Preparation Of Plant Slow-release Carbon Source And Its Application In Low C/N Wastewater Treatment

The traditional biological denitrification process mainly uses microorganisms to denitrify under hypoxia condition to remove nitrogen.Denitrifying bacteria can use carbon source as the electron donor to reduce NO₃^--N and NO₂^--N in water to nitrogen,so as to achieve the purpose of nitrogen removal.In the process of biological nitrogen removal,the ratio of carbon to nitrogen in sewage should be kept above 3,before the significant nitrogen removal rate can be achieved.However,in the actual wastewater treatment operation,there is often a low ratio of carbon to nitrogen in wastewater,and microorganisms cannot carry out denitrification due to insufficient carbon source and lack of electron donor.In order to improve the denitrification efficiency of microorganisms,carbon sources are often needed in the denitrification stage.In recent years,it has become very attractive to study the use of natural plant materials rich in cellulose in the natural environment as external carbon sources to promote microbial denitrification.Natural plant materials have many advantages,such as low cost,renewable,widespread existence in the natural environment,non-toxic effect,and can also be used as a carrier for microbial growth in water.Using plant materials as external carbon sources can effectively improve the ratio of carbon to nitrogen in wastewater and promote the denitrification of microorganisms.In this study,reed commonly found in the natural environment was selected as the test material,and three different pretreatment methods,namely soaking in 2%Na OH solution for24 h,heating in 90?water bath for 2 h,and simple crushing treatment,were used to conduct static release tests on plant carbon sources.The potential release capacity of organic carbon and nitrogen of reed under different pretreatment methods was studied,and the static denitrification test was carried out by adding reed solid carbon sources with three different pretreatment methods to study the feasibility of using reed solid carbon sources as external carbon sources to promote wastewater denitrification.The soluble organic matter released by alkaline treatment reed and its relative distribution was investigated by three dimensional fluorescent-parallel factor analyses.Test use of plant materials,activated sludge microorganism and inorganic materials synthesis plant slow-release carbon source,in the process of study of its static release the release of organic carbon and nitrogen efficiency,and the synthesis of plant slow release carbon source,as constructed wetland and carbon source and the substrate,the additive plant slow release of the carbon source denitrification and phosphorus removal effect of constructed wetland,and further to the constructed wetland in microbial colony Alpha diversity analysis,explore the plant carbon source to promote the feasibility of denitrifying microorganism growth.The test results show that:(1)Alkali treatment,heat treatment and simple treatment are three different pretreatment methods for reed.Among them,alkali treatment can effectively promote the decomposition of reed,and the decomposition rate is more than 27%.In the static release test,the average release amount of COD is 107.4 mg/L,85.4 mg/L and 57.5 mg/L respectively.The average release amount of TN is 2.74 mg/L,3.03 mg/L and 5.18 mg/L respectively.The reed treated by alkali can release higher organic carbon and reduce the release amount of nitrogen.(2)The static denitrification test was carried out by adding different pretreated reed solid carbon sources.From the experimental results,it can be observed that adding reed solid carbon sources can effectively improve the concentration of organic matter in sewage and promote the denitrification of microorganisms.Under different pretreatment conditions,the denitrification efficiency was in order:alkali treatment:67.67%,heat treatment:40.67%,simple treatment:28.73%.Alkali treatment of reed is easier to promote the microbial denitrification,and can effectively maintain the p H stability in the reactor.(3)Three dimensional fluoresce-parallel factor analysis was carried out for soluble organic compounds in reed hydrolysate after alkali treatment.The results show that the dissolved organic compounds released by Phragmites australis plant materials are mainly humic acid,fulvic acid,protein and other compounds,which provides a theoretical reference for understanding the use of plant carbon sources to promote microbial denitrification.(4)Using crushed reed,activated sludge,quartz sand,slag Portland cement to synthesize plant slow-release carbon sources.The synthesized carbon source material has many advantages,such as high mechanical strength,large specific surface area and high microbial diversity,and can be used as a habitat for microbial growth and reproduction.(5)In the static release test of the synthesized plant slow-release carbon source,the average release concentration of COD is 69.33 mg/L,the average release concentration of TN is 1.6 mg/L,and the average C/N is 54.2.Slow-release carbon source can release organic carbon stable in water,and effectively reduce the release of nitrogen substances,effectively improve the utilization rate of plant carbon source and reduce the adverse effects on water quality.(6)The concentration of organic carbon in sewage can be increased by adding plant slow-release carbon sources as additional carbon sources in constructed wetlands.Under the premise of no significant increase in effluent COD,compared with the blank constructed wetland,the removal rate of TN and TP increased from 22.5%to 51.8%and 22.4%to 47.1%in the constructed wetland with slow-release carbon source.The organic matter released by plant slow-release carbon source can be well utilized by microorganisms,and the effect of simultaneous nitrogen and phosphorus removal in constructed wetland is improved.(7)Alpha diversity analysis of the two groups of constructed wetlands showed that the relative abundance of microorganisms related to denitrification was 18.32%in the constructed wetlands with plant slow-release carbon source added,which was much higher than 9.75%in the blank group.The results showed that the addition of plant slow-release carbon source was beneficial to the growth and reproduction of denitrifying heterotrophic bacteria,and improved the nitrogen removal efficiency of constructed wetland.