Effectiveness of supplemental aeration and an enlarged first stage in improving RBC performance

Rotating biological contactors, a type of fixed-film wastewater treatment process, have been used extensively for treating industrial and municipal wastewaters. Several studies have indicated RBC operational problems occasioned by overloaded conditions in the first and second stages, resulting in very low dissolved oxygen levels which further result in heavy biomass growth such as Beggiatoa, thereby deteriorating process efficiency. The effectiveness of supplemental aeration and an enlarged first stage was investigated in a full-scale, four-stage RBC treatment plant having two parallel trains treating domestic and industrial dairy waste. One train was used to evaluate the effects of operational modifications, and the parallel train was used as a control. The study was conducted in two phases. In the first phase the effect of supplemental aeration alone and in the second phase the combined effect of supplemental aeration alone and use of an enlarged first stage on RBC performance were investigated. Each phase was operated separately under a range of low and high organic loading rates;The results indicate that higher removal rates can be achieved with supplemental air, regardless of the organic loading rates. The results also indicated that there is a strong relationship between organic mass loading and removal and these relationships can be used to design RBC systems. Most of the soluble COD was removed in the first stage. Dissolved oxygen levels and oxygen uptake rates were higher with supplemental air, and DO\u27s always remained above 1 mg/L. Growth of Beggiatoa was completely eliminated and thinner biofilms were established. Ammonia nitrogen removal efficiencies of 80.6 and 68.4 percent were observed at low and high organic loading rates in the presence of supplemental air. Carbonaceous substrate removal kinetics were found to be first order when using supplemental air and zero order without the air at higher organic loadings;The SCOD removal efficiencies generally increased with an enlarged first stage alone due to the reduced organic loadings in the initial stages, but removal rates observed when using supplemental aeration and an enlarged first stage were still much superior. Ammonia nitrogen removal efficiencies deteriorated when operating with an enlarged first stage, indicating preference for the plug-flow mode

Effect of Growth Rate on Effluent Suspended Solids in Activated Sludge Systems

Bioenvironmental Engineerin