The effect of addition of potato-processing wastewater on the acidogenesis of primary sludge under varied hydraulic retention time and temperature

Under varied conditions of hydraulic retention time (HRT) and temperature, two bench-scale completely-mixed bioreactors (each equipped with a clarifier and a solids recycle system) were used to investigate the effect of the addition of potato-processing industrial wastewater on the acidogenesis of primary sludge. One bioreactor was fed with a 1:1 mixture by volume of industrial wastewater and primary sludge, while the other was fed with primary sludge alone. Short-chain volatile fatty acids (VFAs), the major products of acid-phase anaerobic digestion, are preferred substrates for the microorganisms involved in biological phosphorus removal processes. It was found that acidogenesis was feasible in both bioreactors. The addition of the starch-rich potato-processing wastewater considerably improved the performance of the system, resulting in an increase in the net VFA and soluble chemical oxygen demand (COD) concentrations and the corresponding specific production rates, higher percentages of suspended solids destruction, and better settling properties of the clarifier. An increase in HRT from 18 to 30 h improved the extent of acidogenesis and substrate solubilization in both reactors. However, an increase in temperature in the range of 22-35 degrees C revealed a different behavior (i.e. a potential optimum value of 30 degrees C for the bioreactor fed with the mixture; a sharp decline in production for the other bioreactor). Overall, gas generation was negligible. The amount of VFAs generated, in most runs, was adequate to support subsequent biological nutrient removal processes. (C) 1999 Elsevier Science B.V. All rights reserved.