The Optimal Control Study Of Using Hydroxyapatite (HAP) Method To Recover Phosphorus In Wastewater In Order To Find The Best Optimum Reaction Conditions

Phosphorus not only is an important elements which caused the water eutrophication,but also is a unrenewable resource. Nowdays,the primary technology of Phosphorus’ removal are chemical coagulation precipitation and biological phosphorus removal,but these cannot solve the problem Primarily. Therefore,removing phosphorus from wastewater is an urgent task to be shovelled.The article based on hydroxyapatite crystallization theory of recovery of phosphorus. Take simulated wastewater as the research object to study the initial phosphorus concentration (IPC), pH, Ca/P and seed dosage which have the reaction of these response factors on the crystallization; The feasibility of phosphorus recovery by hydroxyapatite crystallization from anaerobic supernatant and wastewater from bonderizing process was also analyzed.Here are the general outlines:(1) The theoretical research shows that the optimum pH is10.0;(2) The influeneing factors of phosphorus recovery rate were analyzed by orthogonal and single factor experiment systematically.The experiments show that the influence of IPC on phosphorus recovery by hydroxyapatite crystallization is the greatest,pH is the second,Ca/P is the third, seed dosage is the smallest;The interaction between pH and IPC is apparent on experiment;There are no correlation between the seed dosage and phosphorus recovery; with the increase of IPC,reaction time would reduce gradually,influence of pH and Ca/P on phosphorus recovery would reduce and residual phosphorus concentration could be reduced to a certain limit. So IPC,pH and Ca/P are the most important influence factors on recovery of phosphorus by hydroxyapatite crystallization.(3) The single factor experiment result shows that metal ions don’t have any impact on crystallization reaction which based on the Fe3+、Zn2+and Mg2+;The alkalinity has adverse effect on phosphorus recovery by hydroxyapatite crystallization; CO32-is more stronger than PO43-in attracting Ca2+. So, we should reduce the content of CO32-in wasterwater before phosphorus recovery by hydroxyapatite crystallization.(4) To analyze the content of P of the precipitate, XRD and some other chemical analyses were incoprorated. By comparison with theoretical values,the results indicated that those precipitates are mainly comprised by Hydroxyapatite.(5) The effects of recycle phosphorus from wastewater of the corresponding influence rules by hydroxyapatite crystallization were investigated.The result shows that the optimum value of pH and Ca/P will change accordingly with IPC.From the experiment results, Optimal control factors are determined by the type of wastewater and IPC.