Role Of Alkaline Phosphatases In Phosphorus Tranfer And Transformation In Point And Nonpoint Pollution

Eutrophication is a persistent condition of aquatic ecosystems and a widespread environmental problem. Phosphorus is often regarded as the main culprit in cases of eutrophication in lakes. There are two common sources of phosphorus and other nutrients:point and nonpoint sources. Sewage sludge and agricultural run-off carrying fertilizers are typical examples of phosphorus point source and nonpoint source lead to human-caused eutrophication, respectively. The phosphorus fraction is important to the phsophorus transfer and alkaline phosphatase plays a key role to the phosphorus fraction transformation. For these purposes, the objective of current work was to (1) investigate the influence of metal ions, anions, ortho-phosphate, polyphosphate and organic phosphorus on the activity and kinetics of alkaline phosphatase in aerobic activated sludge; (2) study the alkaline phosphatase activities (APA) and phosphorus fractions in activated sludge during wastewater treatment; (3) assess the phosphorus fractions and alkaline phosphatase activity in sewage sludge, soils and sediments for the effectively evaluating their phosphorus mobility and bioavailability.The results of our studies suggested that:(1) There were three impact models of heavy metals on alkaline phosphatase activity (APA) and most inorganic anions were relatively innocuous at the concentrations from 0-5.0 mM. However, phosphorus especially pyrophosphate had an inhibitive effect on APA, the residual activity of alkaline phosphatase dramatically decreased to 34.8% of the control at the pyrophosphate concentration of 5.0 mM. The inhibition of Cu2+ on alkaline phosphatase was described satisfactorily by uncompetitive type at low concentrations, but mixed of noncompetitive-uncompetitive type at high concentrations. The inhibition of ortho-phosphate was found to be competitive type. VmaX/Km ratio is a good indicator for the catalytic efficiency of alkaline phosphatases in wastewater.(2) The Standards, Measurements and Testing (SMT) harmonized procedure was adopted for determination of phosphorus fractions. The alkaline phosphatase activities were determined by analyzing the production of p-nitrophenol from p-NPP catalyzed by phosphatase in samples. Our results showed that the phosphorus concentration and fractions in activated sludge were highly correlated with the characteristics of influents. Inorganic phosphorus (IP) and non-apatite inorganic phosphorus (NAIP) were the main phosphorus fractions of sludge. A larger phosphorus concentration was found in activated sludge due to the more readily mobilizable and bioavailable forms. The APA in sludge was directly correlated with mixed liquor suspended solids (MLSS) in activated sludge. The APA in the sludge is implicated the depletion of organic phosphorus forms in sludge, whilst also implying its less inhibition of inorganic phosphorus in sludge. The APA and phosphorus fractions in different sludge samples from the same wastewater treatment plant were quite stable. This stability shows their tight interactions in sludge.(3) The results demonstrated that sewage sludge possessed larger amounts of phosphorus than soils and sediments. The inorganic phosphorus (IP) was the main phosphorus fraction of all the samples investigated and it always constituted more than 70% of the total phosphorus (TP). However, the distribution of IP between non-apatite inorganic phosphorus (NAIP) and apatite phosphorus (AP) significantly varied according to the type of samples. NAIP accounted for more than 60% of IP in sediment and sewage sluge samples obtained from domestic wastewater treatment plants. However, AP was more abundant than NAIP in soils samples. For the phosphorus fractions obtained in a closed agriculture test fields, NAIP content showed an obvious increases from soils to sediment samples; This suggests that NAIP is the most easily mobilizable forms of phosphorus. The average alkaline phosphatase activity in sewage sludge samples is significantly higher than that in soils and sediments samples, and it maybe closely attributed to the higher biomass content in sewage samples.