Anaerobic Fluidized Bed Membrane Bioreactor for Wastewater Treatment

TLDR

Anaerobic membrane bioreactors promise energy‑efficient wastewater treatment, but membrane fouling limits their use. A 120‑day, two‑stage anaerobic system operated at 35 °C fed synthetic wastewater (COD ≈ 513 mg L⁻¹) used a fluidized‑bed bioreactor followed by an anaerobic fluidized‑bed membrane bioreactor with 2.0–2.8 h and 2.2 h hydraulic retention times, respectively. Placing membranes directly on granular activated carbon in the AFMBR controlled fouling, enabling two cleanings, a stable flux of 10 L m⁻² h⁻¹ with transmembrane pressure rising only from 0.075 to 0.1 bar, achieving 99 % overall COD removal (permeate COD 7 ± 4 mg L⁻¹) while consuming only 0.058 kWh m⁻³ of fluidization energy—about 30 % of the methane energy produced—and 0.028 kWh m⁻³ for the AFMBR alone, far below other submerged membrane bioreactors.

Abstract

Anaerobic membrane bioreactors have potential for energy-efficient treatment of domestic and other wastewaters, membrane fouling being a major hurdle to application. It was found that fouling can be controlled if membranes are placed directly in contact with the granular activated carbon (GAC) in an anaerobic fluidized bed bioreactor (AFMBR) used here for post-treatment of effluent from another anaerobic reactor treating dilute wastewater. A 120-d continuous-feed evaluation was conducted using this two-stage anaerobic treatment system operated at 35 °C and fed a synthetic wastewater with chemical oxygen demand (COD) averaging 513 mg/L. The first-stage was a similar fluidized-bed bioreactor without membranes (AFBR), operated at 2.0−2.8 h hydraulic retention time (HRT), and was followed by the above AFMBR, operating at 2.2 h HRT. Successful membrane cleaning was practiced twice. After the second cleaning and membrane flux set at 10 L/m2/h, transmembrane pressure increased linearly from 0.075 to only 0.1 bar during the final 40 d of operation. COD removals were 88% and 87% in the respective reactors and 99% overall, with permeate COD of 7 ± 4 mg/L. Total energy required for fluidization for both reactors combined was 0.058 kWh/m3, which could be satisfied by using only 30% of the gaseous methane energy produced. That of the AFMBR alone was 0.028 kWh/m3, which is significantly less than reported for other submerged membrane bioreactors with gas sparging for fouling control.