Research On Treatment Technology Of Corn Deep Processing Wastewater Based On Resources Recovery Of Nitrogen And Phosphorus

Taking the CDPW(Corn Deep Processing Wastewater)as the research object in this paper,apply the method of MAP(Magnesium Ammonium Phosphate)crystallization to recycle nitrogen and phosphorus resources from it.Firstly,a lab-scale experiment was conducted to study the effect of the main factors affecting the crystallization process of MAP on the removal of TP,PO43--P,and NH4+-N.Secondly,on the basis of single-factor experimental studies,RSM(Response Surface Methodology)was used to optimize the significant factors affecting the removal and recovery efficiency of nitrogen and phosphorus from CDPW,and then determine the optimal operating conditions.Thirdly,a pilot-scale fluidized bed crystallizer was used to treat CDPW.Finally,the preliminary economic assessment of the recovery of nitrogen and phosphorus resources from CDPW by the method of MAP crystallization was performed.The main research results are as follows:1)The results of the single-factor experiment show that changes in pH,reaction temperature(T)and Mg/P have a greater impact on the removal of TP,PO43--P,and NH4+-N from CDPW,however,the reaction time,settling time and agitation rate have little effect on it.In addition,it was beneficial to recover the nitrogen and phosphorus resources from CDPW by MAP crystallization for each single factor:pH=9.0,T=25?,Mg/P=1.8,reaction time and precipitation time were 30 min and 60 min respectively,the agitation rate was 120 rpm and the Mg source was MgCl2·6H2O.2)Make use of RSM to design the experiment and determine the optimal reaction conditions.The results are as follows:The effect of pH and T on the removal of TP,PO43--P and NH4+-N from CDPW is greater than that of Mg/P.The optimum reaction conditions were:pH=9.0,Mg/P=1.5,and T=30?.At the same time,the removal ratio of TP,PO43--P and NH4+-N were 90.70%,91,60%and 14.58%,respectively.Compared with the single factor experimental results,the required Mg/P is reduced,which helps to cut down operating costs.In addition,the precipitated product under the optimal conditions was characterized.The results showed that the main component of the product was MAP and the purity was 90.2%.3)The influence of parameters on the operating performance of the pilot-scale fluidized bed crystallizer was studied.The results are as follows:pH,Vup and RR have a greater impact on the removal efficiency of TP and PO43--P,and the effect of pH and Vup on NH4+-N removal was greater.However,the effect of Mg/P on both N and P removal efficiency was little.From this,it was determined that the best operating parameters to treat CDPW using the pilot-scale fluidized crystallizer were:pH=9.0,Mg/P=1.2,Vup=40 mm/s,and RR=50%.Compared with the RSM optimization results,the required Mg/P is reduced again.In this case,there is no need to add Mg sources,further lowering the operating costs,and demonstrating the high operating performance of the pilot-scale fluidized bed crystallizer.4)Under the optimal operating parameters,applying pilot-scale fluidized bed crystallizer to treat CDPW can get satisfactory results:the removal efficiency of PO43--P,NH4+-N and Mg2+ were 84.43?91,32%,8.96?11.22%and 64.22?69.40%,respectively.At the same time,the performance of the pilot-scale fluidized bed crystallizer was evaluated by the thermodynamic equilibrium model and the reactor kinetics model respectively.The results showed a good agreement between the predicted value of the model and the experimental data.Moreover,composition analysis of the crystals harvested from the bottom of the pilot-scale fluidized bed crystallizer were performed,showing that the crystal pellets contain less heavy metal element.The purity is as high as 91.5%,higher than that of RSM optimization result,indicating that the fluidized bed crystallizer can improve the purity of MAP.5)Cost and benefit from the treatment of CDPW by the MAP crystallization method under the lab-scale and the pilot-scale experiment was evaluated.The results showed that the net profit under the two operating modes was 1.70 RMB/m3 and 1.27 RMB/m3,respectively.Therefore,applying the technology of MAP crystallization to treat CDPW can get some benefits.