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Environmental Engineering Lecture 9

Environmental Engineering Lecture 9. Why do we need to treat wastewater ?. To prevent groundwater pollution To prevent sea shore pollution To prevent soil pollution To prevent marine life pollution Protection of public health To reuse the treated effluent For agriculture

riley-clarke
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Environmental Engineering Lecture 9

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  1. Environmental Engineering Lecture 9

  2. Why do we need to treat wastewater ? • To prevent groundwater pollution • To prevent sea shore pollution • To prevent soil pollution • To prevent marine life pollution • Protection of public health • To reuse the treated effluent • For agriculture • For groundwater recharge • For industrial recycle • Solving social problems caused by the accumulation of wastewater

  3. Technical goals of Wastewater treatment • Separation of solids from liquid • Stabilization of separated solids • disinfection of pathogenic micro-organisms • Proper reuse or disposal of treated liquid and solids

  4. Wastewater treatment methods Physical Chemical Biological Aerobic Anaerobic Precipitation Adsorption Disinfection Screening Mixing Flocculation Flotation Filtration Sedimentation Gas Transfer Wastewater treatment Processes

  5. Wastewater Treatment Processes O2 • Secondary treatment • Aerobic, anaerobic lagoons • Trickling filter- activated sludge-oxidation ditch • Mostly BOD removal technology • Primary treatment • screening • grit removal • removal of oil • sedimentation • Tertiary treatment • Nitrate removal • Phosphorus removal • Disinfection

  6. Wastewater Collection System - Definitions

  7. Types of Wastewater

  8. Domestic Wastewater Characteristics

  9. Industrial Wastewater Characteristics

  10. Design of the bar screen channel (Approach Channel) The cross section of the bar screen channel is determined from the continuity equation: Qd = AcVa Ac = Qd/ Va The head loss through the bar screen Qd = design flow, m3/s Ac = bar screen cross section, m2 Va = Velocity in the approach channel, m/s Hl = head loss Va = approach velocity, m/s Vb = Velocity through the openings, m/s g = acceleration due to gravity, m/s2 Usually, rectangular channels are used, and the ratio between depth and width is taken as 1.5 to give the most efficient section.

  11. Example A manual bar screen is to be used in an approach channel with a maximum velocity of 0.64 m/s, and a design flow of 300 L/s. the bars are 10 mm thick and openings are 3 cm wide. Determine The cross section of the channel, and the dimension needed The velocity between bars The head loss in meters The number of bars in the screen 1. Ac= Qd / Va= 0.3/0.64 = 0.47 m2 Ac= W x1.5W =1.5 W x W 3. Head loss: W = 0.56 m, Depth (d) = 1.5 W = 0.84 m = 0.024 m 2. 4) n* t bar + (n-1)Sc = W n x 1 + (n-1) x 3= 56 n= 14.75 = 15 = 0.84 x 0.56 (3/3+1) = 0.35 m2 From continuity equation: Va Ac= Vb Anet Vb= 0.64 x 0.56 x 0.84/0.35 = 0.86 m/s < 0.9 m/s ok

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