Wastewater Treatment

wastewater plant

The principal objective of wastewater treatment is generally to allow human and industrial effluents to be disposed without causing any danger to humans’ health or unacceptable damage to the natural environment.

The design of wastewater treatment plants is usually based on the need to reduce organic and suspended solids loads to limit pollution of the environment.

Conventional wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter and, sometimes, nutrients from wastewater.

FARAN’s wastewater treatment packages/plants include but are not limited to:

  • Preliminary treatment
  • Primary treatment
  • Secondary treatment
  • Tertiary and/or advanced treatment
  • Disinfection

Preliminary treatment

The objective of preliminary treatment is the removal of coarse solids and other large materials often found in raw wastewater. Removal of these materials is necessary to enhance the operation and maintenance of subsequent treatment units. Preliminary treatment operations typically include coarse screening, grit removal and, in some cases, comminution of large objects. In grit chambers, the velocity of the water through the chamber is maintained sufficiently high, or air is used, so as to prevent the settling of most organic solids. Grit removal is not included as a preliminary treatment step in most small wastewater treatment plants. Comminutors are sometimes adopted to supplement coarse screening and serve to reduce the size of large particles so that they will be removed in the form of a sludge in subsequent treatment processes. Flow measurement devices, often standing-wave flumes, are always included at the preliminary treatment stage.

Primary treatment

The target of primary treatment is the removal of settleable organic and inorganic solids by sedimentation, and the removal of materials that will float (scum) by skimming. Approximately 25% to 50% of the incoming biochemical oxygen demand (BOD5), 50% to 70% of the total suspended solids (SS), and 65% of the oil and grease are removed during primary treatment. Some organic nitrogen, organic phosphorus, and heavy metals associated with solids are also removed during primary sedimentation but colloidal and dissolved constituents are not affected. The effluent from primary sedimentation units is referred to as primary effluent.

Secondary treatment

The purpose of secondary treatment is further treatment of the effluent from primary treatment to remove the residual organics and suspended solids. In most cases, secondary treatment follows primary treatment and involves the removal of biodegradable dissolved and colloidal organic matter using aerobic biological treatment processes.

Aerobic biological treatment is performed in the presence of oxygen by aerobic microorganisms (principally bacteria) that metabolize the organic matter in the wastewater, thereby producing more microorganisms and inorganic end-products (principally CO2, NH3, and H2O). Several aerobic biological processes are used for secondary treatment, differing primarily in the manner in which oxygen is supplied to the microorganisms and in the rate at which organisms metabolize the organic matter.

High-rate biological processes are characterized by relatively small reactor volumes and high concentrations of microorganisms compared with low rate processes. Consequently, the growth rate of new organisms is much greater in high-rate systems because of the well-controlled environment. The microorganisms must be separated from the treated wastewater by sedimentation to produce clarified secondary effluent. The sedimentation tanks used in secondary treatment, often referred to as secondary clarifiers, operate in the same basic manner as the primary clarifiers described previously. The biological solids removed during secondary sedimentation, called secondary or biological sludge, are normally combined with primary sludge for sludge processing.
Common high-rate processes include the activated sludge processes, trickling filters or biofilters and rotating biological contactors (RBC).

Aeration Basin

Anaerobic wastewater treatment is the biological treatment of wastewater without the use of air or oxygen. The technology is used for the removal of organic pollution in wastewater, slurries and sludge. The organic pollutants are converted by anaerobic microorganisms to biogas, which is consisted of methane and carbon dioxide. Biogas is a renewable energy source, which can be used for electricity and heat production.

Anaerobic wastewater treatment can be used to treat dilute to concentrated liquid organic wastewaters (distillery, brewery, food and beverage industry, paper manufacturing, petrochemical, etc.).

An anaerobic system can be used for pretreatment prior to discharging to a municipal wastewater treatment plant or before polishing in an aerobic process.

Anaerobic treatment is typically utilized to treat warm, high-strength industrial wastewater containing high concentrations of biodegradable organic matter. This energy-efficient process reliably removes biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total suspended solids (TSS) from wastewater.

Tertiary and/or advanced treatment

Tertiary and/or advanced wastewater treatment is employed when specific wastewater constituents which cannot be removed by secondary treatment must be removed. Individual treatment processes are necessary to remove nitrogen, phosphorus, additional suspended solids, refractory organics, heavy metals and dissolved solids. Because advanced treatment usually follows high-rate secondary treatment, it is sometimes referred to as tertiary treatment. However, advanced treatment processes are sometimes combined with primary or secondary treatment (e.g., chemical addition to primary clarifiers or aeration basins to remove phosphorus) or used in place of secondary treatment.


Disinfection normally involves the injection of a chlorine solution at the head end of a chlorine contact basin. The chlorine dosage depends upon the strength of the wastewater and other factors, but dosages of 5 to 15 mg/l are common. Ozone injection and ultra violet (UV) irradiation can also be used for disinfection but these methods of disinfection are not common. The bactericidal effects of chlorine and other disinfectants are dependent upon pH, contact time, organic content, and effluent temperature.

FARAN’s wastewater treatment packages are applicable for the following industries:

  • Sanitary
  • Food & Beverage (Dairy, Fruit Juice, Meat Processing and Slaughterhouse, Bakery, Agricultural, etc.)
  • Oil, Gas and Petrochemical
  • Textile Dyeing
  • Ceramic, Mineral & Mining Industry
  • Hospital, Surgical and Pharmaceutical
  • Pulp & Paper Industry

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