Effect Of Deionization On The Characteristics And Microbial Community Of The Activated Sludge

Minimizing the volume of organic matters and some nutrient elements(nitrogen and phosphorus)have been considered as key concerns for the municipal wastewater treatment plants.Effluents that contain a huge amount of nutrients or organic maters may expose the danger to the exquisite balance of nature in gaining waters.Municipal wastewater is generally treated in the activated sludge process because of its simplicity and robustness during the operation.In the activated sludge process,microorganisms predominantly bacteria metabolize organic and inorganic matters into eco-friendly compatible form leading to spontaneous aggregation of flocs.This process is called bio-flocculation,which is taken as a central factor for efficient operation in the wastewater treatment plant.Activated sludge dewaterability and settleability properties are two prime important factors of an activated sludge process.That is to say,the poor sludge settling,the more organic matters escape with the effluent from the secondary sedimentation tank.While on the other hand,poor dewaterability not only makes the sludge treatment very complicated but also it is very costly in terms of energy and time.The sedimentation and dewatering properties of sludge are related to the ions in the water,which mainly affect the flocculation of sludge through the theory of DCB(Divalent Cation Bridge)and DLVO(Derjaguin-Landau-Verwey-Overbeek).Here in this thesis,we aimed to deeply investigate the effect of deionization on the characteristics and microbial community of the activated sludge.The first chapter starts with giving a brief background on the investigated topic.The second chapter is wrapped by literature reviews on wastewater treatment mechanisms and on previous progress on the crucial role of the activated sludge in wastewater treatment strategies.The third chapter provides detail on the materials and methods used in this thesis.In the fourth chapter section one,the effect of deionization on activated sludge characteristics taking a case study of activated sludge inoculated in synthetic wastewater by tap water(SWT)and distilled water(SWD)respectively were experimentally examined.The quality of the effluent,both from distilled water reactor and tap water reactor were analyzed to determine the characteristics of activated sludge.Results indicated the increase of the sludge volume index from 51.67 ml/g to 146.9 ml/g leading to the sludge bulking for sludge inoculated in SWD.The Capillary Suction Time(CST)of sludge cultivated in SWD varied from 23.1 to 38.4 s,which suggests poor dewaterability.These have further confirmed by light microscope images that showed a significant difference between the sludge systems cultivated in SWT and those grown in SWD,which can be explained by the fact that filamentous bacteria are able to grow and become dominant bacteria in a deionized environment.In the fourth chapter section two,the microbial community diversity was analyzed by a high-throughput sequencing technique.The results show that Shannon index in deionized samples(SWD on day 6 is lower than it on day 1 because of filamentous bacteria were the dominant bacteria when sludge bulking on day 6,which inhibited the growth of other species.The sequence analysis on the phylum level has shown that Proteobacteria are predominantly found in deionized samples SWD on day 6.They present 52.74% of all phylum,while on the other side for class level,the majorities were Gammaproteobacteria(46.24%)and planctomycetacia(25.21%)respectively.Then on the Genus level has shown that Klebsiella,Gemmata,Raoultella,Tolumonas,Zoogloea and Thauera are predominantly found in deionized samples SWD on day 6 comparing to day 1.In particular,Klebsiella and Tolumonas were 6.91% and 5.25% higher.The results showed that sludge bulking occurred in the deionized samples on day 6,mainly caused by Klebsiella and Tolumonas,which may be the major bacteria that cause sludge filamentous bulking.