| Nutrients such as nitrogen,phosphorus and organic matter in the farmland drainage will be carried into the water body,which will lead to eutrophication of the water body and form water pollution.Aiming at the problem of that nitrogen,phosphorus and other nutrients in farmland drainage exceed the standard,this paper studies the ecological interception technology of farmland drainage oriented by nitrogen and phosphorus reduction.By means of ecological engineering methods,the ecological interception technology model of macrophyte pond-constructed wetland complex system was constructed,and it was used to treat the simulated farmland drainage.The ecological interception effect of the complex system on simulated farmland drainage was investigated.By analyzing the characteristics and diversity of microbial community in the complex system by high throughput Illumina sequencing technology,the purification mechanism of simulated farmland drainage was revealed.The main findings are as follows:(1)The isothermal adsorption experiment was conducted to study the adsorption effect of four matrix combinations on ammonia nitrogen and phosphorus in water.The results showed that the Langmuir equation could better describe the isothermal adsorption characteristics of ammonia nitrogen and phosphorus by different matrix combinations than the Freundlich equation.Langmuir equation showed that the theoretical maximum adsorption capacity of fine zeolite cinder combination to ammonia nitrogen was 526.316 mg/kg.The theoretical maximum adsorption capacity of phosphorus was 460.990 mg/kg for fine sand volcanic rock cinder combination,and the isothermal adsorption constant K_Land K_fvalue of fine sand zeolite cinder combination was the highest,and the adsorption capacity of ammonia nitrogen and phosphorus was the strongest,followed by fine sand volcanic rock cinder combination.Therefore,fine sand volcanic rock cinder combination was selected as the filling matrix of the macrophyte pond,fine sand zeolite cinder combination was selected as the filling matrix of the constructed wetland,and the filling matrix was stratified from top to bottom by mass ratio 2:1:1.(2)There are significant differences in the growth status of emergent and submerged plants in simulated farmland drainage.Ammonia nitrogen and TP removal efficiency of 4 kinds of emergent plants were significantly different.Among them,the removal rate of ammonia nitrogen is in the order of Acorus calamus(82.47%)>Lythrum salicaria(78.49%)>Alisma plantago-aquatica(67.27%)>Typha orientalis(60.91%).The order of TP removal rate is Alisma plantago-aquatica(71.35%)>Lythrum salicaria(68.31%)>Acorus calamus(67.71%)>Typha orientalis(64.84%);The removal rates of Myriophyllum verticillatum on COD,ammonia nitrogen and TP were 75.86%,63.94%and 62.68%,respectively,which were significantly higher than those of Ceratophyllum demersum.Myriophyllum verticillatum was selected as the planting plant in the macrophyte pond,and the combination of Acorus calamus,Alisma plantago-aquatica,Lythrum salicaria were selected as the planting plant in the constructed wetland.(3)The effect of different hydraulic retention times on treatment of the simulated farmland drainage was investigated.When the hydraulic retention time was 4 days,removal rates of COD,ammonia nitrogen and TP were 90.69%,95.43%,and 93.35%,respectively.Therefore,the optimal hydraulic retention e time of the complex system was determined to be 4 days.The effect of different C/N on treatment of the simulated farmland drainage was investigated.The results showed that when C/N was 3.5:1,the removal effects of COD,ammonia nitrogen and TN were the best,with removal rates of92.53%,98.27%and 98.12%,respectively.Therefore,the simulated farmland drainage with C/N of 3.5:1 was selected as the water for the subsequent test.(4)Comparison of the removal efficiency of pollution indexes in simulated farmland drainage by single reactor and complex system showed that the removal effects of COD,ammonia nitrogen,TN and TP in the complex system were higher than that in the single reactor,and the average removal efficiency was 96.80%,98.29%,97.65%and 95.57%,respectively.The removal efficiency of COD,ammonia nitrogen,TN and TP in simulated farmland drainage with high,medium and low concentrations was investigated.The results showed that the removal rate of each pollution index in simulated farmland drainage with different concentrations of the composite system was above 80%,indicating that the complex system had strong impact load resistance to simulated farmland drainage with different concentrations.(5)The bacterial community characteristics of Myriophyllum Verticillatum,Acorus calamus,Alisma Plantago-Aquatica and Lythrum Salicaria in the root systems of the complex system were studied at the initial stage and 3 months later.Bacterial community richness and diversity analysis results showed that after 3 moths of operation,the diversity and richness of bacterial community in the sand increased significantly.The diversity and richness of bacterial communities in the roots of Acorus calamus and Alisma were significantly higher than those at the beginning.However,the diversity and richness of bacterial community in the root of Lythrum salicaria decreased.Through high-throughput sequencing analysis,a total of 40 phyla were detected at the phyla classification level of all samples,with Proteobacteria,Bacteroidetes,Chloroflexi and Firmicutes as the dominant ones.The class level has reached more than 50,mainly including Gammaproteobacteria,Alphaproteobacteria,Betaproteobacteria and Flavobacteriia.At the genus level,Acinetobacter and Cloacibacterium were the two species with the highest abundance in the initial samples.After running for 3 months,the number of Acinetobacter and Cloacibacterium gradually decreased in the roots of fine sand and Acorus calamus,while Acinetobacter and Cloacibacterium even disappeared in the roots of Alisma Planago-Aquatica and Lythrum Salicaria.After running the complex system for 3 months,the relative abundance of Myriophyllum Verticillatum and Acorus calamus roots in acidic ovorax with nitric acid reduction function increased.Myriophyllum Verticillatum,Alisma Planago-Aquatica,Lythrum Salicaria,Acorus calamus,the multifunction water-treated bacteria in the roots,the relative abundance of Pseudomonas increased to 2.15%,1.44%,2.85%and 5.63%respectively.Nitrospira relative abundance increased to 2.54%and 7.91%in the root of Alisma Planago-Aquatica and Lythrum Salicaria,respectively.Pirellula relative abundance increased to 2.67%and 1.47%in the roots of Lythrum Salicaria and Alisma Planago-Aquatica,the typical anaerobic ammox bacteria. |
