Hi

Please, explain for which purposes you need laboratory-cultured activated sludge, if you need pure cultures or mixed ones, pro/eukaryots... I am not able to offer you any standard method. Be sure, if you want to study microorganisms related to real processes, which are functioning in consortia, there is no possibility how to speed it up

From the theory of continuous flow cultivation you must known that you are able to aproximate the steady state (quasi steady-state) passing 5 times the retention time, in your case, the sludge age. For the oxic/anoxic/anaerobic processes it could be 5x20=100 days or more

If you want have a system with a selector (contact zone) effect - with the substrate gradient (e.g., anaerobic-anoxic-aerobic (nitrificating) system), the semi-continuous (repeated-fed batch) system would be O.K. and it could be semi-automatized without big problems but not so easy in sterile conditions (again, it is tricky).

But if you want (ideally) mixed system, it will need to keep the continuous flow system running for too long time (you will sleep in the lab to reach it). No way how to speed it up and probably no way for you.

For mixed anaerobic cultures you could use simpler and continuous-flow systems with biofilms but it will take even more time.

If you are interested in for some special microaerobic/anoxic organisms that are able to grow alone (not only in consortia), you can try to cultivate in the "candle jar" - the standard method for malaria parasite cultivation (burning the candle inside the dessicator; the proportion pO2/pCO2 is favorable for many microaerophilic organisms both eukaryots and prokaryots).

For anaerobic organisms you must buy an anaerostat (quite expensive), moreover, it is tricky. No chance to cultivate pure cultures, all biochemical pathways must be occupied.

I feel the comment on the growth rate (approximated by sludge age) is the most important if you are looking for standard conditions (and the most complicated). If you need to study only microbial composition, any time will be better way to take samples in in situ.

Cheers

The method for anaerobic bacteria count can be done by using standard method count ( Reference - Bacteriological analytical manual -FDA) under  anaerobic condition during incubation by using anaerobic incubator .