General information about the sector
The predominant water treatment method resulting in a high salinity waste stream is desalination. A desalination plant separates saline water into two streams, as shown in the figure below: (i) one with a low concentration of dissolved salts (the fresh water stream) and (ii) another containing the remaining dissolved salts (the concentrate or brine stream). The desalination process requires energy to operate and can use a number of different technologies for the separation. Production of treated water with desalination techniques is a widely used practice. In general, desalination refers to the process of removing salts from waters of different qualities.
Industrial Activity (NACE E36.0)
|
Section |
Division |
Group |
Description |
|
E |
|
|
Water supply; sewerage; waste management and remediation activities |
|
|
E36 |
E36.0 |
Water collection, treatment and supply |
Brine effluent in water treatment process
The characteristics of the concentrate resulting in desalination plants reflect the chemical constituents of the feedwater. The following tables summarize the origin of contaminants in brine wastewater resulted by desalination process and the parameters to consider for the brine effluent from different desalination plants, respectively.
Brine constituents resulted by desalination process.
|
Contaminant |
Characteristics |
Type |
|
Antiscalling additives |
Used to remove the scales formations |
Polymeric substances such as polyphosphates, phosphonates and polycarbonic acids, orthophosphates Membrane desalination plants |
|
Antifouling additives
|
Used to hinder the potential of bacterial, algal and other marine organisms to foul the desalination plant |
Chlorine, hypochlorite, sodium hypochlorite, calcium hypochlorite, ozone |
|
Coagulatnts/ Flocculants |
Used to bind together particulate and colloidal matter so they may be filtered from the feed before the membrane process. Prevents Fouling and Clogging of the Membranes |
Ferric chloride, ferric sulphate, polyelectrolytes |
|
Antifoaming additives |
Used to prevent foam formation in MSF units |
Polyglycol blends |
|
Corrosion products (heavy metals) |
Resulted mainly in MSF plants from the corrosion of copper alloy tubing. The copper concentration increases under high operation temperatures in thermal desalination plants. |
Copper (the most significant heavy metal discharged from desalination plants) , iron, nickel, chromium, zinc, molybdenum |
|
Acids in pretreatment – pH adjustment |
Used mainly as an antiscalant and can produce effluents with significant low pH values |
Sulphuric acid, hydrochloric acid |
|
pH Adjustment to 7 at post-treatment |
Prevent Corrosion in Distribution System, Protect Aquatic Life in case of Surface Discharge
Increase sodium level in produced water and brine concentrate |
Caustic soda, soda ash, lime |
Parameters to consider for the brine effluent from different desalination plants
|
Anions |
Other parameters |
|
SO42- |
TDS |
|
Cl- |
|
|
HCO3- |
ΕC |
|
CO32- |
|
|
Cations |
pH |
|
Ca2+ |
Temperature |
|
Mg2+ |
Other impurities |
|
Na+ |
Electric conductivity |
|
K+ |
The following table summarizes the ions in saline wastewaters resulting from ion exchange processes.
Ιοns in saline wastewaters resulting from ion exchange processes.
|
Ions |
|
Ca2+ |
|
Mg2+ |
|
Na+ |
|
K+ |
|
Si- |
|
Cl- |
|
SO42- |
Parameters/pollutants in the wastewater generated in the desalting process
|
Pollutants |
|
Suspended solids |
|
Oil/oil emulsions |
|
Dissolved hydrocarbons |
|
Phenols |
|
Benzene |
|
BOD |
|
COD |
|
NH4+ |
|
Nitrogen compounds (N-Kj |
|
Sulphides (as H2S) |
|
Na+ |
|
Mg2+ |
|
Ca2+ |
|
Cl- |
|
SO42- |
|
HCO3- |
|
K+ |
|
Br- |
|
I- |
|
Temperature (oC) |