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Industrial Wastewater Treatment: Steps, Process, & Benefits

Many industries use large volumes of water in their manufacturing operations. Because some of this water becomes contaminated, it requires treatment before discharge. Improvements in determining the effects of industrial waste discharges have led to the adoption of stringent environmental laws, which define the degree of treatment necessary to protect water quality.

Wastewater treatment plants are designed to convert liquid wastes into an acceptable final effluent and to dispose of solids removed or generated during the process. In most cases, treatment is required for both suspended and dissolved contaminants. Special industrial wastewater treatment systems are required for the removal of certain pollutants, such as phosphorus or heavy metals.

When the wastewater treatment cycle is properly engaged, it ensures that other users of the water will have a source that meets their needs, whether these needs are for municipal water supply (e.g. water municipal lawns or use in boiler systems), industrial or agricultural uses, or fishing and recreation. Wastewater can be recycled for reuse in plant processes to reduce disposal requirements. This practice also reduces water consumption.

Because the type of industrial pollutants varies—including organic compounds, nutrients, solids, acids and alkalis, and metals—SUEZ North America employs a variety of proven methods and tools.
Wastewater Treatment Water Steps

Because industrial wastewater is varied in its contaminants, the processes needed for wastewater treatment are varied, too. Nonetheless, the basic wastewater treatment steps are often the same for municipal and industrial wastewater:

  • Step 1: screening, first to remove large items and second grit.
  • Step 2: primary clarification to separate solid organic matter.
  • Step 3: aeration to encourage conversion of NH3 to NO3 and provide oxygen for bacteria to grow.
  • Step 4: secondary clarification to allow remaining organic sediment to settle, often through chemical treatment.
  • Step 5: disinfection using chlorination, UV, or other methods.   
  • Step 6: discharge of the water; and disposal of solids; reclamation of biosolids/biogas.

Step 1: Wastewater Screening

The main purpose of screening is to remove solid materials from wastewater that could cause damage to other process equipment, cause reduction in efficiency of the whole system, or contaminate waterways.

SUEZ North America offers a variety of screens, including its Climber Screen, which uses a smooth running, endless track system which employs a gear-driven cleaning rake to carry screenings from a submerged bar rack to a discharge chute for removal—without the use of chains, sprockets, cables or any underwater moving parts. It can tackle large obstructions with ease. The rake simply disengages from the bar rack to clear the object until it can be removed on a subsequent pass.

Step 2: Primary Clarification and Separation

Clarification removes suspended solids from wastewater, providing a clarified liquid effluent for downstream treatment processes.

There are two types of wastewater clarification: primary and secondary.

  • Primary clarification: Removes solids from wastewater prior to biological treatment.
  • Secondary clarification: Rapidly returns activated sludge to the aeration tank after biological treatment.

Solids separation processes are widely used in water and wastewater treatment plants, being critical in the preparation of drinking water, industrial process water and in the pre-treatment of many types of wastewater.

Many industrial wastewaters contain significant quantities of suspended solids. These can be pulp fibers in paper manufacturing wastes, metal particulates from iron and steel processing operation, coke fines from power plants, oil and grease from food processing or oil and gas refining operations, or just clay particulates from plant runoff. Industrial wastewater treatment facilities therefore often include a solids removal step in primary treatment. Solids separation processes are also used later in the wastewater treatment plant to separate and thicken biological solids at the secondary treatment step, to remove or polish residual suspended solids via filtration at the end of the plant, and to remove water from wet solids, or sludge.

When wastewater contains appreciable amounts of hydrocarbons, removal of these contaminants becomes a problem. Oil is commonly lower in density than water; therefore, if it is not emulsified, it can be floated in a separate removal stage or in a dual-purpose vessel that allows sedimentation of solids. For example, the refining industry uses a rectangular clarifier with a surface skimmer for oil and a bottom rake for solids as standard equipment. This design, specified by the American Petroleum Institute, is designated as an API separator.

