Adverse Effect of Sludge Aeration

I'm working with a client that is about to install a sludge mixing system in a retention tank. One of the mixing options that we are looking at is the use coarse air diffuser. We like this approach because the maximum sludge height is only 1.5 m. We also looked at submersible mixers but submergence allowed is 1 m (hence, useful height is only 0.5 m...). My questions for you is: is there an adverse effect of aerating the sludge?