| The main mechanism of phosphorus removal in constructed wetland system is the adsorption,interception,complexation and precipitation of bed-fillers.But with the continuous operation of the system,the amount of phosphorus adsorbed by fillers is increasing.when reaching saturation,the fillers can no longer adsorb efficiently,.Therefore,it is very important to find a kind of low-cost,high-efficient,non-toxic and harmless filler for enhancing phosphorus removal in wetland system.In this research,the adsorption characteristics of natural minerals,industrial and agricultural by-products for phosphorus were investigated,and the phosphorus removal efficiency of 17 kinds of common fillers were measured,from which the best three fillers were selected to mix together to form different combined fillers with different ratios.Then the best combined fillers were used to combining gwith EM and polyphosphate-accumulating bacteria to determine the best combination of.The effects of concentration of solution,particle size of fillers,amount of fillers,Ph and temperature on phosphorus removal of bacteria-carrying fillers were investigated,and the mechanism of phosphorus removal by adsorption was discussed.In order to test the feasibility of phosphorus removal by bacteria-carrying fillers,three sets of pilot-scale systems were constructed,one of which was control group with limestone,and the decontamination effect of three pilot-scale systems was tested after 105 days of continuous operation,.The cost and service life of the system were estimated.The main results are as follows:(1)the selection experiments of fillers for phosphorus removal showthat the phosphorus adsorption capacity of different fillers is significantly different.Among them,steel slag,Oyster Shell and volcanic rock have the best effect of phosphorus removal.When the concentration of TP was higher than 50 mg/L,the three kinds of fillers still had higher phosphorus removal capacity.The theoretical saturated adsorption amounts of steel slag,Oyster Shell and volcanic rock are 7.839,6.135 and 6.258 mg/g,respectively.The combined filler that is made of steel slag,volcanic rock and Oyster Shell,with the mass ratio of 3:2:1,has the phosphorus removal rate for 99.6%,which is obviously higher than that of single steel slag group and other combined group(2)The experimental results showed that the phosphorus removal efficiency of the bacteria-carrying combined filler was significantly higher than that of the filler without bacteria,which indicated that adding bacteria to the filler enhanced the phosphorus removal efficiency.In the comparative experiment of bacteria powder and activated-bacterial solution,the activated solution of polyphosphate bacteria has the best phosphorus removal effect,bacteria-carrying fillerwhich can beused for bacteria-carrying combined filler,in which the ratio is of 3g filler:2mL activated-polyphosphatebacteria solution.Under the 20 mg/L phosphorus concentration,the optimal combination can remove 99.7%phosphorus and the theoretical saturated adsorption capacity is 14.144 mg/L.The phosphorus removal capacity of the bacteria-carrying filler increases with the increase of initial phosphorus concentration.The change of temperature had no effect on the phosphorus removal efficiency,but Ph had significant effect on the phosphorus removal efficiency.When Ph was 7,the highest removal rate of phosphorus was 99.8%.The results showed that the best phosphorus removal efficiency was obtained in the neutral environment.(3)the pilot-scale experiment of phosphorus removal with bacterial-carrying combined filler bed showed that the removal efficiencies of the main pollutants were significantly higher than that of the other two groups,especially the phosphorus removal rate was up to 94.89%,the removal rates of COD,TN and NH4+-N were 73.44%,78.57%and 77.31%respectively.The DO of effluent was higher than the influent,which was related to the classification of wetland system and elevation design.The Ph value of effluent is also slightly higher than that of influentwhich is related to the filler itself.That also meets the discharge standard DB43/1665-2019 for water pollution from rural domestic sewage treatment facilities.The experimental data of the bacterial-carrying filler bed showed that,the phosphorus removal rate of the first-stage of the filler bed filler is 88.73%,the second-stage is 94.03%,and the third-stage is 94.89%,which shows that the first-stage of the filler bed is account for 93.51%.The form of phosphorus in the filler bed was changed at the end of experiment,for the ratio of Ca-P in the filler bed being increased by 3.7%,while FE-P and Al-P decreased,which indicated that the contribution of Fe and Al in the filler bed was not high,and the adsorption of Ca to p is the main part.According to the calculation,the cost of the bacteria-carrying combined filler is 575.48 Yuan/m3,and the service life is 10.81 years,so it can be used as the phosphorus removal unit in the enhanced constructed wetland system with the low cost and the long service life. |
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