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Environmental Engineering Lecture 7 Dr. Hasan Hamouda

Environmental Engineering Lecture 7 Dr. Hasan Hamouda. Coagulation.

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Environmental Engineering Lecture 7 Dr. Hasan Hamouda

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  1. Environmental Engineering • Lecture 7 • Dr. Hasan Hamouda

  2. Coagulation Coagulants and flocculants are chemicals used to precipitate insoluble substances. The purpose of coagulation and flocculation is to cause small pollutant particles such as metals to aggregate and form large enough flocks so that they can be separated from the wastewater through sedimentation. • Rate of flocculation is dependent upon many factors including: • concentration of particles, • particle contact, • range of particle sizes.

  3. Coagulation • the objective is to promote the settlement of suspended Inorganic clay colloids and micro-organisms (10-6 to 10-3 mm) or hydrophobic particles • Settlement of particles occurs when their settling velocity is adequate to cause settling • The coagulation process utilizes what is known as a chemical coagulant (aluminum sulphate or ferric sulphate)) to promote particle agglomeration • rapid mixing (20 to 60 s) is carried out with the objective of producing a microfloc

  4. Coagulation Jar Test Arrangement The jar test is a simple test made up of several one liter beakers with samples of the raw water. To each is added a different and increasing amount of coagulant and rapid mixing is followed for 20 to 60 s. The samples are allowed to settle and that sample with the best settlement characteristic is selected as the coagulant

  5. Coagulation Determine the daily requirement of alum to coagulate a flow of 200L/s, if the jar test indicates that optimum coagulation occurs when 1 liter of water is dosed with 3mL of 10g/L alum solution?

  6. Coagulation

  7. Coagulation Determine the basin dimensions of a uniform depth flocculation basin to treat 36400 m3/day. The detention time is 50 min. Assume the basin width is 25 m consisting of five equal width units separated by perforated concrete walls.

  8. Filtration • Filtration is a process of passing water through a porous media with the expectation that the filtrate has a better quality than the influent. • Media is sand • Filtration types: • Slow or rapid sand filter • Gravity or Pressure filtration

  9. Filtration • Slow Sand Filter: • Total coli form bacteria removal >99 %. • Total particulate removal > 98%

  10. Slow Sand Filter: Design Criteria

  11. Slow Sand Filter: Design Example • Choose a tank 23m long x 10m wide. • From Table 11.11, the height of tank required is: • (a) system under drain = 0.5 m • (b) Filter bed = 0.9 m • (c) Supernatant water = 1 m • Therefore • Total height = 2.5 m • Tank size =2.5 m high x 23 m long x 10m wide.

  12. Rapid Sand Filter • Rapid gravity filtration (RGF) is used to filter chemically coagulated water and so produce a high quality drinking water. • Filtration removes suspended particles (turbidity) by the simple physical method of filtration. • Rapid gravity filters may be of three possible media types: • Single medium, usually sand or anthracite • Dual medium, usually sand and anthracite • Multimedia, usually garnet, sand and anthracite

  13. Rapid Sand Filter

  14. Rapid Sand Filter: Design Criteria

  15. Rapid Sand Filter: Design Example

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