Study On The Start-up And Preliminary Application Of Mixed Algae Bioreactor

There are many kinds of microorganisms in the field waters such as bacteria,zooplankton,phytoplankton,and the environmental conditions change greatly.Which makes the physiological properties of pure algae cultured by traditional indoor culture method different from that of wild microalgae.The relevant experimental conclusions based on the pure algae may also be difficult to apply to the field algae.In addition,it has limitations in the study of physiological characteristics,metabolites transfer and nutrient utilization of microalgae.Because microalgae in traditional culture system were significantly affected by culture time and environmental conditions,making it difficult to capture the physiological status of algae cells.Therefore,it was urgent to find a microalgae culture method which can cultivate microalgae similar to those in the field and provide a steady stream of algae source for the follow-up study of the mechanism of water bloom or control measures.In this study,a method of microalgae culture was proposed.It was continuously cultured using a modified chemostat to obtain a stable algae source similar to wild blooms,with field water as raw water and microalgae as algae source.On this basis,the effects of different dilution rates and nutrient on the water quality,phytoplankton and bacterial community structure were explored.Then the response of photosynthetic activity of mixed microalgae to light time was analyzed.The results showed that the dilution rate 0.2 reactor reached the stable stage on the Day 11 both in the low and high nutrient stage.The dilution rate of 0.3 reactor in the low and high nutrient stage on the Day 15 and Day 11,respectively,and the dilution rate of 0.4 reactor on the Day 14 and Day 10,respectively.In the low nutrient stage,Chl a gradually decreased from 46.12?g·L^-1 at inoculation and then increased.Chl a concentration of the dilution rate 0.2,dilution rate 0.3 and dilution rate 0.4 reactor were24.38?g·L^-1,43.46?g·L^-1 and 11.24?g·L^-1 at stable stage,respectively.And the removal rates of TN and TP were 40%-60%and 76%-85%respectively.n the high nutrient stage,Chl a gradually increased with incubation time,and finally stabilized at48.22?g·L^-1,111.99?g·L^-1 and 197.39?g·L^-1,respectively.The removal rates of TN and TP were 87%-90%and 86%-93%,respectively.The results showed that the nutrient of influent and dilution rate had significant effects on the water quality and biomass.Nitrogen and phosphorus in low-nutrient stage are all restricted nutrients,so it can be fitted by double-substrate limited growth kinetic model.While nitrogen and phosphorus in high-nutrient stage are not restricted nutrients,and the substrate that restricts their growth may be carbon or other trace elements.Although the yield of microalgae with low nutrients is low,the utilization of nutrients per unit of microalgae is high and nutrients are low,so low nutrient culture is a better culture scheme.The microbial community structure in the reactor at the stable stage of low and high nutrients was analyzed.It was found that nutrients and dilution rate had significant effects on the algal cell density and dominant species.In the low nutrient stage,the dilution rate 0.2 reactor formed cyanobacterial blooms do minated by Limnothrix,Merismopedia and Chlorella.The dilution rate 0.3 reactor formed cyanogreen blooms dominated by Limnothrix,Merismopedia,Chlorella and Selenastrum.The dilution rate0.4 reactor formed cyanogreen blooms dominated by Merismopedia and Chlorella.In the low nutrient stage,The dominant cyanobacterial blooms were Limnothrix and Chlorella in all reactors.The results of high throughput sequencing showed that Cyanobacteria,Proteobacteria,Actinobacteria and Bacteroidetes were abundant bacterias at phylums level in the reactor.At genus level,bacterias with abundances above 0.5%were higher and microbial community structure was richer in the low nutrient stage than in the high nutrient stage.But the dominant bacterial at genus level in different reactors were significantly different.The correlation analysis between microorganisms and environmental factors showed that TP,pH,Chl a had significant influence on the microbial community structure.hgcI_clade had significant influence on the dominant algae Limnothrix and Chlorella.It showd that environmental factors have a degree influence on the microbial community in water system.At the same time,there are mutual promotion and restriction among microorganisms.The effects of illumination time on the photosynthetic activity of microalgae at the stable stage in the high nutrients were investigated.It was found that the photosynthetic activity obtained was higher than that in the field.And the photosynthetic activity was significantly affected by illumination time,while different photosynthetic activity parameters were different.Fv/Fm changed greatly,and increased with the increase of illumination time.Fv/Fm of cyanobacteria and diatom reached stability after 6 hours of illumination,while green algae did not reach stability after 12 hours of illumination.The?changed smoothly during the whole illumination period.rETR_max and I_k vary greatly and irregularly with the increase of illumination time.Relevance analysis showed that Chl a was negatively correlated with Fv/Fm,?,rETR_max,I_k,and Fv/Fm.and?reached significant levels.?was positively correlated with Fv/Fm,rETR_maxax and I_k,and rETR_max was positively correlated with I_k.These indicated that these photosynthetic activity parameters affected each other.And the photosynthetic activity was related to the species and biomass of microalgae.The species and density were different under different dilution rates,which made the photosynthetic activity different.