Study On Impact Of Zero Valent Iron Nanoparticles On The Characteristics And Nitrosation Performance Of Granular Sludge

Zero valent iron nanoparticles（n ZVI）are used increasingly in the control of various kinds of pollutants because of high specfic surface area,high activity of redox reaction and high reaction velocity.At the same time,it is worth paying attention to the potential influence of n ZVI on the sewage treatment system and water environment.Nitrification granular sludge（NGS）is a new technology combined biological sludge granulation with stable nitrosation.As an important basis on the practice of "nitrosation route",NGS is beneficial to the high enrichment of ammonia oxidizing bacteria（AOB）and selective inhibition of nitrite oxidizing bacteria（NOB）,resulting in the achievement of high nitrite accumulation and overcoming the disadventage of the traditional nitrification process（eg.SHARON）disadvantage.Based on the research object,the cultivation of the granuler sludge,quick start-up of the nitrification process influence on sludge performance and different sludge particle size were investigated.The main results of this dissertation were shown as follows:1.In order to evaluate the effect of increasing organic loading rate（OLR）gradually on the formation of aerobic granular sludge（AGS）,a lab-scale cylindrical SBR reactor（sodium acetate as carbon source）was constructed and inoculated with sewage sludge.AGS exhibited the highest growth rate under the condition of 3.20-4.84 kg·（m3·d）^-1OLR.Experimental results demonstrated that the accumulated sludge concentration,SVI30,mean granule size,settling velocity and SOUR value of the AGS in steady-state operated SBR were 23.9 g·L^-1,20 m L·g-1,1.4 mm,102 m·h-1 and 50.2 mg·（g·h）^-1,respectively.Meanwhile,linear correlation was observed between the variation of protein/polysaccharide concentration and the granule size of AGS.2.In order to start up an autotrophic partial nitrification process,the coordinated control of the influent C/N loading rate was carried out in the lab-scale sequencing batch reactor（SBR）inoculated with heterogeneous granular biomass.Results showed the nitrite nitrogen（NO₂--N）accumulation rate of SBR achieved around 1.4 kg·（m3·d）^-1,with the persistent enhancement of ammonia-oxidizing bacteria（AOB）activity,represented by specific NO₂--N accumulation rate of μNO₂-N.Moreover,the mean diameter of sludge granular increased from 1.44 mm to around 2.2 mm,with the color of reddish brown,while its settling ability was improved significantly.Benefited from the accumulation of EPS contents,AOB could be immobilized by granular sludge effectively.In addition,the selective inhibition of nitrite-oxidizing bacteria caused by both free ammonia（FA）and free nitrous acid（FNA）during the aeration time was the other main factor for stable partial nitrification.3.Based on batch experiments,the impact of zero valent iron nanoparticles（n ZVI）dosage on the performance of granular nitrosation sludge（NGS）was evaluated in this study.Results indicated,the activity of ammonia oxidation bacteria（AOB）would be enhanced significantly,while the removal efficiency of ammonia nitrogen higher than 95%,and the increase of specific accumulation rate of nitrite concentration（μ（NO₂--N））from 27.3 mg·g^-1·h^-1 to 30.7 mg·g^-1·h^-1 were recorded,with dosing more n ZVI in the range of 0 to 10 mg·L^-1.During the same period,it promoted the production of both polysaccharide and protein in EPS effectively.However,AOB exhibit a lower activity,as well as the apparent loss and accumulation of polysaccharide in EPS and SMP were observed respectively,when the dosage of n ZVI was higher than 25 mg·L^-1.While the initial n ZVI concentration reached 700 mg·L^-1,the value of μ（NO₂--N）was only 17.5 mg·g^-1·h^-1,being equal to 64.1% of the control group.The analysis of scanning electron microscope and energy spectrum analysis showed that the strong adsorption of n ZVI to NGS brought the severe damage of microbial ecology.4.To investigate the ability of NGS to resist the impact of n ZVI with different particle sizes.The results showed that when n ZVI dosage was less than 100 mg·L^-1,particle size of NGS nitrification properties improved,μ_NO2--Nand μ_NO3--Ncompared with the blank group increase of 11% and decline of 15.3% respectively.When the n ZVI dosage reached 900 mg·L^-1,the performance of the sludge will be significantly reduced.In contrast,the addition of low concentration n ZVI did not play a role in promoting the performance of large particle size NGS.When the n ZVI dosage was more than 500 mg·L^-1,the sub nitrification performance of large size NGS will be completely suppressed.By the Haldane kinetic model,the inhibition of n ZVI to SOUR-A was a non competitive inhibition（R2 = 0.9882 and 0.9891）.In addition,with the increase of the dosage of n ZVI,the content of EPS in sludge appeared to increase firstly and then decreased.The adsorption of NGS on n ZVI conformed to Langmuir and Freundlich isothermal adsorption equation.Large size NGS of the adsorption rate was faster,but the adsorption capacity was lower.It may be relevant to the small size NGS with smaller surface microporous aperture was and the more compact structure was.