Requirements for biological treatment end equipment, Part 2: Activated sludge process and its modifications

IS 8413 Part 2 - Scope: Key Specifications & Materials

Scope Summary (Clause 2.0 & 3.1)

• Defines components and construction methods for aeration chambers and wastewater treatment equipment.
• Materials and construction methods are specified in Table 1 (Clause 3.1).

Key Materials & IS References (from Table 1)

Units & Definitions (SI Units)

• Length: metre (m)
• Force: newton (N) = 1 kg·m/s²
• Pressure: pascal (Pa) = 1 N/m²

Summary Diagram of Material Flow

graph TD
    A[Civil Works] -->|Concrete| B[IS 

IS 8413 Part 2: Terminology and Definitions - Key Points

Clause 2.0 defines terminology used in the standard, ensuring uniform understanding.

Key Definitions (Example from Clause 3.1.3)

• Vortair Entrainment Aerator:
  A turbine device placed just below the liquid surface. Oxygen entrainment occurs due to hydraulic phenomena when the turbine rotates, enhancing aeration efficiency.

Units and Symbols (SI Units per IS 8413 Part II)

Construction Materials (Clause 3.1)

• Materials and construction methods for components are specified in Table 1 (not provided here).
• Ensure materials meet durability and compatibility requirements for wastewater equipment.

Summary

• IS 8413 Part 2 standardizes terminology, units, and definitions related to wastewater treatment equipment.
• It includes SI units for engineering parameters.
• Defines key equipment like the Vortair Entrainment Aerator.
• Specifies materials and construction methods for components.

flowchart TD
    A[Terminology & Definitions] --> B[Vortair Entrainment Aerator]
    A --> C[SI Units & Symbols]
    A --> D[Materials & Construction]
    B --> E[Hydraulic Phenomena for Oxygen Entrainment]
    C --> F[Force, Energy, Power, Pressure units]
    D --> G[Table 1: Materials Specifications]

For detailed formulas or tables, refer to the full IS 8413

IS 8413 Part 2: Materials and Construction Practices Summary

Key Materials & References (Table 1, Clause 3.1)

Construction Practices (Clause 4.1.11)

• Inlets/outlets must have valves, gates, stop planks, weirs for flow control.
• Hydraulic design to accommodate max instantaneous load per unit.

Important IS Codes for Materials:

• Concrete: IS 456 (Plain & Reinforced Concrete), IS 3370 (Concrete for liquid storage)
• Masonry: IS 2212 (Brickwork), IS 1597 (Stone masonry)
• Steel & Castings: IS 226 (Structural Steel), IS 210 (Cast Iron), IS 1570 (Steel schedules)
• Electrical

IS 8413 Part 2: Design and Construction Requirements - Key Points

1. Materials and Construction (Clause 3.1, Table 1)

• Civil Works:
  • Reinforced/Plain Concrete: IS 456-1978, IS 3370 (Parts I-IV)
  • Brick Masonry: IS 2212-1962
  • Stone Masonry: IS 1597 (Parts I & II)
• Mechanical Components:
  • Motors, starters, switches: IS 325-1978, IS 996-1964, IS 1766-1973, IS 1822-1967
  • Turn Table & Gears: Cast Iron (IS 210-1978), Steel (IS 1570-1961), Aluminium Bronze (IS 305-1961)
  • Covers & Bases: Mild Steel (Epoxy coated IS 226-1975), Cast Iron (IS 210-1978)
  • Bearings: High Carbon Steel (IS 2898-1976)
  • Gates: Cast Iron/Steel (IS 3042-1965, IS 226-1975)
  • Shafts: Cold Finished Steel (IS 1570-1961)
  • Plastic Components: Diffusers, Deflectors, Floats (Polyethylene, PVC, etc.)

2. Design Verification (Clause 4.2.3)

• Provide oxygen transfer data for aeration tanks:
  • Oxygen transfer characteristic curves
  • Long-term plant performance data under similar conditions

3. Units (SI Units)

• Length: m
• Force: N = kg·m/s²
• Pressure/Stress: Pa = N/m²
• Power: W = J/s

Summary Table: Key Materials & IS Codes

IS 8413 Part 2: Aeration Tank Design Key Points

1. Aeration Tank Volume (Clause 4.1)

• Volume is based on loading rates and Volatile Suspended Solids (VSS).
• Refer to Appendix A for detailed loading rates and VSS values.

