| In the context of global carbon neutrality,low-carbon and resource treatment have become an important direction for wastewater treatment in the future.The microalgal-bacterial consortium（MBC）system provides oxygen for aerobic bacteria through microalgae photosynthesis,and bacteria can provide metabolites and inorganic carbon sources for algae growth,thereby forming a good interaction relationship,improving the efficiency of biological nitrogen removal,and reducing the cost of nitrogen removal.However,as an important influencing factor of MBC system,there are still many problems in the influence of light irradiation on MBC system,such as the description of light irradiation indicators is not in line with practical factors,the light response characteristics of nitrifying bacteria are controversial,and the influence characteristics of denitrification light irradiation are not clear.In this paper,the activity test and specific response of two types of nitrifying bacteria were studied for different light energy density P values,and the advantages of MBC system and nitritation/MBC system were analyzed based on simulation theory.Furthermore,the feasibility of light-induced nitritation of municipal wastewater was explored,and the effects of light on the denitrification process,denitrification products and sludge settleability were investigated.Finally,the regulation method of rapid construction and stable operation and nitrous oxide（N2O）emission reduction of continuous flow in-situ microalgal-bacterial consortium（IMBC）system with low ammonia nitrogen municipal wastewater was studied,which provided theoretical guidance and technical support for the treatment of municipal wastewater MBC system.The main research contents are as follows:（1）Based on the photobacterial-MBC system,the key influencing factors of light treatment,such as the light power,illumination time,sludge concentration,light area,reactor effective volume were determined,and a new parameter that could accurately reflect the light distribution performance-light energy density（P,k J/mg VSS）was introduced first.Furthermore,the specific effect of the light energy density P on the nitrification performance of ammonia-oxidizing bacteria（AOB）and nitrite-oxidizing bacteria（NOB）was investigated.Specifically,suitable light energy density conditions（0.03-0.08 k J/mg VSS）could achieve"promoting A and inhibiting B",that is,promoting AOB activity and inhibiting NOB activity.Based on RT-q PCR analysis,it was found that light conditions promoted amo A and inhibiting nxr B gene expression to achieve"promoting A and inhibiting B".In addition,theoretical calculation results show that nitritation/MBC system with a nitrite accumulation rate（NAR）of 70.0%can save 18.3%oxygen and 26.6%COD demand,and produce less sludge（17.0%）compared to the traditional MBC system.（2）Based on the above research on the influence mechanism of nitritation established by light,the regulation method of mainstream（ONLSBR）and sidestream（OFFLSBR）light treatment of synthetic and real wastewater to achieve nitritation was constructed.Specifically,in ONLSBR,70%and 50%NAR obtained from the treatment of synthetic and real wastewater were achieved,respectively.The low NAR（38.2%）obtained in OFFLSBR may be due to the thickened sludge affecting the penetration of light during sidestream treatment.It was found that light induced different responses between AOB and NOB,which optimized the microbial structure of the system.On the one hand,the operation of the long-term reactor can stimulate the production of new AOBs（Nitrosomonadaceae Ellin6067,etc.）,even if the traditional AOB（Nitrosomonas）was suppressed,it can maintain the ammonia oxidation process stable and smooth.On the other hand,the number of dominant NOBs（Nitrospira）decreased by 86.5%（relative abundance）and 79.6%（OTU number）,respectively,which ensured the rapid establishment of the nitritation by light.（3）Furthermore,the effects of different levels of light energy density P on the denitrification process,the accumulation of intermediate products（NO2-and N2O）and the sludge settleability were studied.Specifically,light promotes the accumulation of NO2-and N2O by inhibiting denitrase activity,gene expression,and the production,transfer,and consumption of microbial electrons.It was found that the reduction of nitrate was significantly inhibited during denitrification（P value greater than 0.5 k J/mg VSS）,while the maximum accumulation of nitrite in the light group was 0.5 h later than that in the control group and increased by 15%,mainly due to the decrease in nitrite reduction rate（23.5%at P value of 0.8k J/mg VSS）.Moreover,the accumulation of N2O was caused by illumination（3.0 times higher than that of the control group at 0.8 k J/mg VSS）.In addition,light worsens sludge settleability by affecting EPS types and compositions and sludge surface characteristics.Light-induced secretion of S-EPS and LB-EPS helps denitrifying bacteria to establish a barrier against light at the distal end,which further affects the settleability of sludge.In addition to the content and composition of EPS,the surface properties and functions of EPS were also affected by light,resulting in the deterioration of sludge settleability,especially the increase of hydrophilic functional groups and electronegative functional groups in EPS.（4）Finally,a continuous flow IMBC system with low ammonia nitrogen municipal wastewater was constructed and stably operated under long-term light conditions,and its nitrogen removal effect,N2O emission and microbial community changes were studied in detail.Specifically,the ammonia nitrogen removal efficiency of the IMBC system was stable at 100%,and even after one month of operation shutdown,the system could recover quickly and the ammonia nitrogen removal rate was stable above 98.8%.There was no denitrification stage in the IMBC system,the average nitrate removal rate was 11.2%（16.2%,over 75 days）due to the assimilation of microalgae,while the baseline stage removal rate was zero.In addition,suitable C/N（2-3）results in chlorophyll a concentrations averaging 7.7±2.9 mg/L（Phase V）,and the photosynthesis of microalgae reduced the need for alkalinity in the system without additional oxygen and halves（96 vs 48 m L/day）.Moreover,the emission of N2O decreased significantly by 69.0%（gas phase）and 64.0%（liquid phase）in Phase V,mainly because the hydroxylamine oxidation process was regulated by hao gene and significantly inhibited under light.In addition,the microbial community in the IMBC system changed significantly,although the bacterial diversity decreased,but some light-resistant bacteria were enriched,especially the light-resistant AOB:the abundance of Nitrosomonadaceae Ellin6067 at genus level was increased from 1.2%（Phase II）to 2.4%（Phase III）and 1.5%（Phase V）respectively,which made the ammonia oxidation process stable and maintained.In this paper,the influence of light on the performance of nitrifying bacteria and denitrifying bacteria was systematically studied,a new strategy of"nitrite type"partial nitrogen removal with light regulation of sequential batch activated sludge system was proposed,and the nitrogen removal characteristics of continuous flow IMBC system under light were explored,which provided important theoretical guidance and technical support for low-carbon treatment of municipal wastewater with low ammonia nitrogen. |
PDF Full Text Request