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The performance and bio‐kinetic coefficients of the activated sludge process (ASP) treating synthesised dairy wastewater were evaluated in a lab‐scale setup. The step‐loading experiment showed that the chemical oxygen demand (COD) removal efficiency, in general, increased with increasing influent wastewater COD concentration from 180 to 1200 mg/L (correlation coefficient was 0.80). The COD removal efficiency ranged from almost 80–88.4% depending on the COD concentration of the influent wastewater. Also, it could be stated that the ASP was probably underfed with organics at COD concentrations <725 mg/L. Monod, Moser, Contois and Chen & Hashimoto substrate utilisation models, relating the growth of micro‐organisms to substrate utilisation, were employed to describe the bio‐kinetics of the ASP at an organic loading rate of 1200 mg/L. Amongst them, the Contois and Monod models predicted the bio‐kinetic reactions of the ASP very well with coefficient of determination (R2) values of 0.95 and 0.93, respectively. The estimated bio‐kinetic coefficients of the Contois model (on COD basis) were as follows: half‐velocity constant (0.20 mg/L), maximum substrate utilisation rate (3.13 per day), biomass yield coefficient (0.68), endogenous decay coefficient (0.07 per day) and maximum specific growth rate (2.13 per day).

Abbreviations: %P, mean relative percent deviation; Ф, spreading pressure (J/m 2); ∆S, change in specific entropy (kJ/mol K); A m , area of a water molecule (1.06 × 10-19 m 2); AOAC, Association of Official Analytical Chemists; a w , water activity; BDDT, Brunauer-Deming-Deming-Teller; BET, Brunauer-Emmett-Teller; dm/dt, rate of change of mass with temperature; DVS, dynamic vapor sorption; EMC, equilibrium moisture content; GAB, Guggenheim-Anderson-De Boer; H L , latent heat of vaporization of pure water (kJ/mol); K B , Boltzmann's constant (1.38 × 10-23 J/K); N, number of adsorbed monolayers; n, number of data points; N A , Avogadro's number (6 × 10 26 molecules/kg mol); R, universal gas constant (8.314 × 10-3 kJ/ mol K); RH, relative humidity; q st , net isosteric heat of sorption (kJ/mol); Q st , isosteric heat of sorption (kJ/mol); R 2 , coefficient of determination; T hm , harmonic mean temperature; UK, United Kingdom.