A wastewater treatment plant based on activated sludge with biological phosphate and nitrogen removal via pre-denitrification. The influent flow (dwf) is 30,000 m3/day and the influent BOD concentration is
300 mg BOD/l. The suspended solid concentration in the influent is 150 mg/l of which 40% is removed in the primary clarifier. The sludge recycle flow ratio (fr) is 0.5, the sludge yield (Y) is 0.6 kgX/kgBODremoved and the SVI is 130 mL/g.
The treatment plant consists of different process units, namely:
Final clarifier
Screen
Aerobic tank
Primary sedimentation
Anoxic tank
Grit chamber
Anaerobic tank
Sludge dewatering
After dewatering the sludge will be directly transported to the sludge incineration plant.
Put the proces units in the right order and indicate what will be removed in each step.
To determine the order of process units and what is removed in each step, let's analyze the provided information.
1. Grit chamber: The wastewater passes through the grit chamber first, which is designed to remove inorganic solids such as sand, gravel, and grit. These settle at the bottom due to their higher density.
2. Screen: Following the grit chamber, the wastewater is directed to a screen, which removes larger solid debris like paper, plastics, and other floating materials.
3. Primary sedimentation: After passing through the screen, the wastewater enters the primary sedimentation tank (also known as primary clarifier) where a portion of the suspended solids settles under gravity. According to the information given, 40% of the suspended solids are removed in this step.
4. Anaerobic tank: The wastewater then enters the anaerobic tank where organic matter is further degraded in the absence of oxygen. This process promotes the conversion of complex organic compounds into simpler forms.
5. Anoxic tank: Next, the wastewater is transferred to the anoxic tank. In this tank, the conditions are specially controlled to promote the growth of specific microorganisms that facilitate denitrification. Denitrification is the process where nitrate (NO3-) is converted to nitrogen gas (N2) and released to the atmosphere.
6. Aerobic tank: After the anoxic tank, the wastewater enters the aerobic tank. This tank provides oxygen-rich conditions to support the growth of aerobic microorganisms. These microorganisms will consume the remaining organic matter and remove nitrogen compounds, as well as phosphorus, through biological processes.
7. Biological phosphate and nitrogen removal via pre-denitrification: As mentioned earlier, the activated sludge process is used in this treatment plant. The combination of anaerobic, anoxic, and aerobic tanks allows for the biological removal of both phosphate and nitrogen. In the anaerobic and anoxic tanks, denitrification occurs, reducing nitrogen levels. In the aerobic tank, the remaining organic matter is degraded, and both phosphorus and nitrogen compounds are taken up by the activated sludge.
8. Final clarifier: The effluent from the aerobic tank is then directed to the final clarifier. Here, the remaining suspended solids, including the biomass (activated sludge), settle at the bottom through gravity. The clarified effluent is then discharged from the top, while the settled sludge is either recirculated back into the process or sent for further treatment.
9. Sludge dewatering: The settled sludge from the final clarifier is transported to the sludge dewatering unit. This process involves removing excess water from the sludge, resulting in a more concentrated and manageable sludge cake.
10. Sludge incineration plant: Finally, the dewatered sludge, now in the form of a sludge cake, is directly transported to the sludge incineration plant for disposal.
To summarize, the correct order of process units in the wastewater treatment plant based on activated sludge with biological phosphate and nitrogen removal via pre-denitrification is as follows:
Grit chamber -> Screen -> Primary sedimentation -> Anaerobic tank -> Anoxic tank -> Aerobic tank (Biological phosphate and nitrogen removal) -> Final clarifier -> Sludge dewatering -> Sludge incineration plant
Each step removes specific components from the wastewater, such as inorganic solids in the grit chamber, larger debris in the screen, suspended solids in the primary sedimentation, organic matter in the anaerobic and aerobic tanks, nitrogen compounds in the anoxic and aerobic tanks, and excess water in the sludge dewatering unit.