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Water stress is a major concern in today’s world as many cities worldwide face fast depleting potable water supply. The prevailing water emergency warrants a conscious effort to reuse mitigated wastewater such that the use of residual natural reserves is limited to drinking purposes only. To accomplish adequate wastewater remediation, the greatest challenge, apart from policy and implementation fronts, lies in maximizing the overall efficiency of wastewater treatment (WWT) systems. In light of this, the current review makes a unique effort to help navigate the challenge by summarizing the present scenario of WWT technologies, focusing on the progress so far and the prospects in the next 30 years or so. The study comprehensively reviews various wastewater technologies and aims to help countries, like India, deal with the obstacles encountered while selecting and engineering suitable systems. It compares them based on their advantages and disadvantages, including budget allocation and timeframe for installing and commission of the treatment plants. Depending upon the wastewater characteristics and the expected end-use of treated wastewater, a comprehensive survey of prevalent aerobic, anaerobic, and biological treatment techniques has been done. Emerging WWT technologies, such as advanced oxidation processes, membrane filtration techniques, microbial electrolysis cell technologies, and in situ methods, which are currently in the development and deployment stages, have also been discussed. The study outlines the scope, limitations, and advancements of existing and prospective wastewater remediation approaches and suggests their decentralized implementation at the community scale as stop-gap solutions to poor wastewater management. Graphical abstract

Simulation of large basins (over 1000 km 2 ) can have a significant impact on the planning of large-scale water resources management. However, due to the increasing volume of calculations and the increasing heterogeneity of the different parts of these basins, the simulation of these basins has always faced challenges. Also, in areas with severe withdrawal of water resources, the importance of simulating and having the ability to predict future changes in the area is twofold, while these severe withdrawals lead to more complicated issues and more difficulty in simulations. The aim of this study is to evaluate ability of hydro geo-sphere fully integrated hydrologic model in simulating a large basin area (Hamadan-Bahar) with a total area of 2456 km 2 and in severe withdrawal from groundwater resources. In this study, fully integrated surface/subsurface flow modeling was performed using hydro geo-sphere model. Simultaneous solving of surface and groundwater flow equations in this model and also the calculation of actual evapotranspiration as a function of soil moisture in each unit of evaporation zone improves simulation of interdependent processes such as aquifer drainage and feeding, which is one of the most difficult issues in the modeling. To obtain the initial conditions, the model was performed in steady-state mode using 20-year average of rainfall data and withdrawal from the aquifer. Then, to implement the model in a non-steady state and evaluate its performance in daily stresses, the model was performed during the period of 1992–2005 and parameters were calibrated. Validation phase was performed during the period of 2006–2010, which indicated the acceptable ability of this model in hydrologic simulation of the study area.

Multispectral and hyperspectral images captured by remote sensing satellites or airborne sensors contain abundant information that can be used to study and analyze objects of interest on the surface of earth and their properties. The potential of remotely sensed images for studying natural resources like water has been studied by researchers over the past many years. As water is an important natural resource that needs to be conserved, such studies have been of great interest to the scientific community. By employing appropriate digital image processing techniques on images taken from remote sensing satellites or airborne sensors, an effective system can be developed to study the quantitative and qualitative changes happening to surface water bodies over a period of time. Surface water detection and mapping is a crucial and necessary step in such studies and different automated and semi-automated methods have been developed over the years for mapping water in remotely sensed images. Remote sensing sensors capture images at multiple bands corresponding to different wavelength ranges in the EM spectrum. Digital image processing based techniques for water mapping falls predominantly into four categories; (i) single band based methods, (ii) spectral index based methods, (iii) machine learning based methods and (iv) spectral mixture analysis based methods. This paper presents a review of techniques, methods, algorithms and the sensors/satellites that have been developed and experimented with to perform surface water body detection and delineation from remote sensing images.

