Model evaluation of temperature dependency for carbon and nitrogen removal in a full-scale activated sludge plant treating leather-tanning wastewater

Abstract

Organic carbon and nitrogen removal performance of a full-scale activated sludge plant treating pre-settled leather tanning wastewater was evaluated under dynamic process temperatures. Emphasis was placed upon observed nitrogen removal depicting a highly variable magnitude with changing process temperatures. As the plant was not specifically designed for this purpose, observed nitrogen removal could be largely attributed to simultaneous nitrification and denitrification presumably occurring at increased process temperatures (T > 25°C) and resulting low dissolved oxygen levels (DO < 0.5 mgO₂/L). Model evaluation using long-term data revealed that the yearly performance of activated sludge reactor could be successfully calibrated by means of temperature dependent parameters associated with nitrification, hydrolysis, ammonification and endogenous decay parameters. In this context, the Arrhenius coefficients of (i) for the maximum autotrophic growth rate, _A, (ii) maximum hydrolysis rate, k_hs and (iii) endogenous heterotrophic decay rate, b_H were found to be 1.045, 1.070 and 1.035, respectively. The ammonification rate (k_a) defining the degradation of soluble organic nitrogen could not be characterized however via an Arrhenius-type equation.

Keywords:

• Leather tanning wastewater
• nitrogen removal
• temperature
• ammonification
• hydrolysis
• simultaneous nitrification and denitrification
• Arrhenius.

Acknowledgements

Environmental Solutions R&D Ltd. is gratefully acknowledged for sharing the data of leather tanning wastewater treatment plant.

Notes

*NO₂-N concentration negligible (< 2.0 mg/L);

**TN = TKN + NO₃-N; NA = Not Available.

*Not compatible with Arrhenius type equation.