| Domestic sewage treatment always remains challenging problems such as high cost,poor effects,heavy odor,and large remaining sludge output.These current problems have caused serious side effects such as heavy financial burden,secondary environmental pollution,opposition from residents,and equipment out of use.In addition,the reuse of domestic sewage is regarded as a significant potential water resource,to realize the reuse of reclaimed water through advanced technology.It can not only effectively reduce the total amount of pollutant disposed,but also protect the over-exploitation of the groundwater resource,which has important strategic significance for my country.Therefore,the development of new low-cost,high-standard water treatment technologies remains an urgent problem to be immediately solved.The micro-aerobic biology has many advantages,including good effluent quality,saving energy,and minimization of excess sludge production.However,several shortcomings,such as complexity,difficulty in control,instability of mechanical aeration,inability to remove phosphorus,and the poor quality of effluent,are necessary to be improved.To solve these issues,we employed waterfall aeration instead of traditional mechanical aeration and designed a MUOD reactor coupled with Fe-C micro-electrolysis,in which the performances were evaluated.In addition,microbial community,EPS,metabolic regularity,influent quality,and working condition characteristics are considered to be closely related.To clearly understand the pollution removal mechanism,it is greatly essential to conduct the regularity and characteristics in the MUOD reactor.The main conclusions obtained in this work are summarized as follows.(1)A MUOD reactor coupled with Fe-C micro-electrolysis by waterfall aeration was designed for treating real municipal wastewater,and the IV standard of the environmental quality standard was achieved.The concentration of DO played a key role in MUOD,and the optimized operational parameters were obtained,including the up-flow rate(3.5 m/h),waterfall height(10 cm),reflux ratio(2:1),number of stages(three),and iron dosing(a minimum amount of 2 g/L).The results showed that under the conditions of the average influent concentrations of COD,NH4+-N,TN,and TP were 131.52±10.50,20.01±1.22,21.98±1.25 and 2.59±0.25 mg/L,respectively,the elimination efficiencies of COD,NH4+-N,TN,and TP were obtained to be84.48±2.05%,99.90±0.09%,93.67±0.59%,88.52±1.50%,respectively,while the average effluent concentrations of COD,NH4+-N,TN,and TP were determined as20.30±2.32,0.02±0.02,1.39±0.09,and 0.29±0.03 mg/L,respectively.Furthermore,the DO concentration in the MUOD reactor formed a gradient distribution within the whole process.(2)The physical-chemical properties of EPS from seed sludge and MUOD reactor were compared.The protein and polysaccharide content of EPS in each chamber of MUOD were close to and above the seed sludge,while the ratio of protein and polysaccharide were less than that of seed sludge.3D-EEM analysis showed that the key components of EPS have been changed after long-term adaption to a low oxygen environment.Cell lysis released much more biodegradable substances under the microaerobic conditions,which improved the performance of the MUOD reactor.The FTIR analysis proved that the spectrums of these samples were similar,but their unique absorption peaks might be related to the important role of carbohydrates obtained in the biological wastewater treatment.MALDI-TOF-MS exhibited that the mass of EPS was between 270,000 and 290,000.Samples in the MUOD reactor were similar,but a bit different from that existed in seed sludge.Additionally,new compounds also were formed.Finally,an IC-MS coupled with online pretreatment of column switching technique was proposed to detect monosaccharides hydrolyzed from extracellular polysaccharides in the activated sludge.The results revealed its distinctive feature of the monosaccharide composition of polysaccharides(PS)and further confirmed that PS plays an important role in wastewater treatment.(3)High-throughput sequencing analysis confirmed the co-existence of various functional groups of bacteria(such as AOB,NOB,An AOB,autotrophic/heterotrophic denitrifying bacteria,GAOs,DPAOs,anaerobic fermentation bacteria,etc.)in the MUOD reactor,and indicated that nitrogen was removed via multi-mechanisms,including nitrification,partial nitrification,denitrification,and anammox.Moreover,the abundance of filamentous bacteria that caused activated sludge micro-bulking increased,which effectively enhanced the pollutant removal efficiency.(4)The metagenomic analysis further confirmed the changes of bacterial community structure in the MUOD reactor and unraveled its metabolic mechanisms at the genomic level.The bacterial community associated with carbon and nitrogen metabolisms has changed based on the KEGG database,which improved the pollutant removal efficiency.Based on the egg NOG database,the numbers of unigenes related to replication,recombination and repair and cell wall/membrane/envelope biogenesis were significantly lower in MUOD than seed sludge,while others(energy production and conversion,metabolism,signal transduction mechanisms,transcription,posttranslational modification,protein turnover,chaperones,cell cycle control,cell division,chromosome partitioning,and signal transduction mechanisms)were dramatically higher.The variation can withstand the unfavorable habitat,to improve cell vitality and removal efficiency.(5)UPLC-MS-based metabolomics revealed microbial endogenous metabolites from seed sludge and MUOD reactor,and significant differences were obtained.For example,Choline,Sucrose,Pyrrolidonecarboxylic acid,Lyso PE(16:1(9Z)/0:0),Lyso PC(18:1(9Z)),Trimethylamine N-oxide,L-Carnitine,6-Deoxyfagomine and1-(4-chlorophenoxy)-1-imidazol-1-yl-3,3-dimethylbutan-2-one were found to significantly increase in MUOD reactor,while amines and nucleic acid decreased dramatically.The variation was a response of microorganisms to the unfavorable environment,and microbial community and metabolic pathways were greatly changed,which was consistent with the results of genomics.Based on the above conclusions,the MUOD reactor has the advantages of simplicity,economy,and high efficiency,which might be utilized to overcome the shortages of the present methods,and has great theoretical and practical application significance. |
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