The growing menace of global warming and restrictions on access to water in each region is a huge threat to global hydrological sustainability. Hence, the perspective at which hydrological studies are currently being carried out across the world to quantify and understand the water cycle modeling requires a further boost. In the past few decades, the theoretical understanding of machine learning (ML) algorithms for solving engineering issues, and the application of this method to practical problems have made very significant progress. In the field of hydrology, ML has been using for a better understanding of hydrological complexities. Then, using ML-based approaches for hydrological simulation have been a popular method for runoff modeling in recent years; it seems necessary to understand the application of ML in runoff modeling fully. Current research seeks to have an overview for rainfall–runoff modeling using ML approaches in recent years, including integrated and ordinary ML techniques (such as ANFIS, ANN, and SVM models). The main hydrological topics in this review study include surface hydrology, streamflow, rainfall–runoff, and flood modeling via ML approaches. Therefore, in this study, the author has critically reviewed the characteristics of machine learning models in runoff simulation, including advantages and disadvantages of three widely used machine learning models.

Global water shortages force the world to explore every possible way to reduce water consumption and reduction of exploitation of freshwater resources. In 2025, some estimates predict that 60% of the world's population will live in water-deficient regions. Nanofiltration (NF) membranes have been used in many fields, including water treatment, agriculture, pharmaceuticals, and biotechnology. NF stands out for its ability to effectively eliminate impurities, sediments, chemical effluents, and even hazardous substances like arsenic. This makes it a versatile approach for enhancing water quality. Nanofiltration membranes are a cutting-edge type of membrane technology that can be classified into two categories: organic (polymeric) and inorganic. The selection of membranes with appropriate selectivity based on applications of interest are vital to achieving the highest separation efficiency. During the first section of this review, the discussion will follow the background of membrane-based filters with solutes separation from the solution in the range of molecular weight from 500 to 10,000 g/mol, their characteristics, the benefits, and drawbacks of nanofiltration, and their cost-effectiveness of them. In the next part, various types of NF membranes, and their excellent properties, including high permeation to monovalent ions and low permeation to divalent ions, as well as higher flux, reliability, and integrity with longer cycle times and thereby lower costs, are examined. This article aims to discuss some of the most significant and pioneering applications of nanotechnologies in different water sources, including surface water, groundwater, and industrial wastewater streams. Although nanofilters have shown great promise, there are still some outstanding challenges that hinder their widespread adoption. We also provide a comprehensive overview of challenges and opportunities related to using nanotechnology in the future. The next decade is predicted to bring a lot of progress in NF. Graphical abstract

Levofloxacin (LEV) is an antibiotic that has a negative ecotoxicological effect. Its mitigation from the aqueous environment is achievable by adsorption. The aim of this paper was to review the removal of LEV from aqueous media via adsorption. The goal was to carefully study the trends of research findings by various authors over the past two decades, analysing key results, observing trends and similarities and identifying interesting areas that future researchers should consider. It was observed that modified carbon-based adsorbents are the best class of adsorbent for LEV uptake. The highest reported adsorption capacity for LEV is 1111 mg/g for corncob–Ag NPs composite adsorbent. This was the only adsorbent that could remove more than its weight of LEV. The major mechanisms of uptake of LEV are π–π interactions, electrostatic interactions, complexation and hydrogen bonds. The Langmuir or Freundlich classical isotherm model was the best fit in most cases to describe the adsorption equilibrium. LEV is easily desorbed from various adsorbents, It possesses a desorption rate > 60% after the first regeneration cycle. Also, > 20% retention of original adsorption capacity can still be achieved after about 5 cycles. The uptake of LEV is seriously hampered (20–60% decrease) by salt competing species in the aqueous phase. Interesting areas for future research identified were the choice of eluent for desorption, the choice of competing species, and statistical physics modelling. Graphical abstract

Usable water resource is limited, even though 71% of world is covered by water. Therefore, enough conflicts to the usable water can be found throughout the world. Usable water for irrigation is a top priority, probably it would be seconding only to the drink water supply. However, prioritizing one usage over another is challenging to many stakeholders. Therefore, sustainable water usage is essential to avoid any conflicts among the stakeholders; nevertheless, highly challenging in the developing world. Therefore, this paper discusses the water saving irrigation practices and ways to use agriculture around the world, including Uzbekistan. Relying on the ancient irrigation technologies used by ancestors and also modern irrigation methods, different irrigation water management technologies are presented to apply for various weather conditions and water availability situations. Suitable irrigation practices are discussed based on the water needs especially the arid countries, such as Uzbekistan. The results of an experiment conducted for hilly areas of Uzbekistan using “mulching” agro-technology is presented along with its suitability for Uzbekistan. Therefore, the expectations of sustainable water usage for irrigation is proposed.

