I am looking for any helpful feedback regarding aerobic digester coarse bubble diffuser problem. This municipal SBR wastewater treatment plant thickens the WAS from 0.8 percent to a range of 2.5 to 3.5 percent. The thickened sludge is then put into the first of two aerated digesters. The design was for these digesters to have an aeration cycle of 1 hour on and 1 hour aeration off or 2 hours on and 2 hours off. The diffusers used were stainless course bubble diffusers with no back flow prevention. Mechanical plugging started almost immediately causing the workers to cease cycling the aeration due to hard blower starts, no blower VFD, and excessive blower pressures. I have cleaned the piping and am controlling the ph presently by manipulating the sludge depth in the aeration tanks to approximately 2.2 meters (available tank depth is 5.25 meters). The aeration designers are suggesting we now change the diffusers to fine bubble and doubling the amount of them. Concerns: Will I get enough mixing action to prevent solid accumulation. I have poor oxygen transfer now unless I most of the available digester depth, I am assuming this will improve with fine bubble. The fine bubble should create more back pressure on the blowers and I am already at 6 psi at 2.2 meter depth. My blower maximum operating pressure is 8.5 psi with the relief valve set at 9.3 psi. The last concern is how long would these last in the sludge?

I know the guages are correct and that both blowers show the same pressure. I have never ran the system dry so I don't know what the pressure would be with no liquid in the tank. I do understand that it would be easier to figure out the pressure increase if I knew the dry pressure and then just added the head pressure.