Where the density differential is not sufficient to separate oil and oil-wetted solids, air flotation may be used to enhance oil removal. In this method, air bubbles are attached to the contaminant particles, and thus the apparent density difference between the particles is increased. Dissolved air flotation (DAF) is a method of introducing air to a side stream or recycle stream at elevated pressures in order to create a supersaturated stream. When this stream is introduced into the waste stream, the pressure is reduced to atmospheric, and the air is released as small bubbles. These bubbles attach to contaminants in the waste, decreasing their effective density and aiding in their separation.

Step 3: Areation

Aeration is a critical stage in the activated sludge process. Several methods of aeration are used:

  • High-rate aeration: High-rate aeration operates in the log growth phase. Excess food is provided, by recirculation, to the biomass population. Therefore, the effluent from this design contains appreciable levels of biochemical oxygen demand, or BOD (i.e., the oxidation process is not carried to completion).
  • Conventional aeration: The most common activated sludge design used by municipalities and industry operates in the endogenous phase, in order to produce an acceptable effluent in BOD and total suspended solids (TSS) levels. Conventional aeration represents a “middle of the road” approach because its capital and operating costs are higher than those of the high rate process, but lower than those of the extended aeration plants.
  • Extended aeration: Extended aeration plants operate in the endogenous phase but use longer periods of oxidation to reduce effluent BOD levels. This necessitates higher capital and operating costs (i.e., larger basins and more air). In conjunction with lower BOD, extended aeration produces a relatively high suspended solids effluent when optimum natural settling ranges are exceeded.
  • Step aeration/tapered aeration: In a plug flow basin, the head of the basin receives the waste in its most concentrated form. Therefore, metabolism and oxygen demand are greatest at that point. As the waste proceeds through the basin, the rate of oxygen uptake (respiration rate) decreases, reflecting the advanced stage of oxidation.

Step 4: Secondary Clarification

Finely divided particles suspended in surface water repel each other because most of the surfaces are negatively charged. Coagulation and flocculation are used here.

Coagulation can be accomplished through the addition of inorganic salts of aluminum or iron. These inorganic salts neutralize the charge on the particles causing raw water turbidity, and also hydrolyze to form insoluble precipitates, which entrap particles. Coagulation can also be affected by the addition of water-soluble organic polymers with numerous ionized sites for particle charge neutralization.

In most clarification processes, a flocculation step then follows. Flocculation starts when neutralized or entrapped particles begin to collide and fuse to form larger particles. This process can occur naturally or can be enhanced by the addition of polymeric flocculant aids. Flocculation, the agglomeration of destabilized particles into large particles, can be enhanced by the addition of high-molecular-weight, water-soluble organic polymers. These polymers increase floc size by charged site binding and by molecular bridging.

Step 5: Disinfection

Effluent wastewater from an industrial facility may carry a broad and variable range of contaminants—including BOD, chemical oxygen demand, or COD (the amount of oxygen that can be consumed by reactions in a measured solution), color, phenols, cyanides, sanitary waste and a host of complex chemicals.

Ozone, in combination with ultraviolet (UV) and/or other physical, chemical or biological processes, has the potential to treat complex industrial wastes due to its strong oxidative nature. In combination with medium pressure UV, ozone exhibits the power of advanced oxidation for TOC reduction, as well as destruction of organics. Potential industries that can benefit from ozone and UV include pharmaceuticals, textiles, automotive, foundry, etc.

UV disinfection is environmentally safe and recognized as highly effective on a wide range of pathogens, including viruses. We have 20 years’ experience providing UV systems for disinfection, reuse and recycling. Today, we offer UV products for municipal wastewater, municipal drinking water and a variety of industrial applications including process water, pools and spas, and ozone destruction.

UV irradiation systems disinfect by inactivating pathogenic microorganisms, such as viruses, bacteria and parasites. In the UV-C light spectrum (200-280 nm), the wavelength 254nm has been proven to be the most efficient wavelength to inactivate microorganisms by damaging the nucleic acids (DNA and RNA), which disrupts the organism’s ability to replicate.

In normal applications, UV has the advantage that no chemicals are added to the water being treated and that no disinfection by-products are formed. Due to the small footprint, the UV equipment can be easily integrated into most existing water treatment plants.

