aquakin.size_activated_sludge#

aquakin.size_activated_sludge(*, SRT, Q, HRT=None, HRT_h=None, n_tanks=1, volume_fractions=None, wastage_from='mixed_liquor', thickening_ratio=1.0, internal_recycle_ratio=None, ras_ratio=None)[source]#

Size an activated-sludge basin from SRT / HRT design targets.

The two standard sizing relations:

  • Volume from HRT: V = Q × HRT – the aeration volume is the design flow times the chosen hydraulic retention time.

  • Wastage from SRT: the sludge age is the system solids mass over the rate solids are wasted. Two wasting strategies:

    • wastage_from="mixed_liquor" (default, “hydraulic”/Garrett SRT control): wasting mixed liquor straight from the aeration basin gives SRT = V·X / (Qw·X) = V/Qw independent of the (unknown, time-varying) solids concentration, so Qw = V/SRT exactly.

    • wastage_from="underflow": wasting from the thickened RAS line gives SRT = V·X / (Qw·X_r), so Qw = V / (SRT × thickening_ratio) with thickening_ratio = X_r/X (the underflow-to-reactor TSS ratio, > 1).

This is the nominal design; the realised SRT also depends on the effluent solids loss and (for underflow wasting) the actual thickening, so confirm it on a solved plant with sludge_metrics().

Parameters:

  • SRT (float) – Target solids retention time (days). Must be > 0.

  • Q (float) – Design (average) influent flow (m³/d). Must be > 0.

  • HRT (float, optional) – Hydraulic retention time in days. Supply exactly one of HRT / HRT_h.

  • HRT_h (float, optional) – Hydraulic retention time in hours (the usual engineering unit).

  • n_tanks (int, optional) – Split the aeration volume into this many equal tanks (a CSTR cascade). Default 1. Ignored when volume_fractions is given.

  • volume_fractions (list of float, optional) – Explicit per-tank volume fractions (must be positive and sum to 1); sets tank_volumes and overrides n_tanks.

  • wastage_from (str, optional) – "mixed_liquor" (default) or "underflow" – see above.

  • thickening_ratio (float, optional) – Underflow-to-reactor TSS ratio for wastage_from="underflow" (must be > 0; ignored for mixed-liquor wasting). Default 1.

  • internal_recycle_ratio (float, optional) – If given, also report the internal-recycle / RAS pump flows as ratio × Q.

  • ras_ratio (float, optional) – If given, also report the internal-recycle / RAS pump flows as ratio × Q.

Returns:

Volume, wastage flow, tank split and recycle flows.

Return type:

ActivatedSludgeSizing

Raises:

ValueError – On non-positive SRT/Q/HRT, an ambiguous or missing HRT, a bad wastage_from, a non-positive thickening_ratio, or volume_fractions that are non-positive / wrong length / do not sum to 1.

Examples

>>> s = size_activated_sludge(SRT=10.0, HRT_h=8.0, Q=18446.0, n_tanks=5)
>>> round(s.volume), round(s.wastage_flow)
(6149, 615)