Study On The Efficacy Of Mycelium Pellets In Regulating Filamentous Bulking Sludge

Filamentous sludge bulking is the most common operation problem in activated sludge wastewater treatment system.At present,the main measures to deal with sludge bulking are adding flocculants,weight gain agents or fungicides in order to rapidly improve the sludge settlement performance.However,the sludge bulking in this treatment method is easy to occur repeatedly,and the reagent cost is expensive.There is also a method of using biological selector to control sludge bulking,which can better solve the problem of repeated overgrowth of filamentous bacteria,but the construction cost is high,the treatment cycle is long,resulting in increased operating costs.As a biomass carrier,mycelium pellet have good sedimentation performance,adsorption performance and biocompatibility,and the cost is low,which has the potential to regulate the sedimentation performance of expanded sludge.In order to solve the problem of filamentous sludge bulking,this thesis proposed a biological control method based on mycelium pellet to improve the performance of bulking sludge.Combined with the strengthening measures such as activated carbon and bio-flocculant,the feasibility of mycelium pellet for regulating filamentous sludge bulking was discussed.Combined with the variation law of microbial community structure,the potential mechanism of mycelium pellet for regulating filamentous sludge bulking was analyzed.In this study,the biological control technology of mycelium pellet for sludge bulking was innovatively proposed.The research results provided the preliminary basis and support basis for the further in-depth and systematic study of the theoretical system and operation parameters optimization of the technology,and had very important application value and guiding significance for solving the problem of sludge bulking in the activated sludge system.In order to study the biological inhibitory effect of mycelium pellet on the growth of filamentous bacteria,Sphaerotilus natans,a typical filamentous sludge bulking microorganism,was mixed with mycelium pellet.The results showed that the mycelial growth of S.natans could be effectively inhibited by adding mycelium pellet into the special CGY culture medium beneficial to the growth of S.natans.The actual wastewater from municipal wastewater treatment plant was used as the influent substrate to investigate the efficacy of mycelium pellet in regulating the performance of filamentous bulking sludge in SBR reactor.The results showed that adding mycelium pellet could effectively improve the settling performance of filamentous bulking sludge.When the addition ratio of mycelium pellet(V_{mycelium pellet}/V_{30min settling sludge})was 25%,the sludge volume index SVI₃₀decreased rapidly from235m L/g to 107m L/g two days before operation.Compared with adding 1g/L powdered activated carbon in the system,the sludge SVI₃₀value can be reduced from 235m L/g to73m L/g,adding 25%(V_{mycelium pellet}/V_{30min settling sludge})mycelium pellet combined with0.5g/L activated carbon,5‰biological flocculant and other strengthening measures can achieve similar effect(sludge SVI₃₀reduced to 78-82m L/g).Different from the physical and chemical control methods of expanded sludge,adding mycelium pellet can improve the protein content of extracellular polymeric substances（EPS）in activated sludge system,enhance the hydrophobicity of sludge and improve the sludge sedimentation performance.Due to the hydraulic conditions and other factors of the system operation,the mycelium pellet began to dissolve after 8 days of operation,and the mycelium pellet were completely broken on the 17th day.The scattered hyphae formed a new sludge aggregates as the skeleton of activated sludge bacterial micelles,but the total sludge of the system did not increase due to the addition of mycelium pellet.During the operation period,Bellworms and rotifers appeared in the system,indicating that the activated sludge system was mature and stable,and the water quality was good.As a biological control measure,mycelium pellet can effectively improve the deterioration of sludge sedimentation caused by filamentous bacteria and simultaneously improve the removal efficiency of pollutants in sewage.After 3 days of operation,the COD removal rate increased from about 50%to about 80%,and the ammonia nitrogen removal rate increased from about 50%to about 98%after 10 days of operation.It can be seen that mycelium pellet have the effect of improving the settling performance of expanded sludge,and have the feasibility of controlling filamentous bulking sludge.Mi Seq high-throughput sequencing technology was used to analyze the microbial community structure,diversity and function of mycelium pellet in the regulation of expanded sludge.The results of bacterial community structure analysis showed that the abundance and diversity of bacterial species were improved after the sludge bulking problem was effectively repaired.During the regulation process,the abundance of Caldilineaceae and Flavobacteriaceae decreased,while the abundance of Zoogloea,which secreted viscous substances,increased.The results of fungal microbial community structure analysis showed that the abundance and diversity of fungal species decreased and returned to the normal activated sludge level with the operation of mycelium pellet to repair the expanded sludge system.If only activated carbon was added,the fungal community structure in the sludge system was similar to that of the original expanded sludge even if the performance of expanded sludge was improved.The results of bacterial function analysis showed that during the operation of the system,the carbon cycle-related function was enhanced,the organic degradation ability of macromolecules was improved,the sulfur production ability was reduced,and the sulfur oxidation ability was enhanced.