The most promising opportunities for new water treatment technologies are those that offer improve methods of removal of dissolved and suspended solids, biological wastewater treatment and disinfection. This subsection includes an overview of these technologies, how they work, and when they might be used. We will expand this subsection in January 2015, with the publication of our new report, Industrial Water Technology Markets 2015. The report will contain detailed analysis of the opportunities for these technologies in different industries, including upstream oil & gas, refining, power generation, mining, food & beverage, pharmaceuticals, pulp & paper, and microelectronics.
Membrane technologies allow dissolved and suspended solids to be separated from a feedwater stream. A pressure gradient forces water molecules through the membrane from a more concentrated solution to a less concentrated solution.
Electrical charge separation
The following terms are useful when considering technologies that separate contaminants by their electrical charge:
Seawater desalination technologies
In areas of the world where the supply of freshwater is limited, extracting freshwater from seawater by desalination becomes economically viable. The most common technologies used for seawater desalination are reverse osmosis (SWRO), multi-effect distillation (MED) and multi-stage flash evaporation (MSF). Thermal processes, including MED and MSF, are able to produce product water with a lower concentration of dissolved solids than reverse osmosis. MED and MSF systems require a large input of energy to evaporate the seawater. These processes are most commonly used when there is a cheap source of steam to heat the seawater.
High recovery technologies
Water that contains a high concentration of dissolved and suspended contaminants cannot be discharged without further treatment. The following technologies separate the dissolved solids from highly concentrated wastewater. The solids can be removed by continuously evaporating the water in a brine concentrator and removing the crystals that form in rapidly cooling water in a crystalliser. Water can be removed mechanically by compressing the concentrated wastewater in a filter press. Energy for these processes can be produced without an external source of heat by compressing the water vapour.
Lime softening removes dissolved compounds from the water. It is a necessary pretreatment step if the water is going to be boiled or distilled, because it removes the compounds that would precipitate and cause scaling. The dissolved compounds are present in the water as ions. These compounds can be categorised in several ways:
The removal of suspended and colloidal particles from a water source is improved if particles can be brought together in large quantities. Coagulation occurs when particles overcome the electrically repulsive forces that keep them apart. Flocculation occurs when charged groups on long chain polymers attract many groups of coagulated particles. The aim of this process is to decrease the time it takes for suspended particles to settle, or to increase the chance that a particle will be removed by later filtration.
Biological wastewater treatment
In biological treatment processes, bacteria are added to wastewater to break down organic material. Bacterial processes are characterised by the availability of oxygen:
Chlorine-based compounds are used in most municipal wastewater treatment systems to prevent the growth of micro-organisms. The addition of chlorine compounds to water as a disinfection is known as chlorination. Chlorine gas forms hydrochlorous acid on reaction with water. This weak acid can damage bacterial cell walls, affect the uptake of oxygen by cells, and reduce the reproduction rate of DNA. The compounds that are most commonly used to produce hydrochlorous acid for disinfection are chlorine gas, sodium hypochlorite, and calcium hypochlorite.