Use of biotechnology in the treatment of municipal wastes and hazardousindustrial effluents
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Industrial wastewater is generated by industrial activities and requires treatment due to its high levels of pollutants, usually through biological methods. Sewage, another type of liquid waste, is treated to reduce pollution using advanced biotechnological techniques, involving primary, secondary, and tertiary treatment stages. Biological processes, including aerobic and anaerobic systems, are employed to efficiently remove organic matter and heavy metals from wastewater.
Use of biotechnology in the treatment of municipal wastes and hazardousindustrial effluents
- 1. Sijo.A
- 2. INDUSTRIAL WASTE WATER Industrial waste water is a type of waste water produced by industrial activity, such as that of factories, mills and mines. It is characterised by its large volume, high temperature, high concentration of biodegradable organic matter and suspended solids, high alkanity or acidity and by variations of flow. The treatment of wastes by micro-organisms is called biological waste treatment.
- 3. BENEFITS 1. Used to develop method for the treatment of toxic compounds. 2. Improving the design and operation of biomechanical treatment system used for degradation of toxic compounds. 3. Improvement of public health, sanitation, soil integrity and the conservation of fresh water resources. 4. Reduce BOD and COD. 5. Remove odour.
- 4. SEWAGE Sewage is the liquid waste released from the community. It contains worthless materials discharged from industries, kitchens, food industries, health sanitaries, municipalities etc. The sewage has been treated for reducing the pollution hazards. Biotechnology has provided powerful methods for the treatment of sewage and waste waters. These methods uses the properties of micro-organisms to reduce the toxicity of heavy metals present in the sewage water.
- 5. THE PROCESS OF WASTE WATER TREATMENT Once the level of pollutants in water is determined, treatment of the water proceeds through the following four stages. (i) Primary treatment (ii) Secondary treatment (iii) Tertiary treatment
- 6. PRIMARY TREATMENT It involves the removal of solid wastes floating on the sewage and other sedimentable wastes from the sewage. They are removed by screening and sedimentation methods. 1. Screening It is the first step of sewage treatment. The sewage is passed through a screen fitted in the opening. Usually screens of uniform size are used for the screening. The screening protects the operation unit from the excessive dumping of solid wastes. The screens are classified into three groups, namely coarse screens, medium screens and fine screens.
- 7. 1. Coarse screen It is also called racks. It is used to remove the floating materials like rags, paper, wood etc. from the sewage. It is made up of steel bars with a space of 50mm between two adjacent bars.
- 8. 2. Medium screens It is used for removing some amount of organic materials from the sewage. Here screen bars are 40mm apart from one another.
- 9. 3. Fine screen It helps in the removal of suspended particles from the sewage. It has a perforations of 1.5mm to 3mm size.
- 10. 2.SEDIMENTATION The separation of solid suspended particles from the sewage is called sedimentation. The tank is often referred to as sedimentation tank or settling tank. Sedimentation prevents sludge formation in the treatment unit. It reduces BOD of sewage water. Sedimentation is carried out by adding some coagulants into the sewage. Such sedimentation process is called chemical precipitation. Eg: Alum, Ferric chloride, Ferric sulphate and Chlorinated copper.
- 12. 2. SECONDARY TREATMENT In this treatment, non sedimentable wastes are removed from the sewage. So it will decrease the level of organic chemicals and nutrients (nitrogen and phosphorous) present in the water. The secondary treatment is carried out by biological method. The biological treatment of sewage treatment includes aerobic process and anaerobic process. Depending on the nature of the use of microorganisms, the biological processes are categorized as suspended growth systems and attached growth systems.
