A Novel Wastewater-phosphate Recovery Process Based On Reversible Phase Transition Between Nano-MgO And Mg（OH）₂

Wastewater phosphorus recovery is not only conducive to protecting the aquatic environment,but also conducive to promoting the sustainable development of agriculture.Existing adsorption phosphorus removal technologies generally have problems such as high adsorbent cost,low product phosphorus content,and poor anti-interference ability in the adsorption process.In this study,magnesium oxide/magnesium hydroxide was used as the adsorbent,and based on the reversible phase transition process of magnesium oxide/magnesium hydroxide,a new type of cyclic phosphorus removal process that is expected to be applied to the recovery of phosphorus from black odor sewage was developed.The main research contents include:1.In-depth study of the mechanism of phosphorus removal by Mg O adsorption,and the development of a new process for phosphorus removal sludge thermal regeneration-cyclic phosphorus removal based on the Mg O-Mg（OH）₂ reversible phase change process;2.Exploring the application potential of the Mg O cyclic phosphorus removal process in the phosphorus removal process of black and odorous sewage;3.Generate Mg（OH）₂ in situ to realize high-efficiency wastewater phosphorus recovery.The research conclusions are as follows:（1）When nano-Mg O is hydrated into brucite,its adsorption capacity is not fully utilized.Calcination is an effective method to restore adsorption capacity without desorption.Phosphate can accumulate to a higher level,even exceeding the theoretical equilibrium adsorption limit,so as to obtain high-quality fertilizer（124.5 mg-P/g-Mg O）.Phosphorus ions exist in the adsorbent in the form of HPO₄^2-and PO₄^3-,which is the main reason for the existence of phosphorus ions during the phase transition of the adsorbent from periclase to brucite.（2）The maximum Langmuir adsorption capacity reaches 408 mg-P/g-Mg O in the presence of HA.Research inferred that Mg O removed most of the HA by coagulation,phosphate and a small amount of HA by adsorption.Weak acidic conditions are more advantageous for the removal of HA and phosphate.Also,the Mg（OH）₂/Mg-HA/Mg-PO₄ composite material was calcined at 500℃,Mg（OH）₂ was converted into Mg O,HA was degraded,phosphate was still retained in the adsorbent,and the material could still be recycled.（3）In situ formation of Mg（OH）₂ can effectively remove phosphate through precipitation,flocculation,adsorption.This method requires a low magnesium salt dose,and the reaction is rapid.In this method,the p H of solution,stirring speed and coexisting ions all have a great influence on the phosphate removal rate.In summary,this study proposes a new effective phosphorus recovery strategy based on the reversible phase transition of Mg O/Mg（OH）₂,which avoids the waste of adsorbents and the pollution of adsorbents by HA,and reduces the use cost of reagents.The phosphate can be efficiently enriched and recycled,which has good reference significance and application potential for the treatment of waste leachate and black and odorous water bodies.