| Granular sludge originally appeared with the treatment of organic industrial wastewater.It first appeared in some anaerobic reactors in the 1970 s.At present,anaerobic granular sludge has been widely used in the treatment of high concentration organic wastewater.In contrast,aerobic granular sludge technology appeared much later,until 1991 Mishima and other scholars first reported the emergence of aerobic granular sludge in AUSB reactor.However,the operating conditions of AUSB are harsh,and pure oxygen aeration is needed to produce aerobic granular sludge.Subsequently,the research on aerobic granular sludge cultivation gradually increased,and the research on sludge bulking in the mid-1990 s accelerated the research progress of aerobic granular sludge.Morgenroth et al.learned from the cultivation experience of anaerobic granular sludge in SBR,successfully cultured aerobic granular sludge in SBR using organic matter as the substrate,which laid a foundation for the research of aerobic granular sludge.The advantages of aerobic granular sludge have been accepted by most researchers.On this basis,the research of aerobic granular sludge has been developing rapidly since 1997.Up to now,granular sludge process is one of the recommended technologies in the field of wastewater treatment,and has been applied in the treatment of some special wastewater.However,because the mainstream reactor is still the continuous flow reactor in the current sewage treatment plant,the sequencing batch reactor is less used,and the production of granular sludge in the continuous flow reactor has more restrictive conditions,such as the continuous flow reactor can not form a state of microbial starvation-satiety-starvation,so it can not stimulate activated sludge to produce EPS.Extracellular secretions conducive to microbial aggregation,and because the continuous flow reactor can not control the reaction time,it can not form an effective hydraulic selective pressure to screen granular sludge with good sedimentation performance.Because of the above reasons,the popularization and application of granular sludge technology is limited.Therefore,it is necessary to develop a more suitable granular sludge culture system in continuous flow reactor by creating a new way in the current aerobic sludge culture reactor.After consulting all kinds of previous data and related literature,it is known that the key control factors of granular sludge formation include sludge settling time,reactor height-diameter ratio,hydraulic shear force,CODCr volume load and other parameters.Based on the existing research results,a continuous flow granular sludge reactor was designed and manufactured.It was proposed to provide growth environment for microbial film hanging by adding a mesh plate in the reactor.At the same time,the air flow and hydraulic dithering caused by aeration could promote the biofilm falling off.Finally,the flow pattern of Karman Vortex Street was formed in the back of the mesh,and the microorganisms falling off could be granular sludge.Formation provides "nuclei".In order to ensure the universal applicability of the research results in this paper,domestic sewage is used as the experimental water.During the experiment,the cultivation time,optimal operation parameters and removal efficiency of granular sludge are explored by adjusting the mesh diameter,mesh rope material,air-water ratio and so on.Experiments were carried out in a continuous flow granular sludge reactor with an additional mesh plate.In the initial stage,aerobic granular sludge can form in 12-15 days,and produce better pollutant removal efficiency.But in the 20 days or so,the removal efficiency decreases and granular sludge begins to take over.In the follow-up,the stable operation of granular sludge can be guaranteed by changing mesh diameter,changing mesh rope material,adjusting air-water ratio and adjusting flow rate.There are six stages in the experiment.The main adjusting parameters are mesh diameter and material.It is found that the increase of mesh diameter can not increase the microbial shedding volume after film hanging.The mesh rope made of multi-strand rope is easy to retain a large amount of sludge and prevent its shedding.Therefore,adjusting the material of the mesh rope and the diameter of the single strand,and conducting the fourth stage experiment,it can be found that the cross section of the mesh reactor is reduced,the overflow flow is adjusted to 50L/h,and the mesh jitter is strengthened by intermittent reflux,so that the formed biofilm can be guaranteed to fall off.At the same time,it was found that too high air-water ratio was not conducive to the shaking of the mesh rope,on the contrary,the formation of higher dissolved oxygen made filamentous bacteria grow in large quantities,which was more conducive to the formation of biofilm falling off.After reducing the air-water ratio and replacing the material of aeration pipe to improve the uniformity of aeration in the reactor,the granular sludge can form a fast start-up and achieve a stable treatment effect.The final operating parameters of the mesh reactor are flow rate of 50-120 L/h,mesh size of 10 mm *10 mm,mesh rope diameter of 3 mm,mesh rope material of nylon rope,diameter of 1 mm of filament.The ratio of air to water is controlled from 7.7:1 to 8.5:1.Eventually,after 12 days of startup,granular sludge and conventional floc sludge coexist under aerobic conditions,but the granular sludge gradually increases and the particle size gradually increases.At 20 days or more,80%-90% sludge is transformed into granular sludge,and the particle size gradually increases to 2 mm,the maximum is about 3 mm,and individual sludge can reach 4 mm,which means that the sludge studied in this paper is fast.The start-up technology has achieved some results.The aerobic granular sludge has good removal efficiency for pollutants.The removal rates of CODCR,NH4-N,TN and TP are 82.2%,79.6%,66.7% and 66%,respectively.The effluent indicators meet the first A standard of "Pollutant Discharge Indicators of Urban Sewage Treatment Plants". |
