Forward osmosis dewatering of seawater and pesticide contaminated effluents using the commercial fertilizers and zinc-nitrate blend draw solutions

Comprehensive Analysis of Common Heavy Metals in the Yellow River Over 20 Years: Spatiotemporal distribution, Migration Characteristics, Traceability, and Potential Risk Evaluation

Heavy metal pollution posed a great threat to the global aquatic ecological environment, especially in the Yellow River where the utilization rate of water resources was as high as 80%. This study addressed the spatiotemporal distribution, sources, and ecological risks of seven heavy metals (As, Cd, Cr, Cu, Ni, Pb, Zn) in the Yellow River by analyzing historical data collected from 2000 to 2020. The annual heavy metal fluxes increased from Qinghai to Henan section, then decreased from Henan to Shandong section. Similarly, concentrations of Cu, Ni, Pb, and Zn peaked in the sediments of the Henan section. These trends might be attributed to the interception effects of the Xiaolangdi and Sanmenxia Dams. The annual fluxes from 2016-2020 increased by an average of 162.6% compared to that from 2011-2015, likely reflecting the impact of ongoing economic growth (33.36%) and SS increase (69.68%). The annual fluxes of SS demonstrated a significant correlation with all heavy metal fluxes, underscoring their role as a critical transport medium in aquatic ecosystem. The fluxes of Cd and Pb were most strongly influenced by human factors. While most metals in surface water present negligible risks to aquatic life, Cd in sediments presents a considerable ecological threat. Furthermore, the highest potential ecological risk index (RI) was observed in the river sections in Gansu and Inner Mongolia, mainly due to Cd, which contributed up to 85.87%. The findings establish a fundamental framework for safeguarding the aquatic ecosystem of the Yellow River and managing its heavy metal contamination.

Reverse Solute Diffusion Enhances Sludge Dewatering in Dead-End Forward Osmosis

Wastewater treatment plants produce high quantities of excess sludge. However, traditional sludge dewatering technology has high energy consumption and occupies a large area. Dead-end forward osmosis (DEFO) is an efficient and energy-saving deep dewatering technology for sludge. In this study, the reverse osmosis of salt ions in the draw solution was used to change the sludge cake structure and further reduce its moisture content in cake by releasing the bound water in cell. Three salts, NaCl, KCl, and CaCl2, were added to the excess sludge feed solution to explore the roles of the reverse osmosis of draw solutes in DEFO. When the added quantities of NaCl and CaCl2 were 15 and 10 mM, respectively, the moisture content of the sludge after dewatering decreased from 98.1% to 79.7% and 67.3%, respectively. However, KCl did not improve the sludge dewatering performance because of the "high K and low Na" phenomenon in biological cells. The water flux increased significantly for the binary draw solute involving NaCl and CaCl2 compared to the single draw solute. The extracellular polymer substances in the sludge changed the structure of the filter cake to improve the formation of water channels and decrease osmosis resistance, resulting in an increase in sludge dewatering efficiency. These findings provide support for improving the sludge dewatering performance of DEFO.

Removal of multiple pesticides from water by different types of membranes

Pesticides are used in agriculture to protect crops from pathogens, insects, fungi and weeds, but the release of pesticides into surface/groundwater by agriculture runoff and rain has raised serious concerns not only for the environment but also for human health. This study aimed to investigate the impact of surface properties on the performance of seven distinct membrane types utilized in nanofiltration (NF), reverse osmosis (RO) and forward osmosis (FO) processes in eliminating multiple pesticides from spiked water. Out of the membranes tested, two are self-fabricated RO membranes while the rest are commercially available membranes. Our results revealed that the self-fabricated RO membranes performed better than other commercial membranes (e.g., SW30XLE, NF270, Duracid and FO) in rejecting the targeted pesticides by achieving at least 99% rejections regardless of the size of pesticides and their log Kow value. Despite the marginally lower water flux exhibited by the self-fabricated membrane compared to the commercial BW30 membrane, its exceptional ability to reject both mono- and divalent salts renders it more apt for treating water sources containing not only pesticides but also various dissolved ions. The enhanced performance of the self-fabricated RO membrane is mainly attributed to the presence of a hydrophilic interlayer (between the polyamide layer and substrate) and the incorporation of hydrophilic nanosheets in tuning its surface characteristics. The findings of the work provide insight into the importance of membrane surface modification for the application of not only the desalination process but also for the removal of contaminants of emerging concern.

