Research On Technology And Mechanism Of Compound Ecological Floating Bed To Treat Village Surface Runoff

Compared with the traditional urban sewage treatment process in China,the ecological floating bed has advantages in terms of investment and operation cost,operation management and so on.Although it is widely used in rural areas,there are still some problems.For example,the pollutant removal efficiency of traditional plant ecological floating beds is low,and the influence of water depth,humus,inactive phosphorus and large influent concentration range on the treatment effect is not clear.Therefore,based on the ecological floating bed process,this study set up 4 groups of control experiments（artificial roots,pure substrates,pure plants,plants+substrates）,which are named G1、G2、G3and G4 separately,to monitor effluent quality indicators,pay attention to the short-term and long-term dynamic changes of pollutants and explore the purification mechanism of ecological floating beds.To provide technical guidance and theoretical support for the practical application and strengthening of ecological floating beds,the main conclusions are as follows:（1）The effects of water depth,inactive phosphorus and humus on the purification of pollutants in the ecological floating bed system were investigated.It was found that water depth had a certain impact on the removal performance of pollutants in the ecological floating bed system.The removal effect of pollutants was better in the water depth of 30 cm,but the water depth of 50 cm was better in terms of stability.Under the conditions of four kinds of different inactive phosphorus,the ecological floating bed system had a good removal effect on COD and nitrogen,but the removal effect on phosphorus was not stable.The effect was better at high concentration,and the concentration of SRP in non-plant groups（G1 and G2）increased at low concentration.Although humus has a certain optimization effect on nitrogen removal,it has no obvious optimization effect on phosphorus removal,and even causes obvious release phenomenon.（2）Through the set of 4 sets of control experiments,it was found that the ecological floating bed treatment effect of the combination of plants and substrates was the best.Artificial roots with a specific surface area similar to that of living plant roots do not provide equivalent treatment effects.The ability of the substrate to remove pollutants as a single part is not outstanding,but it is not affected by conditions such as temperature,dissolved oxygen,etc.,so it can work best when combined with plants.The ecological floating bed has a good removal effect on nitrogen and phosphorus pollutants under the operating conditions of high and low concentrations.（3）During the test period,the aquatic part of the plant was harvested once.Harvesting had a temporary impact on the removal effect of the ecological floating bed system,but the recovery was quick.The plants can be harvested before the plants fall.（4）The aerated block has a good adsorption effect on 2-Phosphonobutane-1,2,4-tricarboxylic（PBTC）、Ethylene diamine tetra methylene phosphonic acid（EDTMP）、Adenosine 5’-monophosphate（AMP）and Sodium tripolyphosphate（TPP）.The adsorption capacity from large to small is TPP>EDTMP>PBTC>AMP,the maximum adsorption capacity of TPP is 198.41 mg/kg,and the desorption ratio is average small,basically will not cause secondary pollution.（5）Kaolin has a good adsorption effect on AMP,EDTMP,PBTC and TPP.The adsorption capacity from large to small is TPP>PBTC>EDTMP>AMP,and the maximum adsorption capacity for TPP is 122.25 mg/kg.Except for the significant release of AMP,the rest of the inactive phosphorus is basically not desorbed.（6）The absorption characteristics of nitrogen and phosphorus by vetiver are also significantly different.Comparing the Imax and Km values of the two,it can be seen that vetiver absorbs nitrogen significantly faster than phosphorus,but the affinity is opposite.When the system is under low nutrient operating conditions,vetiver will preferentially absorb PO₄^3--P.The Km values of vetiver absorbing NH₄⁺-N were all lower than those of NO₃^--N,indicating that vetiver showed a greater affinity for NH₄⁺-N and had a tendency to preferentially adsorb NH₄⁺-N.（7）The nitrogen content of the stems and leaves of vetiver grass in the two groups ranged from9.79 to 14.77 mg N/g,and the phosphorus content ranged from 0.784 to 0.899 mg P/g;while the nitrogen and phosphorus contents of the roots were 17.26 to 24.42 mg N/g and 0.867～0.95 mg P/g.There was little difference between the groups.The total nitrogen content per unit mass of vetiver was much higher than the total phosphorus content,which directly reflected that the plant’s ability to absorb nitrogen was much greater than that of phosphorus.Different parts also showed differences in the distribution of nitrogen and phosphorus,and the nitrogen and phosphorus contents in the upper part（stem and leaf）were lower than those in the underwater part（root）.（8）G3 and G4 had higher microbial abundance and more diverse microbial species,and biofilm samples were mainly composed of three bacterial groups,namely Proteobacteria,Actinobacteria and Planctomycetes.The proportion of Proteobacteria was the highest among all samples.The enriched microorganisms made a great contribution to the denitrification of the ecological floating bed system.