How about nano? Impact of size of plastics on plastic pollution and the magnitude of the problem

In the last decade we have realized that the plastics we use every day, and for practically everything, may be the biggest environmental polluters humans have ever released to the environment (EU DG, 2011). Since the first reports of plastic pollutions, we have learned so much about the issue. Macro and micro plastic pollution topics have been extensively studied, investigated, regulated, and in some cases litigated (Uren Webster et al., 2020)(Barnes, Galgani, Thompson, Barlaz, 2009)(Environment Agency, 2018). As it happened in most of the past cases, we have started with the most obvious and visible problem: macro plastics

Removal of microalgae from seawater using chitosan-alum/ferric chloride dual coagulations

During algal bloom, it's a challenge to provide good quality feed water, and ensure sustainable RO plant operations without an adequate pre-treatment of seawater. In this paper, the effectiveness of the coagulation process with the individual and dual coagulants, using alum, FeCl3 and chitosan, were explored aiming to remove microalgae from seawater. The coagulation-flocculation-sedimentation (C-F-S) experiments were conducted by optimizing multiple process strategies to reduce the amounts of coagulants and also to shorten the sedimentation process time. The coagulation-flocculation-dissolved air flotation (C-F-D) experiments were performed to generate the process data in order to evaluate the dual coagulation process performance of the C-F-S system. C-F-S experiments using FeCl3 coagulant gave better process performance (20 ppm FeCl3 dose, 8.2 pH, 30 min sedimentation time and 98% microalgae removal efficiency) when compared to alum and chitosan based individual coagulations. The process time of the coagulation process was significantly reduced by the addition of chitosan as a flocculent aid. For dual coagulation using alum (10 ppm) as coagulant and chitosan (1 ppm) as flocculent aid improved microalgae removal efficiency to 98% at a reduced process time of 5 min, making C-F-S process as attractive as C-F-D process

Detection of trace sub-micron (nano) plastics in water samples using pyrolysis-gas chromatography time of flight mass spectrometry (PY-GCToF).

The identification and quantification of micro and nanoplastics (MPs and NPs respectively) requires the development of standardised analytical methods. Thermal analysis methods are generally not considered a method of choice for MPs analysis, especially in aqueous samples due to limited sample size introduction to the instrument, decreasing the detection levels. In this article, pyrolysis - Gas chromatography time of flight mass spectrometry (Py-GCToF) is used as a method of choice for detection of MPs and NPs due to its unprecedented detection capabilities, in combination with PTFE membranes as sample support, allow for smaller particle sizes (>0.1 μm) in water samples to be identified. The utilisation of these widely used membranes and the identification of several and specific (marker) ions for the three plastics in study (polypropylene (PP), polystyrene (PS) and polyvinyl chloride (PVC)), allows for the extraction of individual plastics from complex signals at trace levels. The method was validated against a number of standards, containing known quantities of MPs. Detection levels were then determined for PVC and PS and were found to be below <50 μg/L, with repeatable data showing good precision (%RSD <20%). Further verification of this new method was achieved by the analysis of a complex sample, sourced from a river. The results were positive for the presence of PS with a semi-quantifiable result of 241.8 μg/L. Therefore PY-GCToF seems to be a fit for purpose method for the identification of MPs and NPs from complex mixtures and matrices which have been deposited on PTFE membranes

Advances in forward osmosis membranes: Altering the sub-layer structure via recent fabrication and chemical modification approaches

The forward osmosis process has obtained renewed interest nowadays and it might become an alternative solution for many industrial applications to meet the current and future requirements for potable water. The FO process depends on the osmotic pressure gradient between a high salinity draw solute and low salinity feed solution across a semi-permeable membrane to extract pure water. Despite the potential advantages of FO, there are some technical drawbacks that hinder FO application for water desalination. One of the most significant critical challenges is the need for membrane compatible with the FO process. To improve FO desalination feasibility, membrane development is required to obtain maximum water permeability and minimum reverse solute flux over long-term operations. Therefore, this review starts by demonstrating the fundamentals and membrane development over the years. Fabrication modifications for the support layer of FO membranes and the crucial challenges of the FO process are summarized. Recent trends of the chemical modifications of the bulk and substrate are discussed. The advantages and disadvantages of the modifications on the FO membrane productivity are also addressed. Finally, concluding with future perspectives

Thermodynamic optimization of Multistage Pressure Retarded Osmosis (MPRO) with variable feed pressures for hypersaline solutions

