The "3 R" principle—Reduce, Recycle, and Reuse—must be examined for application in each Industrial Effluent Treatment Plant (ETP). Only the wastewater must be treated after using the basic and fundamental procedures of strength reduction, volume reduction, proportioning, segregation, and combining of effluents.
Different technologies used in Effluent Treatment Plants or ETPs
In an industrial effluent treatment facility, the following procedures are used in combination.
· Equalization and Neutralization
· Ratio of COD/BOD
· Monitoring of ETP
· Oxidation and Reduction
· Chemical Coagulation and Precipitation
· Settling Treatment
· Segregation
· Thermal Processes
· Activated Carbon
· Stripping
· Disinfection
· Adsorption
· Sewage Tertiary Treatment
· Solid waste disposal, and
· Colour removal
Let us discus?s these technologies in detail.
· Equalization and Neutralization
Alkaline effluents from one operation can be blended with acidic effluents from another for neutralization. The pH of the effluent will be brought to a range of 6 to 9 via neutralization. The same equalisation tank may also be used for neutralisation. For the majority of biological treatment techniques to be effective, the pH must be between 6 and 8.5.
Salt + Water = Acid + Base
Slaked lime, Caustic Soda, NaOH, or soda ash Na2CO3 are used as bases, whereas acids such H2SO4, HCI, or CO2 are used as acids. The quantity and quality of effluent vary throughout the day. However, ETPs are made to handle certain flows and concentrations of contaminants, as MLSS, BOD, and others.
Prior to being fed to ETPs, the effluent is first transferred to the Equalization Tank, for Quality and Quantity Equalization. Equalization is crucial, since all biological treatment processes are extremely sensitive to changes in quality and quantity.
· Ratio of COD/BOD
Biological treatment techniques will be cost-effective if the COD/BOD Ratio is 2 or less, or more than roughly 0.5. When the COD/BOD ratio is extremely high, biological treatment is only appropriate after using chemical precipitation methods first.
The COD/BOD ratio drops once the non-biodegradables (COD) are removed, and if it is below-2, biological treatment techniques such as trickling filters, the activated sludge process, oxidation ponds, etc., may be used.
· Precipitation and Chemical Coagulation
Chemical precipitation is done using Al2 (SO4)3. 18H20 or FeSO4.7H20 is advised before using biological treatment procedures.
· Settling
The objective of the settling process is the elimination of items that will float (scum or trash), and the expulsion of settleable organic and inorganic solids by sedimentation. The sewage must first go through a settling process to get rid of waste materials including wood, paper, and plastic, as well as oil and grease skimming’s.
Prior to shipping wastewater for biological treatment, hazardous chemicals like chromium, cadmium, cyanide, and arsenic must be removed. Alkaline chlorination (i.e., chlorination at pH > 10) or activated carboncan be used, to remove almost all harmful chemicals including arsenic, selenium, cadmium, nickel, etc.
· Segregation
Streams with high concentrations of a certain pollutant and dangerous compounds, such as cyanide and chromium are present. pH and BOD should be handled differently.
Segregation or separation is the process of dividing wastewater streams into distinct quality categories. Large-scale cooling tower blow downs that don't contain, any major contaminants should be processed separately, and kept apart from other waste. The same applies to mixing tiny streams that contain high concentrations of pollutants, with larger ones.
· Monitoring of ETP
The effluent treatment plant requires on-going observation. It is crucial to keep a close eye on the biological treatment process, while it operates. Before beginning any biological process, hazardous chemicals including As, Hg, and chlorine must be removed from the effluent. By using the right neutralising agents, the pH level must be between 6.5 and 8.5.
Hazardous substances are transformed into innocuous or less toxic/hazardous forms, through oxidation and reduction.
· Disinfection
In addition to boiling, KMnO4, UV rays, bromine and iodine, excess lime, and other disinfectants, chlorination is the most popular method for sterilisation. At the head end of a chlorine contact basin, a chlorine solution is frequently injected during disinfection.
Chlorine dosages of 5 to 15 mg/l are typical but vary depending on the wastewater and other factors.
· Carbon Activated Adsorption
Adsorption is a phenomenon that occurs on surfaces and involves the transfer of contaminants, from one surface to another. Adsorbent efficiency rises as surface area per gram of adsorbent increases.
Activated carbon has a surface area of more than 1000m2/gram, compared to normal carbon's surface area of 0.001 m2/gram. Molecular sieves are another option for treating effluents with harmful compounds, but their effectiveness is only increased in the presence of an effluent, free of major contaminants such as clay, MLSS, and TDS.
· Modern Demineralization Methods
It is comparable to reverse osmosis, freezing, ion exchange, distillation, and evaporation.
· Stripping
Gases dissolved in wastewater can be eliminated through desorption or stripping. When effluent is sprayed or sprinkled into the air as droplets through nozzles, gases are reabsorbed and the temperature of the effluent falls, as a result of steam escaping.
· Thermal Mechanisms
Hazardous wastes, both organic and inorganic, can be thermally destroyed by incinerating C, H, O, S, N, and heavy metals, at temperatures of 8000°C or more.
· Biological treatment
An Oxidation Pond is always advised after the Secondary Clarifier, since it gives the wastewater a tertiary treatment and gives it a polishing character.
A stabilisation pond with algae is a relatively affordable treatment option that is also quite effective, at removing BOD. If correctly managed, organic loadings as high as 300 kg BOD/ha/day and detention times of 10 to 15 days, result in up to 90% BOD elimination.
If BOD is greater than 2000 mg/l, anaerobic ponds may be employed. 60% of BOD/COD is removed using an anaerobic pond with a 3-month retention period and a 5-meter depth. Additionally, this requires no maintenance at all.
· Colour removal
While, manganese gives water a black hue, iron gives water a red or reddish brown colour. While other dissolved organics, etc., provide water other hues and scents, zinc gives water opalescence, a whitish colour. In the last stages, chlorination can eliminate the majority of the manganese found in iron, as well as the related colour and odour.
Activated Carbon, Activated Silica, or Molecular Sieves are used as a tertiary treatment, to further remove colour and odour. 90% of colour is removed by activated carbon at a pH of 3. As colour is a common person's indicator of pollution, after the colour is effectively removed, consumer acceptance will increase and public outcry will decrease. The most popular methods used to remove colour include coagulation, flocculation, carbon adsorption, and chlorination.
· Getting Rid of Solid Waste
The majority of toxic compounds are found in precipitates or solid wastes, which are removed annually by the local pollution control board, because they are deemed harmful. During this time, the solid wastes must be kept in watertight storage tanks and do not require additional treatment.
Manufacturers of effluent treatment plants in India
Netsol Water is the leading producer and supplier of sewage and effluent treatment systems in India. Our system is exceptionally reliable and cost-effective for use in an industrial environment. We work with each of our clients to give high-quality filtration systems at affordable pricing, since we are aware that you need the best systems available, at fair and competitive prices.