Kinetics of COD removal in the activated sludge process, including bioflocculation

The activated sludge system consists of an aeration tank into which sewage and a controlled amount of activated sludge are aerated together by some means for a period of time. After the aeration time elapsed, the mixed sewage and activated sludge pass to a final sedimentation tank where the sludge is settled out and clarified effluent is obtained. A fraction of the sludge is recycled to the inlet of the aeration tank, and the excess sludge generated in the process by the production of biomass and by the settling of inert material is usually wasted from the recycled line.; The aim of this investigation was to study the removal mechanisms for particulate COD in the aeration basin of the activated sludge process, and to develop an understanding of the factors affecting such removal process.; Total chemical oxygen demand (COD) can be defined as the sum of particulate COD (PCOD) and soluble COD present (DCOD). For the purpose of this investigation, the PCOD made up of organic suspended solids and organic colloids present in the wastewater (PCOD = SSCOD + CCOD).{09}On the other hand, the dissolved COD is defined as the truly soluble biodegradable material present in the wastewater.; The existing theories incorporated into the IWA/IAWQ consensus models indicate that the removal of particulate organics from the liquid in the activated sludge process is a two-step process, being, rapid enmeshment of particles and hydrolysis followed by oxidation. However, observations made at the University of New Orleans experimental station indicate that the removal of organic particles is not instantaneous; and therefore, it needs separate attention. This removal process can actually be described as a three-step process, namely, flocculation, hydrolysis and finally oxidation.; Research performed at the University of New Orleans experimental station at Marrero, Louisiana, USA, observed that most of the total organic material from many municipal wastewaters is in the form of organic particulate material that can be removed by flocculation. Therefore, the removal of organic particles is of vital importance on achieving the effluent standards.; This project was carried out using both bench-scale batch reactors and a 6m3/d continuous-flow pilot plant treating municipal sewage.