Water treatment (NACE code: E36.0)

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)