Development Of MBR Suitable For Retrofit With Flat Sheet Membrane

Abstract
In sewage works of Japan near bay areas, the tightening of restrictions on nitrogen and phosphorus has resulted in greater needs for reconstruction and replacement of infrastructure, to switch from the conventional activated sludge process to the advanced treatment process without newly expanding aeration tanks. Thus, we have developed a membrane bioreactor while maintaining the treatment capacity by using only existing reactors for the conventional activated sludge process. The results of a demonstration experiment with a pilot plant show satisfactory nitrogen and phosphorus biological removal performance. The expected process performance is as follows: T-N < 10 mg/L, T-P < 0.5 mg/L. Also, it is possible to treat sewage with 0.31 to 0.48 kWh/m3 of energy by using energy-saving measures such as a siphon filtration system and airlift recirculation in a full-scale test plant of 5000 m³/d.

INTRODUCTION
The strengthening of nitrogen and phosphorous regulations centred on the closed water areas of Japanese sewage works has resulted in greater needs for reconstruction and replacement to switch from the conventional activated sludge process (hereinafter referred to as “CAS”) to an advanced treatment process without newly expanding aeration tanks.１） Thus, we started on the development of a membrane bioreactor process (hereinafter referred to as “Retrofit-MBR”) that uses only the existing reactors for CAS to enable the handling of nitrogen and phosphorous elimination while maintaining permeate volume. At the start of development, we used the plans of 10 existing sewage works in Japan that use the CAS to investigate the problems and design/construction restrictions, etc., that would occur when reconstructing facilities using MBR to determine the optimum MBR process. Next, we confirmed treatment performance in a demonstration test at a pilot plant designed based on the results of those investigations. The demonstration test carried out at the Research and Technology Development Experimental Center of the Japan Sewage Works Agency.Consequently we have achieved good nitrogen and phosphorous elimination performance and significant energy savings with Retrofit-MBR in a pilot plant, thus we report as follows.