Heavy metals like arsenic, copper, cadmium, chromium, nickel, zinc, lead, and mercury are major pollutants of fresh water reservoirs because of their toxic, non‐biodegradable, and persistent nature. The industrial growth is the major source of heavy metals introducing such pollutants into different segments of the environment including air, water, soil, and biosphere. Heavy metals are easily absorbed by fishes and vegetables due to their high solubility in the aquatic environments. Hence, they may accumulate in the human body by means of the food chain. Various methods have been developed and used for water and wastewater treatment to decrease heavy metal concentrations. These technologies include membrane filtration, ion‐exchange, adsorption, chemical precipitation, nanotechnology treatments, electrochemical and advanced oxidation processes. In this review, the methods as well as their mechanisms and efficiency are discussed.

Most of the studies done on kinetic hydrate inhibitors (KHIs) are related to the effect of KHIs on hydrate formation, and there are a limited number of research works on hydrate dissociation conditions in the presence of KHIs. In the subject of hydrate remediation, knowing the effects of KHIs on hydrate dissociation conditions is necessary. In this work, first, the effect of the presence of poly vinyl caprolactam (PVCap) as a KHI on methane hydrate dissociation conditions has been studied and the results show that dissociation temperature of methane hydrate in the presence of PVCap is higher than the noninhibited system and increases hydrate stability conditions. Then, at the second stage, the effects of EMIM-BF4 as a synergist for PVCap on methane hydrate dissociation conditions have been investigated. Different concentrations of EMIM-BF4 and PVCap have been studied, and a thermodynamic model has been developed to predict hydrate dissociation temperature. The experiments reveal that adding EMIM-BF4 to an aqueous solution of PVCap does not have a significant effect on methane hydrate dissociation conditions. The model has been developed based on the fact that the presence of PVCap changes the large to small cavity ratios, L/S, from its theoretical value, i.e. 3/1. It has been assumed that the number of small cavities to water molecules for methane hydrates in the presence of PVCap depends on PVCap concentration. A correlation is proposed to indicate this dependence. Different activity coefficient models have been tested to calculate water activity in the presence of PVCap and IL. The agreement between the experimental data and model results is found to be satisfactory.

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The inhibition of gas hydrate (clathrate hydrate) formation plays an important role in petroleum industries. A way to prevent this problem is injecting chemical inhibitors to the transportation pipelines. Two typical kinds of chemical inhibitors are thermodynamic and kinetic inhibitors. The main goal of the current work is to provide a thermodynamic model without using any adjustable parameters for prediction of the dissociation conditions of hydrate for pure and mixed gases including several thermodynamic inhibitors of ethylene glycol (EG), methanol (MeOH), potassium chloride (KCl), calcium chloride (CaCl 2 ), and sodium chloride (NaCl). For this purpose, application of the extended UNIQUAC activity coefficient model along with the van der Waals-Platteuw solid solution theory has been proposed. A comprehensive literature survey has been performed to provide a complete set of experimental data, and 1455 data points have been provided. Comparing the current model results with the experimental data reported in literature, the average absolute deviations (AAD) is 0.50 K which shows the accuracy of the results of the model developed in the current study.

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