Effect Of Salinity On Biofilm Performance And Community Structure In SBBR Reactor

With the rapid development of petrochemical,food,pharmaceutical and leather industries,the salty organic wastewater produced by these industries is also discharged in large quantities.Such wastewater not only contains refractory organic substances and nitrogen and phosphorus,but also contains high salt.Most recent studies have focused on using different treatment processes to improve the effect of wastewater removal under salinity conditions,with few studies on the effect of salinity on activated sludge and biofilm performance.Therefore,in this study,the sequential batch flow bed biofilm reactor（flow filler SBBR）was used to treat the salt wastewater,which explored the treatment performance,biofilm characteristics and the composition of the flow filler SBBR process under different salinity,and selected the salt resistant strains for the preliminary study of salt resistance mechanism.In order to clarify the treatment effect of the flow packing SBBR process under different salinity stress,and provide theoretical reference for the treatment of saline wastewater by the flow packing SBBR process.This experiment was conducted in the SBBR reactor with an effective volume of 6 L,the film filler with polyurethane sponge material,experimental temperature and dissolved oxygen control at 25-28℃and 5-5.5 mg/L respectively,the water intake was simulated high salt wastewater,the salinity was calculated as sodium chloride（Na Cl）,0 g/L,8 g/L,16 g/L,24 g/L,the salinity gradient was gradually increased during sludge domestication,and the SBBR reactor operated for three cycles a day.The experimental results are shown as follows:（1）The effect of salinity on the removal effect of SBBR and the biofilm performance was investigated.With the increasing salinity gradient,When the system is stable,the removal efficiency of ammonia nitrogen（NH₄⁺-N）,chemical oxygen demand（COD）and total phosphorus（TP）decreases from 98%,98%and 97%in the absence of salinity to 84%,73%and 47%at the salinity of 32 g/L;Salinity stresses polyphosphobacteria than nitrated and denitrifying bacteria;With the continuous increase in salinity,Sludge sedimentation performance has increased significantly;Microbial activity characterized by the biofilm specific good consumption rate（SOUR）and dehydrogenase activity（DHA）increases at less than 8 g/L salinity,Shdecrease after greater than 8 g/L;The salinity increases the content of extracellular polymer（EPS）in the biofilm from 26.15 mg/g SS to 216.27 mg/g SS,The polysaccharide（PS）content showed the most significant increase in TB-EPS,The increase of EPS can improve the resistance to salinity and the protection of cells;At different salinity levels,Protein in biofilm EPS are mainly tryptophan-like proteins,Salinity will increase the production of soluble microbial byproducts;The main functional groups of various substances in EPS are,—OH,N—H,C=O,C—N,And the salinity reduces the C—O in the polysaccharide substance.（2）The effect of salinity on the microbial community structure in the SBBR system was studied.The bacterial diversity in the biofilm at 0 g/L salinity varied significantly from that at other salinity,However,with the increase of salinity,the difference between adjacent samples is gradually narrowed;Higher salinity and lower microbial community richness and microbial community diversity,Salinity inhibited the growth of some microorganisms;In biofilms of different salinity,Actinobacteria,Proteobacteria,and Patella bacteria are the largest three dominant phyla,The cumulative mean relative abundance was maintained between 72%and 83%,Of which the relative abundance of Actinobacteria increased significantly with increasing salinity,The relative abundance of variable bacteria decreased with increasing salinity;The relative abundance of Aceococcus,Microalbicans,and TM7a increased rapidly with the rise in salinity,At 32 g/L salinity,it has become the largest three dominant genera.（3）The screening of salt-resistant bacteria and the mechanism of salt resistance in SBBR system were studied.Two salt-tolerant strains W1 and W2 were purified from biofilms at 32 g/L salinity,and strain W1 was identified as Anarchaeum and strain W2 as Halomonas.In the salinity range from 0 to 60 g/L,Exiguobacterium and Halomonas can grow,Both strains had optimoptimal p H around 8,And the growth number and growth rate of Exiguobacterium increased with the increase of salinity;In a high-salt environment,When the salinity exceeds the range of deep-sea M.microvivum and Halomonas themselves,They can be transported via extracvar cations(e.g.,Na⁺,Cl^—,SO₄^2-,NO₃^-,K⁺,Ca²⁺)and exogenous compatible substances（e.g.,betaine,proline,glycine,trehalose）,And reduced protein synthesis and increased consumption of sugars to jointly maintain extracellular osmotic balance,Resistance the stress caused by high salinity environment.