Membrane fouling behavior in membrane bioreactors for nitrogen-deficient wastewater pretreated by ammonium ion exchange

Nitrogen is a critical element closely related to the synthesis of cellular membrane fouling behaviors in membrane bioreactors (MBRs). In this study, a novel pretreatment process by coupling chemically enhanced primary treatment (CEPT) with ammonia nitrogen ion exchange and regeneration (AIR) was proposed to analyze their influences on sludge properties and membrane fouling in MBRs. The MBRs with CEPT and AIR pretreatment obtained the effluent with chemical oxygen demand (COD) and ammonium nitrogen (NH₄⁺-N) levels comparable to the conventional anoxic/aerobic MBR, but with much lower concentrations of total nitrogen (≤3.0 mg/L) and total phosphorous (≤0.15 mg/L). CEPT and AIR remarkably removed particles and soluble proteins from the influent, prohibited EPS secretion by 62.9–79.1% and elevated viscoelasticity of EPS, and thus alleviated membrane fouling. Membrane foulant in the experimental MBRs had unstable EPS structures easily detached, and low biofilm roughness to prevent the adsorption of organic matters. Nitrogen load had significantly positive correlations with EPS contents, viscoelasticity of EPS, and the total filtration resistance. The nitrogen-deficient condition enriched quorum quenching bacteria and microbes surviving retarding EPS production, and inhibited the overgrowth of filamentous bacteria. Therefore, nitrogen separation from wastewater in advance can effectively alleviate membrane fouling and improve pollutant removal in MBRs.