S D I

Tank 3

FIG. 11.18.3 Typical flow conditions (i.e., diurnal flow rate variation). Illustrations show static fill (Fs), aerated fill (Fa), react (R), settle (S), draw (D), and idle (I) for a three-tank system. Fill periods are shaded to demonstrate that inflow continuously occurs into one of the three tanks, and draw periods are cross-hatched to show the periodic nature of effluent flow.

Reservoir Reservoir

FIG. 11.18.4 Illustration of a laboratory SBR system.

Reservoir Reservoir

FIG. 11.18.4 Illustration of a laboratory SBR system.

SBR. Liquid level switches can be used to control the fill and draw volume, or, as an alternative, suction tubes can be placed at an elevation to prevent pumping excessive volumes. The suction tube alternative will result in too little addition or removal if minor changes occur in the pumping rates, but this is minimized by frequent monitoring and occasional manual over-ride at the end of a pumping cycle, or simply recorded to reflect a slightly different loading rate. System control is provided with a microprocessor-based timer and controller that turns pumps on and off, opens and closes the air shut-off valve, and turns the mixer on and off at appropriate times.

Laboratory studies include a start-up period to develop a biomass enriched for organisms acclimated to the waste-water constituents. Start-up time is minimized by including these organisms in the initial seed biomass. Aeration of some wastewaters alone will result in an accumulation of a suitable biomass. At other times, activated sludge collected from nearby municipal or industrial wastewater treatment plants may be needed. Finally, for difficult to degrade wastes, organisms are taken from: soil samples collected from waste spill sites; sediments collected from nearby receiving waters; or from residues in contact with waste constituents for long periods of time. During startup, fill and draw periods are controlled manually after substrate reduction is observed. Once an enriched and acclimated biomass is developed, automatic SBR operation is used to determine the appropriate operating strategy, as described above under the explanation of the different phases of the SBR cycle.

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