Rengo Co., Ltd. Yashio Mill has installed a new wastewater treatment facility for the use of recycling water due to the decreased performance and aging structure of the existing facility. Under the spatial constraint, a highly-efficient, energy-saving, compact system had to be designed in the renewal project. Eventually, Sumi-Sludge® System, a high-rate coagulation system, was selected after a comparative investigation of those including suspended carrier process, oxygen aeration process, multi-stage biological process, and membrane bioreactor. The new system is equipped with high-rate coagulation precipitators, Sumi-Thickner®, which concentrate the activated sludge to a high extent. With the aeration tanks also keeping the MLSS in high consistency, the system is designed to treat the wastewater efficiently with the BOD volume load of 2 to 3 kg-BOD⁄m
3⁄day.
As the characteristics of the system, it keeps good conditions of the microbiological ecosystem and sedimentation property which enable a highly efficient treatment while the property and flow rate of the wastewater are kept stable. On the other hand, owing to the space-saving design, the surface level of the activated sludge tends to fluctuate widely once the sedimentation property worsens. Besides, high consumption of chemicals such as coagulant, and high sensitivity of the performance to the fluctuation of the wastewater property and flow rate are also observed.
Here we report the implemented measures against the above, including the control of MLSS, adjustment of effluent flow rate, reselection of chemicals, and additional installation and modification of auxiliary machines. These subjects need to be resolved continuously for the future by accumulating operational experiences and further improvements.
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