Research On The Effect Of Different Wetland Plants And Their Combinations On Denitrification And Phosphorus Removal From Domestic Sewage

In recent years,with the progress of society and the improvement of people’s material living standards,the environmental problems are becoming more and more serious.Water pollution is a serious environmental problem in today’s society,among which eutrophication is a problem that the world needs to deal with.Especially in many underdeveloped countries and regions,due to the lack of sewage treatment equipment,a large number of untreated sewage is directly discharged into rivers and lakes,which seriously aggravates the eutrophication and seriously affects people’s lives.The existing municipal wastewater treatment plants can reduce the nitrogen and phosphorus in the municipal sewage through certain technical means,but the nutrient concentration in the sewage is still high,which will cause the eutrophication after being discharged into the natural water body.The treatment of eutrophic water is urgent.Wetland plants can absorb nutrients in water to maintain their own growth.In addition,plants can also transport oxygen to the root area through photosynthesis,thus increasing the concentration of dissolved oxygen in water.Wetland plants root microorganisms also play an important role in the transformation of nitrogen and phosphorus.Therefore,it is very important to select the wetland plants with good purification effect and strong anti pollution ability for improving the removal of pollutants in sewage.In this study,three common wetland plants in Northeast China:Iris sibirica L.,Acorus calamus L.and Oenanthe javanica（Blume）DC.were selected as the research objects.Different concentration gradient pollution loads and different plant configuration modes were set up.The treatment effects of different plants and their combinations on different concentrations of municipal sewage were compared and analyzed by measuring and analyzing the sewage quality,plant physiological indexes and nitrogen and phosphorus accumulation in plants.The main results and conclusions are as follows（1）In the study of plant hydroponics,there are great differences in the removal of pollutants in wastewater with different concentration gradients.In high concentration wastewater,the removal rates of TN,NH₄⁺-N,NO₃^--N,TP and cod were 26.20%～93.23%,54.53%～99.21%,57.90%～84.96%,30.00%～100%and68.63%～85.29%,respectively,The results showed that the removal efficiency of the system with plants was better than that of the blank control;In medium concentration wastewater,the removal rates of TN and NH₄⁺-N were 26.87%～56.53%and 44.66%～70.11%,respectively.The removal rates of NO₃^--N and TP were poor,and the removal rates of cod were 29.79%～51.06%;In the low concentration wastewater,the removal efficiency of TN and NO₃^--N in each system was very low,and the removal rate of NH₄⁺-N was 67.58%～97.85%.The removal rate of NH₄⁺-N in the system with plants was higher than that in the blank control,and the removal rate of COD was 29.41%～67.65%;TN,NH₄⁺-N,NO₃^--N and TP in the park lake sewage have good removal effect,which is related to the low initial value of pollutants in the water.（2）In the study of plant hydroponics,the removal of pollutants by different wetland plants under the same concentration gradient was significantly different.Among the high concentration wastewater,the system of I.sibirica+A.calamus has the best removal effect,and the removal rate reaches 84.96%～99.47%;In the medium concentration wastewater,the best removal effect is A.calamus+O.javanica,and the removal rate reaches 48.94%～81.08%,especially for TP,which is much higher than other systems;In the low concentration wastewater,I.sibirica+O.javanica was the best for nitrogen removal,with the removal rate of 97.46%.A.calamus+O.javanica was the best for TP and COD removal,with the removal rates of 84.44%and 67.65%respectively.（3）In the study of plant substrate joint hydroponics,The stability of the system was accelerated by the addition of substrate,and the time to reach the stability of the system with substrate was shorter than that with plant.The results of the system added with substrate were similar to those of the plant treatment.The pollutants in the high concentration wastewater were well removed,and the removal rate was 57.83%～98.34%;Compared with plant treatment,the removal rate of TP increased by 48.25%～84.21%.The removal of pollutants in low concentration wastewater is similar to that in medium concentration wastewater,which has excellent performance in the removal of NH₄⁺-N,TP and COD,especially in the removal of TP,the removal rate reaches 86.96%～100%.The removal rate of TN is between 25%-35%.（4）In the study of plant substrate joint hydroponics,the same plant or combination has different removal effects on pollutants of the same concentration of wastewater.In the high concentration wastewater,the mixed plants have good removal effect on pollutants,especially I.sibirica+A.calamus,the removal rate of pollutants reaches 60.96%～98.34%.In medium concentration wastewater,A.calamus+O.javanica had better removal effect on nitrogen and COD,with removal rates of 70.68%and 93.94%respectively,and O.javanica had better removal effect on phosphorus,with removal rate of 89.47%.In the low pollution wastewater,I.sibirica has a good ability to remove nitrogen,phosphorus and COD.（5）There were significant differences in plant biomass under different pollution loads.The relative growth rate（RGR）of plants in the low and medium concentration groups was significantly higher than that in the high concentration group,which indicated that the high pollution load had a certain inhibitory effect on the growth of plants;the RGR of different plants also had significant differences under the same pollution load,which showed as A.calamus>O.javanica>I.sibirica.（6）Under different pollution loads,the contents of nitrogen and phosphorus in plants were significantly different.The contents of nitrogen and phosphorus in plants under high and low pollution load were higher than those under medium pollution load.On the whole,the difference of nitrogen and phosphorus content between the aboveground part and the underground part of three wetland plants was very small.According to the research results,the three selected wetland plants have good adaptability to the water environment,especially A.calamus has the strongest adaptability and good removal effect on nitrogen and phosphorus in sewage,and can be used as the plant selection of constructed wetland or ecological floating bed.The selected fly ash ceramsite has strong adsorption capacity for nitrogen and phosphorus,and can be used as the preferred substrate in domestic sewage treatment process.