Twenty six steady state runs based on quality were
recorded. Average hydraulic-detention time in the total
system (combined aerobic and anoxic) was 24 h. Sludge
wastage was performed daily by discarding sludge from the
bottom of the clarifier. Wastage solid mass was calculated on
the basis of average solid-mass in all tanks with targeted
average sludge-age of 15 d. Sludge age varied within the
range of 13 to 16.5 d. Average inflow rate in the system was
1.56 l/h while average return sludge flow was 1.5 l/h. First
tank receiving inflow and return sludge was mixed very gently
to add to floc formation in the absence of any air supply. The
oxygen level in this tank remained around 1 mg/l. The last
tank was maintained at anoxic conditions and its contents
received constant gentle mixing to keep the solids suspended.
The oxygen level in the fifth tank mostly remained below 1
mg/l. Oxygen level in the three aerated tanks was maintained
at an average of 2.5 mg/l. The water temperature and pH were
within the range of 22 to 23oC and 6.3 to 8.7, respectively