Page 404 - Industrial Wastewater Treatment, Recycling and Reuse

376 Industrial Wastewater Treatment, Recycling, and Reuse

Table 9.1 Comparison between different activated sludge processes
Extended
Process Conventional Aeration Contact Stabilization
Description Activated Sludge Activated Sludge Activated Sludge
Hydraulic 4-8 h 12-14 h 0.3-3 h in contact
retention time tank and 4-8 h in
(HRT) stabilization tank
MLSS in aeration 1000-4000 mg/L 2000-5000 mg/L 1000-3000 mg/L
basin contact tank
2-6 times
concentration in
stabilization tank
System SRT 3.5-10 days >10 days <3.5 days
System F/M ratio 0.25-0.5:1 0.05-0.15:1 0.5->1.0:1

solid/liquid separation, and treated effluent removal) by using a single
variable volume basin in an alternating mode of operation that dispenses
with the need for final clarifiers and high-RAS pumping capacity. With
continued value addition, the performance of the SBR system can be
enhanced with a high level of process sophistication in a configuration that
is cost and space effective and offers a methodology with operational sim-
plicity, flexibility, and reliability that is not available in conventionally con-
figured activated sludge systems. Also with this advancement, it is possible to
control the growth of filamentous sludge bulking, a common problem with
conventional processes and other activated sludge systems (Mittal, 2011).
SBR utilizes a simple repeated time-based sequence that incorporates:
• Fill–aeration (for biological reactions)
• Fill–settle (for solid/liquid separation)
• Decant (for treated effluent removal).

9.4.2.1 Advantages of SBR (Mittal, 2011)
• It operates under continuous reduced loading through simple cycle
adjustments.
• It operates with feed-starve selectivity, So/Xo operation (control of
limiting substrate to micro-organism ratio), and aeration intensity to
prevent filamentous sludge bulking and ensures endogenous respiration
(removal of all available substrate), nitrification, and de-nitrification
together with enhanced biological phosphorus removal.
• It operates simultaneous (co-current) nitrification and de-nitrification by
variation of aeration intensity.