Zeolite‑integrated airlift membrane bioreactor for citrus processing wastewater: enhanced COD removal and fouling...

Citrus-processing wastewater (CPWW) is challenging to treat due to low pH, high organic load, and inhibitory effects of d-limonene, which suppress biological activity and exacerbate membrane fouling. Conventional membrane bioreactors (MBRs) often fail under these conditions. This study presents an innovative split-plate airlift MBR integrated with zeolite. Zeolite acts both as an adsorbent and a support promoting additional biofilm development, offering a treatment advantage rarely demonstrated for real CPWW. Despite operating at a modestly higher organic loading rate (3.53 vs. 3.04 kg COD·m^-³ d^-1, ∼16% increase), the zeolite-assisted MBR consistently achieved >98% COD removal and permeate COD <30 mg L^-1, while the control unit reached only 85-90% removal with 100-250 mg·L^-1 COD. In the control MBR, TMP (transmembrane pressure) rose rapidly (approaching 900 mbar), causing severe fouling and requiring four membrane cleanings in 30 days, whereas no cleaning was needed in the zeolite-enhanced unit. Resistance analysis indicated that zeolite reduced cake-layer resistance and enabled partial biomass immobilization and supplementary biofilm growth on the zeolite bed, lowering fouling pressure on the membrane. This study was conducted within the PRIMA-funded SWRIPS project (ANR and PRIMA, Horizon 2020 Art. 185), which develops resilient, resource-efficient treatment solutions for industrial wastewater.