- 13. AEROBIC SUSPENDED GROWTH SYSTEMS The most important suspended growth biological treatment systems used for the removal of organic matter are listed. Activated sludge process Aerated lagoons Sequencing batch reactor
- 14. ACTIVATED SLUDGE PROCESS The activated sludge process is the most commonly used modern process for the biological treatment of sewage. It was first developed in England in 1914. In this method, the sewage containing organic matter with the micro organisms are aerated in an aeration tank. The reactor contents are referred to as mixed liquor. Under aerobic conditions the microorganisms metabolize the soluble and suspended organic matter. The generalised metabolic reaction is as follows: COHNS+ O2+ Nutrients Co2+ NH3+ H2O (New cells + other products)
- 15. A small part of organic matter is utilized for the synthesis of new bacterial cells while the remaining gets oxidised to Co2 and H2O. The newly formed microorganisms are agglomerated to form flocs, technically referred to as sludge. The sludge is seperated from the settled tank and returned to the aeration tank and recycled. The activated sludge recycled in aeration tank serve as a seed or inoculum. The excess sludge can be removed. Growth of protozoa in a sludge is an indication of its healthy condition.
- 17. ADVANTAGES 95% of BOD, 98% of bacteria (particularly coliform) and 95% suspended solids can be removed. The excess waste sludge has a high fertilizer value. Low cost and highly efficient biological treatment system.
- 18. AERATED LAGOONS Aerated lagoons are also called aerated ponds. They re he facultative stabilization ponds where surface aerators are installed to overcome the bad odours. (due to overload of organic materials). It has large surface area, so it is more susceptible for temperature effects.
- 20. SEQUENCING BATCH REACTOR (SBR) SBR is a modification of activated sludge treatment system. The two processes like aeration and sedimentation are carried out sequentially in the SBR tank. Hence it regarded as fill-and-draw activated sludge process. The process is carried out in 5 steps- filling, aeration, sedimentation, decanting and idle.
- 22. AEROBIC ATTACHED GROWTH SYSTEM It is used to remove organic matter present in sewage. It is useful for nitrification process (conversion of ammonia to nitrate). The commonly used attached growth processes are Trickling filters Rotating biological filters Packed red reactors
- 23. TRICKLING FILTERS Trickling filters are also known as percolating or sprinkling filters. It is commonly used for the biological treatment of domestic sewage and industrial waste water. In trickling filter, the sewage is sprayed on a hard and porous material. After two weeks, the biomass attached to the surface of media and forms a layer known as biological film or microbial slime. It has a thickness of 0.1 to 2.0mm and is rich in microorganisms. It includes bacteria-Pseudomonas, Flavobacterium, Alcaligenes and algae –Chlorella, Ulothrix. As the biofilm ages, its thickness increases and it automatically settles to the bottom of the tank.
- 25. ROTATING BIOLOGICAL REACTORS (RBC) RBC is a recent device for the biological treatment of sewage. It operates on the principle of aerobic attached growth system operated on the moving media. It is suitable for the treatment of domestic and industrial sewage in small and medium towns. It has high BOD removal efficiency.
- 26. dd It consists of series of light weight circular discs are called biodiscs. They are made up of PVC or polyethylene. These discs are mounted on a horizonthal shaft and partially (40- 60%) submerged in sewage. It allows the disc to pick up a thin layer of sewage & then oxidise the absorbed substrates. The unoxidised substrate fall back into the sewage.
- 27. PACKED-BED REACTORS It is also called Fluidized bed reactor. A reactor is packed with a medium to which the microorganisms get attached and forms biofilms. The sewage along with air (pure O2) is introduced from the bottom of the reactor.
- 28. ANAEROBIC TREATMENT OF WASTE WATER BY MICROBES The anaerobic digestion process involves a wide variety of organisms, bacteria being the most predominant. The microbes digest the organic molecules like lipids, carbohydrates, proteins into CH4 and Co2. The waste water contains Sulphate and nitrate. 1. So4-2 is used as electron acceptor by bacteria like Desulphovibrio during the oxidation of organic compounds; they reduce S2-. 2. So4-2S2- 3. Denitrifying bacteria oxidise organic substrattes and No3- as electron acceptor; they liberate N2 in the process.
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