Lecture 4.pptx releated to environmental engineering

Environmental Engineering

1. Treatment of Sewage

2. DISSOLVED OXYGEN (DO): Amount of oxygen dissolved (and hence available to sustain marine life) in a body of water such as lake, river or stream . Dissolved oxygen is the indicator of water pollution . DO levels in natural and waste water depend on physical , chemical and biological activities in water body. Amounts of oxygen that can be dissolved in water by temperature .

3. CHEMICAL OXYGEN DEMAND (COD ) : COD is an empiric laboratory assay which measured the amount of organic matter contained in a water sample with the help of chemical oxidizing agents such as potassium dichromate and potassium permanganate . COD is a means of measuring all organic matter (biodegradable and non- biodegradable ) . This test is useful in studying pollution strength of domestic and wastewater . COD values are greater than BOD values .

4. BIOLOGICAL OXYGEN DEMAND (BOD) : BOD is the amount of dissolved oxygen required to breakdown the organic material of the sample by aerobic biological microorganisms at certain temperature over a specific period of time . Th i s parame t e r i s determine d w i t h th e con s umpt i on of oxygen by microorganisms during 5 days of incubation at 20°C .

5. Purpose Of Wastewater Treatment Treatment of water thus aims at reduction of BOD, COD, eutrophication etc. of receiving water bodies and prevention of bio-magnification of toxic substances in food chain. To make wastewater usable for other purpose Prevention of harmful diseases. To prevent offensive odour in the water.

6. Primary Treatment Secondary Treatment Tertiary Treatment 3 Stages Of W aste w at e r Treatment

7. Primary Treatment of Wastewater    This is the first step in wastewater treatment and its objective is to remove large debris, coarse solids and heavy inorganic material contained in the wastewater flow . Approximately 25 to 50% of the incoming biochemical oxygen demand (BOD 5 ), 50 to 70% of the total suspended solids (SS), and 65% of the oil and grease are removed during primary treatment. It may be considered sufficient treatment if the wastewater is used to irrigate crops that are not consumed by humans or to irrigate orchards, vineyards, and some processed food crops.

8. Secondary Treatment of Wastewater   This treatment involves a biological process and it’s objective is the further treatment of the effluent from primary treatment to remove the residual organics and suspended solids. 1. Biological treatment process for secondary treatment are classified as aerobic (in the presence of oxygen) and anaerobic (in     the absence of oxygen ). Tertiary/Advanced Treatment of Wastewater:  It is the final treatment stage of wastewater processing and its main objective is the removal of specific wastewater constituents which cannot be removed in previous stages and thereby increase the quality of the effluent to higher degree. 1. It utilizes some form of filtration to remove higher level of suspended solids which was not possible through primary and secondary screening and sedimentation.

9. Primary and Secondary Sewage Treatment Raw sewage from sewers Bar screen Grit chamber Settling tank Aeration tank Settling tank Chlorine disinfection tank Sludge Sludge digester Activated sludge Air pump (kills bacteria) To river, lake, or ocean Sludge drying bed Disposed of in landfill or ocean or applied to cropland, pasture, or rangeland Primary Secondary

10. Primary Treatment of Sewage

11. Design aspects of Grit Chamber Shape: Rectangular/Circular Cleaning interval:1-2 weeks Depth = 2- 3 m with 300 mm free board Detention period: 1 Minute Velocity = 200-300 mm/sec

12. Design aspects of Detritus Tank Shape: Rectangular/Circular Depth : 2.5 m-3.5 m Detention period: 3-4 minutes Velocity of flow : 200-400 mm/sec

13. Design aspects of Skimming Tank Shape: elliptical or circular Depth : 2.5 m-3.5 m Detention period: 3-5 minutes Velocity of flow : 200-400 mm/sec

14. Design aspects of Sedimentation Tank Reduces sewage strength 30-35% and solids up to 80% Shape: Rectangular/Circular/Hopper bottom Ratio of L/W = 4-5 Ratio of W/D = 2-3 Detention period: 1-3 hours