For over 40 years, Ozonia ozone, UV, and advanced oxidation processes (AOP) have been used in a wide variety of municipal and industrial water treatment applications. Ozone has been a best-in-class solution for decades in drinking water applications but oxidation’s unique properties make it a powerful tool for water users across all industry sectors.

Ozone, UV and AOP solutions are in applications for wastewater and reuse, process water, ultrapure water, aquaculture, pulp bleaching, chemical synthesis and flue gas scrubbing. AOP are aqueous phase oxidation methods consisting of highly reactive species used in the oxidative destruction of target pollutants.

AOP creates a more powerful and less selective secondary oxidant, hydroxyl radicals, in the water. This secondary oxidant can cause the oxidation of most organic compounds until they are fully mineralized as carbon dioxide and water. The hydroxyl radical has a much higher oxidation potential than ozone or hydrogen peroxide and usually reacts at least one million times faster, thus leading to a smaller contact time and footprint.

Chlorine and chlorine derivatives are among the most versatile chemicals used in industrial water and wastewater treatment. These powerful oxidizing agents are used for:

  • disinfection
  • control of microorganisms
  • removal of ammonia
  • control of taste and odor
  • color reduction
  • destruction of organic matter
  • hydrogen sulfide oxidation
  • iron and manganese oxidation

Although chlorine is beneficial for many uses, dechlorination is often required prior to discharge from the plant. Also, high chlorine residuals are detrimental to industrial systems, such as ion exchange resins, and some of the membranes used in electrodialysis and reverse osmosis units. Chlorine may also contribute to effluent toxicity; therefore, its concentration in certain aqueous discharges is limited. Sometimes, dechlorination is required for public and industrial water supplies.

Step 6: Disposal of Solids

Disposal of the solids generated by industrial wastewater treatment plants is dependent on government regulations, geographical location, and sludge characteristics, among other things. Final disposal methods include reclamation, incineration, land application, and landfill.

Sources of Wastewater

SUEZ North America treats wastewater from a broad swath of industries. Each has specific needs to limit their environmental damage.

For example, the power industry—one of the largest consumers of water—is also one of the biggest polluters. Coal-fired plants regularly discharge cadmium, chromium, and lead into public waterways. Mercury, too, increasingly has become a significant contaminant in coal-fired plants, as the installation of wet flue gas desulfurization (FGD) systems at many coal-burning facilities. The FGD process has resulted in a significant reduction in air emission of mercury but has done this by transferring the mercury contaminants to a wastewater stream. Other industries such as petroleum refining, natural gas recovery and other light and heavy industries also generate mercury contaminated wastewater.

Food processors, such as meat rendering plants, need to limit the fats, oils and grease that are released in their effluent, or risk having their plants shut down.

Pulp and paper companies need to reduce the hydrogen sulfide generated at their waste treatment facilities, including odors emanating from clarifiers and sludge dewatering equipment. Paper manufacturers are also being pressured to improve dissolved oxygen levels in their effluent, which can kill higher aquatic life forms.

SUEZ North America has wastewater treatment solutions for

  • prepared food manufacturers
  • pulp and paper
  • upstream oil and gas
  • refining
  • chemical processing
  • microelectronics
  • metal and mining
  • pharma and life sciences
  • power
Wastewater Treatment Benefits

Properly treating industrial wastewater can help your company protect the environment, protect your equipment, and protect your reputation. For example, food processors have found that by implementing SUEZ North America’s solutions, they were able to avoid regulatory fines and shutdown, control emissions, and resume compliant wastewater discharge.

Power plants have used SUEZ solutions to comply with the Coal Combustion Residuals (CCR) rule through pond dewatering, treatment of low-level waste, leachate, coal pile and runoff streams and groundwater remediation. And chemical processing companies found that by collaborating with SUEZ on an integrated and collaborative approach throughout the product lifecycle they could reduce their environmental footprint while preserving their competitiveness.


Contact a representative to learn more about SUEZ' industrial wastewater treatment services.

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