Removal Properties And Mechanisms Of Purple Parent Rock Combined With Ferric Sulfate For Nitrogen And Phosphorus In Landscape Water

With the development of economy and the improvement of people's living standards,the construction of landscape water body for recreation or beautification of living environment is more and more popular.However,many landscape water bodies are closed or semi-closed drainage,and pollution sources such as agricultural waste water,ornamental fish excretion,rainwater,and air pollution will easily lead to eutrophication of landscape water bodies,and water bodies even turn "green" and"stinking",it seriously affects the surrounding living environment and urban environment.Therefore,finding an effective treatment technology to remove the undesirable nutrient of landscape water is essential and urgent.Many studies have shown that the primary cause of eutrophication is due to the excess of nitrogen and phosphorus in urban landscape water.Therefore,the reduction of nitrogen and phosphorus in water body is the key point of landscape water eutrophication control.At present,the most common method for the treatment of landscape water are adsorption and flocculation,and the choice of adsorbent and flocculant has a significant impact on the removal efficiency.The traditional adsorbent such as steel slag,fly ash and zeolite,has the advantages of wide source and reasonable price,but it has the poor effect on the treatment of landscape water.The modification of the traditional adsorbent can significantly improve the purification effect of landscape water,but the modification has the disadvantages of high cost and easy to cause the second environmental pollution.Hence,it is an important work to find the efficient,cheap and environmental friendly adsorbent.Purple parent rock is a kind of sedimentary rock,which is widely distributed in southwest China.It contains complex mineral composition,high clay mineral content,and the ability of absorbing phosphorus.Studies have shown that the use of purple parent rock as matrix or barrier material can both effectively control the nitrogen and phosphorus pollution of landscape water body.As a kind of important inorganic polymer flocculants,polymeric ferric sulfate(PFS)has shown various advantages,for example,it is applicable in a wide range of pH values,in high-density floc and fast sedimentation.Our preliminary study found that the TN and TP in landscape water can been effectively removed by using the combination of purple parent rock and polymeric ferric sulfate(PFS).This study selected four kinds of purple parent rock as adsorbent,and polymeric ferric sulfate(PFS)as flocculant,studied the removal efficiency and mechanism of TN and TP in landscape water by using the combination of polymeric ferric sulfate(PFS)and four kinds of purple parent rock.The objective of the study is to provide an efficient and low-cost method for the treatment of landscape water body.The main results are as follows:(1)Under the same experimental conditions(reaction system:1L.Mixing parameters:The waste water was stirred rapidly at the set agitation speed(380 rpm)for a predetermined rapid mixing time(2 min),followed by a slow mixing phase at a predetermined agitation speed(100 rpm)for a certain slow mixing time(10 min),and then a 3h settling.),the adsorption effect of TN and TP by using 4 kinds of purple rock powder(J3p,J2s,T1f,J3sn)and PFS alone,and by using the combination of purple parent rock and polymeric ferric sulfate(PFS)were compared.The results showed that the removal rate of TN,TP by using polymeric ferric sulfate(PFS)was 15.11%,62.83%,respectively;J3p(one kind of purple parent rock)showed the best adsorption effect of TN,TP,the absorption rate of TN,TP was 42.56%,20.35%,respectively;J3p+PFS composite treatment agent(one kind of composite treatment agent)showed the best removal effect of TN,TP,the removal rate of TN and TP was 50.84%,81.41%respectively.The removal effects of TN and TP by using composite treatment agent were better than single treatment agent,this might because that PFS has the advantages of high removal rates of TP,purple parent rock taking the advantages of high removal rates of TN,so the use of compound can effectively remove TN and TP.In order to be able to determine an optimal treatment method,J3p+PFS composite treatment agent was selected for the next step of the optimization experiment.(2)Studies on the influence factors of composite treatment agent for nitrogen and phosphorus in landscape water illustrated that TN and TP removal efficiency of 54.10%and 86.48%were achieved with coagulant dosage of 6 g·L-1 J3p and 30 mg·L-1 PFS,water temperature of 30? and initial pH value of raw water of 9,which indicated that the J3p+PFS composite treatment agent is a new type of composite treatment agent,can be used in micro polluted water treatment.(3)Removal mechanisms of purple parent rock combined with ferric sulfate(PFS)for nitrogen and phosphorus in landscape water showed that the potential of Zeta increased significantly after treated by J3p+PFS composite treatment agent,but still less than 0;the content of chlorophyll a decreased significantly;the type and content of microorganisms were significantly decreased;X-ray diffraction analysis found that when dealing with the landscape water,the J3p+PFS complex treatment agent reacted with the pollutant in the water,and the calcite(CaCO3)and hematite(Fe2O3)in J3p+PFS composite treatment agent was activated and moved to the surface of floc after treatment;infrared spectrum analysis showed that the-OH,-C=C,Fe-OH-Fe and Fe-0 groups and ion adsorption played a major role in the treatment of TN,TP by using J3p+PFS composite treatment agent;scanning electron microscopy and energy spectrum analysis showed that the floc formed by the reaction of J3p+PFS complex treatment agent with pollutants in landscape water was more compact,most of the metal content decreased,and there appeared the energy spectrum peak of P element.The comprehensive analysis showed that the treatment of TN,TP by using J3p+PFS composite treatment agent was take advantage of the flocculation function of PFS,the adsorption function as well as the function of changing the microbial activity in the water of J3p,the flocculation mechanism was mainly charge neutralization,adsorption mechanism was mainly physical and chemical adsorption.Among them,J3p+PFS composite treatment agent reduced the content of TN in the water through physical adsorption which could reduce the content of chlorophyll a and microorganisms in the water;J3p+PFS composite treatment agent reduced the content of TP in the water through physical and chemical adsorption of phosphorus in water.