Study On The Technology Of Biomass Carbon Source Enhanced Constructed Wetland To Reduce Tail Water Pollutants

The tail water quality of urban sewage plants is characterized by high nitrogen and phosphorus content and low organic matter concentration,and the use of constructed wetlands for deep nitrogen and phosphorus removal will be limited by carbon sources.In order to enhance the removal of nitrogen and phosphorus pollutants in wetlands,horizontal subsurface flow constructed wetlands were selected as the main research object in this study,and common plant materials were selected as additional biomass carbon source to enhance the ability of constructed wetlands to reduce tail water pollutants.Through the comparison of the carbon and nitrogen release capabilities and physical and chemical properties of plant materials,the best biomass carbon source,pretreatment methods and optimal conditions were determined.Through the comparison of the decontamination capabilities of the fillers in different treatment units along the wetland,the main area of denitrification and the carbon source addition locations of the wetland device in this experiment were determined.Mixing the pretreated biomass material with glucose to form a mixed carbon source,and comparing the nitrogen removal effect of the mixed carbon source and the two traditional carbon sources,glucose and sodium acetate.Changing the influent carbon-to-nitrogen ratio of the device and the dosage of pretreated biomass materials to study the effects on the removal of pollutants in this experiment.The main conclusions of this paper are as the following:?1?The carbon and nitrogen release capacity of six biomass materials,wheat straw,rice straw,rice husk,corncob,corn straw and loofa sponge,were compared and analyzed.It was found that the average carbon release rate of washed and dried corn straw was 11.18 mg·g^-1d^-1 in 8 days,and the average TN release rate was 0.20 mg·g^-1d^-1.After the corn stalk was heat-treated with NaOH,the carbon release ability increased significantly.The average carbon release rate was increased to21.90 mg·g^-1d^-1 in 8 days,which was higher than the rate under the same treatment conditions of Ca?OH?2.The average release rate of TN in the aqueous solution of corn stalk was low,only 0.13mg·g^-1d^-1 in 8 days,which was slightly higher than the rate under the same treatment conditions of Ca?OH?₂.This indicated that NaOH heat-treated corn stalk will not increase the denitrification load of the system while improving the carbon release capacity,so it is suitable for denitrification of biomass carbon source.?2?The results of SEM,EDS and lignocellulosic component analysis showed that the untreated corn straw had natural porous structure and orderly fiber arrangement.However,NaOH heat-treated destroyed the structure of lignocellulosic inside the material,made the lignocellulosic swelling,increased the internal surface area,improved the surface adhesion and was conducive to microbial growth.In addition,NaOH heat-treated reduced the content of hemicellulose,lignin and some soluble components,and increased the content of cellulose.?3?Through the orthogonal test analysis of three factors and three levels,based on the difference between the daily average release of COD and the ratio of carbon to nitrogen on the fourth day,the primary and secondary relations of the three influencing factors including heating temperature,soaking time and NaOH concentration were comprehensively analyzed.It was determined that the optimal conditions for corn stalk pretreatment were heating temperature 95?,soaking time 0.5h and NaOH concentration 4%.?4?The constructed wetland device was divided into 4 processing units along the water flow direction,the removal of NH₄⁺-N and TN from the simulated sewage by different types of fillers in the four treatment units of the constructed wetland device mainly occurred within 6 to 24 hours of the experiment.The fillers of No.1 and No.2 treatment units in the first half of the constructed wetland plant had higher removal rates of COD and NH₄⁺-N,while the fillers of No.3 and No.4treatment units in the second half had higher removal rates of TN.Denitrification mainly occurred in the second half of the wetland.In order to achieve the purpose of efficient denitrification,the position of adding organic carbon source should be set in No.3 treatment unit at 3/4 of constructed wetland device along the water flow direction.?5?Three organic carbon sources,glucose,sodium acetate and glucose+alkali-heat-treated corn stalk,were added to the filler-simulated sewage system.The addition of different kinds of carbon sources had little effect on the removal of COD,and the removal rate of COD ranges from69.71%to 80.49%.However,the concentration of NH₄⁺-N,NO₃^--N and TN decreased significantly during the 6?24 h.At 72 hours,the concentration range of the three in the system was 1.73 mg/L?3.36 mg/L,3.15 mg/L?5.53 mg/L,and 6.91 mg/L to 9.34 mg/L.The sodium acetate carbon source and glucose+alkali-heat-treated corn stalk mixed carbon source system had higher TN and NO₃^--N removal rates,from the economic and ecological point of view,glucose+alkali heat-treated corn stalk mixed carbon source was more suitable as an organic carbon source for enhanced denitrification and denitrification in constructed wetlands than sodium acetate carbon sources.?6?Under the condition of using glucose to prepare COD of influent water as the sole carbon source,the removal rate of COD,TN and TP of the wetland device gradually increased with the increase of the carbon-to-nitrogen ratio of the inlet water.When the carbon-to-nitrogen ratio exceeded 7,the removal rates of COD and TN of the three groups of wetland systems decreased slightly,while the removal rate of NH₄⁺-N gradually decreased with the continuous increase of the carbon-to-nitrogen ratio.When the carbon-to-nitrogen ratio of the inlet water was 7,the COD and TN purification effect of the wetland unit was the best,and the NH₄⁺-N and TP concentrations of the outlet water were also low.The removal rate of COD ranged from 89.73%to 95.15%,the removal rate of TN ranged from 54.67%to 59.24%,the removal rate of NH₄⁺-N ranged from 44.29%to 54.31%,and the removal rate of TP stabilized at 56.94%to 72.32%.?7?The dosage of alkali-heat-treated corn stalk in the processing unit No.3 of the horizontal subsurface flow constructed wetland device had a significant impact on the removal effect of wetland pollutants.With the increase of corn straw dosage,the average concentration of COD,NH₄⁺-N and TP increased,while the average concentration of TN decreased.When the dosage was 30g and 50g,the removal rate of COD and TN in the system was not significantly different under the two dosage,and the denitrification capacity did not increase with the increase of corn straw dosage.Therefore,the dosage of the carbon source of alkali-heat-treated corn stalk in the treatment unit No.3 of the horizontal subsurface constructed wetland in this experiment should be 30g.At this time,the average removal rates of COD,NH₄⁺-N,TN and TP of the three groups of wetland devices were 47.22%?53.27%,89.54%?90.70%,59.47%?64.13%and 45.04%?62.37%,respectively.?8?By Comparing the purification effects of three groups of wetland device fillers on pollutants,the results showed that the ceramsite filler had good COD and TP removal effects,the ceramsite zeolite mixed filler had good NH₄⁺-N removal effect,and the plastic filler had good NO₃^--N and TN removal effect.