Chemicals commonly used in wastewater treatment

Wastewater treatment is a critical process for environmental protection and public health. During this process, various chemicals are used to remove contaminants, disinfect water, and improve its quality. In this comprehensive article, we will review the most important chemicals used in wastewater treatment, their mechanism of action, and their applications.

Introduction: The importance of using chemicals in wastewater treatment

is almost impossible to treat wastewater without the use of chemicals. These chemicals are used at different stages of wastewater treatment for several reasons:

• Neutralization of acids and bases

• Coagulation and agglomeration of suspended particles

• Heavy metal removal

• Odor and foam control

• Disinfection and elimination of pathogens

• Remove organic matter and nutrients such as nitrogen and phosphorus.

Choosing the right chemicals depends on a variety of factors, including wastewater composition, discharge standards, and operating costs.

Classification of common chemicals for wastewater treatment

1. Chemicals to adjust pH

PH control is an important step in wastewater treatment, as many subsequent processes require an appropriate pH value.

Alkaline substances:

• Lime (Ca(OH)₂):  the most commonly used substance, which raises the pH and promotes coagulation.

• Sodium hydroxide (NaOH):  A strong base that can precisely adjust the pH.

• Sodium carbonate (Na₂CO₃):  It has a softer effect and better dilution properties.

Acidic substances:

• Sulfuric acid (H₂SO₄):  The most  commonly used  acid to reduce pH.

• Hydrochloric acid (HCl):  used in special cases

• Carbon dioxide (CO₂)  : It has a slight effect in lowering the pH.

2. Coagulant

These substances neutralize the charge of colloidal particles and form larger molecules.

Metal coagulants:

• Alum (aluminum sulfate – Al₂(SO₄)₃):  the most commonly used coagulant

• Ferric chloride (FeCl₃):  effective for some wastewater

• Polyaluminium chloride (PAC)  : high efficiency and low sludge production

Organic coagulants:

• Polyamine

• Poly-Dadmac

• Polyacrylamide Cationic

3. Chelating substances

These substances cause small particles to stick together and form larger, heavier blood clots.

Polymeric coagulant:

• Polyacrylamide (PAM)

• Anionic polymer

• Cationic polymers

• Non-ionic polymer

4. Disinfectants

Chlorine and its compounds:

• Chlorine (Cl₂):  effective but dangerous

• Sodium hypochlorite (NaOCl):  safer than chlorine

• Calcium hypochlorite (Ca(OCl)₂)  : special applications

Other disinfectants:

• Ozone (O₃):  High capacity, but expensive and complex.

• Chlorine dioxide (ClO₂)  : used for some wastewater.

• Perracetic  acid: an emerging alternative

• Ultraviolet  radiation: No chemicals are needed, but clean water is needed.

5. Substances that remove nutrients (nitrogen and phosphorus)

Phosphorus removal:

• Aluminum salt (alum)

• Iron salt (ferric chloride)

• Calcium (cal)

To remove nitrogen:

• Methanol  : as a source of carbon in the denitrogenization process

• Urea  : in some biological processes

6. Deodorant

• Potassium permanganate (KMnO₄)

• Hydrogen peroxide (H₂O₂)

• Activated carbon

7. Materials for removing heavy metals

• Sodium  hydroxide : used for mineral precipitation.

• Sodium sulfide: used to precipitate  some minerals.

• Activated  carbon : absorbs some minerals.

The mechanism of action of chemicals in wastewater treatment

a) Coagulation and agglomeration mechanism

1. Charge neutralization:  A coagulated metal with a positive  charge neutralizes the negative charge of colloidal particles.

2. Surface  adsorption: Metal ions are absorbed on the surface of the particles.

3. Bridge  : Clumping polymers build bridges between molecules and bind them together.

4. Sedimentation  : Larger blood clots are deposited due to gravity.

b) Disinfection mechanism

1. Oxidation  : Disinfectants oxidize the cell walls of microorganisms.

2. Destruction of enzymes  : the activity of important enzymes is destroyed.

3. DNA  damage: Under the influence of ultraviolet radiation, the DNA of microorganisms will be directly damaged.

Factors influencing chemical selection

1. Wastewater  installation: types and concentrations of pollutants

2. Wastewater  pH : Some substances work best at  certain pH levels .

3. Cost of materials  : includes the price of materials, in addition to transportation and storage costs.

4. Safety and ease of use  : Some hazardous materials require special equipment.

5. Amount of sludge produced  : Some materials produce a greater amount of sludge.

6. Environmental  impact: Waste in wastewater

7. Compatibility with subsequent  processes: overlap with other purification steps

Advantages and disadvantages of various chemicals.

a) Benefits

•   Efficient removal of contaminants

• Faster impact   than biological methods

• Ability to precisely   control purification parameters

•  Flexible response  to changes in wastewater quality

b) Defects

• High operating   costs for some materials

• Chemical   sludge generation that needs to be managed

• Security   risks during transportation and storage

• Environmental   impact of residual substances in wastewater

Emerging innovations and alternatives

1. Use of green  polymers: naturally sourced and biodegradable polymers

2. Nanomaterials  : such as iron nanoparticles, to remove specific contaminants.

3. Environmentally  friendly compounds: less toxic alternatives

4. Hybrid  systems: a combination of chemicals with membranes or biological methods

5. Chemical  restoration: e.g. recovery of alum from sewage sludge

Safety considerations when  using wastewater treatment chemicals

1. Staff  training: Know the risks of each subject.

2. Personal  protective equipment: gloves, goggles, masks.

3. Storage  conditions: suitable temperature, away from light and moisture.

4. The ventilation  :  system is especially suitable for volatile substances.

5. Emergency  Instructions: Spillage or skin contact

6. Chemical  sludge management: safe disposal of sludge generated

Conclusion

Chemicals play an essential role in wastewater treatment, and their choice of suitable treatment directly affects treatment efficiency and cost. As technology advances, new materials with higher efficiency and lower environmental impact are being developed. Smart management of these materials not only improves wastewater quality, but also reduces operating costs and ensures environmental sustainability.

Ultimately, the design of the wastewater  treatment system should be based on a detailed analysis of the incoming wastewater, output parameters, and a comprehensive technical and economic assessment to select the optimal mix of chemical, physical and biological processes.