| Microalga-bacteria aggregates(MABAs)is a new type of biofilm and wastewater treatment technology formed by microalgae and bacteria,which satisfys the needs of current recycling biological economy and sustainable development.Compared with the traditional activated sludge process,it has lower energy consumption,higher pollutant removal efficiency and better resource recovery prospect.MABAs can be divided into static MABAs and hydraulic MABAs according to different cultivation methods.Among them,the study of static MABAs is still in its infancy,and the influence of the characteristics of inoculated sludge,organic carbon sources and other culture conditions on the formation of static MABAs is still unclear.Moreover,the cultivation of hydraulic MABAs is usually carried out under aeration condition,which weakens the energy saving benefit of MABAs system.In addition,different culture conditions and culture methods will lead to different aggregate structures and symbiotic relationship between microalgae and bacteria,and different symbiotic mechanisms of microalgae and bacteria in wastewater treatment.Therefore,it is necessary to study the culture of the two MABAs and the symbiotic mechanism of algae and bacteria,which will help to accelerate the practical application process of MABAs.Based on this,this thesis explored the cultivation of static MABAs and hydraulic MABAs without aeration and the symbiotic mechanism of algae and bacteria in the treatment of pollutants,aiming to give full play to the energy saving advantages and emission reduction potential of MABAs and provide theoretical basis for its practical application.The main research contents and conclusions include:(1)Cultivation of static MABAs and its symbiosis mechanisms.The effects of exogenous organic carbon source and settling ability of inoculated sludge on MABAs formation were investigated under static condition without aeration,and the symbiotic relationship and oxygen production capacity of MABAs were also studied.The results showed that MABAs could be formed in the experimental group with poor sludge settling ability under static condition.Whether or not organic carbon source was added resulted in different granulation mechanism.The starvation environment without additional organic carbon source resulted in higher success rate of MABAs culture and shorter formation time.The concentration of total phosphorus(TP)and tightly bound extracellular polymer(TB-EPS)in the successful group were significantly higher than that in the failed group.Microbial community analysis showed that filamentous phosphorus-accumulating organisms(such as Run-SP154)in the inoculated sludge,and spontaneous growth cyanobacteria(Cyanohece)created conditions for the successful cultivation of static MABAs.M ABAs had stable and excellent pollutant removal efficiency and net oxygen production capacity without aeration.Theoretical calculations and changes in pollutant concentrations indicated that cultured static MABAs could remove pollutants through nitrification,denitrification and assimilation of algae and bacteria.In this study,it was found for the first time that the phosphorus release process and starvation conditions were beneficial to the cultivation of static MABAs,providing a new idea for its rapid cultivation.(2)Cultivation of hydraulic MABAs and its symbiosis mechanisms.MABAs systems of different C/N wastewater were constructed without aeration at hydraulic conditions,in order to study the formation process of MABAs,the pollutant removal capacity and symbiosis mechanisms of algae and bacteria.The results showed that compact,stable and good sedimentation MABAs could be formed from spontaneous chlorella in the wastewater C/N systems of 8 and 2 respectively,and TB-EPS might play an important role in the formation of aggregates.Different C/N resulted in different symbiotic relationships between algae and bacteria.At C/N=8,the symbiotic system of ammonia oxidizing bacteria(AOB),nitrite oxidizing bacteria(NOB),heterotrophic bacteria(HB)and algae was assembled when the system was stable.However,when C/N=2,the symbiotic system of AOB,HB and algae was formed due to the double inhibition of NOB by high free ammonia(FA)and low dissolved oxygen(DO),which could achieve stable short-cut nitrification.The analysis of symbiosis mechanisms between algae and bacteria showed that under high C/N conditions,bacterial assimilation removed 69.53%C and 30.6%N,nitrification removed 38.45%N,and algal assimilation removed 53.34%C and 32.87%N.Under low C/N conditions,62.17%C and 9.86%N were removed by bacterial assimilation,12.73%N by nitrification,and 37.83%C and 21.58%N by algal assimilation.The study confirmed the adaptability of MABAs to different C/N wastewater and the potential of pollutant removal in the non-aeration culture under hydraulic conditions,which provided a certain basic theory for the application of MABAs process. |
