Study On Nitrogen And Phosphorus Removal Of In-situ Multi-enhanced Technology For Ecological Pond

As an indispensable part of human living environment,urban water is closely related to human activities and has a small environment capacity,which can easily lead to severe environmental problems,such as eutrophication.Due to its low energy consumption and low cost,ecological pond is usually used to improve the purification ability of urban water.However,because of the large area and low liquidity,its effect is not outstanding.With the purpose of improving the removal of nitrogen and phosphorus in multistage ecological ponds,while considering the landscape effect,according to the local condition,the technical scheme of“guiding corridor-plant-combined ecological floating bed-local purification field”was constructed.the in-situ multi-enhanced technology for ponds was studied.Based on the realization of the pusher flow in ponds,a tank-in-series model was study.And combined with the laboratory test,the nitrogen and phosphorus removal mechanism of in-situ multi-enhanced technology for ponds was study,and the pollution load reduction capacity of each technology unit was quantified.Based on corridor diversion,the tank in series model was built to study the superposition effect of several small enhanced units.This technology had been applied to the construction of demonstration project of the National Major Science and Technology Program for Water Pollution Control and Treatment and effectively reduced the risk of nutrient pollution in the inflow stream of landscape lake.The main outcomes of this work are as follows:(1)The technical scheme of in-situ multi-enhanced technology for the removal of nitrogen and phosphorus in ponds was studied.Because of the corridor in ecological pond,the flow path from the inflow to outflow changed from linear to curvilinear.And the ecological purification potential was enhanced by optimizing the plants and management.Based on the guiding effect of the corridor,some combined ecological floating beds was installed along the flow-path of each pond and works by the plant uptake and the biofilms of carriers to enhance the nitrogen and phosphorus removal.The local purification field were filled with zeolite at the junction of ponds and worked though physical intercession,adsorption and microorganism under the condition of high dissolved oxygen caused by falling water to enhance the in-situ pollution-holding capacity.(2)The nitrogen and phosphorus removal effect and mechanism of combined ecological floating beds(EFBs)was studied.The addition of the stereo-elastic packing increased nitrogen removal by 22.6%.Although the addition reduced the plant uptake by 14.8%,it increased the sediment storage by 68.6%and microbial transformations by 22.2%.Temperature had a great influence on the nitrogen removal of EFBs,especially the denitrification which is the main mechanism of nitrogen removal.The denitrification of the same carrier was also different at different temperature.It was found that,compared with at33?,the denitrification rate of each carriers was inhibited by 54.8%-98.6%at 14.7-20.3?.And no matter what kind of the carrier,the lower the temperature,the the higher inhibition rate of NO₃-N removal rate,but the inhibition rate of NO₂-N removal rate was always above92%in the denitrification process.At the same time,the lower the temperature,the higher the remaining TN,and compared with the ceramisite,the nitrogen removal potential of stereo-elastic packing is more limited by temperature.But no matter how changes in temperature,the biomass and microbe diversity of carriers increased gradually along with the growth of the running time in the whole operation process.And the abundance of all genus related to nitrogen removal such as Gemmobacter and Aridibacter also showed an increasing trend.(3)The nitrogen and phosphorus removal effect and mechanism of local purifying field was studied.As a local water quality purification link between the multistage pond,local purifying field increased 3.6%-13.6%the dissolved oxygen by falling water between ponds and take advantage of the inter-pond distance to form an adsorption channel of zeolite to enhance the removal of phosphorus.The phosphate adsorption of zeolite in local purifying field only reduced by 4%after more than 2 years of use,indicating that the zeolite can keep the phosphate adsorption for a long time,and the porous structure of zeolite is conducive to the enrichment of microorganism.The zeolite at different position enrich different functional bacteria,thus promoting the removal of different forms nitrogen in denitrification process.The zeolite in the surface has a stronger ability to removal NO₂-N because of the enrichment of nir S,while the zeolite in deep is conducive to the removal of NO₃-N due to the enrichment of nar G.(4)Based on the principle of complete mixing and first-order kinetics,a tank-in-series model of the multistage pond was built to simulate the removal process of nitrogen and phosphorus in original multistage pond.Considering the denitrification of the carriers,the adsorption of zeolite and absorptiong of plant in floating bed,a new 36 tank-in-series model of enhanced multistage pond with EFBs and local purification was built.And good simulation results of these two models were obtained(the Nash-Sutcliffe efficiency?0.75).And It is found that each combined ecological floating bed and local purification field contributed0.059%-6.22%to the nitrogen removal and 0.26%-2.95%to the phosphorus removal,which lead to the enhancement of nitrogen and phosphorus removal by 42.9%and 18.8%in the whole multistage ponds,proving that the superposition of several units can effectively improve the water quality.(5)The water quality improvement effect of the multistage ponds by in-situ multi-enhanced technology in demonstration project was studied.After the enhanced technology set up,the TN and TP removal in five stage pond which is the inflow of famous landscape lake increased from 30.8%and 53.9%to 43.0%and 64.8%,which was similar to the model.And the average concentration of dissolved oxygen was also increased.At the same time,At the same time,there was little risk of the sediment pollution.The average removal rate of TN and TP per unit area was 1.17 and 1.18 times of other multistage pond which has the similar ecological environment and no reinforcement.Moreover,this technology system not only had a good performance of nitrogen and phosphorus removal,but also the construction and maintenance costs are much lower than those of other conventional technologies.