Study On The Growth Regulation And Modification Of Mycelial Pellets Of Aspergillus Niger 557 By Optimized Culture System

Mycelial pellets are used as biocarriers in the field of immobilization of functional microorganisms,because they have high biocompatibility,easy preparation process,and no toxic effects.The team has used mycelium pellets to load activated sludge to conduct research on artificially producing aerobic granular sludge.To obtain granular sludge with stable structure,the mycelium pellets as the core carrier have extremely high requirements.At present,when using conventional pellets for granulation,there are two main problems.First,the biological yield is not high enough to meet the granulation requirements.Second,the characteristics of the carrier are unstable and cannot be stored for a long time.The biological yield and carrier characteristics of the pellets are greatly affected by the culture system.Therefore,by optimizing the cultivation conditions,not only can the biological yield of the pellets be improved,but also the preliminary modification of the biological carrier can be completed to obtain pellets with dense,stable and excellent characteristics.This is an effective means to solve the current pellets application problems.In this study,Aspergillus niger 557 with good formation effect was used as the starting strain,considering the influence of different culture factors on the morphological structure and growth parameters of pellets,the cultivation conditions were explored one by one,and the entire culture system was finally optimized.The optimized expansion system is: constant temperature 30?,160rpm/min,each 250 ml conical flask is filled with 150 m L culture medium,spore inoculation volume is 104/150 m L,carbon source is sucrose,concentration is 10g/L,nitrogen source is NH4NO3,concentration is 1.5g/L,KH2PO4·3H2O1g/L,Mg SO4·7H2O 0.51g/L,initial p H 6.0.Compared with the original culture system,the pellets of the new culture system is mellow and dense,with a slight increase in biological yield.At the same time,the upper limit of mycelium density is increased by 51.4%.And the culture time is significantly shortened,18 hours ahead that meets the access criteria.The pellets formation mechanism of Aspergillus niger 557 under the optimized expansion system was investigated.The experimental results show that in addition to the conventional spore aggregation formation mechanism,there are also three specific pellets formation mechanisms in the optimized expansion system,which are mycelial reunion,fragments reconstruct and swallowed-assimilated into pellets.The respective regulation methods and intervention time of the four ball-forming mechanisms were explored,and the effects of each mechanism on the growth of the groups' number and the particle size distribution of each period were analyzed.Based on this,the four major periods of population growth are summarized,namely the pre-growth period and the sudden growth period dominated by the conventional mechanism,the secondary growth period dominated by the specific mechanism,and the decay period after all mechanisms stop functioning.The particle size distribution model is influenced by the conventional mechanism and the specific mechanism,and then it shows two evolution modes of single peak shift in regular period and double peak alternation in irregular period.The optimized expansion system has an excellent modification effect on the mycelium pellets.The settlement experiment results show that the optimized pellets have significantly improved settlement.The destructive experiments prove that they have stronger stability and anti-swelling and floating properties.The adsorption of functional bacteria is remarkable,and SEM shows that the optimized mycelial density and pore distribution of the carrier are more reasonable.At the same time,related factors that affect the characteristics of the carrier such as individual particle size,growth area and physiological activity were studied.The modified pellets were used as biological carriers,and single function bacteria as well as activated sludge were used as loading objects,respectively.SEM results show that the effect of hanging film of functional bacterial has changed from the early "point adsorption" to the later "surface adsorption",while the effect of activated sludge has changed from the early "surface adsorption" to the later "body adsorption",the latter has a faster hanging film rate and better loading effect.