The risk and the transition time: two aeration tanks in parallel adjust to anoxic tank and aeration tank in series

Dear all,

The process deal with high chloride (about 10,000 ppm) wastewater is two aeration tanks in parallel now, we plan to adjust the aeration tanks to anoxic tank and aeration tank in series, while we need to keep the effluent COD <50 ppm and ammonia nitrogen <5 ppm for the continuous water monitoring system . Could someone kindly tell us the risk and the time of transition, thanks all.

The hydraulic retention time of two aeration tanks in parallel is about 12 hrs , the pH about 8, the DO 3~4 ppm, the MLSS 4,000 ppm, the temperature of aeration tanks about 33~36°C.the influent COD is about 1,000 ppm, the Kjeldahl nitrogen about 50 ppm; the effluent COD is about 40~50 ppm, the Kjeldahl nitrogen about 2~5 ppm.