Industrial Effluent Treatment Process For Waste Water Treatment

The treatment process varies as per the type of effluent generated. Wastewater enters the treatment plant and goes through several processes before the effluent is released to the environment. Industrialeffluent treatment process includes the following stages:

* Preliminary treatment is aimed at removing the large sized contaminants from waste water. It includes following activities:

a. Screening: This is the first operation carried out in wastewater treatment plants. A screen is a device with uniform openings and its purpose is to remove large floating solids.

b. Sedimentation: It is a physical method to have the solid contaminants get settled at bottom of any container using gravity so as to remove suspended solids from water.

c. Grit Chamber: The wastewater that passes through the grit chamber removes the dense inorganic solids such as gravel, metal   fragments and sand which have made their way into the sewers. Removal of grit can prevent damaging of pumps & other operational difficulties.

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d. Clarifiers: Clarifiers are the tanks built with mechanical means for continuous removal of solids being deposited by sedimentation process before getting it treated through biological means.

* Primary treatment is a basic method of cleaning the solids or chemicals from the waste water. In this treatment, water is temporarily stocked in an immovable basin in which heavy solids are retained at the bottom surface whereas chemicals, light solids or oils float to the above water surface. Basically, its objective is physical separation of large sized contaminants. The settled solutes are removed from the bottom and upper surface and the remnant waste water may be left free or re-cycled through secondary treatment. Primary treatment includes the following:

a. Flocculation: Flocculation is when microscopic particles bind together to form larger particles in liquids. Flocculation occurs when small particles in a solution lose their repelling forces and begin to attract one another. The small particles then bond together to form “flocs” or “flakes.” Under most circumstances, a flocculant is necessary to begin the flocculation process. The most common flocculants are iron, aluminium, magnesium, and calcium. When flocs are fully formed, they can be removed from the solution they are in through traditional filtration methods. Flocculation is a physical process and does not involve the neutralization of charge. It involves the addition of destabilized particles together into large aggregates so that they can be easily separated from the water.

b. Coagulation: is a process in which coagulants are added for the purpose of rapid settlement of minute solid particles in a liquid into larger mass. It permits particle removal by sedimentation and for filtration. Coagulation is a chemical process that involves neutralization of charge. In a colloidal suspension, particles will settle very slowly or not at all because the colloidal particles carry surface electrical charges that mutually repel each other. A coagulant (typically a metallic salt) with the opposite charge is added to the water to overcome the repulsive charge and destabilize the suspension.

c. Neutralization: The aim of neutralization is to modify an acid or base water flow to a neutral pH (approximately 7). The most important objectives are to make the wastewater treatable using biological purification and/or make it comply with discharge criteria. Neutralization generally takes place by adding chemicals directly to the wastewater flow. Thus, equipment consists of storage and reaction tanks and a dosage and mixing installation.

* Secondary treatment is basically used to remove the biological waste that arise through household chaos, such as washing, cleaning or bathing. This treatment is performed through biological process in which micro-organisms are separated from the discharged water prior to territory treatment to make the water re-usable. The objective of this process is the further treatment of the effluent from primary treatment through biological and chemical processes to remove the suspended solids and residual organics. Following are involved as secondary treatment process:

a.    Activated Sludge Process: Activated sludge is a process for treating sewage and industrial wastewater using air and a biological floc composed of bacteria and protozoa. The process involves introduction of air or oxygen into a mixture of primarily treated wastewater combined with organisms to develop a biological floc which reduces the organic content of the sewage. A conventional activated sludge system commonly includes an aeration tank, which is used for biological degradation, and a secondary clarifier (sedimentation tank), where the sludge is separated from the treated wastewater.

b.    Aerated Lagoons: Is a treatment pond provided with artificial aeration to promote the biological oxidation of waste water. Aerated lagoons are an efficient and cost-effective system for primary and secondary wastewater treatment in small communities. They can be integrated very well into the surrounding landscape. If appropriate aerators are used the power input is similar to a comparable activated sludge plant. In addition to sufficient oxygen transfer the aerators have to provide for mixing and circulation.

c.    Trickling Filters: Trickling filters, also known as sprinkling filters, are commonly used for the biological treatment of domestic sewage and industrial waste water. A trickling filter is a fixed-bed, biological reactor that operates under (mostly) aerobic conditions. Pre-settled wastewater is continuously ‘trickled’ or sprayed over the filter made out of rocks, gravel, plastic modules. As the water migrates through the pores of the filter, organics are degraded by the biofilm covering the filter material.

d.    Rotating Biological Contactor: It involves allowing the wastewater to meet a biological medium in order to remove pollutants in the wastewater before discharge of the treated wastewater to the environment.
Rotating biological contactors also called rotating biological filters, are fixed-bed reactors consisting of stacks of rotating disks mounted on a horizontal shaft. They are partially submerged and rotated as wastewater flows through them. They are used in conventional wastewater treatment plants as secondary treatment after primary sedimentation of the effluent. The microbial community is alternately exposed to the atmosphere and the wastewater, allowing both aeration and assimilation of dissolved organic pollutants and nutrients for their degradation.

Read More: Effluent Treatment Plant (ETP) Technology for Waste Water Treatment

 
* Tertiary treatment helps is removing more than 90% of solutes which is completely disinfected. This kind of treatment is quite expensive and performed under special circumstances. This treatment is eco-friendly and almost produces the quality of drinking water. The purpose of tertiary treatment is to provide a final treatment stage to raise the effluent quality to the desired level before it is reused, recycled or discharged to the environment. Tertiary treatment is the final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment.

The treatment removes remaining inorganic compounds, and substances, such as the nitrogen and phosphorus. Bacteria, viruses and parasites, which are harmful to public health, are also removed at this stage. Tertiary process involves the following:

a.  Chemical Coagulation and sedimentation: Further coagulation and sedimentation processes are used to enhance the removal of solids from effluent after the secondary treatment.

 b. Filtration: Filtration is a process that removes particles from suspension in water. Removal takes place by a number of mechanisms that include straining, flocculation, sedimentation and surface capture.  As the discharge requirements for treated secondary effluent become more restrictive, effluent filtration is becoming a more integral part of tertiary treatment. Because a high-quality effluent is produced after filtration, the potential for reusing treated effluent is being examined by a number of municipalities, especially those in the water-short areas. A new concept of filtration in reuse applications and an innovative filter technology is being used to help alleviate some of these problems. The clarified wastewater is first passed through the adjacent filtration plant which contains large filter blocks to ensure high quality water.

c.  Reverse Osmosis: Reverse osmosis water treatment separates molecules and ions from their solutions, and is used in the production of potable, ultrapure and process water.  By applying external pressure, reverse osmosis drives a given solution through a semi-permeable membrane designed to overcome its osmotic pressure. Under normal osmotic circumstances, the solution would travel from lower saline concentration to high concentrations. In this process, pressure is used to force effluent through a membrane that retains contaminants on one side and allows the clean water to pass through the other side.

d. UV Disinfection:  It is a physical process that instantaneously neutralizes microorganisms as they pass by ultraviolet lamps submerged in the effluent. The process adds nothing to the water but UV light, and therefore, has no impact on the chemical composition or the dissolved oxygen content of the water. It is considered as an ideal disinfectant for industrial waste water as it leaves no residual disinfectant in the water by ensuring the water quality. It does not produce any disinfection by-products.