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

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 degrees C) and resulting low dissolved oxygen levels (DO < 0.5 mgO(2)/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, <(mu)over cap>(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.