Thermodynamic analysis of energy density in pressure retarded osmosis: The impact of solution volumes and costs

Water Treatment: Are Membranes the Panacea?

Alongside the rising global water demand, continued stress on current water supplies has sparked interest in using nontraditional source waters for energy, agriculture, industry, and domestic needs. Membrane technologies have emerged as one of the most promising approaches to achieve water security, but implementation of membrane processes for increasingly complex waters remains a challenge. The technical feasibility of membrane processes replacing conventional treatment of alternative water supplies (e.g., wastewater, seawater, and produced water) is considered in the context of typical and emerging water quality goals. This review considers the effectiveness of current technologies (both conventional and membrane based), as well as the potential for recent advancements in membrane research to achieve these water quality goals. We envision the future of water treatment to integrate advanced membranes (e.g., mixed-matrix membranes, block copolymers) into smart treatment trains that achieve several goals, including fit-for-purpose water generation, resource recovery, and energy conservation.

Modeling and Simulation Studies Analyzing the Pressure-Retarded Osmosis (PRO) and PRO-Hybridized Processes

Pressure-retarded osmosis (PRO) is viewed as a highly promising renewable energy process that generates energy without carbon emissions in the age of the climate change regime. While many experimental studies have contributed to the quest for an efficiency that would make the PRO process commercially viable, computational modeling and simulation studies have played crucial roles in investigating the efficiency of PRO, particularly the concept of hybridizing the PRO process with reverse osmosis (RO). It is crucial for researchers to understand the implications of the simulation and modeling works in order to promote the further development of PRO. To that end, the authors collected many relevant papers and reorganized their important methodologies and results. This review, first of all, presents the mathematical derivation of the fundamental modeling theories regarding PRO including water flux and concentration polarization equations. After that, those theories and thermodynamic theories are then applied to depict the limitations of a stand-alone PRO process and the effectiveness of an RO-PRO hybridized process. Lastly, the review diagnoses the challenges facing PRO-basis processes which are insufficiently resolved by conventional engineering approaches and, in response, presents alternative modeling and simulation approaches as well as novel technologies.

Investigations of inorganic and organic fouling behaviors, antifouling and cleaning strategies for pressure retarded osmosis (PRO) membrane using seawater desalination brine and wastewater

By employing seawater desalination brine (SWBr) and wastewater brine (WWBr) as the feed pair, membrane fouling behaviors as well as antifouling and cleaning strategies for the state-of-the-art thin-film composite polyethersulfone (TFC-PES) hollow fiber membrane have been systematically investigated under pressure retarded osmosis (PRO) operations. Fouling on the polyamide selective layer induced by the SWBr draw solution is relatively mild because of the outstanding membrane rejection and the hydration antifouling layer formed by the permeating water. However, using WWBr as the feed causes fast and severe internal concentration polarization (ICP) and fouling within the porous PES substrate, which result in dramatic flux and power density declines. In addition, the PRO fouling upon and within the porous substrate is highly irreversible. Experimental data show that both anti-scalant pretreatment and pH adjustment of WWBr could effectively mitigate inorganic fouling, while increasing feed flow velocity along the substrate surface is ineffective for fouling control. To clean the fouled membranes, hydraulic-pressure induced backwash and flushing with alkaline and NaOCl solutions on the fouled surface are effective strategies to remove foulants and regenerate membranes with a flux recovery of 83-90%. However, osmotic backwash shows low cleaning efficiency in PRO. In summary, a proper combination of feed pretreatment and membrane cleaning strategies has been demonstrated in this study to sustain PRO operations with a high water flux and power density.

Aspects of Mathematical Modelling of Pressure Retarded Osmosis

In power generating terms, a pressure retarded osmosis (PRO) energy generating plant, on a river entering a sea or ocean, is equivalent to a hydroelectric dam with a height of about 60 meters. Therefore, PRO can add significantly to existing renewable power generation capacity if economical constrains of the method are resolved. PRO energy generation relies on a semipermeable membrane that is permeable to water and impermeable to salt. Mathematical modelling plays an important part in understanding flows of water and salt near and across semipermeable membranes and helps to optimize PRO energy generation. Therefore, the modelling can help realizing PRO energy generation potential. In this work, a few aspects of mathematical modelling of the PRO process are reviewed and discussed.