| Aerobic granular sludge（AGS）exhibits a dense structure,quick settlement,great biomass enrichment and a large number of functional microorganisms and AGS could tolerance the impact load of wastewater and resist toxic and harmful substances.AGS technology have become hot topics in the field of water treatment research.At present,the technology is being transferred from laboratory scale to pilot and actual engineering scale.However,there are some problems in the practical application of AGS,such as long start-up time and unstable long-term operation,which limits its practical application in actual wastewater treatment.Therefore,this study first proposed the strategy of adding fungal mycelium pellets in AGS system to evaluate the influence of fungal mycelium pellets on the stability of AGS system.And then this study investigated the removal performance of aerobic granular sludge composite system for the removal of nutrients such as carbon,nitrogen and phosphorus.Finally,this study attempted to screen and enrich indigenous fungi from the aerobic wastewater treatment unit of a paper mill in Henan and establish the fungal bacterial granular sludge composite system.Sodium lignosulfonate was the typical refractory pollutant in the paper mill wastewater to prove the feasibility of the fungi-bacterial AGS composite system to remove the refractory organic matter in the wastewater.The main results of this study are summarized as follows:（1）Initial characteristic changes of fungi mycelium pellets in mature AGS system.This study took Phanerochaete chrysosporium as the research object and cultured the mycelium pellets under the best culture conditions(p H was 6,the temperature was30°C,the inoculation amount was 106 CFU/m L and rotating speed of 150 rpm.The mycelium pellets was added to AGS system,which operated stably for 260 days,and the change characteristics of mycelium pellets in the initial stage of system operation were observed.The mycelium pellets can still maintain a complete structure,with good mechanical strength（integrity coefficient greater than or equal to 87%）and good sedimentation performance（42.44±3.13 m/h）,average particle size of 2.23±0.01 mm and density of 1.021～1.022 g/cm3 after being added the reactor within eight days.The scanning electron microscope observation showed that the mycelium pellets could still maintain the intertwined filamentous structure in the initial stage,providing rich pore structure on the surface with many microorganisms,indicating that the mycelium pellets can be used as a biological carrier for flocs and broken granules to promote the stability of granular sludge.（2）The performance and microbial community structure of mycelium pellets-AGS composite system.Two groups of parallel AGS reactors were used,in which the control group R1 system was not added with mycelium pellets,and the experimental group R2system was added with mycelium pellets.The continuous experiment was carried out for more than 300 days.The results showed that compared with the control group R1（no seeded mycelium pellets）,R2 system（inoculated mycelium pellets）has better removal efficiencies of carbon,nitrogen and phosphorus.In the stable stage（from day165 to day 328）,the removal efficiencies of chemical oxygen demand（COD）,total nitrogen（TN）and total phosphorus（TP）were 91.69±4.71%,91.93±3.72%and 95.04±2.08%,respectively.The biomass MLSS of AGS reached 9.54 g/L and the sludge sedimentation index SVI30 was less than 25 m L/g.The extracellular polymers（EPS）reached 120 mg/g MLSS,respectively),and the content of extracellular protein（100mg/g MLSS）was higher than that of R1（70 mg/g MLSS）.The main functional bacteria in R2 system（calculated by abundance percentage）included ammonia oxidizing bacteria（0.13%）,nitrite oxidizing bacteria（53.05%）,denitrifying bacteria（0.01%）,phosphorus accumulating bacteria（0.08%）,denitrifying phosphorus accumulating bacteria（0.82%）,sulfur reducing bacteria（1.22%）and sulfur oxidizing bacteria（1.38%）,among which the abundance of denitrifying bacteria Thiotrix was the highest（41.34%）.The analysis of microbial population distribution in the inner and outer layers of a single mature ags showed that ammonia oxidizing bacteria and most denitrifying bacteria and phosphorus accumulating bacteria were mainly distributed in the outer layer of the granules,while some sulfur reducing bacteria and sulfur oxidizing bacteria were mainly distributed in the granules.The long-term operation results showed that the fungi mycelium pellets in R2 system significantly improved the stability of AGS system.In order to promote the growth of fungi and strengthen the removal efficiency of refractory organics by AGS,the study should be considered to screen functional fungi from the actual wastewater treatment unit to form fungi mycelium pellets.（3）The enhancement of removal performance of refractory organic matter by fungi-bacterial AGS system.Three fungi resistant to sodium lignosulfonate were screened,separated and purified from the aerobic activated sludge of a paper mill in Henan.Batch experiments showed that the removal efficiency of mixed fungi mycelium pellets for sodium lignosulfonate was better than that of single fungus mycelium pellets.The removal efficiency of sodium lignosulfonate in mixed fungi mycelium pellets AGS system was stable at 50.91±0.54%.The specific oxygen uptake rate in R2 system reached 42.90±6.67 mg O2·g-1MLVSS-1·h-1,and the activities of Li P,Mn P and Lac secreted by R2 system were higher.The GC/MS showed that R2 system could gradually degrade sodium lignosulfonate through multi anaerobic/aerobic process.At the end of the reaction,most amides,phenols and esters in water samples have been degraded and some relatively simple organic compounds have been generated.The results of high-throughput sequencing in R2 system showed that the mycelium pellets had the ability to increase the richness and diversity of mature granular microorganisms.The fungi that could degrade lignin detected in the system were Aspergillus,Bjerkendera and Sporidiobolus,and the bacteria that could degrade lignin were Acinetobacte and Desulfomicrobium. |
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