How to remove sulphate from Industrial waste water?

Sulphate has traditionally been thought to be a relatively harmless substance in the eco system. Mining and smelting, steel manufacturing, kraft pulp and paper mills, and flue gas desulphurization circuits all discharge sulphates into the aquatic systems. Furthermore, sulphate is released into water from natural sources such as mineral weathering, decomposition, volcanoes, organic matter combustion, and sea salt.

Water naturally runs underground, absorbing some of the minerals it dissolves from the surrounding soil and rocks. Sulphates are commonly found in almost every type of water found in nature, including groundwater, oceanwater, and rainwater, as well as crude oil and brines. They are also found in many industrial wastes as a result of the facility's process, particularly in mining and mineral processing applications where sulphates are extracted from minerals such as calcium sulphate (gypsum), magnesium sulphate (Epsom salt), and sodium sulphate (Glauber's salt).

Sulphates, in high concentrations, can be hazardous to human health and the environment, as well as corrosive to pipes and equipment, so they are something that many industrial facilities strive to remove, whether for release into the local POTW or environment, or for reuse in the facility's process.

Techniques to remove sulphate from water

1-Adsorption:

Adsorption is the process of capturing contaminants from a liquid stream by using molecular forces of attraction. The process involves passing a liquid stream through some type of porous, adsorbent media, and when the soluble pollutants are more attracted to the adsorbent media than to the water in the stream, the contaminants bind to the media's surface while the liquid effluent goes through.

Adsorption is effective for removing sulphates at low concentrations and can be accomplished using technologies such as granular activated carbon filtration. Although the technology is generally inexpensive, the media will most likely need to be replaced on a regular basis, which can add up in both cost and time.

2-Distillation:

Distillation involves heating sulphate-saturated liquids to boiling, then cooling the resulting water vapour in a condenser and collecting the purified water in a sterile container. Whereas some separation processes remove contaminants from the liquid stream, distillation separates the liquid from the contaminants that remain in the still after the water has evaporated.

Although distillation is extremely effective at removing sulphates, keep in mind that for most industrial applications, distillation necessitates significant energy expenditures for heating, circulation, and cooling, particularly for the large volumes of water required to support industrial production. Innovations such as vapour compression and multiple effect distillation setups have increased energy efficiency over the last few decades, but they are still expensive to operate in comparison to other purification technologies.

3-Ion exchange:

Ion exchange (IX) systems are used for water softening, purification, and separation in a variety of industries. While the chemistry of individual ion exchange reactions varies depending on the application, IX is a treatment method in which soluble ions are replaced by other, more desirable ions of a similar electrical charge. This reaction usually occurs in an IX column or vessel where a process or waste stream is passed through a specialised resin that facilitates ion exchange.

When looking for the best ion exchange system for removing sulphates, look for a resin system that contains both cationic (to remove calcium and magnesium) and anionic resins.  The IX process works best for burnishing and with a background stream that contains few competing salts.

4-Membrane filtration:

Membrane filtration (also known as reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF)) is one of the most efficient methods for removing sulphates from industrial processes and wastewaters. The technology can also be used to treat sea water and brine during the oil extraction process. Sulphates must be removed efficiently to avoid system scaling and the formation of hydrogen sulphide, a harmful gas that can be produced during the oil extraction process when bacteria break down sulphates.

Often used in conjunction with other technologies to reduce membrane fouling and the need for backwashing or membrane replacement, your facility may employ a variety of filters to gradually narrow the particle size allowed through—for example, depending on the sulphate concentration, some facilities may find it beneficial to pre-treat their water and brine streams with UF before passing through an NF or RO unit.

For more information, contact Netsol water.