In activated sludge process, continuous culture of heterogenic microorganisms grow on organic and inorganic substrates. Biooxidation removes soluble substrate and solid-liquid separation removes colloidal or suspended solids including biomasses from the wastewater.
Maximum floc formation and bio-oxidation could be achieved at different microbial cell growth phases under different physical conditions. Generally, activated sludge process is so designed and operated that these two non-compatible removal mechanisms occur in the same aeration tank. Therefore maximum removal capacity of these processes is not fully utilized. Many studies have been conducted to make best use of respective process, while few researches tried to improve the both processes in simultaneous.
The objective of these study is to optimize activated sludge system by incorporating a bioflocculation tank with high- and row-rate aeration tanks in which microbial growth phases differ.
Two major tests have been made in this research; how biomass conversion is affected by MCRT (mean cell residence time) and how microbial flocculation and settling characteristics are affected by the effects of organic loading, mixing intensity, and sludge characteristics.
The following conclusions were made in this study.
1. Y(observed yield coefficient) at 4-day MCRT was 1.6 times greater than at 10-day MCRT.
2. The low SVI(<100) appeared at both high F/M(1.2) and low F/M(0.05). The maximum SVI was 210 at F/M(1.0)
3. Mixing intensity affected more on supernatant COD than on SVI ; when SVI is smaller than 200, supernatant COD and SVI increase as mixing increases. While SVI of greater than 200, SVI and supernatant COD decrease as turbulence increases.
4. When the tank volume of low-growth rate is equal to that of high-growth rate, the original volume could be decreased by 11 to 18 percent.
5. It was proved that bioflocculation decreased effluent COD as well as contribute to the optimization of activated sludge process.
