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?