2. Types of Aeration Tanks (Clause 4.1.2)

• Diffused Aeration Tanks: Oxygen supplied via diffusers at the bottom.
• Mechanical/Surface Aeration Tanks: Oxygen supplied by surface aerators (rotors, paddles).

3. Oxygen Transfer Requirements (Clause 4.2.3 & 4.2.2)

• Oxygen transfer capacity must match BOD removal and VSS maintenance.
• Designers must provide:
  • Oxygen Transfer Characteristic Curves or
  • Long-term performance data from similar plants.

4. Design Considerations

• Oxygen transfer rate (OTR) depends on:
  • Aerator type and capacity
  • Tank volume and mixing efficiency
  • BOD load and microbial mass (VSS)

Typical Formula for Aeration Tank Volume (V):

[ V = \frac{Q \times L}{k \times X} ]

Where:

• ( V ) = Volume of aeration tank (m³)
• ( Q ) = Flow rate (m³/day)
• ( L ) = Organic loading (BOD kg/m³)
• ( k ) = Reaction rate constant (day⁻¹)
• ( X ) = Concentration of active biomass (VSS, kg/m³)

Simplified Aerator Oxygen Transfer Capacity Table (Indicative)

flowchart LR
    A[Influent Wastewater] --> B[Aeration Tank]
   

IS 8413 Part 2 – Aeration Equipment Key Points

1. Oxygen Transfer Capacity

• Capacity must relate to BOD removal and Volatile Suspended Solids (VSS) maintained.
• Designer must provide oxygen transfer characteristic curves or long-term plant data proving equipment meets oxygen demand.

2. Aerator Types (Fig. 1 to 6)

• Diffused Air Systems: Ridge & furrows, Spiral flow (Fig. 1 & 2)
• Mechanical Systems: Impeller draft tube, Brush, Paddle-wheel with diffused air (Fig. 3 to 6)

3. Design Criteria (Ref. Clause 4.1.7)

• Aeration equipment must satisfy:
  • Adequate oxygen transfer rate (OTR)
  • Energy efficiency
  • Uniform oxygen distribution

4. Typical Oxygen Transfer Rate Formula

[ OTR = K_L a \times (C^* - C) ]

• (K_L a): Overall oxygen transfer coefficient (1/min)
• (C^*): Saturation oxygen concentration (mg/L)
• (C): Actual oxygen concentration in water (mg/L)

5. Performance Verification

• Provide data on:
  • Oxygen transfer efficiency (%)
  • Power input (kW/m³)
  • Air flow rate (m³/min)

flowchart LR
    A[Wastewater with BOD] --> B[Aeration Tank]
    B --> C[Aeration Equipment]
    C --> D[Oxygen Transfer to Water]
    D --> E[Microbial BOD Removal]
    E --> F[Effluent with Reduced BOD]

Summary: Ensure aeration equipment matches oxygen demand based on BOD and VSS, validated by oxygen transfer data and aligns with IS 8413 Part 2 sketches and design clauses.

Return Sludge Recycling System (IS 8413 Part 2)

Key Specifications:

• Capacity basis (Clause 4.4.1): [ \text{Return Sludge Flow} = \frac{\text{MLSS in Aeration Tank} \times \text{Aeration Tank Volume}}{\text{Suspended Solids Concentration in Return Sludge}} ]

• Pumping capacity (Clause 4.4.2):

  • Pump capacity = 100% of calculated return sludge flow.
  • Provide standby pump for reliability.

