The design of an external circulation reactor dealing with algae in Taihu lake was improved

and the performance of its quick start-up process and microbial properties of granular sludge were investigated. Cyanobacteria could be treated in around 35 d when running under the condition of dosing seed sludge

continuous operation with increasing load by steps

and intermittent agitation.When start-up finished

the removal rate of chemical oxygen demand(COD)by the reactor was about 85%

and gas production rate was about 380 ml·(g COD)-1.In addition

the removal rate of microcystins reached 92%. Microorganisms in granular sludge were mainly cocci and filamentous bacteria

containing lots of Methanococcus

and plentiful holes in granular sludge provided the condition for transport of matter and degradation of microorganisms.The dominant methane-producing archaea in the granular sludge were Methanosphaera

Methanolinea

Thermogymnomonas

Methanoregula

Methanomethylovorans

Methanosaeta. Protease and coenzyme F420 in the sludge particles showed higher activity.Intermittent stirring device and reflux system could overcome the drawbacks of floating and crusting of cyanobacteria in the reactor and at the same time accelerate mass transfer in the reactor so as to contribute to faster startup of the reactor.