The Study On The Degradation Of Typical PPCPs By Strengthened Microorganisms In Constructed Wetlands

In recent years,due to the extensive use of drugs and personal care products(PPCPs),they are widely found in natural water bodies such as rivers and lakes in our country,and their content ranges from ng/L to ?g/L.Although the content of PPCPs is relatively low in the water environment,due to the limited removal effect of such pollutants by traditional sewage treatment plants,PPCPs accumulation in the water environment presents a "pseudo-persistence" phenomenon as the tail water of the sewage treatment plants continuously enters the water environment,while long-term exposure of human or animals to the water environment containing PPCPs will pose potential threats to the health of human or animals.As an ecological sewage treatment measure,the existing research shows that the constructed wetland has good removal effect on most PPCPs.Due to the rapid development of cities,domestic urban water resources are increasingly scarce.In order to respond to the construction of The Sponge City,constructed wetlands are used to purify rainwater runoff to achieve the purpose of rainwater reuse.However,due to the erosion of urban roads and farmland soil by rainwater,various pollutants exist in rainwater runoff,of which PPCP PS will also enter rainwater runoff with the erosion of rainwater.Therefore,the removal effect of constructed wetlands on PPCPs should be paid attention to when purifying rainwater runoff.In this paper,two typical sulfanilamide antibiotics sulfamethoxazole(SMX),sulfadiazine(SDZ)and one quinolone antibiotic ciprofloxacin(CIP)are selected as target PPCPs to study the effect of horizontal subsurface flow constructed wetland in treating PPCPs in rainwater runoff.Three PPCPs degrading bacteria are obtained through enrichment,domestication,purification and identification,and the screened degrading bacteria are optimized to construct a composite microbial agent to biologically enhance the degradation effect of PPCPs on microorganisms in the constructed wetland.In addition,the principle of removing PPCPs in constructed wetlands strengthened by composite microbial agents was explored,so as to provide reference for the application of biological enhanced constructed wetlands to remove PPCPs in rainwater runoff in practical projects.The main contents of this paper are as follows:(1)The constructed wetland is started by simulating the quality of rainwater runoff in Beijing through artificial water distribution,where the concentration of SMX,SDZ and CIP is 100 ?g/L.After 45 days of operation,the constructed wetland has a stable removal effect on various pollutants,and the removal effects on SMX,SDZ and CIP are 74.24%,64.70% and 51.53% respectively.The substrate was taken from the surface layer of the constructed wetland with stable operation 5~10cm,and six PPCPs degrading bacteria were obtained through enrichment,domestication,purification and screening,named J-2~J-7,in which J-2 and J-5 were SMX degrading bacteria,J-3 and J-6 were SDZ degrading bacteria,J-4 was CIP degrading bacteria,and J-7 had good degrading effects on SDZ and CIP.According to the morphological characteristics and physiological and biochemical characteristics of six degrading bacteria,J-4 and J-7 were preliminarily identified as Proteus Hauser,J-2 and J-5 as Pseudomonas,J-3 and J-6 as Bacillus.(2)The degradation combination of the same PPCPs is determined by the diameter of the antibacterial ring produced by the microbial antagonism experiment.It is found that when J-2 and J-5 are used as SMX degrading mixed bacteria,J-3,J-6 and J-7 are used as SDZ degrading mixed bacteria,and J-4 and J-7 are used as CIP degrading mixed bacteria,the antibacterial ring is the smallest.The three mixed bacteria are compounded in different proportions to construct a composite microbial inoculum.When the ratio of SMX mixed bacteria: SDZ mixed bacteria: CIP mixed bacteria is 2:1:1,the composite microbial inoculum has the best removal effect on the three PPCPs.The optimal degradation conditions of the composite microbial inoculum are explored by controlling different p H,temperature and inoculation amount.It is found that the composite microbial inoculum has the highest degradation effect on the three PPCPs when p H=7,temperature is 35? and inoculation amount is 1.5%,and the degradation rates of SMX,SDZ and CIP are 67.4%,47.6% and 50.8% respectively.(3)With the optimal inoculation amount of 1.5%,the compound microbial flora is added into the 2# constructed wetland.When HRT=48h,the removal rates of SMX,SDZ and CIP of the 2# constructed wetland strengthened by the compound microbial flora are increased by 8.88%,3.88% and 6.68%,respectively.By controlling HRT of different constructed wetlands for 12 h,24h,36 h and 48 h,It was found that the degradation effect of 2# constructed wetland on SMX and SDZ firstly increased and then decreased,reaching the maximum at 36 h,with the removal rates of SMX and SDZ being 86.34% and 76.36% respectively.The removal effect of CIP gradually increased with the increase of HRT in constructed wetland,and the maximum removal rate was 57.72% at 48 h.Under this HRT,the removal rate of SMX and SDZ decreased by 6.71% and 9.70%,respectively,and The daily sewage treatment volume of constructed wetland decreased.When the HRT was shortened from 48 h to 36 h,although the CIP removal rate decreased,it was only 2.38%.Considering the influence of hydraulic retention time on the removal rate and daily sewage treatment volume,the optimal HRT=36h was finally determined.(4)The number of bacteria,fungi,actinomycetes and soil enzyme activity in the 2# constructed wetland have significantly changed after being strengthened by the composite microbial inoculum.The number of bacteria in the upper,middle and lower layers of the constructed wetland have all increased by 1~2 orders of magnitude.The number of actinomycetes has increased by 1.08,1.06 and 1.87 times,and the number of fungi has gradually decreased,indicating that the constructed wetland has gradually changed from fungal wetland to bacterial wetland,and the treatment effect has been improved,with 36.18%,13.60% and 10.14% respectively in the upper,middle and lower layers.POD,DHA,PPO and UR activities were also significantly increased,and showed the most significant improvement effect in the upper matrix.POD activity increased by 100.0%,75.0% and 64.0%,DHA activity increased by 100.0%,84.0% and 96.8%,PPO activity increased by 207.1%,166.7% and 139.4%,UR activity increased by 38.14%,33.38% and 36.77%,respectively,in the three sampling positions of the upper substrate.The results showed that after the compound microbial agent was added to the constructed wetland,the microbial activity in the upper substrate was mainly improved.(5)Through correlation analysis,it is found that the change of bacteria quantity has significant influence on SMX,SDZ and CIP degradation,while the change of fungi quantity and actinomycetes quantity has no significant relationship with the change of SMX and SDZ removal rate,while the change of fungi quantity has weak negative correlation with CIP.The change of SMX removal rate has a significant positive correlation with the change of POD activity and UR activity.The change of SDZ removal rate has a significant positive correlation with the change of POD activity,while UR and PPO activities have a positive correlation with CIP degradation.