Comparative investigations on COD-removal in sequencing batch reactors and continuous flow plants

Investigations on enhanced COD removal from municipal wastewater were performed over a period of 2.5 years, comparing three different types of reactor. The main idea was to determine the influence of the mixing characteristics of the reactor on the treatment processes and the effluent quality. Therefore three pilot plants (a completely mixed reactor, a cascade of three reactors and a SBR) were operated under equal conditions (wastewater, hydraulic load, temperature, sludge age) in parallel to each other. Investigations were carried out at different sludge ages. It could be shown that within one sludge age the CODf removal efficiency increased, when mixing characteristics came closer to the plug flow and it also increased with higher temperatures. A significant correlation was observed between the COD removal efficiency and the sludge load. The higher the sludge load was the greater the CODf concentration in the effluent. Especially the SBR reactor showed an excellent performance under the given operating conditions. Dynamic simulation calculations were carried out, to investigate whether the influence of the type of reactor on the COD-elimination could be described theoretically by combining growth kinetics and the mixing characteristics of the individual reactors. The results showed that performance was better when mixing characteristics came closer to plug flow.