Investigation On Filamentous Sludge Bulking Control By Improving Gas-liquid Mass Transfer Efficiency

This article was investigated the sludge structure, settling properties, filamentousbacteria species, water treatment capabilities and relationship between the amount offilamentous bacteria and the sludge settling properties in the reactor with differentgas-liquid mass transfer efficiency from the activated sludge system, the relationshipbetween the growth state of sludge and gas-liquid mass transfer efficiency wasresearched under oxygen limited conditions. The volumetric oxygen transfer coefficient(kLa) of filamentous sludge with different floc structure were measured and theinfluence of gas-liquid mass transfer efficiency on filamentous bulking controlling wasevaluated. The experimental result suggested that the effect of filamentous sludge ongas-liquid mass transfer efficiency depends mainly on settleability rather than on thetotal length of filamentous bacteria. By means of improving the filamentous flocstructure, it could effectively enhance the oxygen transfer coefficient from the view ofmicrobe, and this finding provides a new way for filamentous bulking controlling.Results shows that:(1) The floc structure is different in the reactor with different gas-liquid masstransfer efficiency during the operation of the reactor. When the filamentous bacteria inthe reactor is proliferated, the reactor which the gas-liquid mass transfer efficiency is0.086min-1has high treatment ability, most of the filamentous bacteria is the thiothrix,type1851, the floc structure is dense, which floc sludge entwined with filamentousbacteria and maintaining good settlement ability, the SVI of sludge is about150ml·g-1;but in the reactor which the gas-liquid mass transfer efficiency is0.072min-1, most ofthe filamentous bacteria is type0581and M.parvicella., the filamentous floc structureloose and the SVI of sludge is up to2300ml·g-1. (2) Floc structure and gas-liquid mass transfer efficiency of the sludge is closelyrelated, the volumetric oxygen transfer coefficient (kLa) and settleability of filamentoussludge with different floc structure were measured and the experimental resultsuggested filamentous sludge, which has high sedimentation and the floc structure wasdense, also has high volumetric oxygen transfer coefficient, and the filamentous sludgewith bad settling characteristics inhibit the volumetric oxygen transfer coefficient. Theeffect of filamentous sludge on gas-liquid mass transfer efficiency depends on thesettleability of filamentous sludge, and the filamentous sludge which had bettersettleability also with high gas-liquid mass transfer efficiency.(3) By investigate different ways to improve the volumetric oxygen transfercoefficient of the sludge, found that aeration on mass starvation can improve gas-liquidmass transfer efficiency of filamentous sludge. When filamentous sludge bulking wascaused by low dissolved oxygen, the volumetric oxygen transfer coefficient could beincreased by improving the filamentous floc structure, i.e., elimination of the externalconditions that caused the oxygen deficiency could be obtained by controlling the flocstructure, and thus effectively controlled the sludge bulking.