As per Koble reaction, biphenyl(insoluble into water) will be created when electrolyse sodium benzoate, but from anode side, the white solid material sediment I got together with few bigger air bubble was very easy to be dissolved again.
I suppose that white material is not biphenyl, instead, as Ph value of anode side is very low(2~3), that maybe sodium benzoate percipitated, Ph value went up again after mix the solution, thus the white sediment disappeared.
But I still wonder what really happened to anode, anybody has done the same experiment, please help.