Description

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.
Q1:Put the proces units in the right order and indicate what will be removed in each step.

Screen

Grit chamber
Primary sedimentation
Anaerobic tank
Anoxic tank
Aerobic tank
Final clarifier
Sludge dewatering

To determine the order of the process units in the wastewater treatment plant and understand what will be removed in each step, we need to consider the different treatment processes involved in a typical activated sludge system with biological phosphate and nitrogen removal via pre-denitrification. Here is the order of the process units and the removal achieved in each step:

1. Grit chamber: This is the first step in the treatment process and is designed to remove large particles such as sand, gravel, and other debris that may be present in the influent wastewater. It helps protect the downstream units from damage.

2. Screen: Following the grit chamber, the influent wastewater passes through a screen or bar rack. This unit removes smaller debris, such as leaves, plastics, or other large floating objects that were not captured in the grit chamber.

3. Primary sedimentation: The wastewater is then directed to the primary clarifier, where heavy suspended solids settle down as sludge, which is later removed and processed separately. In this step, around 40% of the suspended solids are removed.

4. Anaerobic tank: In the anaerobic tank, organic matter in the wastewater is broken down by anaerobic bacteria. This step helps in further reducing organic load before entering the main treatment process.

5. Anoxic tank: In the anoxic tank, denitrification occurs, converting nitrate (NO3-) into nitrogen gas (N2). This step removes nitrogen from the wastewater, especially reducing the levels of nitrate, which is a common pollutant in wastewater.

6. Aerobic tank: The wastewater then enters the aerobic tank, where aerobic bacteria are introduced to oxidize the remaining organic matter in the wastewater. This process utilizes oxygen to biologically stabilize and remove the remaining organic load, including the biological oxygen demand (BOD) present in the influent.

7. Biological phosphate removal: Within the aerobic tank or a separate tank, specialized bacteria remove phosphate from the wastewater by storing it as polyphosphate granules. This helps reduce phosphorus concentration, which is another common pollutant in wastewater.

8. Final clarifier: The final clarifier is the last unit in the treatment process, where the remaining suspended solids, biomass, and any leftover sludge settle out. The clarified water or effluent is released from this unit, while the sludge is recycled back to the process.

9. Sludge dewatering: After the clarifier, the sludge is taken to a dewatering unit. This process reduces the moisture content of the sludge, making it easier to handle and transport for further treatment or disposal.

10. Sludge incineration: The dewatered sludge is finally transported to the sludge incineration plant, where it is thermally treated to reduce its volume and eliminate any remaining pathogens or organic matter.

By following this sequence of process units, the wastewater treatment plant can effectively remove solids, organic matter (BOD), nitrogen, and phosphate from the influent wastewater, producing a treated effluent that meets environmental regulations.