobilized.According to the single factor and orthogonal multiple factor experiments,the optimum preparation was obtained.The concentration of PVA was 8%,the concentration of NaNO3 was 25%(w/v),the mass ratio of CSH to PVA was 1:10,and the cross-linking time was 2 h.(3)The physicochemical properties of PVA-CSH were analyzed by FTIR,BET and SEM.The results showed that the groups of CSH were unchanged before and after immobilizing.Immobilized material of large pore size(average pore size of 249.370 ?),and by SEM,it can be seen that the surface and section of PVA-CSH contains a large number of pores,forming a network,which will be conducive to the free access of ions.The energy spectrum analysis showed that the P element was adsorbed on the material.(4)The adsorption of phosphorus from aqueous solution onto CSH and PVA-CSH was investigated using sequencing batch experiment.The results indicated that the adsorption isotherm accorded with the Langmuir isotherm equation.The theoretical maximum adsorption capacity of CSH and PVA-CSH were 31.06 mg/g and 28.25 mg/g.PVA added will have some impact on the phosphorus adsorption rate,but equilibrium adsorption capacity was unaffected.When the phosphorus concentration was low(TP<2 mg/L),the equilibrium was reached at about 120 min,while the equilibrium time of PVA-CSH was 240 min,equilibrium absorption capacity was 0.96mg/g and 0.95 mg/g respectively.The adsorption fitted well with the pseudo-second-order kinetic model.(5)Based on the powder materials and immobilized powder materials to construct the CSH and PVA-CSH continuous adsorption filtration column system,loading 40 gCSH and PVA-CSH material containing 40 gCSH,the hydraulic retention time of 20 min,5 and 7 days of continuous operation can ensure the effluent TP<0.5 of mg/L respectively.For filter column PVA-CSH,the effluent concentration of COD was always lower than 10 mg/L and the effluent concentration of NO3--N was always lower than 2 mg/L,the effluent of turbidity was close to 0 NTU,which was significantly better than that of CSH powder.(6)Using air-water flushing and acid flushing desorbed PVA-CSH respectively,the results showed air-water flushing was difficult to make the phosphorus desorption,acid flushing can dissolve the surface of calcium phosphate precipitation,while the adsorption sites reexposuring,but corroding the material itself,after 4 days the effluent value exceeded the critical requirements(0.5 mg/L),and their regeneration methods need further study.