Impact of nitrogen loading rates on treatment performance of domestic wastewater and fouling propensity in submerged membrane bioreactor (MBR)

• Higher nitrogen loading rate adversely affected nutrient removal efficiency.
• Soluble EPS concentration increased with increasing ammonium nitrogen concentration.
• High soluble EPS concentration caused higher cake layer membrane resistance.
• Membrane filtration performance deteriorated with increasing nitrogen loading rate.

In this study, performance of laboratory-scale membrane bioreactor (MBR) was evaluated in treating high strength domestic wastewater under two nitrogen loading rates (NLR) i.e., 0.15 and 0.30 kg/m3/d in condition 1 and 2, respectively, while organic loading rate (OLR) was constant at 3 kg/m3/d in both conditions. Removal efficiencies of COD were above 95.0% under both NLR conditions. Average removal efficiencies of ammonium nitrogen (NH4+–N), total nitrogen (TN) and total phosphorus (TP) were found to be higher in condition 1 (90.5%, 74.0%, and 38.0%, respectively) as compared to that in Condition 2 (89.3%, 35.0%, and 14.0%, respectively). With increasing NLR, particle size distribution shifted from narrow (67–133 μm) towards broader distribution (3–300 μm) inferring lower cake layer porosity over membrane fibers. Soluble extracellular polymer substance (sEPS) concentration increased at higher NLR due to biopolymers released from broken flocs. Higher cake layer resistance (Rc) contributed towards shorter filtration runs during condition 2.