Design an aerobic digester to treat the waste sludge produced by the activatedsludge treatment plant. Assume that the following conditions apply:

The amount of waste sludge to be digested is $2057kg$ TSS$/$d$.$

The minimum and maximum liquid temperatures are $15C$ for winter operation and $25C$ for summer operation.

The system must achieve a reduction of $40$ percent in volatile solids in the winter.

The minimum SRT for winter conditions is $60d.$

Waste sludge is concentrated to $3$ percent, using a gravity$-$belt thickener.

The specific gravity of the waste sludge is $1\mathrm{.}03.$

Sludge concentration in the digester is $70$ percent of the incoming thickened sludge concentration.

The reaction rate coefficient $k_d$ is $0\mathrm{.}06d$ at $15C.$

Volatile fraction of digester TSS is $0\mathrm{.}80.$

No primary solids are included in the influent to the digester.

Diffused$-$air mixing is used.

Air temperature in diffused air system $=20C.$