Investigation On Structure Of Filamentous Sludge Underoverspreading Growth Conditions And Densification Of Filamentous Sludge

Activated sludge process has been widely applied in wastewater treatment system,but sludge bulking caused by filamentous bacteria is one of the most common andintractable problems since it was developed.The traditional method of controllingsludge bulking caused by filamentous is to kill filamentous or inhibit their growth.Recent years studies have pointed out that filamentous bacteria can also form largebioaggregates or particle, it provides a new approach to control filamentous sludgebulking.While, the study of filamentous bacteria are mainly focus on comparison ofgrowth conditions between filamentous and zoogloea, and the main purpose is toestablish operating conditions which can promote zoogloea breeding and inhibitfilamentous bacteria; but the field of the growth of filamentous bacteria itself and thecharacteristics of mycelium are still lack of systemic research.Features of filamentous bacteria in different growth stage,including self-structure,growth potential,storage capacity of substrate,surface characteristics, oxygen masstransfer, quality of effluent water, were analysed;And succession law of filamentousmycelium in different processes was also investaged for seeking the method offilamentous densification, then solving the problem of separation of solid and liquid,improving quality of effluent water.Results showed that:（1） Large bioaggregates of filamentous under overspreading growth conditionscould be significantly found in the reactor, exhibited low SVI（30⁴0mL/g）, highsettling velocity（the average speed of large bioaggregates of filamentous are close togranular sludge, and the maximum settling velocity can reach100m/h）,so they could be easily separated during settling periods. However,the large bioaggregates wouldalso caused ununiform distribution of dissolved oxygen in the reactor as changing ofoxygen transfer path and decreased oxygen mass transfer efficiency. Additionally, thequality of effluent is not ideal in the reactor, which ammonia nitrogen removal ratefluctuate between30⁴0%.（2） New concept-“node density” and “ovality” were introduced to characterize thestructure feature of filamentous mycelia. Node density of filamentous is used tocharacterize the intersection of mycelium in unit length, and ovality of mycelia is usedto characterize the shape formed by mesh.Results show that the node density offilamentous was positive correlated with SVI,while the ovality of filamentous meshwas negative correlated with SVI.（3） Results show that species which form large bioaggregates of filamentous areselective,those who have bent,strong or large storage ability of mycelium areadvantage for forming aggregatical growth. Additionally, different types of filamentoushave different growth potential and storage capacity, exhibited growth potential offiner filamentous mycelium is more faster, for example:growth potential of Type1851is faster than Type021N.And the storage ability of PHB granules of filamentous in thetest from high to low are:Nostocoida limicola Ⅱ,Tpye1851,Type0701,Type021N.While Nostocoida limicolaⅡis advantage for substrate utilization when coexistwith H.hydrossis.While ability of substrate utilization between H.hydrossis and Type0914are similar.（4） Volumetric oxygen transfer test showed that morphology of mycelia and it’sswing performance have positive effects on mass transfer （KLa value increased by3.9%）.But overall sludge morphology and changing of EPS content are moresignificant influence on the mass transfer （KLa value fell by39%）.（5） Organic matter（maize）, as kernel and carbon source, were put into the reactor inthis test;Expect that filamentous can adhere to kernel and the winding growth so as tochange its divergent growth mode to density growth mode. Filamentous begin toadhere to maize can be observed after adding maize in short time. After a period oftime, the maize will be slowly disintegrated, growth mode of filamentous becomewounding the kernel and adhesive growth, and even some filamentous pierce the maize. But the improvement of precipitation performance is short-term, as maize would bebroken down.（6） The value of Cmand k are respectively:1000mg/L and0.00033mg^-1·L·h^-1by thecarbon release curve when maize as a carbon source. For the reactor of R1and R4,adding carbon source （maize）,the unit of ammonia nitrogen and denitrification removalrate increase slowly in the trend. So,maize has a positive impact on water quality ascarbon source. Compared with method of adding reagent, adding carbon source toinhibiti filamentous expansion is safe and reliable.