Effect Of Fe³⁺ On Removal Of High Ammonia Nitrogen From Simulated Slaughter Wastewater By SBBR Process

Slaughter wastewater contains high concentrations of ammonia nitrogen and organic compounds,which are difficult to remove by conventional chemical and physical methods.However,it is biodegradable and suitable for biological treatment.As one of the biological methods,sequencing batch biofilm method?SBBR?has the characteristics of simultaneous nitrification and denitrification.It does not need an external carbon source,and it can save cost and obtain high processing efficiency at the same time.Fe³⁺has higher flocculation capacity than divalent cations,and can promote the removal of nitrogen and phosphorus in biological methods,but relatively few studies have been conducted on it.The addition of iron ions into SBBR can provide reference for the practical application of biological nitrogen removal in slaughter wastewater,which has certain application value.In this experiment,simulated slaughtering wastewater was prepared according to the characteristics of slaughtering wastewater.Different concentrations of Fe³⁺ions were added in 2 L SBBR to explore their influence on NH₄⁺-N,NO₃^--N,NO₂^--N,COD,particle size,microbial community distribution and simultaneous nitrification and denitrification rate.The changes of characteristic functional groups before and after the addition of iron ions were investigated though Fourier transform infrared spectroscopy?FTIR?.The combination of element analysis and X-ray fluorescence spectrum analysis?XRF?were used to investigate the changes of element types and content in activated sludge,and the morphology and distribution characteristics of the microflora were observed by scanning electron microscope and optical microscope.The conclusions are as follows.?1?By exploring the influence of aeration volume?0.2,0.4,0.6,0.8 L/min?,aeration time?10,12,14,16 h?and concentration of Fe³⁺?0,5,10,20,30,40,50 mg/L?on nitrogen removal.It was found that,under the conditions of aeration volume of 0.6 L/min,the aeration time of 14 h,the Fe³⁺concentration of 10 mg/L,the removal rates of NH₄⁺-N and COD were92%and 97%respectively,and the concentrations of NO₃^--N and NO₂^--N were 1 mg/L and 0mg/L respectively.When the concentration of Fe³⁺is higher than 10 mg/L,it will produce biological toxicity,inhibit microbial activity and reduce the efficiency of treatment.?2?From the content of nitrate nitrogen and nitrite nitrogen,the addition of ferric iron increased the activity of nitrifying and denitrifying bacteria,enhanced their competitiveness with heterotrophic bacteria,and reduced the accumulation of NO₃^--N and the content of NO₂^--N was close to 0.The group containing Fe³⁺retained more biomass in the reactor and ensured a higher removal rate of pollutants.The addition of Fe³⁺reduced the accumulation of H⁺in the system and kept the effluent of pH relatively stable.?3?SEM and microscopic observation showed that the microbial phase in sludge containing Fe³⁺was more abundant.The system containing Fe³⁺mainly contained spherical nitrifying bacteria with finer floc particles,which reduced the mass transfer resistance of oxygen at low oxygen level.Particle size analysis showed that the addition of Fe³⁺reduced the dispersion trend of particle size distribution and ensured the uniform distribution of granular sludge in the reactor.?4?At low temperature,the E_SND of the group with and without Fe³⁺were 87.08%and78.65%respectively,and E_SND of the group with Fe³⁺was 8.43%higher than that of the group without Fe³⁺.The addition of ferric iron improved the resistance of system to low temperature loads and can obtained higher simultaneous nitrification and denitrification rate at low temperature.At high temperature,and the E_SND of the group with and without Fe³⁺were99.94%and 97.54%respectively,and the difference was only 2.4%.?5?After adding ferric iron,the number of peak and intensity of the absorption peak increased significantly.O-H stretching vibration of polysaccharide and protein,C=O stretching vibration of amide I band and the protein,and C-OH bending vibration of polysaccharide were enhanced.The results showed that the content of protein and polysaccharide were increased.