What happens when mercury is dumped into the environment?
Mercury is different from other metals, as it is able to evaporate when released into soil or water. Additionally, bacteria can transform inorganic forms of mercury into organic forms, which aquatic life can collect.
In order to lower the quantities of mercury in their liquid streams and emissions, industrial and commercial facilities that handle mercury, often need to implement water treatment systems like reverse osmosis, to remove mercury.
In this article, we'll look at some of the benefits of reverse osmosis & other technologies, for mercury removal from water and wastewater.
What are the effective techniques for mercury removal in water?
Reverse Osmosis or membrane filtration, precipitation, adsorption, and biological treatment, are the most popular methods used to treat mercury-contaminated water. Each of these water treatment systems has benefits, but they all largely depend on the installation's particular process parameters.
· Mercury removal through reverse osmosis
Size exclusion is the underlying principle, behind the physical separation method known as membrane filtration. A liquid stream is passed across a membrane that is semi-permeable, and has precisely designed pores that allow smaller molecules and particles to flow through, while blocking bigger ones. As a result, membrane filtration is categorised depending on pore size and includes reverse osmosis (RO), microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF).
While RO has pores small enough to hold divalent cations like mercury, its usage is often limited to secondary or tertiary treatment, because to their proneness to clogging and fouling brought on by their small pore sizes.The key benefit of membrane separation is how quickly mercury and other pollutants are removed. Due to this benefit, it is an excellent fit for facilities that need to treat wastewater or process water for re-use, or that must adhere to strict mercury or other heavy metal discharge restrictions.
· Mercury removal through Adsorption
Another water treatment method that is frequently used for applications, removing mercury is adsorption. It has several key benefits, including no sludge production, excellent selectivity for mercury or other heavy metals, and versatility in adsorption media material selection. It has the ability to lower mercury concentrations below 2 g/L.
Adsorbate accumulates on the surface of a solid (adsorbent), through the process of adsorption under the influence of molecular forces. A liquid stream is often passed through a bed of adsorbent material, in water treatment applications. Dissolved contaminant molecules attach to the adsorbent media, as the stream passes through, and they are subsequently removed from the liquid stream. The adsorbent media will eventually become saturated from use, which will reduce its capacity to eliminate specific pollutants. By using heat or other techniques to desorb previously collected pollutants, some adsorbent medium can be regenerated for additional use cycles. But eventually, it will be necessary to switch out the used adsorbent material.
· Precipitation
Due to its affordability and ease of use, chemical precipitation is by far the most widely used method of water treatment, for removing mercury from both groundwater and wastewater. A facility initially adds a chemical precipitant to the stream, in order to remove mercury through chemical precipitation. One of two ways that the precipitant interacts with dissolved constituents to help remove mercury from the stream, is by either creating insoluble mercury compounds or elemental mercury, or by creating particulate solids that adsorb the dissolved mercury, already present in the stream.
The facility then uses a physical separation technique, such as clarifying or filtration, to remove insoluble solids from the liquid stream, after the precipitation reaction. Sulphides, ferric salts, ferric sulphates, and calcium hydroxide, are often employed chemicals in mercury precipitation, while other less common chemicals, such as lignin, are also sometimes used. Chemical precipitants must be carefully chosen based on process requirements for best performance and cost-effectiveness. This includes taking into account the stream's contents, process conditions, pH, downstream equipment specifications, and other considerations.
Choose Netsol Water as your water treatment expert for mercury removal!
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