class qsdsan.processes.Decay(ID='', ins=None, outs=(), thermo=None, init_with='WasteStream', F_BM_default=1, **kwargs)

A generate class for non-steady state degradation.

property COD_decay

[float] Fraction of removed COD that degrades.

property COD_max_decay

[float] Maximum fraction of COD degraded during storage given sufficient time.

property COD_removal

[float] Final COD removal.

property MCF_decay

[float] Methane correction factor for COD decay.

property N2O_EF_decay

[float] N2O emission factor, [fraction of degraded N].

property N_max_decay

[float] Maximum fraction of N degraded through denitrification during storage given sufficient time.

property N_removal

[float] Final N removal.

static allocate_N_removal(tot_red, preferred_N)

Allocate the total amount of N removal to NH3 and non-NH3 components.

  • tot_red (float) – Total amount of N to be removed.

  • preferred_N (float) – Current content of the N that will be removed first.


N removal – Amount of preferred N to be removed, amount of other N to be removed.

Return type:


property decay_k_COD

[float] Rate constant for COD decay, the time unit is year.

property decay_k_N

[float] Rate constant for N decay, the time unit is year.

property degraded_components

[Iterable(str)] IDs of components that will degrade at the same rate as COD.

first_order_decay(k, t, max_decay, t0=None, tot=1)

Calculate first-order degradation loss based on Trimmer et al..

\[C_{deg} = tot * max_{decay}\]
\[t_f = t_0 + t\]
\[C_{avg} = \frac{C_deg}{k*t} * (e^{-k*t_0}-e^{-k*t_f})\]
\[loss = C_{deg} - C_{avg}\]
  • k (float) – Degradation rate constant.

  • t0 (float) – Degradation time prior to current process.

  • t (float) – Degradation time in current process (i.e., tf-t0).

  • max_decay (float) – Maximum removal ratio.

  • tot (float, optional) – Total degradable amount. If set to 1 (default), the return is the relative ratio (i.e., loss/tot).


loss – Amount lost due to degradation.

Return type:



[1] Trimmer et al., Navigating Multidimensional Social–Ecological System Trade-Offs across Sanitation Alternatives in an Urban Informal Settlement. Environ. Sci. Technol. 2020, 54 (19), 12641–12653.

property if_N2O_emission

[bool] Whether to consider N degradation and fugitive N2O emission.

property if_capture_biogas

[bool] If True, CH4 generated from COD degradation will be captured as biogas; if False, it will be treated as fugitive emission.

property max_CH4_emission

[float] Maximum methane emission as a fraction of degraded COD, [g CH4/g COD].

property t0

[float] Degradation time prior to current process.

property tau

[float] Retention time of the unit, [d].