6. Elaboration Question 2

Course subject(s) 6. Digestion of sludge and sewage

Question 2: Sludge treatment process

A sewage treatment plant treats an average flow of 60,000 m3/day, with an influent concentration of 200 mg BOD/l. For the disposal of the surplus sludge, a sludge treatment system is designed. This treatment line consists of:

  • Sludge digestion
  • Centrifugation
  • Sludge thickening
  • Rejection water treatment
  • Transport to the incineration plant
  • a. Draw a schematic overview of the sludge treatment (water line, sludge line and biogas production), including the process units mentioned above.
  • b. If the sludge growth yield is 0.6 kg X/kg BOD, how much biomass will be produced per day?
  • c. The sludge entering the treatment line consists of 1% SS (70% organic). Estimate the tons of treated dewatered sludge per year that have to be transported to the incineration plant. The efficiency of organics removal in the digester is 50%. Estimate the dewatering per process unit
  • d. Calculate the percentage volume reduction for the overall sludge treatment chain.
  • e. Through incineration the volume is reduced a further 88%. What is the volume of ash remaining? What is the total volume reduction for the entire process including incineration?

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