Influence Mechanisms And Effects Of Anionic Surfactant On Aerobic Denitrification In Polluted And Compound Urban Water

Aerobic denitrifiers are widely used in water treatment with the advantages of simultaneous nitrification-denitrification and high dissolved oxygen tolerance.However,the efficiency of denitrification is prone to influence by the external environment.Some cities have formed seriously polluted composite water,which is due to the unclear division of residential areas and production and commercial areas,and the integrated mixing system of rain and sewage.In addition to the nitrogen,the pollutants existing in the water includes anionic surfactants,metal ions and other pollutants.The aerobic denitrification efficiency,oxygen transfer efficiency and the removal efficiency of other pollutants may be influenced by anionic surfactants when the technology of aerobic denitrification was used to treat nitrogen-polluted water.Additionally,the influenced mechanism varies considerably depengding on the environmental conditions and coexisting-pollutants.Therefore,this study analysed the influence of sodium dodecyl benzene sulfonate(SDBS)and sodium dodecyl sulfate(SDS)on aerobic denitrification.Secondly,the effects of anionic surfactants on aerobic denitrification efficiency and the microbial community structure were analysed under different concentrations of Fe²⁺,Mn²⁺and Cr(?).Thirdly,the effects of SDBS and SDS on water oxygen transfer efficiency,aerobic denitrification efficiency and microbial community were analysed.Finally,water treatment experiments were carried out to explore the feasibility of using aerobic nitrogen removal technology to treat nitrogen-containing pollutants water,and the optimization of technical parameters was discussed.The results can provide theoretical basis for the treatment of serious urban pollution.The main conclusions are as follows:(1)The anionic surfactant could inhibit or stimulate aerobic denitrification,which is related to the concentration of anionic surfactant.The removal efficiency of total nitrogen(TN)decreased with the concentration of SDBS increased.When the SDBS concentration was 100 mg/L,the TN removal efficiency was the minimum(4.04%).Compared with the Control,the activities of nitrate reductase(NR)and nitrite reductase(Ni R)involved in denitrification were the lowest(13.83%and 32.55%respectively),and the Achromobacter only accounted for 3.13%while the Cupriavidus accounted for74.06%.With the increase of SDS concentration,the TN removal efficiency presents a tendency of increase firstly and then decreased.When the SDS concentration was 50mg/L,the TN removal efficiency was the maximum(71.71%).Compared with the Control,the activities of NR and Ni R separately were 102.31%and 87.67%.When the SDS concentration was 100 mg/L,NR activity was the minimum(74.64%).The dominant genus in SDS-50 were changed from Cupriavidus(accounted for 40.40%)and Agrobacterium(accounted for 29.40%)to Cupriavidus(accounted for 50.45%),and the relative abundance of Agrobacterium was falling to 20.40%.In conclusion,SDBS and SDS affect the denitrification efficiency by controlling the community structure,enzyme activity and cell membrane permeability.(2)The SDBS and SDS had a stronger promotion effect on aerobic denitrification by increasing of the Fe²⁺concentration,and the maximum TN removal efficiency was respectively 62.84%and 70.46%(Fe²⁺concentration was 2 mg/L).Pearson also showed that the Fe²⁺concentration had significant positive correlation with the TN removal efficiency.The abundance of Cupriavidus and Achromobacter(42.11%and37.43%,respectively)in SDBS-Fe and the abundance of Cupriavidus and Agrobacterium(43.71%and 39.72%,respectively)in SDS-Fe had no significantly changed.It was speculated that the complexes(Fe²⁺-SDBS and Fe²⁺-SDS)could provide electrons for the denitrification process and promote denitrification efficiency.With the concentration of Mn²⁺and Cr(?)increasing,the effect of SDBS and SDS on aerobic denitrification first increased and then decreased.The maximum removal efficiency of TN was appeared in SDBS-Mn-0.5(56.08%)and SDS-Mn-1(57.40%)after adding Mn²⁺,respectively.The maximum TN removal efficiency was appeared in SDBS-Cr(?)-1(60.23%)and SDS-Cr(?)-0.25(57.43%)after adding Cr(?),respectively.It indicated that the low concentration of complexes(Mn²⁺-SDBS,Mn²⁺-SDS,Cr(?)-SDBS and Cr(?)-SDS)could promote the denitrification efficiency while the high concentration of the complex will inhibit it.Compared with the aerobic denitrifiers in SDBS-Control,the abundance of Cupriavidus in SDBS-Mn and SDBS-Cr(?)increased to 57.34%and 73.83%,respectively,while that of Acromobacter decreased to 20.73%and 15.9%,respectively.Compared with SDBS-Conrol,Cupriavidus in SDS-Mn and SDS-Cr(?)increased to 57.31%and79.25%,respectively,while the abundance of Agrobacterium decreased to 24.93%and9.91%,respectively.It was postulated that the TN removal efficiency was related to these microorganisms.(3)The increase of quantity aeration and modes would dramatically improve the nitrogen removal efficiency in the groups of SDBS.The TN removal efficiency increased from 57.50%(SDBS-1L/min)to 74.84%(SDBS-2 L/min)and from 63.43%(SDBS-I)to 72.58%(SDBS-C),respectively.However,the TN removal efficiency of SDS groups had no significantly changed.It was indicated that the changes of aeration condition could effectively improve the tolerance of aerobic denitrifiers to SDBS toxicity.A significant positive correlation between aeration and TN removal efficiency was analyzed by Pearson.The community structure and the abundance of nitrogen metabolism genes of aerobic denitrifiers was significantly changed by aeration modes and quantity aeration.The abundance of Acromobacter and Comamonas in SDBS and SDS increased with the quantity aeration increased,while Cupriavidus and Acinetobacter decreased.The abundance of Nap AB and Nir K in SDBS and SDS increased with quantity aeration increased,while the abundance of Nir S decreased.In addition,the abundance of Acromobacter and Pseudomonas in SDBS and SDS increased with the change of aeration modes,while the abundance of Cupriavidus and Agrobacterium decreased significantly.Furthermore,the abundance of Nap AB and Nir K increased with the abundance of Nir S decreased.It was speculated that the TN removal efficiency were related to nitrogen metabolism genes and aerobic denitrifiers.(4)Based on the results above,the experiments were explored by adjusting the process parameters of quantity aeration,aeration modes,and whether to add iron powder.It could be seen that the highest denitrification efficiency was observed in Group 4(quantity aeration of 2 L/min,continuous aeration and iron powder).The maximum removal efficiency of TN,NO₃^--N and NH₄⁺-N were 67.32%-71.48%,67.14%-68.21%and 69.81%-71.61%,respectively.The abundance of Cupriavidus,Acromobacter and Pseudomonas increased with the iron powder and quantity aeration increased.A significant positive correlation between NH₄⁺-N and TN removal efficiency and the abundance of Pseudomonas was analyzed by Pearson.In summary,this study analysed the effects of anionic surfactants and coexisting metal ions on aerobic denitrification in Li Wan River where was defined as the heavily polluted and compound water,and a significant dose relationship was observed.The effect of anionic surfactant types,aeration conditions,quantity aeration and aeration modes on aerobic denitrification under aeration conditions was discussed.In addition,a simulation experiment of water with such characteristic was carried out based on the conclusions.The results show that adding the appropriate amount of iron powder to increase quantity aeration and change aeration mode can effectively enhance the efficiency of aerobic denitrification.This study finds a new way to the pollution source control of complex heavily polluted water,and also provides guidance and reference for aerobic denitrification technology.