COD/DOC balanced models for the oxidation process of organic compounds

Abstract

Nowadays, several advanced oxidation and enzymatic processes are available for the removal of organic compounds. Mathematical models are crucial to optimize the operating conditions and to reduce the costs associated with the studied oxidation process. The present work deals with a procedure to develop COD/DOC balanced models to represent the oxidation process of organic compounds. The procedure is of general nature since no hypothesis is made regarding the identity of the organic compounds or the oxidant employed. Using the developed procedure, proposed oxidation pathways always fulfill elemental and electron balances. Several examples of oxidation pathways were studied to demonstrate the usefulness of the procedure. From the analysis of a particular pathway, several restrictions regarding the range of possible values of the model coefficients can be found. These restrictions can be used to enhance the robustness of the fitting procedure of the model by using different types of data, such as COD, DOC and/or the actual concentration of some relevant species. This work will help researchers in areas related to the removal of organic compounds using any oxidation process.

Appendix: COD/DOC balanced models to represent the oxidation of organic compounds

Parallel pathways with partial oxidation

In this example, the oxidation of S₀ by an oxidant (Ox) produces two intermediates S₁ and S₂. While S₁ is further oxidized to CO₂, the oxidation of S₂ release a non-oxidizable product S₃. Considering that the elemental composition of a given compound S_i is $CH_{\alpha i} O_{\beta i} N_{\gamma i} S_{\delta i} P_{\varepsilon i} M_{mi}$, the reaction scheme to represent this case is the following:

$$ S_{0} + \nu_{0} Ox\mathop \to \limits^{{R_{0} }} f_{1} S_{1} + f_{2} S_{2} + \left( {1 - f_{1} - f_{2} } \right)CO_{2} + \left( {\gamma_{0} - f_{1} \gamma_{1} - f_{2} \gamma_{2} } \right)NO_{3}^{ - } + \left( {\delta_{0} - f_{1} \delta_{1} - f_{2} \delta_{2} } \right)SO_{4}^{2 - } + \left( {\varepsilon_{0} - f_{1} \varepsilon_{1} - f_{2} \varepsilon_{2} } \right)PO_{4}^{3 - } + \left( {m_{0} - f_{1} m_{1} - f_{2} m_{2} } \right)M^{ + } $$

(48)

$$ S_{1} + \nu_{1} Ox\mathop \to \limits^{{R_{1} }} CO_{2} + \gamma_{1} NO_{3}^{ - } + \delta_{1} SO_{4}^{2 - } + \varepsilon_{1} PO_{4}^{3 - } + m_{1} M^{ + } $$

(49)

$$ S_{2} + \nu_{2} Ox\mathop \to \limits^{{R_{2} }} f_{3} S_{3} + \left( {1 - f_{3} } \right)CO_{2} + \left( {\gamma_{2} - f_{3} \gamma_{3} } \right)NO_{3}^{ - } + \left( {\delta_{2} - f_{3} \delta_{3} } \right)SO_{4}^{2 - } + \left( {\varepsilon_{2} - f_{3} \varepsilon_{3} } \right)PO_{4}^{3 - } + \left( {m_{2} - f_{3} m_{3} } \right)M^{ + } $$

(50)

See Table 6.

Table 6 Stoichiometric matrix corresponding to the analyzed pathway