New Approaches to the Coexistence of Water Quality Improvement and GHG Reduction in Wastewater Treatment

Important issue of global warming attributed to elimination of several greenhouse gases like carbon dioxide has been frequently reported as a serious problem in recent years. Several countermeasures or trials aimed to its inhibition were introduced in world-wide scale. Effective measures of regulation for reduction of CO2 emission in industry field were started as a middle and 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 the reduction of electrical requirement for waste water treatment consisted of 33% amounts of emission from treatment plant had been constantly conducted. Here we report three effective results in respect to reduce energy consumption by three operation methods upgraded the activated sludge process.First is the optimization of air volume supply at aeration by means of controlling dissolved oxygen according to NH4−N concentration. We have more efficient operation of activated sludge process in aeration tank by utilize this method. Operation using the parameter configured in this experiment made 15% at maximum of air volume consumption cut off at monthly relative to the method using simply dissolved oxygen control.Next is restricted A2/O process with nitrified liquor recirculation on the basis of the conventional activated sludge process. Nitrogen removal ratio could be achieved 70% by means of this process, higher than conventional activated sludge process but equal level comparing to A2/O process. In addition, its phosphorus removal ratio was also higher than conventional activated sludge process, meanwhile less than restricted A2/O process. Electric power consumption supplied to the restricted A2/O process was equal level comparing to conventional activated sludge process and 25% higher than A2/O process. Therefore, introduction of restricted A2/O process in substitution for standard A2/O process will not only achieve initial and running cost savings, but also maintain much good final effluent water quality of waste water treatment plant.Lastly, the control of air flow volume on the basis of monitoring characteristics of influent waste water had been discussed. Adoption of feed-forward control instead of feed-back control can be a key to appropriate air supply for treatment of waste water. This trial indicated possibility feed-forward control by monitoring electric conductivity of influent to attain saving electric energy consumption and improvement of effluent water quality.