Failure Analysis of an Effluent Treatment Plant in an Oral Care Industry

Abstract

Reports of environmental pollution by industries worldwide call for an urgent need to assess wastewater treatment facilities in various industries. This study presents an assessment of a wastewater treatment plant in an oral care (toothpaste) industry. The industry was visited, facilities for wastewater treatment were assessed (based only on efficacy to remove selected environmental and human’s health-related pollutants) and measurement of essential design parameters and facility characteristics were conducted. The study revealed that the averages of flow rate, biochemical oxygen demand at 5 days (BOD₅), chemical oxygen demand (COD), suspended solids (SS), iron concentration, and total solids (TS) in the influent wastewater into the plant were 4.96 ± 0.6 m³/d; 90 ± 5 mg/L; 224 ± 8 mg/L; 1266.78 ± 10.24 mg/L; 0.31 ± 0.11 mg/L, and 2198.65 ± 20.44 mg/L, respectively. Individual efficacies were as follows: 0.49, 0.28, and 0.38% for SS, TS, and calcium, respectively. The overall efficacy of the wastewater treatment facility was found to be 0.020% which was significantly lower than expected. This indicates that no treatment was conducted on the wastewater and that the wastewater is being discharged into the environment essentially untreated. Equalization time (t _eq) was found to be 2.0 h with equivalent equalized BOD₅ concentration of 90 ± 5 mg/L, while expected volume for the equalization tank is 1.5 m³. It was concluded that failure (lower overall efficacy) of the system can be attributed to lack of an equalization tank, inadequate treatment processes, and refusal to apply standardized engineering code and practices. Although such conditions are rare in developed nations, these results demonstrate the problems in pollution control in developing communities.

Appendix: Derivation of Equations for Treatment Plant’s Efficacy

The pollutants that are removed by the treatment plant can be divided into two parts of a and b; “a” represents the turbidity removed and “b” represents microorganisms reduced specifically bacteria. Under normal condition or operation of wastewater treatment pollutants are expected to be removed or reduce to FEPA [1] standard limits. Let F _a denote the concentration of pollutant in the raw water (F), O _a denote the fraction of “a” removed from the raw wastewater but in the floc (O); and U _a denote the fraction of “a” present in the treated wastewater (U). Then, the pollutant removed from the raw wastewater can be expressed as follows [2, 3]:

$$ F(F_{\text{a}} ) = O(O_{\text{a}} ) + U(U_{\text{a}} ) $$

which can be expressed as follows [3]:

$$ F = O + U $$

Elimination of O _a or U _a from the above equations

$$ \frac{F}{U} = \frac{{O_{\text{a}} - U_{\text{a}} }}{{O_{\text{a}} - F_{\text{a}} }} $$

and

$$ \frac{F}{O} = \frac{{O_{\text{a}} - U_{\text{a}} }}{{F_{\text{a}} - U_{\text{a}} }} $$

It can then be shown that the efficacies of the treatment plant in removing COD (E _u) and BOD₅ (E _o) are as shown:

$$ E_{\text{u}} = \frac{{{\text{amount}}\;{\text{of}}\;{\text{COD}}\;({\text{mg/L}})\;{\text{removed}}}}{{{\text{total}}\;{\text{amount}}\;{\text{of}}\;{\text{COD}}\;({\text{mg/L}})\;{\text{of}}\;{\text{raw}}\;{\text{wastewater}}}} $$

$$ E_{\text{u}} = \frac{{O(O_{\text{a}} )}}{{F(F_{\text{a}} )}} = \frac{{O_{\text{a}} (F_{\text{a}} - U_{\text{a}} )}}{{(O_{\text{a}} - U_{\text{a}} )F_{\text{a}} }} $$

$$ E_{\text{o}} = \frac{{{\text{amount}}\;{\text{of}}\;{\text{BOD}}_{5} \;({\text{mg/L}})\;{\text{removed}}}}{{{\text{total}}\;{\text{amount}}\;{\text{of}}\;{\text{BOD}}_{5} \;({\text{mg/L}})\;{\text{of}}\;{\text{raw}}\;{\text{wastewater}}}} $$

$$ E_{\text{o}} = \frac{{U - U(O_{\text{a}} )}}{{F - F(F_{\text{a}} )}} = \frac{{U(1 - O_{\text{a}} )}}{{(1 - F_{\text{a}} )F}} = \frac{{(O_{\text{a}} - F_{\text{a}} )(1 - O_{\text{a}} )}}{{(O_{\text{a}} - U_{\text{a}} )(1 - F_{\text{a}} )}} $$

These indicate that overall efficiency of the treatment plant can be expressed as follows [2, 3]:

$$ E = E_{\text{o}} \,E_{\text{u}} $$