This study investigated the efficacy of membrane bioreactor (MBR) technology in treating saline industrial wastewater, focusing on the impact of the organic loading rate (OLR) and the food-to-microorganism (F/M) ratio on treatment performance. This research utilized saline industrial wastewater from Al-Hasa, which had salinity levels ranging from 5000 to 6900 mg/L. It explored treatment processes at varying Chemical Oxygen Demand (COD) concentrations of 800, 1400, and 2000 mg/L, corresponding to an OLR of 0.80 ± 0.05, 1.41 ± 0.07, and 1.98 ± 0.12 g COD/L, respectively. The average F/M ratios used were 0.20, 0.36, and 0.50 g COD/g MLSS·d, maintaining a constant Sludge Residence Time (SRT) of 12 days, a hydraulic retention time (HRT) of 24 h (hrs.), and a flux of 10 L/m²·h. The MBR system demonstrated high COD removal efficiencies, averaging 95.7 ± 1.6%, 95.5 ± 0.4%, and 96.1 ± 0.3%, alongside Biochemical Oxygen Demand (BOD) removal rates of 98.3 ± 0.2%, 99.8 ± 0.1%, and 98.5 ± 0.1%, respectively. However, an increased OLR led to elevated residual COD and BOD levels in the treated effluent, with COD concentrations reaching 34.2 ± 12.8, 63.3 ± 5.9, and 76.5 ± 5.4 mg/L, respectively. This study also reveals a significant decline in ammonia and Total Kjeldahl Nitrogen (TKN) removal efficiencies as OLR increases, dropping from 96.1 ± 0.5% to 80.2 ± 0.9% for ammonia and from 83.8 ± 3.4% to 65.8 ± 2.3% for TKN. Furthermore, higher OLRs significantly contribute to membrane fouling and elevate the transmembrane pressure (TMP), indicating a direct correlation between OLRs and operational challenges in MBR systems. The findings suggest that for optimal performance within the Saudi disposal limits for industrial wastewater, the MBR system should operate at an F/M ratio of ≤0.33 g COD/g of Mixed Liquor Suspended Solid (MLSS)·d. This study underscores the critical role of the OLR and F/M ratio in treating saline industrial wastewater using MBR technology, providing valuable insights for enhancing treatment efficiency and compliance with environmental standards.

This study investigated the potential impact of salinity levels on the treatment performance and membrane fouling of MBR seeded with sludge from saline industrial effluent treatment plants. A pilot-scale MBR received mixed saline industrial effluents at an organic loading rate (OLR) of 1.3 g COD/L·d and a feed-to-micro-organism (F/M) ratio of 0.33 g COD/g TSS. The effects of the variable salt concentrations of 5, 10, 20, and 25 g/L were investigated. The ranges of ammonia and total nitrogen (TN) concentrations were 22.2–26.3 mgN/L and 55.1–59.2 mgN/L, respectively. The MBR achieved promising results for chemical oxygen demand (COD) and biochemical oxygen demand (BOD), with removal ranges of 95.4–97.2% and 98.3–98.8%, respectively. The system provides 93.2–96.7% and 81.6–92.5% for ammonia and TN removal. Up to a 20 g/L salinity level, there were no significant effects on treatment performance, but 25 g/L significantly declined daily and specific COD removal load. Despite this, residual values at 25 g/L were better and met the Saudi standard for effluent discharge. This is due to membrane fouling which declined the flux rate with a spontaneous reduction of OLR and F/M ratio. The MBR system inoculated with high-salinity-adapted sludge could be managed to release treated effluent that meets Saudi disposal limits by modifying the F/M ratio via reducing the flux or increasing the mixed liquor suspended solid (MLSS) concentration.