Effect of HRT on Acidogenic Digestion of Primary Sludge

Abstract
A series of bench‐scale, continuous‐flow experiments, using primary sludge from a local municipal wastewater‐treatment plant, has been employed to investigate the effect of hydraulic retention time (HRT) on the acid‐phase anaerobic digestion process. Results show that both volatile fatty acid (VFA) production and chemical oxygen demand (COD) solubilization increase significantly with increasing HRT up to 12 h, but drop moderately at a longer HRT. Acetic acid and propionic acid are the main VFAs formed, averaging 46% and 32% of the total, respectively. Variation in HRT has a profound effect on organic substrate degradation as well. Regardless of the prevailing experimental conditions, lipids and carbohydrates are converted at higher percentages than proteins. Furthermore, protein utilization appears to be independent of reactor configuration, but carbohydrate and lipid degradation patterns are a function of the reactor regime.