The twenty-first century is witnessing an explosion in global population, environmental changes, agricultural land disintegration, hunger, and geopolitical instabilities. It is difficult to manage these conditions or standardize improvement systems without thinking of the three main elements or subsystems that are necessary for any meaningful development—namely water (W), energy (E), and food (F). These key elements form what is globally agreed upon as the “WEF Nexus.” While considering them, one should think about the other key factors that influence WEF Nexus, including population’s growth, impacts of environmental changes (including climate change), moderation and adaptation regimes to climate change and climate resilience, loss of biodiversity, and sustainable nature. Together, the WEF Nexus subsystems represent a framework to ensure environmental protection that should be seen as an ethical and socioeconomic obligation. Issues, such as protection of water resources, and strategies and management tools or mechanisms for the use of water assets and agricultural innovations under the obligations of sustainable use, are investigated in this paper. Attention is paid to the relationship between water and food (WF Nexus) or water for food security in various world regions, including the Gulf Cooperation Council (GCC) countries, Central Asia countries and the Caucasus, China, Africa, and Canada. This paper also presents analyses of a great number of up-to-date publications regarding the “Nexus” perspective and its applications and limitations. This paper suggests that the Nexus’ approach, in its different concepts (WEF, WE, WF and EF), can promote sustainable development and improve the quality of life of communities, while preserving natural, human, and social capital, addressing sustainability challenges, and protecting natural resources and the environment for long-term use.

The number of industries releasing heavy metals and dyes has increased drastically, as an outcome of increased consumption of cosmetics, textiles, printing, automobiles, pesticides, etc. The source water quality is getting deteriorated due to increased toxicity imparted by such contaminants, which are getting mixed in the potable water resources. This has adversely affected the life of humans and aquatic creatures. Many conventional treatment streams and mechanisms are available and have been applied for the recovery of dyes and heavy metals. Incessant research and development in this domain have devoured many state-of-the-art techniques and approaches which are environmentally friendly for removal and recovery of dyes and heavy metals and for reuse of such treated wastewater. The technologies elucidated in this paper have shown immense potential and include applied nanotechnology, smart membrane techniques, natural recyclable adsorbents, advanced oxidation mechanisms, novel biological approaches and hybrid blend of electrochemical methods. Research in this sector needs to be upgraded to full scale for its promising implementation in industries. Moreover, the development of suitable hybrid methods needs to be focused on for apprehending an increased efficiency for the removal and recovery process of reclaimed dye and heavy metal wastewater. This critical review captures several conventional and novel methods, including their merits, demerits, several tech no-commercial considerations before adopting them to suit the purpose of removal, recovery of dyes and heavy metals and wastewater reuse. Graphical abstract Process-flow of treatment of wastewater

Recently, getting pure water easily is becoming a difficult task for the world. Different sources such as industrial, municipal, urban, and agricultural runoff are principal contributors to water pollution. Nitrate, an inorganic form of nitrogen, one of the water pollutants, can destroy water quality ecologically and clinically by causing eutrophication in the aquatic bodies and, methemoglobinemia (blue baby syndrome) in human infants, other health complications in animals. Traditionally, various methods have been trailed by the industries and wastewater plants to diminish the concentration of nitrate from the polluted water before discharging into the nearby water bodies. In the current decade, innovative, tremendous, and efficient technologies have been developed to reduce nitrate concentration and boost water quality. This paper highlights the most used physical and chemical approaches (ion exchange, reverse osmosis, adsorption, electrodialysis, electrocoagulation, electroreduction, etc.) and biological approaches (microbial, phytoremediation), other hybrid systems and their unique features. In addition, operational conditions, mechanisms, advantages, shortcomings, recent advancements, removal efficiency, and cost-effectiveness were discussed to help the world eliminate this significant problem associated with water pollution and further develop a sustainable hybrid system. Besides it, the paper presents the recovery procedure for nitrate and ammonium. From the detailed literature gathered, the hybrid technology was fantastic compared to stand-alone approaches. The biological methods were unmatchable with others regarding cost, energy consumption, nitrate reduction, nitrate removal, and energy harvest.