New approaches to the coexistence of water quality improvement and GHG reduction in wastewater treatment

摘要

Important issue of global warming attributed to elimination of several greenhouse gases likecarbon dioxide has been frequently reported as a serious problem in recent years. Severalcountermeasures or trials aimed to its inhibition were introduced in world-wide scale. Effectivemeasures of regulation for reduction of CO_2 emission in industry field were started as a middleand long term goal in Japan. In Tokyo, one of a strategic plan “Earth Plan 2010” followed by“Earth Plan 2004” was set as a regional goal for prevention of global warming, therefore thereduction of electrical requirement for waste water treatment consisted of 33% amounts ofemission from treatment plant had been constantly conducted. Here we report three effectiveresults in respect to reduce energy consumption by three operation methods upgraded theactivated sludge process.First is the optimization of air volume supply at aeration by means of controlling dissolvedoxygen according to NH_4-N concentration. We have more efficient operation of activatedsludge process in aeration tank by utilize this method. Operation using the parameter configuredin this experiment made 15% at maximum of air volume consumption cut off at monthlyrelative to the method using simply dissolved oxygen control.Next is restricted A~2/O process with nitrified liquor recirculation on the basis of theconventional activated sludge process. Nitrogen removal ratio could be achieved 70% by meansof this process, higher than conventional activated sludge process but equal level comparing toA~2/O process. In addition, its phosphorus removal ratio was also higher than conventionalactivated sludge process, meanwhile less than restricted A~2/O process. Electric powerconsumption supplied to the restricted A~2/O process was equal level comparing to conventionalactivated sludge process and 25% higher than A~2/O process. Therefore, introduction ofrestricted A~2/O process in substitution for standard A~2/O process will not only achieve initialand running cost savings, but also maintain much good final effluent water quality of wastewater treatment plant.Lastly, the control of air flow volume on the basis of monitoring characteristics of influentwaste water had been discussed. Adoption of feed-forward control instead of feed-back controlcan be a key to appropriate air supply for treatment of waste water. This trial indicatedpossibility feed-forward control by monitoring electric conductivity of influent to attain savingelectric energy consumption and improvement of effluent water quality.