increased and the
amount of oxygen needed to support them also need to increases. The longer the
time, the level of quality water was increased which the amount of pollutant
was decreased because the biodegradation process was happening. So it will make
the oxygen can easily dissolve in the water.(Seman et al., 2013)  


Besides, the controlling
the RAS pumping rate is very important to maintain the biomass in the process.
If sludge is allowed to remain in a secondary clarifier too long it will begin
to float to the surface of the clarifier due to nitrogen gas released during
the biological process of denitrification. (Nagwekar et al.,2014).Typically,
RAS pumping rates of between 25% and 150% of the influent flow are commonly
used but the best percentage is around 15% to 30%. (Biggs et al., 2000).The
percentage of RAS was already calculated in appendix H1 and the value is 33.74%
and it is shown that the RAS in this treatment is in good conduction and
function properly that can maintain the biomass in the process. (Roslan et al.,
2013).So that the microorganism can degrade the pollutant again. So, the RAS
can give another advantage to the company that used this type of treatment
because of more economical and eco-friendly.It is because the microorganism was
reused back and just need to supply oxygen also microorganism to complete this

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The last factor
that affecting the activated sludge treatment is needed to maintain the
properly mixed liquor concentration. As the mixed liquor flows into a secondary
clarifier, the organism’s activity slows and they begin to clump together in a
process known as bio-flocculation. To function efficiently, the mass of
organisms needs a steady balance of food. If too many organisms are allowed to
grow in the aeration basin, there will not be enough food for all of them. ( Drozdova, 2013).


This balance
between the available food (F) and the mass (M) of microorganisms is described
as the F: M ratio of the system. The job of an activated sludge wastewater
treatment plant operator is to maintain the correct mass of microorganisms for
the given food supply. ( Drozdova
et al., 2013).The
range for Conventional activated sludge plants is often given as 0.2 to 0.5.So,
the ratio of F: M was already calculated and the ratio is 0.2 in appendix H1
and shown that it was under the range. It means, in this treatment was
successful to balance the food and microorganisms. (Sperling et al., 2007)


Then, the mass of
organisms that need to maintain is a function of the mixed liquor suspended
solids (MLSS) concentration in the aeration basin. (Venkatesh et al., 2011). By lowering the MLSS concentration
(increased wasting), the mass of organisms can reduce the system.The analysis
for MLSS and MLVSS was already done and according to the USEPA, the typical
range of the MLVSS for conventional activated sludge is 1600-2400mg/L and it
should lower than MLSS. It is because the MLSS value is inorganic and organic
solids. While the MLVSS is the organic solids consist of living and non-living
organic.(Ahansazan et al., 2014)