Smart utilisation of reverse solute diffusion in forward osmosis for water treatment: A mini review

Forward osmosis (FO) has been widely studied as a promising technology in wastewater treatment, but undesirable reverse solute diffusion (RSD) is inevitable in the FO process. The RSD is generally regarded as a negative factor for the FO process, resulting in the loss of draw solutes and reduced FO efficiency. Conventional strategies to address RSD focus on reducing the amount of reverse draw solutes by fabricating high selective FO membranes and/or selecting the draw solute with low diffusion. However, since RSD is inevitable, doubts have been raised about the strategies to cope with the already occurring reverse draw solutes in the feed solution, and the feasibility to positively utilise the RSD phenomenon to improve the FO process. Herein, we review the state-of-the-art applications of RSD and their benefits such as improving selectivity and maintaining the stability of the feed solution for both independent FO processes and FO integrated processes. We also provide an outlook and discuss important considerations, including membrane fouling, membrane development and draw/feed solution properties, in RSD utilisation for water and wastewater treatment.

Second-Generation Magnesium Phosphates as Water Extractant Agents in Forward Osmosis and Subsequent Use in Hydroponics

The recovery of nutrients from wastewater streams for their later use in agricultural fertilization is an interesting approach. Wastewater recovered magnesium phosphate (MgP) salts were used in a forward osmosis (FO) system as draw solution in order to extract water and to produce a nutrient solution to be used in a hydroponic system with lettuces (Lactuca sativa, L.). Owing to the low solubility of the MgP salts (i.e., struvite, hazenite and cattiite) in water, acid dissolution was successfully tested using citric and nitric acids to reach pH 3.0. The dilution by FO of the dissolved salts reached levels close to those needed by a hydroponic culture. Ion migration through the membrane was medium to high, and although it did not limit the dilution potential of the system, it might decrease the overall feasibility of the FO process. Functional growth of the lettuces in the hydroponic system was achieved with the three MgP salts using the recovered water as nutrient solution, once properly supplemented with nutrients with the desired concentrations. This is an innovative approach for promoting water reuse in hydroponics that benefits from the use of precipitated MgP salts as a nutrient source.

Introduction of poly(acrylic acid) sodium into traditional draw solution to enhance its driving capacity in forward osmosis process

In this study, poly(acrylic acid) sodium (PAA-Na) salt was selected as representative polymer additive and the effect on forward osmosis (FO) performance of traditional draw solute NaCl was investigated. Results showed that PAA-Na increased water flux in both FO and PRO mode at 25 °C (up to 50%). Water flux and specific RSF firstly increased and then kept stable with the increasing concentration of PAA-Na additive. However, PAA-Na cannot enhance water permeation effectively at 35 and 45 °C. PAA-Na influenced FO performance by (1) increasing membrane hydrophilicity, which can increase water permeation, and was dominant at low temperature, and (2) causing pore-clogging, leading water flux decline, which was significant at high temperature. Furthermore, the influence of PAA-Na was compared with another polymer PAM and divalent salts MgCl₂. The addition of PAM increased water flux slightly (lower than 25%), but increased RSF at the same time, due to the negative charge. Although MgCl₂ decreased RSF and kept water flux fixed, its role was not obvious. In all, PAA-Na had advantages to improve FO performance.

Membrane technology for pesticide removal from aquatic environment: Status quo and way forward

The noxious side effects of pesticides on human health and environment have prompted the search of effective and reliable treatment techniques for pesticide removal. The removal of pesticides can be accomplished through physical, chemical and biologicals. Physical approaches such as filtration and adsorption are prevailing pesticide removal strategies on account of their effectiveness and ease of operation. Membrane-based filtration technology has been recognized as a promising water and wastewater treatment approach that can be used for a wide range of organic micropollutants including pesticides. Nanofiltration (NF), reverse osmosis (RO) and forward osmosis (FO) have been increasingly explored for pesticide removal from aquatic environment owing to their versatility and high treatment efficiencies. This review looks into the remedial strategies of pesticides from aqueous environment using membrane-based processes. The potentials and applications of three prevailing membrane processes, namely NF, RO and FO for the treatment of pesticide-containing wastewater are discussed in terms of the development of advanced membranes, separation mechanisms and system design. The challenges in regards to the practical implementation of membrane-based processes for pesticide remediation are identified. The corresponding research directions and way forward are highlighted. An in depth understanding of the pesticide nature, water chemistry and the pesticide-membrane interactions is the key to achieving high pesticide removal efficiency. The integration of membrane technology and conventional removal technologies represents a new dimension and the future direction for the treatment of wastewater containing recalcitrant pesticides.