Rapid Cultivation Of Aerobic Granular Sludge For Treating Formaldehyde Wastewater

Aerobic granular sludge treatment of formaldehyde wastewater can slow down its toxic impact and avoid phenomenon of sludge bulking.Aiming at the problem of long start-up time of aerobic granular sludge cultivation,anaerobic granular sludge was used as seed sludge to transform aerobic granules by aeration to shorten start-up time,and its transformation process was analyzed.Then,using the above methods,SBRs of different aeration rates were established to cultivate aerobic granular sludge with the ability to degrade formaldehyde;The influence of the aeration rate on the degrading-formaldehyde aerobic granular sludge was explored through analysing the granules properties and reactor performance;Finally the microbial community structure and functional genes in different reactors were analyzed by high-throughput sequencing.When anaerobic granular sludge was used as seed sludge,sodium acetate was used as carbon source,and the aeration rate was 1 L/min,the 4-6 days of operation,the color of granules was from black to orange,and aerobic granular sludge was cultivated successfully.In the process,the particle size of granular sludge decreased gradually from 2-5 mm to 0.5-3 mm;The settling rate increased from 2.29 cm/s to2.98 cm/s,and the sludge activity increased,c ATP content increased to 6616.48ng/g SS.In the process of anaerobic granular sludge transformed to aerobic granules,the abundance of anaerobic microorganism Longilinea in the reactor decreased from10.67%to 4.51%,and aerobic or facultative microorganisms such as Syntrophobacter（16.20%）,Flavobacterium（10.94%）and Pseudomonas（7.15%）were enriched in the reactor.The change of relative abundance of microorganisms in the reactor reflected its response to the change of culture conditions.On this basis,sequencing batch reactors（SBRs）R1-R4 with 0.25 L/min,0.5L/min,1 L/min,1.5 L/min aeration rates were established to cultivate degrading-formaldehyde aerobic granular sludge.The formaldehyde concentration increased from 50 mg/L to 150 mg/L during operation.The results indicated:Within 7d of operation,orange aerobic granular sludge was formed in R1-R4.A large number of zoogloea appeared on the surface of granules when the concentration of influent formaldehyde increased to 150 mg/L.SEM showed,microorganisms in aerobic granules with formaldehyde were mainly cocci,and the cells were arranged tighter under high aeration with more cellular secretion on the surface.extracellular polymeric substances（EPS）measurements showed,the aeration rate had a certain effect on the secretion of EPS by microorganisms,among which the EPS amount in the R4 reactor was the highest,up to 330.72 mg/g SS,this reflected the microbial response to formaldehyde and high aeration.The water treatment performance of the four reactors was gradually optimized from the start of the reactor to 62 days of operation.The removal efficiency of formaldehyde could always reach over 95%in R1-R4;The removal efficiency of COD in the reactor reached over 90%;The nitrification of the reactor gradually increased,NH₄⁺-N removal efficiency was stabilized above 98%finally;The TN removal efficiency of R1-R4 were 95.1%,81.9%,72.5%and 76.5%,respectively,the TN removal efficiency of R1 was the highest,because of the large particle size of the granules in R1,which provided favorable conditions for denitrification.High-throughput sequencing of mature aerobic granules from the R1-R4 on the62nd day showed:Compared with anaerobic granules,the diversity and abundance of bacteria in R1-R4 increased significantly,and a large number of functional bacteria were enriched,such as formaldehyde degrading bacteria:Paracoccus,Methanothrix,Methanobacterium and Methanomassiliicoccus,nitrification and denitrification bacteria:Thauera,EPS excretion bacteria:Gemmatimonas and Comamonas;Compared with aerobic granules based on sodium acetate,formaldehyde degrading bacteria enriched in degrading-formaldehyde aerobic granules with a total abundance of over 27.02%.Based on the prediction results of KEGG functional genes:the enrichment of enzyme genes associated with formaldehyde degradation and nitrification-denitrification in degrading-formaldehyde aerobic granules,the good treatment performance of the reactor for formaldehyde wastewater was explained from the microbial community and functional gene level.In this study,aerobic granules with good properties was successfully cultivated,which provided a new idea for the degradation of formaldehyde.