The Experimental Study Of A New Aluminum Sludge Matrix Used To Intercept Nitrogen And Phosphorus Pollution In Farmland

Aluminum sludge from water supply plant is a by-product of city waterworks,in this study,the sludge's capacity of absorbing nitrogen and phosphorus pollutants was improved by organic modification and its granulation was optimized by response surface method.Therefore,a new type of aluminum sludge matrix filler was developed to simulate the construction of tidal flow artificial wetland.By changing the law of water intake to create a micro environment of aerobic/hypoxic circulation,microbial activity can be improved,and explore its ability to intercept nitrogen and phosphorus pollutants in farmland drainage under different hydraulic retention time conditions.First,the study tried to use cetylpyridine chloride?CPC?to make modified aluminum sludge powder.And the aluminum sludge matrix's surface characteristics and structure were studied by SEM,XRD and EDS.The SEM results showed that the surface of the modified aluminum sludge was uneven and porous,and the specific surface area increased.XRD analysis showed that aluminum sludge was of complex composition,containing a variety of metal compounds,including a large number of SiO₂ and AlPO₄,EDS analysis shows that the aluminum sludge is mainly composed of C,O,Al and Si,in addition to a small amount of Fe,Mg,K.Then a new granular aluminum sludge matrix?GASM?was obtained by granulating aluminum sludge powder.Through the characterization,it can be seen that its outer surface is rough,with many gullies,and its inner pores are developed and mostly connected.XRD analysis shows that the Al element in GASM mainly exists in amorphous form of AlPO₄,which makes it strongly adsorb anions.The additive sodium silicate increases the content of SiO₂ and makes GASM have certain particle strength,the EDS characterization results show that the content of Al and C in GASM is reduced and the content of Si is increased due to the addition of sodium silicate.In order to investigate the adsorption effect of modified aluminum sludge on nitrogen and phosphorus pollutants,static adsorption experiment was conducted on CPC modified aluminum sludge powder.In addition,orthogonal tests were conducted to investigate the significant influence of the value of sludge addition,the initial concentration and the initial pH value on the experiment.Then adsorption kinetics and adsorption isotherm experiments were carried out to test the adsorption mechanism.Finally,the reusability of the substance was investigated through desorption experiments.The experimental results show that:The adsorption effect of modified aluminum sludge powder on phosphorus was obviously improved,but the adsorption effect on nitrate nitrogen was limited,Under acidic conditions,the adsorption effect of it on phosphate and nitrate nitrogen is obviously better than that under alkaline conditions.Orthogonal experiment showed that the effects of influencing factors to the adsorption were in the order of pH>dosage>initial concentration of phosphorus>reaction time.The data were analyzed by analysis of variance,which showed that pH value was the significant influence factor of the experiment.Kinetic experiments revealed that the adsorption process of CPC modified aluminum sludge powder on phosphorus was favorable,and the main mechanism was electrostatic attraction and ion exchange;In the process of nitrate nitrogen adsorption,chemical adsorption and particle diffusion play a leading role.The adsorption isotherm was fitted to obtain the maximum unit adsorption capacity of phosphorus,which was 5.3mg/g.The result of desorption experiments showed that it can be reused.Through analyzing the experiment that use response surface method to optimize the granulation test of aluminum sludge matrix,it can be seen that the three factors--calcination temperature,raw material ratio and the proportion of additive,have an interactive influence on GASM comprehensive index.When the ratio of additives is the central value,the interaction between the ratio of aluminum sludge and calcining temperature is the most significant.The optimum preparation conditions were obtained as follows:the calcination temperature maintained at about 1010?,the ratio of aluminum sludge to fly ash is 73:27,and 11%additive.The CPC modified GASM was applied to the tidal flow constructed artificial wetland experimental device.The experimental results showed that:with the increase of hydraulic retention time,the removal rate of total nitrogen and total phosphorus both have a trend that increasing first and then decreasing.The optimal hydraulic retention time is 12h.The maximum removal rates of total nitrogen and total phosphorus in simulated farmland drainage were 54.58%and 72.91%respectively,showing better removal efficiency.Due to the limitations of time and experimental conditions,there are still some deficiencies in this study,which needed to be further studied.For example,in this study,the adsorption effect of CPC modified aluminum sludge powder on nitrate nitrogen was significantly different from the expected.The simulated tidal flow constructed wet land system in this study should also be further experimented in pilot-scale.In addition,emergent plants can be added,so that they will play the role of absorbing nitrogen and phosphorus pollutants in farmland drainage to achieve better retention effect.