Optimisation of the design parameters in an activated sludge system for the wastewater treatment of a potato processing plant

Abstract Aerated biological reactors at a laboratory scale, fed continuously with a model wastewater system, were used to obtain design parameters of an activated sludge process for the wastewater treatment of a potato processing plant. Experiments were performed using different dilution rates ( D ) ranging between 0.01 and 0.13 h −1 to determine parameters such as: maximum specific microbial growth rate ( μ max ), saturation constant ( K s ), coefficient of microbial decay ( k d ) and true biomass yield ( Y X/S ). Design parameters were calculated from the mass balances of substrate consumption and biomass production under steady state, considering a Monod-type equation to represent the effect of substrate concentration on biomass production rate. The values of Y X/S and k d were obtained from the linear plot of q S (specific rate of substrate consumption) vs. D . Experimental data regression led to Y X/S =0.45 gVSS/g COD and k d =0.024 h −1 . By non-linear regression of q S vs. substrate concentration ( S S ) data the following values were obtained μ max =0.09 h −1 and K s =0.006 g/l. Critical dilution rate was also calculated; it corresponds to the D value for which the cells of a reactor operating under such conditions are destroyed or are eliminated from the system at the same rate than they are produced.