Salinity gradient processes, such as Forward Osmosis and Pressure Retarded Osmosis, have been proven to be promising technologies for reducing the energy consumption in water treatment processes, for energy production, and for energy recovery. In such processes higher power densities can be achieved by applying higher hydraulic pressures on the draw solution, this requires greater mechanical stability of the membrane to be able to withstand these higher hydraulic pressures. Therefore, there is a limitation to the salinity of the draw solution which can be used in the PRO processes. This being dependent on the concentration of the hypersaline solution and hence overall hydraulic pressure, necessitating the use of an ultra-thick support layer for maximum energy production and/or recovery. In this theoretical and simulative optimization of the PRO process, we achieved the optimum energy recovery from a hypersaline solution (TDS ~ 300,000 mg/L) by using a multistage PRO (MPRO) system which included implementing variable applied feed pressures to each stage. The results showed that the volumetric flow rate of the hypersaline draw solution increased by up to a factor of 10 during the MPRO process in single pass, and the concentration of the hypersaline draw solution diluted up to 10x accordingly

Nanofiltration and ultrafiltration of endocrine-disrupting compounds

Endocrine disrupting compounds (EDCs) have been considered emerging pollutants and have been found in various water sources around the world. Two of the main issues in removing EDCs from water sources are the size and the functionality (functional groups, charge, etc.) of the EDCs, which makes them harder to remove with loose membrane processes and low oxidation potential oxidants. Specialized ultrafiltration (UF) and tight nanofiltrations (NF) could offer a more economical and less energy dependent solution to EDCCs removals from water sources. In this chapter we have looked at the current developments in UF and NF membranes and how they could be used to remove EDCs

Direct and Indirect Seawater Desalination by Forward Osmosis

Forward osmosis (FO) is an emerging membrane technology with a range of possible water treatment applications including desalination. The FO process itself can directly desalt seawater as a feed solution by employing a draw solution with higher osmotic pressure than seawater. However, the energetics of product water recovery and draw solution reuse is not favorable. Alternatively, the FO process using seawater as a natural draw solution and quality-impaired water as the feed can potentially couple with low-pressure reverse osmosis as a hybrid to be a lower-energy desalination process, in which indirect desalination is achieved. Most organic fouling in FO desalination process is reversible. However, the mechanism of scaling formation in FO desalination is more complicated than the conventional RO process. Both feed and draw solution can influence the scaling formation and its reversibility. The economic feasibility of FO desalination process depends on the operational mode (direct and indirect) as well as the plant scale and level of commercialization. Although there are still some choke points in the current deployment of FO desalination, the future development of efficient draw solution and novel FO membrane will significantly promote FO desalination technology

Pressure Retarded Osmosis (PRO): Past experiences, current developments, and future prospects

Pressure Retarded Osmosis (PRO) has attracted worldwide attention with respect to its salinity gradient energy production potential, and low energy desalination applications. PRO processes, which use Seawater Reverse Osmosis (SWRO) brine as draw solutions, have a higher potential of being applied to any new, and existing membrane based seawater desalination systems, as an energy production and/or conservation process. Hydraulic pressure is applied on a high salinity draw solution, and the hydraulic pressure of the high salinity draw solution can be kept relatively constant during operation, even though the volumetric flow rate is to be increased. Therefore, the draw side of the PRO process can be considered near-isobaric, in most cases. The harvested Gibbs free energy of mixing, and the volumetric expansion can explain this near-isobaric behavior of the draw side in the PRO process. Thus, PRO can be used to multiply the internal energy of the draw solution with respect to the ratio of the permeated water flux. Even though PRO has very high theoretical potential for energy production and/or recovery, there are several shortcomings, which should be answered before the realization of the scale up applications, such as; thermodynamic process optimization, high power density membranes, and high efficiency hydraulic pressure conversion and recovery systems. This review gives detailed information about the PRO process including; (1) theoretical background, (2) membranes for PRO, (3) experimental and large scale applications, and (4) economic feasibility of PRO applications

An overview of oil–water separation using gas flotation systems

Oil concentration levels in municipal waste water effluent streams are stringently regulated in most parts of the world. Apart from municipal waste, stricter oil/grease discharge limits are also enforced in oil and gas sectors as large volumes of produced water is being discharged to open ocean. One of the feasible, practical and established methods to remove oil substances from waste water sources is by gas flotation. In this overview, gas flotation technologies, namely dissolved and induced flotation systems, are discussed. Physico-chemical interaction between oil–water-gas during flotation is also summarized. In addition to a brief review on design advancements in flotation systems, enhancement of flotation efficiency by using pre-treatment methods, particularly coagulation-flocculation, is also presented

Principle and theoretical background of pressure-retarded osmosis process

Pressure-retarded osmosis (PRO) uses a semipermeable membrane to control the osmotic mixing to generate renewable osmotic power from a salinity gradient. The main goal of a PRO system is to economically provide an appropriate amount of green energy. Furthermore, one of the key factors for a successful PRO system is the selection of a suitable draw solution that possesses a greater osmotic pressure than that of the feed solute to drag water through the membrane. Therefore quantifying the osmotic pressure and the extractable mixing energy is required. In this chapter, we discuss the general principles of PRO, before addressing modeling of the osmotic pressure associated with the osmotic power generation