Effect And Mechanism Of Phosphorus Removal By Circulating Aluminum Sludge Advanced Treatment Process

Phosphorus is the main limiting factor of algae growth.Excessive phosphorus discharge into water will lead to eutrophication.China’s comprehensive sewage discharge standard(GB18918-2002)requires TP<0.5mg/L in grade A standard.Biological or chemical phosphorus removal is generally adopted in sewage treatment plants.Biological phosphorus removal can only reduce TP to 1～2mg/L,while chemical phosphorus removal will bring adverse effects on biological treatment and sludge treatment.The aluminum sludge is used as the adsorbent of secondary effluent phosphorus in sewage treatment plant,which has the sustainable development concept of"treating waste with waste".Based on this,a circulating intermittent dephosphorization and dephosphorization process for aluminum sludge was proposed in this study.At the same time,the mechanism of phosphorus removal from aluminum sludge was discussed by means of electron scanning electron microscope,pH and Fourier transform infrared spectroscopy.The main conclusions are as follows:(1)The static equilibrium adsorption capacity of aluminum sludge on phosphorus was 3.6mg/g of dry mud,and stirring could accelerate the removal of phosphorus by aluminum sludge.The optimal stirring time was 30min andthe optimal stirring strength was 150rpm.(2)The dephosphorization process of aluminum sludge generally conforms to the pseudo second order kinetic model.Therefore,the design and calculation of aluminum slime amount can be carried out according to TP amount and water amount.When the concentration of secondary effluent TP is 1mg/L,0.48g aluminum mud(dry mud)is needed to treat 1m3 wastewater.(3)No release of Al3+and organic matter was found in the dephosphorization process of aluminum sludge,and the removal of TN,NH4-N+and trace organic matter in the secondary cfflucnt was basically not effective.(4)The operation process of circulating intermittent aluminum sludge treatment dephosphorization process is as follows:adding mud-water-mixing and stirring-precipitation and clarification-drainage.Aluminum second pond,the water and mud in the first hybrid mixture stirring pool is used(30 min),mud into the settling basin for precipitation(2h)together by the inlet valve control,mixing 30 min,supernatant fluid discharge,the mud from the bottom of the tank through the exhaust pipe after the separation,sand water separator to separate the aluminium to enter the system with water and mud circulation use repeatedly,until the water TP concentration does not meet the discharge standard after replacing aluminum clay,or regular replacement and supplement.The separated wastewater is returned to the pretreatment system of the sewage treatment plant for treatment and clarification for 2h,and then discharged with the decanter.The supernatant may contain some refractory particles with larger particle sizes.The subsequent end can appropriately add filtration units to further reduce suspended matter(SS).(5)The mechanism of removing phosphorus from aluminum slime is mainly chemical adsorption.In other words,the hydroxyl group and the hydrated group of the aluminum sludge coordinate with the phosphate group to form a stable structure and adsorb the phosphate group on the surface of the aluminum sludge.Through the analysis of phosphorus morphology,it is concluded that the form of Al-p accounts for about 68.3%,the form of Fe-p accounts for about 11.4%,and the form of Ca-p accounts for about 7.8%,while the soluble P and other forms of P account for about 12.5%in total.