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thickener.rst

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Thickener

.. index::
   pair: watertap.unit_models.thickener;thickener

The main assumptions of the implemented model are as follows:

  1. Single liquid phase only
  2. Steady state only
  3. Has no volume

Introduction

Sludge thickening is a process commonly used in wastewater treatment plants to increase the sludge concentration of a stream as well as reduce its volume by removing free water. In doing so, the thickener reduces the load of downstream processes, such as digestion and dewatering. This implementation of the thickener unit is based on the IDAES separator unit.

Degrees of Freedom

The degrees of freedom in a thickener unit model are the inlet feed state variables:

  • temperature
  • pressure
  • component mass compositions

Model Structure

The thickener unit model does not use ControlVolumes, and instead writes a set of material, energy and momentum balances to split the inlet stream into two outlet streams. Thickener models have a single inlet Port (named inlet) and two outlet Ports (named overflow and underflow).

Sets

Description Symbol Indices
Time t [0]
Phases p ['Liq']
Particulate Components j ['X_I', 'X_S', 'X_P', 'X_BH', 'X_BA', 'X_ND']
Non-particulate Components j ['H2O', 'S_I', 'S_S', 'S_O', 'S_NO', 'S_NH', 'S_ND', 'S_ALK']

NOTE: These components are defined in the ASM1 Property Package documentation.

Parameters

Description Symbol Variable Name Index Value Units
Percentage of suspended solids in the underflow p_{thick} p_thick None 0.07 \text{dimensionless}
Percentage of suspended solids removed TSS_{rem} TSS_rem None 0.98 \text{dimensionless}

Equations and Relationships

Description Equation
Suspended solid concentration C_{TSS} = 0.75 (C_{X_{I}} + C_{X_{IP}} + C_{X_{BH}} + C_{X_{BA}} + C_{X_{S}})
Thickening factor f_{thick} = p_{thick} (\frac{10}{C_{TSS}})
Remove factor f_{q_{du}} = \frac{TSS_{rem}}{100 * f_{thick}}
Overflow particulate fraction split_{particulate} = 1 - TSS_{rem}
Overflow soluble fraction split_{soluble} = 1 - f_{q_{du}}

Class Documentation

.. currentmodule:: watertap.unit_models.thickener


.. autoclass:: Thickener
    :members:
    :noindex:

References

J. Alex, L. Benedetti, J.B. Copp, K.V. Gernaey, U. Jeppsson, I. Nopens, M.N. Pons, C. Rosen, J.P. Steyer & P. A. Vanrolleghem Benchmark Simulation Model no. 2 (BSM2)