Recommended Loading Rates (Table from Clause 3.3 / Appendix A):

Additional Notes:

• For cold climates (<15°C), increase loading rates temporarily.
• Use formula: [ U = \frac{\text{kg BOD removed}}{\text{kg VSS} \cdot \text{day}}, \quad Y = \text{yield coefficient}, \quad k_d = \text{decay rate} ] to adjust design parameters.

flowchart LR
    A[Aeration Tank] -->|Return Sludge Flow| B[Return Sludge Pump]
    B -->|Recycle| A
    B -->|Excess Sl

IS 8413 Part 2: Sludge Handling & Removal - Key Points

1. Loading Rates & Parameters (Appendix A, Clause 3.3)

• SRT = Sludge Retention Time
• MLSS = Mixed Liquor Suspended Solids
• BOD₅ = 5-day Biochemical Oxygen Demand

2. Excess Sludge Removal (Clause 4.5)

• Waste activated sludge can be sent to:
  • Primary tanks
  • Concentration tanks
  • Aerobic/anaerobic digesters
  • Sludge drying beds (especially for extended aeration systems)

3. Important Formula

[ U = \frac{\text{kg BOD removed}}{\text{kg VSS/day}}; \quad Y = \text{yield coefficient (mg VSS/mg BOD removed)}; \quad k_d = \text{decay rate (day}^{-1}) ]

Where:

• (U) = process loading
• (Y) = biomass yield
• (k_d) = microorganism decay rate

Notes:

• In cold climates (<15°C), increase loading rates temporarily.
• Excess sludge = microbial mass growth wasted from underflow or secondary settling tank.

Operational Considerations per IS 8413 Part 2 (Clause 3.3 & Appendix A)

Key Parameters for Activated Sludge Treatment Systems

Important Formula for Sludge Retention Time (SRT)

[ SRT = \frac{Y \times U}{k_d} ]

• U = Process loading (kg BOD removed/kg VSS/day)
• Y = Yield coefficient (mg VSS/mg BOD removed)
• k_d = Specific microorganism decay rate (per day)

Notes:

• For winter temperatures below 15°C, increase loading rates temporarily.
• Designers must provide oxygen transfer data (oxygen transfer characteristic curves or long-term plant data) to ensure aeration equipment capacity (Clause 4.2.3).

Material Specifications for Construction (Clause 3.1)

• Concrete: IS 456-1978, IS 3370 (Parts I-IV)
• Brick Masonry: IS 2212-1962
• Stone Masonry: IS 1597 (Parts I & II)
• Motors & Electrical: IS 325-1978, IS 996-1964, IS 1766-1973, IS 1822-

IS 8413 Part 2: Recommended Loading Rates for Activated Sludge Systems

Key Notes:

• Loading (U) = kg BOD removed/kg MLSS/day
• Yield coefficient (Y) = mg VSS/mg BOD removed
• Decay rate (kd) = specific microorganism decay rate/day
• For cold climates (<15°C), increase loading rates temporarily.
• Aeration tank volume is calculated based on loading rates and VSS (Clause 4.1).

Formula for Sludge Retention Time (SRT):

[ SRT = \frac{Y \times U}{k_d} ]

flowchart LR
    A[Influent BOD] --> B[Aeration Tank]
    B --> C[Activated Sludge]
    C --> D[Settling Tank]
    D --> E[Effluent]
    D --> F

IS 8413 Part 2: Types of Aerators Commonly Employed

Key Types of Mechanical Aerators (Clause 3.1):

1. Impingement Aerator (Appendix B-1, Fig. 7)
   • Water jets impinge on a surface, entraining air.
2. Surface Aerator (Clause 3.1.1)
   • Circular flat plate with radial blades rotating just below water surface.
   • Creates vortex and hydraulic jump, entraining air.
3. Surface Impeller with Draft Tube
   • Draws liquid through a draft tube, spreads it over surface.
4. Vortair Entrainment Aerator
   • Uses vortex action to entrain air.

Specifications & Design Considerations:

• Capacity related to BOD removal and Volatile Suspended Solids (VSS) maintained (Clause 4.2.2).
• Aerator capacity must ensure adequate oxygen transfer matching organic load.

Typical Surface Aerator Parameters:

flowchart LR
    A[Water Inlet] --> B[Impeller/Plate with Blades]
    B --> C[Creates Vortex & Hydraulic Jump]
    C --> D[Air Entrainment]
    D --> E[Oxygen Transfer to Water]

For detailed design, refer to IS 8413 Part 2 figures and tables for dimensioning and power requirements.