| In recent years,the Algal-bacterial granular sludge(ABGS)formed by combination of aerobic granular sludge(AGS)and microalgae has attracted much attention in wastewater treatment.In photoreactor,bacteria and microalgae could form ABGS through self-coagulation.In the actual living environment,the time ratio of light to darkness(light-dark ratio)has periodic variation,which has a significant effect on the growth and activity of microalgae.However,the ecological effect mechanism of light-dark ratio on bacteria-algae symbiosis during the formation of bacteria-algae symbiotic granular sludge is not clear.In addition,in order to shorten the culture cycle of granular sludge,the stored mature bacteria-algae symbiotic granular sludge is often used for inoculation,the performance of this kind of granular sludge needs to be further studied.Therefore,this study explored the effects of different light-dark ratios(0h/24 h,8h/16 h,16h/8h and 24h/0h)on the formation of ABGS,and made clear the shaping of the ecological relationship between bacteria and algae by analyzing the physicochemical properties,biological characteristics and community structure of granular sludge.Moreover,the mature granular sludge was stored in cold storage(4℃,100 d)and then cultured to compare and analyze the difference of biochemical properties,pollutant removal efficiency and community structure between AGS and ABGS.This study can provide a valuable reference for the cultivation,storage and re-culture of ABGS.The main results are as follows:(1)After 102 days of culture,the particle size of granular sludge cultured in 4 systems with different light-dark ratio(0h/24h(R1),8h/16h(R2),16h/8h(R3)and 24h/0h(R4))was R1>R3>R4>R2.The results of scanning electron microscope showed that there were significant differences in the morphological characteristics of granular sludge among the 4 systems.By comparing MLSS,MLVSS,SVI,sludge moisture content,particle integrity coefficient(IC),relative hydrophobicity(RH),extracellular polymer,chlorophyll content and oil content in each system,it was found that in R3 system,granular sludge showed the tightest structure,the highest chlorophyll content and the highest oil content.In R4 system,the biomass of granular sludge was the highest and its resistance to mechanical impact was the strongest.(2)The analysis results of the pollutant removal ability of the four reaction systems showed that the removal efficiency of TOC,ammonia nitrogen,total nitrogen and orthophosphate were more than 90%,85%,58% and 55% respectively.The analysis results of microbial communities in different systems showed that there were significant differences in miciobial communities among the 4 kinds of granular sludge,the dominant species accounted for the largest proportion of total biomass in R3 system,and the relative abundance of Thauera,Nitrospira,Paracoccus and Leptolyngbya in the 4 kinds of granular sludge was high.(3)In the experiment of activity recovery of granular sludge after cold storage at 4℃,both AGS and ABGS showed strong recovery ability.After 92 days of recovery culture,AGS had a larger particle size than ABGS.Compare with AGS,ABGS had lower moisture content,tighter particle structure,higher chlorophyll content and stronger stability.Both AGS and ABGS showed strong pollutant removal ability: the removal rates of TOC,ammonia nitrogen and total nitrogen were more than 90%,94% and 63%,respectively.(4)The results of community structure analysis of AGS and ABGS before and after cold storage and recovery culture showed that the bacteria with higher abundance in ABGS before inoculation was Micropruina,while the higher abundance of bacteria in AGS was Thauera.The bacteria with higher abundance in the two systems after cold storage and recovery culture were Thiothrix,Enterobacter,Paracoccu and Acinetobacter,indicated that the bacterial community structure of AGS and ABGS systems changed after cold storage and recovery culture.This study not only provides a new research idea for the construction of ABGS system and the improvement of sewage treatment efficiency,but also provides the theoretical basis and data support for the research of ABGS system,and promotes the practical application of ABGS technology. |
PDF Full Text Request