Impact Of Sulfur On The Environmental Behavior Of Endogenous Phosphorus And Their Algae Growth Potential In Urban River

It is well recognized that phosphorus release from the sediments can exert a significant impact on accelerate the eutrophication even after malodor is effectively reduced.Phosphorus（P）has long been considered as an essential nutrient limiting the primary production for aquatic ecology.Sulfur is important element in the geochemical cycle with higher content than P,the effect of sulfur on the environmental behavior of endogenous P cannot be ignored.In this research the effects of different forms and concentrations of sulfur on the release of endogenous P were investigated,both their environment behavior and the coupled relationship were analyzed.Besides,the bio-availability of released P fractions driven by sulfur was discussed on the basis of Algae Growth Potential（AGP）experiments.This research can provide theoretical evidence for enriching“Sulfur-driven Eutrophication”theory and technical support for the treatment of endogenous pollution in polluted rivers and lakes.The main results are as follows:（1）In the study of the effects of different concentrations of sulfur on the environmental behavior of endogenous P,it was found that the release of P caused by reduced sulfur(S^2-)has stage characteristics.The first stage was dominated by chemical reduction,there was a positive correlation between the intensity of P release or the content of FeS_x and the concentration of Na₂S（1⁶mM）,which indicates that the release of P was dominated by the S^2-reduced metal which bound P in this stage.The second stage was dominated by bio-chemical processes,only after the reduction of SO₄^2-to S^2-with the participation of microorganisms,can the chemical process（first stage）be realized.Therefore,this stage showed the characteristics of low concentration of Na₂S（1⁴mM）promoted the release of P when the high concentration（6mM Na₂S）inhibited.Compared with the control,4mM Na₂S has the highest concentration of PO₄^3-（efficiency of increase:51.063±2.24%）,when the PO₄^3-concentration of 6mM Na₂S was lower than the control.This may be due to the fact that 6mM S^2-obviously inhibited microbial activity in the first stage by measured the value of APA,which made the reduction of SO₄^2-to S^2-cannot be happen.Compared with Na₂S,the P release of Na₂SO₄ groups were obviously delayed,only after 30 days,the correlation between the release of PO₄^3-and the concentration of Na₂SO₄ has appeared.Compared with the control,8mM Na₂SO₄ has the highest concentration of PO₄^3-（efficiency of increase:50.827±1.43%）,which may due to the highest value of APA（0.15 mM/（g·min））.It is believed that the key of the P release is the formation of S^2-.（2）In the study of the effects of different forms of sulfur on the environmental behavior of endogenous P,it was found that the dissolved sulfur（Na₂SO₄、Na₂S、Na₂S₂O₃）have promoted the release of endogenous P,while the solid sulfur（FeS、FeS₂、S⁰）have reduced the concentration of PO₄^3-in the overlying water.At the same molar concentration（the concentration of S）,the P release intensity was Na₂S>Na₂S₂O₃>Na₂SO₄,and the P inhibition intensity was FeS₂>FeS>S⁰.The difference of P release intensity of dissolved sulfur（Na₂SO₄、Na₂S、Na₂S₂O₃）due to different S^2-concentration.The process of P release have become more faster and stronger after Na₂S and Na₂S₂O₃ input due to they can produce S^2-directly.The increase efficiency of PO₄^3-concentration in the overlying water was respectively152.29%and 120.63%.The reduction of Na₂SO₄ to S^2-must with the participation of microorganisms,which caused the P release of Na₂SO₄ group was obviously delayed,and the intensity of phosphorus release was 29.224%.S^2-can compete with PO₄^3-for metal ions（such as Fe and Mn）and combine with metal ions to form FeS_x which solubility was lower than P bound to Fe and Al compounds,this process may promote the release of endogenous P.Due to the low solubility of solid sulfur（FeS、FeS₂、S⁰）,the concentration of S^2-was low,and there was no obvious effect on the release of P.（3）Through the analysis of endogenous P forms after sulfur input,it was found that NaOH-P was most affected by sulfur,which may be related to the reduction of metal ions by S^2-.SO₄^2-can also promote the release of D.HCl-P and C.HCl-P by promoting the mineralization of organic phosphorus.In addition,the input of sulfur also promoted NaOH-P and D.HCl-P（P forms with medium bioactivity）to Resin-P and NaHCO₃-P（P forms with high bioactivity）.On the basis of AGP experiments,Resin-P and NaHCO₃-P with high bioactivity which the growth rate of Chlorella Vulgaris were respectively 0.375μ/d at 0.1mg/L（Resin-P）and 0.254μ/d at 0.05mg/L（NaHCO₃-P）.The promoting effect of NaOH-P was positively related to its concentration.At high concentration（≥0.20mg/L）,NaOH-P promoted algae growth remarkably as effectively as available P.In a word,the input of sulfur was not only lead to the release of NaOH-P,but also promoted the transformation of low bioavailability P forms to high bioavailability P forms.This research helps to gain improved understanding of the ecological risk on sediment P,the effect of sulfur plays an important role in“eutrophication”.