Environmental Water Treatment Knowledge: Meaning and Role of Sludge Loading

Sludge loading refers to the kilograms of five-day biochemical oxygen demand (BOD5) borne per kilogram of activated sludge per unit time within the aeration tank. Its unit of measurement is usually expressed as kg/(kg·d).

At different stages of sludge growth, the sludge loading varies, and the purification effect is also different; therefore, sludge loading is one of the main parameters in the design and operation of the activated sludge process. Generally, when the sludge loading is in the range of 0.3-0.5 kg/(kg·d), the BOD5 removal rate can reach over 90%, the SVI is 80-150, and both the adsorption and sedimentation performance of the sludge are good.

Ns = F/M = QS/(VX)

where Ns - sludge loading, kgCOD(BOD)/(kg sludge·d);

Nrs = [Q(Sa-Se)]/(XvV), unit: kgBOD/[kgMLVSS·d]

S - COD(BOD) concentration, mg/L;

V - effective volume of aeration tank, m³;

X - sludge concentration, mg/L.

BOD-sludge removal loading

BOD-sludge removal loading Nrs indicates: within the aeration tank, the amount of organic matter (BOD) in the sewage that is degraded and removed through the action of activated sludge microorganisms, per unit weight (kg) of activated sludge (MLVSS) per unit time (1 d).

Q - daily influent flow, m³/d;

where Q - sewage flow, m³/d;

Sa - the amount of organic pollutants (BOD) contained in the sewage entering the aeration tank after pretreatment, kg/m³;

Se - the amount of organic pollutants (BOD) remaining in the treated water after activated sludge treatment, kg/m³;

V - effective volume of aeration tank, m³. [1]