Author: Ijomah Toochukwu Sylvester
Department: Chemical Engineering
Affiliation: Nnamdi Azikiwe University Awka

The restaurant wastewater (RW), paint wastewater(PW) and pharmaceutical wastewater (PHW) were treated using anaerobic digestion in a batch process for a period of 45 days. The temperature was always between 29 to 32oC while the pH fluctuated between 6.1 and 8.9 for the three wastewaters. The physicochemical characterization showed that the levels of most parameters reduced drastically after the digestion. The kinetic parameters such as maximum rate of substrate utilization (K), half velocity or saturation constant (KS), endogenous decay coefficient (Kd), biomass or microbial growth yield (Y) and maximum specific microorganism growth rate (μmax) were calculated for the wastewaters’ digestion. The kinetics of the anaerobic digestion followed first-order kinetic model for the three wastewaters. The μmaxcalculated were0.0316, 0.0572 and 0.0789 day-1 for PHW, PW and RW respectively while the Kd values of 0.0112 day-1(PHW), 0.003 day-1 (PW) and 0.0282 day-1 (RW) were obtained. Simulations of kinetic model for the design of continuous reactor for the anaerobic digestion of the wastewaters were carried out using the kinetic parameters obtained from the batch digestion. The hydraulic retention time (HRT) and solid retention time (SRT) were mainly estimated by varying different model parameters like efficiency of reactor, influent substrate concentration and biomass concentration. The HRT increased with increase in varying substrate concentration while the SRT decreased in a hyperbolic pattern as the influent substrate concentration was increased. With increase in influent substrate concentration, at 70% efficiency, the SRT deceased up to 149 hours for PHW, 120 hours for PW and 144 hours for RW. The plot of the SRT followed a decreasing hyperbolic pattern. The design tables and charts were prepared and can readily be used in designing the plant.

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