Blowers
Every book you read says you must use PD blowers for aerobic digesters, and cannot use centrifugal blowers. This is a lie. (I'd use stronger words, but someone would be offended). Centrifugal blowers can be used, and can supply multiple tanks. All you, the operator, has to do is use the air flow control valve on the drop header to each tank, and pinch back the tank with the lowest level so all the air does not flow into that tank. Stop watching the TV and do a little work. Why use centrifugals? They are more efficient than PD blowers and much quieter. The PD blower manufacturers are now offering PD blowers with VFD for speed control and nice enclosures to get the noise level down to 70 dB or even less. Aerzen, for one has a nice package for that, and easy access for maintenance as well.
In addition to air flow control valves, each tank drop should have a flow meter. Why? BECAUSE IF YOU CANT MEASURE IT YOU CAN'T CONTROL IT! I know, I'm a slave driver, spoiling your day making you write down all these data boo hoo.
Diffusers
There are numersou diffusers, both fine bubble and coarse bubble that can be used. I think that some are better than others. Mooers flex cap diffusers work well in digesters and are better at resisting fouling that some.
Fine bubble diffusers can be used for aerating digesters, and require less air than coarse bubble diffusers. They are more prone to fouling, but EDI promotes fine bubble diffusers for aerobic digesters.
As I said earlier, the kind of diffuser you use limits the reactor total solids. With fine bubble diffusers, the tanks solids should be less than 3% TS. For coarse bubble duffusers, less thatn 4% TS. If you want to see proof, write to me and I'll bore you with all the calculations.
ORP meters.
To know the conditions inside the tank, an ORP (oxidation-reduction potential) meter is better than a DO meter. ORP tells you how and how to cycle the air flow to good effect in part trois.
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