オゾンを用いた活性汚泥法における汚泥減容化の基礎的研究

抄録

Basic research was carried out to study sludge reduction by ozonation in an activated sludge process. This basic research was done towards the development of a wastewater biological treatment method with minimized excess sludge. Continuous tests were conducted, mainly to study the relationship between sludge liquefaction by ozonation and sludge reduction, as well as the stability of treatment in which activated sludge is deactivated in the liquefaction process. Studies were also made, through batch tests of activated sludge liquefaction by ozone injection, on the behavior of matter and changes in the degree of activated sludge nitrification activity. The liquefied sludge amount (ΔL) increased along an increase in the amount of injected ozone per day, as did the amount of sludge reduction (ΔX_R). The amount of sludge reduction versus the amount of sludge liquefaction (ΔX_R/ΔL) immediately after ozonation was 13, while that versus the same including the liquefied amount in the aeration tank was approximately 0.8. The S-BOD in treated water showed almost no increase, while the S-TOC, S-COD_Mn, and TP did. Comparing treatment by acidic ozonation, by which activated sludge was deactivated after the liquefaction process, and conventional ozonation, it was found that the quality of treated water worsened especially under high BOD sludge loads (0.2kg/kg/d), indicating that an effective sludge reduction was not being achieved. Batch test results showed that there was a progress in activated sludge liquefaction along an increase in the injected ozone. However, there was a drop in the relative sludge nitrification degree, a drop to 20% at an ozone injection rate exceeding 40 mg-O₃/g-MLVSS. A relation was also indicated between the elusion of K (Potasium) and the degree of activated sludge activity.