SPACE AND ENERGY SAVING SYSTEM FOR ADVANCED WASTEWATER TREATMENT INTRODUCING PRE-COAGULATION AND BIOFILM PROCESS

摘要

The Osaka Prefectural Government seeks to introduce an advanced wastewater treatment systemrnat the wastewater treatment plant, to preserve water quality in Osaka Bay and to create a newrnwater circulation process. However, due to space limitation at the existing wastewater treatmentrnplants in urban areas, it is difficult to introduce the conventional type of advanced wastewaterrntreatment system. As such, there is a need for a new type of space and energy saving wastewaterrntreatment system. Since October 2000, an experimental study has been in progress at the actualrnpractical level at the Konoike Sewage Treatment Plant of the Neyagawa Regional SewagernSystem in Osaka prefecture.rnThis process consists of pre-coagulation and sedimentation process, and nitrification andrndenitrification process, using attached-growth media of biofilm, without using activated sludge.rnTo complete denitrification in the 2nd Anoxic tank, organic matter is required as hydrogen donorrnin the 2nd Anoxic tank. The organic matter is obtained as organic acid by fermentation ofrnpre-coagulated sludge.rnThis system can reduce organic load to biological treatment process and the HRT of thernbiological treatment is shortened to 8 hours (at design maximum daily flow, 3,500m3/day).rnThe effluent from a grit chamber at the Konoike Sewage Treatment Plant located in OsakarnPrefecture, Japan, was introduced to the pre-coagulation process. FeCl3 and an anionic highrnmolecular coagulant were added, in amounts of 0.1mg-Fe/mg-SS and 0.5mg/L, respectively.rnThe retention time at the primary sedimentation tank was 1.4 hours.rnThe pre-coagulation and sedimentation process is followed by the biological reaction tanks,rnwhich consist of four tanks. The names of the respective tanks and their retention times are asrnfollows: 1st anoxic tank (1.8 hours), aerobic tank (3.6 hours), 2nd anoxic tank (1.6 hours) andrnPost-aeration Tank (1.0 hours). The total retention time is 8 hours. Media were added to thernaerobic tank at the additive ratio of 10%, to promote nitrification and to remove organicrnmaterials and were aerated by diffuser. To prevent media from becoming one-sided, they arernreturned to the inlet area of an aerobic tank from the end point of the tank, by means of an air liftrnpump. Media were also added to 1st and 2nd Anoxic Tanks, at the additive ratio of 17%, tornpromote denitrification. A draft tube was used as an agitator. Media are made of polyvinylrnalcohol (PVA) and have an outside diameter of 4mm. The influent goes through the 1st Anoxic