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Forward osmosis membrane bioreactors (FOMBRs) are currently gaining attention from the wastewater treatment industry, for their potential to produce high effluent quality and a relatively better flux stability against fouling. However, only using physical cleaning methods is not sufficient to recover the water flux performance satisfactorily under a long-term operation. This study comprehensively investigated the efficiency of a hybrid, environmentally-friendly cleaning strategy involving a combination of physical and free nitrous acid (FNA) cleanings under a long-term FOMBR operation. During 92 days of FOMBR operation, physical cleaning recovered the water flux by 85%, whilst FNA cleaning contributed to an additional 5% of the recovery. In addition, FNA cleaning also offered a retardation of fouling deposition by maintaining the water flux 18–30% more than that obtained by only the physical cleaning. A possible mechanism for FNA's role as the cleaning reagent was proposed for the first time in this study based on the water flux performance and membrane autopsy analysis. The results showed FNA cleaning broke down the residual fouling layer, preferencing protein-based substances. A lower ratio of protein to polysaccharides of the residual fouling layer contributed to a more negatively charged membrane surface (- 42.34 ± 0.30 mV) compared to the virgin one (- 17.54 ± 0.81 mV). This resulted in a stronger electrostatic repulsion between the foulants and the membrane surface, and thus slowed down the biofouling deposition process. This study suggested FNA solution has the great potential not only to recover the membrane performance, also as a strategy to slow down fouling deposition. [Display omitted] • FNA cleaning results in a more negatively charged membrane surface (- 42.34 ± 0.30 mV). • Stronger electrostatic repulsion between foulants and membrane after FNA cleaning. • FNA cleaning contributed to 90% of the overall water flux recovery of the membrane. • A mechanism of reduced fouling due to FNA cleaning is proposed for the first time. [ABSTRACT FROM AUTHOR]

Forward osmosis membrane bioreactor (FOMBR) is an integrated physical-biological treatment process that has received increased awareness in treating municipal wastewater for its potential to produce high effluent quality coupled with its low propensity for fouling formation. However, reverse salt diffusion (RSD) is a major issue and so far limited studies have reported long-term FOMBR operation under the elevated salinity conditions induced by RSD. This study investigated the performance of a FOMBR in treating municipal wastewater under a controlled saline environment (6–8 g L−1 NaCl) using two separate sodium chloride draw solution (NaCl DS) concentrations (35 and 70 g L−1) over 243 days. At 35 g L−1 NaCl DS, the water flux performance dropped from 6.75 L m−2 h−1 (LMH) to 2.07 LMH after 72 days of operation in the first experimental stage, when no cleaning procedure was implemented. In the subsequent stage, the DS concentration was increased to 70 g L−1 and a weekly physical cleaning regime introduced. Under stable operation, the water flux performance recovery was 67% after 21 cycles of physical cleaning. For the first time in FOMBR studies, a shortcut nitrogen removal via the nitrite pathway was also achieved under the elevated salinity conditions. At the end of operation (day 243), the ammonia-oxidising bacteria (Nitrosomonas sp.) was the only nitrifier species in the system and no nitrite oxidising bacteria was detected. The above study proves that a FOMBR system is a feasible process for treating municipal wastewater. Image 1 • 99% nitrite accumulation was facilitated by optimising the reverse salt diffusion. • Nitrosomonas sp. was the only detected nitrifier in the system on day 243. • FOMBR achieved >97% nutrients removal efficiency over 171 days of operation. • Under long-term operation, physical cleaning recovered 67% of water flux. • Structural deterioration of CTA membrane was observed in the long-term operation. [ABSTRACT FROM AUTHOR]

This analysis explores the research landscape on palm oil mill effluent (POME) treatment through coagulation-flocculation (C-F), utilizing 84 documents extracted from the Web of Science database spanning the years 1987–2023. Engineering emerges as the most prominent research area, underscoring the significance of technological solutions in addressing POME treatment challenges. Notably, the Chemical Engineering Journal stands out as the primary publication venue, with the highest number of published papers in this domain. Malaysia emerges as the foremost contributor to this research field, with a substantial share of 78 articles. This dominance reflects Malaysia's pivotal role in the global palm oil industry, showcasing the country's commitment to addressing environmental concerns associated with palm oil production. The identified clusters in the bibliometric analysis reveal thematic focuses, including the utilization of natural coagulants, process and parametric optimization, and advancements in C-F processes. The evolution of C-F treatment technologies is discussed, providing insights into the shifting trends and innovations in POME treatment methodologies. The three identified clusters reflect the multifaceted nature of research, indicating a holistic approach toward addressing the challenges of POME treatment. As the analysis delves into the historical development of the field, it also serves as a guide for future research directions. The study not only emphasizes the current state of knowledge but also lays the foundation for continued advancements in C-F treatment for POME, fostering sustainable practices in the palm oil industry. • Scientific production on POME treatment by coagulation-flocculation is analysed. • An emerging trend on this topic is observed based on 84 publications. • Malaysia is the top productive country in this topic. • The integration of technologies is likely to be a focal point for future research. [ABSTRACT FROM AUTHOR]

Free nitrous acid (FNA), the protonated form of nitrite, has historically been an unwanted substance in wastewater systems due to its inhibition on a wide range of microorganisms. However, in recent years, advanced understanding of FNA inhibitory and biocidal effects on microorganisms has led to the development of a series of FNA-based applications that improve wastewater management practices. FNA has been used in sewer systems to control sewer corrosion and odor; in wastewater treatment to achieve carbon and energy efficient nitrogen removal; in sludge management to improve the sludge reduction and energy recovery; in membrane systems to address membrane fouling; and in wastewater algae systems to facilitate algae harvesting. This paper aims to comprehensively and critically review the current status of FNA-based applications in improving wastewater management. The underlying mechanisms of FNA inhibitory and biocidal effects are also reviewed and discussed. Knowledge gaps and current limitations of the FNA-based applications are identified; and perspectives on the development of FNA-based applications are discussed. We conclude that the FNA-based technologies have great potential for enhancing the performance of wastewater systems; however, further development and demonstration at larger scales are still required for their wider applications. Image 1 • Underlying mechanisms of FNA inhibitory and biocidal effects are reviewed. • FNA is used to control sewer corrosion and odor, and membrane fouling. • FNA improves wastewater treatment, sludge management and algae harvesting. • Knowledge gaps and current limitations of the FNA-based applications are identified. • Perspectives on the development of FNA-based applications are discussed. [ABSTRACT FROM AUTHOR]