Study On EBPR Treatment Of Phosphorus-Containing Wastewater And Recovery Of Phosphorus By Vivianite Crystallization

Enhanced biological phosphorus removal（EBPR）is a commonly used wastewater treatment process,and its core is to remove phosphorus from wastewater.The successful operation of the EBPR process is mainly dependent on the enrichment of polyphosphate accumulating organisms（PAOs）,which can store phosphorus in the form of polyphosphates in cells.Vivianite（Fe₃（PO₄）₂·8H₂O）is a stable iron-phosphorus compound,which has been widely distributed in deep-water lakes and bottom sediments of the ocean.It has high economic value,not only as a raw material for phosphate fertilizer,but also can be used to synthesize lithium batteries.Large particles,high purity vivianite also has a high collection value.Immobilization of phosphate in the form of vivianite is a very promising phosphorus recovery method.This study covered the feasibility of recovering phosphorus source by blue iron ore crystallization method with phosphorus-rich aerobic granular sludge-EBPR sludge and phosphorus-containing industrial waste-phosphogypsum as phosphorus recovery objects.The main research contents are as follows:（1）The construction and cultivation of EBPR reactor.The water quality treatment in the domestication process,the water quality change in the typical cycle,the mid-infrared spectra of the intracellular storage substances（PHA,glycogen,polyphosphate）of the sludge in the typical cycle and the three-dimensional fluorescence spectrum of the supernatant were analyzed.The results showed that the COD concentration of EBPR sludge seriously affected the treatment effect of phosphorus in the treatment process of phosphorus in sewage.Low C/P caused insufficient synthesis of PHA in anaerobic period and cannot meet the absorption of phosphorus in aerobic period.After the varition of intracellular substances concentration in sludge was analyzed,with infrared spectroscopy in typical cycles,the conclusion was in line with the law of EBPR:the content of glycogen and phosphorus is gradually reduced in the anaerobic stage,and increased in the aerobic stage.PHA is continuously accumulated in the anaerobic stage and decomposed in the aerobic stage.（2）EBPR reactor was used to treat soybean products wastewater.The concentration of soybean products wastewater was controlled by dilution of the stock solution,and four gradients（COD concentrations were set to 230-270 mg/L,490-530 mg/L,800-920 mg/L,1300-1500 mg/L,respectively）were used as the influent of the reactor.It was found that when the influent COD concentration was set to 1300～1500 mg/L,the effluent COD concentration reached 100～150 mg/L,and the effluent water quality only met the secondary standard requirements of Integrated Wastewater Discharge Standard（GB8978-1996）,and sludge bulking occurred,which was not conducive to the long-term effective treatment of bean curd residue wastewater by the reactor.The influent concentration:COD is 800～920 mg/L,TN is 30～36 mg/L,TP is 7.50～8.00 mg/L,and the effluent quality met the first level standard under this working condition.The EBPR reactor can effectively treat the bean curd residue wastewater for a long time under this working condition.（3）The excess sludge discharged from EBPR reactor contained a large amount of phosphorus source.The feasibility of phosphorus recovery from this kind of high phosphorus sludge by vivianite crystallization method was explored.The co-digestion experiment of Fe³⁺+EBPR excess sludge was carried out by adding different quality of synthetic Fe OOH to explore the effect of different iron-phosphorus ratio on the formation of vivianite and anaerobic digestion process.The results showed that Fe³⁺in the anaerobic digestion system with different Fe OOH dosage was gradually reduced to Fe²⁺by dissimilatory metal reducing bacteria（DMRB）and formed vivianite with PO₄^3-released by sludge cells.When the molar ratio of iron to phosphorus is controlled at 2.28:1,the removal of phosphorus in the supernatant of the digestive system was the most effective,which could reduce the phosphorus concentration in the supernatant from about 2450 mg/L to 24.35 mg/L,and the phosphorus removal rate reached 99.00%.The Fe bound phosphorus in the sludge was the most（up to 83%）,so it was speculated that the vivianite was the main compound by qualitative and quantitative analysis.The addition of iron can promote the degradation of sludge and increase the release of NH₄⁺-N,TN,COD and VFAs in the anaerobic digestion system.（4）Taking industrial waste-phosphogypsum as the research object,the effects of liquid-solid ratio,reaction time,reaction temperature,type and volume ratio of acid in leaching solution on phosphorus leaching from phosphogypsum were investigated.The conditions for efficient extraction of phosphorus were determined as follows:the liquid-solid ratio was 10:1,the reaction time was 60 min,the reaction temperature was55°C,and the volume of sulfuric acid in the leaching solution was 1/3.The aqueous solution can efficiently extract the phosphorus source in phosphogypsum while reducing the production of impurities such as calcium ions.We researched the vivianite crystallization by adding ferrous ions and adjusting different p H in the leaching solution.The results showed that when p H=8,the phosphorus in vivianite-P bound form was the most,accounting for 28.98%of the total phosphorus.The possibility of recovering phosphorus from phosphogypsum by vivianite crystallization method was confirmed.It provided an important idea for the recovery of phosphorus source in phosphogypsum,an industrial solid waste,and provided a reference for dealing with“phosphorus pollution”and“phosphorus recovery”.Figure[51]Table[21]Reference[114]...