Biological nutrient removal in an sequencing batch membrane bioreactor treating municipal wastewater

The advantages associated with the use of membrane bioreactors (MBR) in wastewater treatment are widely known [1]. MBR have been recently applied to the biological nutrients removal from wastewater, especially nitrogen and phosphorus. Recent studies [2; 3] have demonstrated that the operation of MBR in sequencing batch results in benefits to the treatment system and can be an interesting alternative when the goal is the nutrient removal. In spite of the cited studies, there are few researches in the literature with membrane bioreactor operated in sequencing batch treating real municipal wastewater. Therefore, this study aimed to evaluate the performance of a sequencing batch membrane bioreactor (SBMBR) treating real municipal wastewater for nutrient removal. The reactor, which was built on a pilot scale with a volume of 15 L, was operated for 240 days using two submerged hollow fiber membrane module (Polymen Co. France) with total filtration surface area of 0.18 m. The SBMBR was operated under a sequencing batch modality with a total cycle time of 4 h, which was broken down into 2 min at the feeding stage, 58 min of an anoxic/anaerobic phase and 180 min of aeration and filtration phase. Was used the volumetric exchange rate of 20%, which resulted in a hydraulic retention time of 20 hours and filtration flux of 6.2 L m h. The SBMBR presented efficient carbon and nitrogen removal, with COD, ammonium nitrogen and total nitrogen removal efficiencies averaged at 97.1%, 99.1% and 82.2%, respectively. The high nitrogen removal observed indicates that the SBMBR was able to promote effective nitrification and denitrification, with a concentration below 15 mg L of this parameter in the permeate. The total phosphorus efficiency removal reached 50.5 %, with averaged concentration in the permeate of 4.8 mg L. The phosphorus uptake (Puptake) by poly-phosphate organisms accumulating (PAO) and denitrifying poly-phosphate organisms accumulating (DPAO) increased progressively over reactor operation time. The Putptake rates after 190 days of operation reached 8.3 mgP.gSSV.h and 5.1 mgP.gSSV.h for PAOs and DPAOs, respectively. The increased in the Puptake demonstrates that the activity of OAPs and OAPDs increases substantially in MBR operating in sequencing batch modality. Fluorescence in situ hybridization (FISH) shows the temperature effect on diversity POA and GAO organisms. The membrane performance was affected by the growth of filamentous bacteria in the reactor, which resulted in an increased of fouling rate of 0.34 mbar d to 1.2 mbar d.