Enhanced Cultivation And Chaficteritics Of Algal-Bacterial Granular Sludge

Algal-bacterial aerobic granular sludge(ABGS)is a new type of bacteria and algae symbiosis system,which has the advantages of excellent sedimentation performance,efficient nitrogen and phosphorus removal ability,high recycling value,etc.,solves the difficulty of collecting microalgae and the problem of loose immobilization of bacteria and algae,and it is expected to greatly reduce the aeration energy consumption of wastewater treatment systems.It is a sewage treatment strategy with huge application prospects.However,ABGS was found too short,so people do not know enough about the cultivation process and unique characteristics of this granules,and there is currently no attempt to use ABGS to produce oxygen instead of artificial aeration.These factors have seriously hindered the practical application of ABGS.This thesis focuses on the culture process and granular performance of ABGS,in addition,a laboratory-scale attempt is made on the application of ABGS under low aeration.The purpose is to explore the fast and stable granulation method and mechanism of ABGS,and provide some reference for the practical application of ABGS.The main research contents and conclusions are as follows:(1)An algal-bacterial aerobic granular sludge with excellent decontamination performance and stability was cultivated at a low temperature(12±4℃),and the granular characteristics of ABGS were studied by comparison with conventional aerobic granular sludge(AGS)cultured at the same time.The formation process of ABGS is similar to that of conventional aerobic granular sludge.It can be considered as a self-aggregation process of microorganisms.The granulation process requires the activation of quorum sensing and the adhesion of extracellular polymers to microorganisms.The amount of algae has a certain effect on the formation of the granules and the properties of the granules.According to the experimental results,it is found that the lack of algae biomass can prolong the time required for normal granulation and reduced system decontamination efficiency;but more algae have Conducive to the normal formation of ABGS and the efficient decontamination performance of the system.Compared with conventional AGS,the particle size of ABGS is smaller,so the corresponding sedimentation speed will be slower,and the hydrophobicity of the particle surface will be lower,but the density and biological activity of ABGS are relatively high.(2)A culture method and mechanism for accelerating the granulation of algal-bacterial aerobic granular sludge by applying a low-intensity magnetic field was proposed.We analyzed the sludge and water quality indicators during the cultivation,the biological and physical and chemical properties of the sludge such as EPS,density,elemental composition,and microbial community composition.It is proved that the application of low-intensity magnetic field can accelerate the formation of ABGS.The main formation mechanisms are:low-intensity magnetic field increases the algae growth rate in the reactor,algae with higher content is beneficial for a tight combination of algae and bacteria,thereby promoting the formation of ABGS;inorganic ions enriched in low-intensity magnetic field can accelerate The formation of crystal nuclei,and is also conducive to ionic bridging in extracellular polymers,thus accelerating the formation of ABGS.As a simple and economical method for cultivating algal-bacterial aerobic granular sludge,the application of a magnetic field to accelerate the formation of ABGS has positive significance for the practical application of ABGS.(3)Reduce the aeration of the system and maintain it for a period of time,observe and study the performance of ABGS and conventional AGS.It was found that after reducing the aeration amount,ABGS can maintain efficient decontamination performance and stable particle morphology,while the traditional aerobic granular sludge has a lower N and P removal efficiency and a lower hydrophobicity,which shows that the ABGS system is more suitable for lower aeration.Through batch tests of oxygen and monitoring of specific oxygen consumption rate and specific oxygen production rate,it was found that the ABGS system produced enough oxygen to maintain the stability and efficiency of the system.When ABGS is placed in a non-aerated light shaking incubator,it has considerable decontamination performance after a certain period of adaptation.However,the problem that is difficult to overcome is that algae no longer completely adheres to the surface of the granules,resulting in suspended algae in the effluent.