RRR
30 KLD Sewage Treatment Plant — ASP (Activated Sludge Process)
Turnkey 30 KLD STP designed on ASP for residential complexes, schools, hostels, small industrial estates and institutions. Includes collection, equalization, ASP aeration, secondary clarifier, polishing & disinfection, sludge handling and instrumentation.
Quick Summary
Capacity: 30 KLD (30 m³/day). Typical application: residential complexes, schools, small hospitals, hostels. Design operational hours (default): 20 hours/day (we use this for working calculations). Final design to be confirmed after site survey & influent characteristics (BOD, COD, TSS, FOG, pH).
Process Flow (Text Diagram)
Sewage inlet → Bar screen / Grit & Grease removal → Collection / Equalization Tank → Raw sewage pump → Primary Treatment (if required) → ASP Aeration Tank (diffused aeration) → Secondary Clarifier (gravity) → Polishing (Sand/Cartridge/UF) → Disinfection (UV / Sodium Hypochlorite) → Treated water tank → Reuse / Discharge (as per TNPCB/CPCB norms).
Sludge from primary/secondary → Sludge sump → Sludge thickening → Dewatering (drum/centrifuge or drying bed) → Disposal.
Sludge from primary/secondary → Sludge sump → Sludge thickening → Dewatering (drum/centrifuge or drying bed) → Disposal.
Design Basis & Digit-by-Digit Calculations
Given: Design flow Qday = 30 m³/day (30 KLD).
Two options shown: continuous 24-hour operation and design using 20 hours/day (user earlier selected 20 hrs).
Two options shown: continuous 24-hour operation and design using 20 hours/day (user earlier selected 20 hrs).
Flow conversions
1) If 24 hours operation: Q = 30 ÷ 24 = 1.25 m³/hr (≈ 1250 LPH).
2) If 20 hours operation (design basis used here): Q = 30 ÷ 20 = 1.50 m³/hr (≈ 1500 LPH).
2) If 20 hours operation (design basis used here): Q = 30 ÷ 20 = 1.50 m³/hr (≈ 1500 LPH).
Aeration Tank Volume (HRT method)
For ASP typical mixed-liquor hydraulic retention time (HRT) = 4–8 hours. We choose HRT = 6 hours (balance of footprint vs performance).
Using Q (operational) = 1.50 m³/hr → Volume V = Q × HRT = 1.50 × 6 = 9.0 m³ (9,000 L).
Using Q (operational) = 1.50 m³/hr → Volume V = Q × HRT = 1.50 × 6 = 9.0 m³ (9,000 L).
V_aeration = 1.50 m³/hr × 6 hr = 9.0 m³ → 9,000 L
Recommended: provide freeboard & baffling → physical tank volume ~ 10.5 – 11 m³ (include 15–20% freeboard).
MLSS & Mixed Liquor Volume
Design MLSS = 2,500 mg/L (2.5 g/L) typical for municipal ASP. Biomass mass in aeration tank = MLSS × V = 2.5 kg/m³ × 9.0 m³ = 22.5 kg MLSS mass.
MLSS mass = 2.5 kg/m³ × 9.0 m³ = 22.5 kg
Secondary Clarifier – Surface Area (SOR method)
Use surface overflow rate (SOR) = 30 m³/m²·day (typical small STP design: 25–35).
Area A = Q_day ÷ SOR = 30 ÷ 30 = 1.0 m².
Circular clarifier diameter d = √(4A/π) = √(4 × 1 / 3.1416) ≈ 1.13 m (practical choose 1.5–2.0 m diameter for weir & maintenance).
Area A = Q_day ÷ SOR = 30 ÷ 30 = 1.0 m².
Circular clarifier diameter d = √(4A/π) = √(4 × 1 / 3.1416) ≈ 1.13 m (practical choose 1.5–2.0 m diameter for weir & maintenance).
A = 30 ÷ 30 = 1.0 m² → d ≈ 1.13 m → select practical diameter 1.5 m (to allow better weir loading)
Air Requirement (approximate)
Assume influent BOD₅ = 250 mg/L (typical domestic sewage varies 200–400 mg/L). Use conservative value; final calculation requires actual lab report.
BOD load per day = Q_day × BODconc = 30 m³/day × 250 mg/L = 30 × 250 g/day = 7,500 g/day = 7.5 kg BOD/day.
Typical oxygen requirement ≈ 1.2 – 1.6 kg O₂/kg BOD removed. Assume 1.4 kg O₂/kg BOD and 80% removal design → O₂ demand = 7.5 × 1.4 = 10.5 kg/day. Blower sizing (including safety & system losses): assume 1.0–1.2 kg O₂/kW (practical) → approximate blower power ~ 1.5 – 3.0 kW (choose 2 kW blower with blowers redundancy for reliability).
BOD load per day = Q_day × BODconc = 30 m³/day × 250 mg/L = 30 × 250 g/day = 7,500 g/day = 7.5 kg BOD/day.
Typical oxygen requirement ≈ 1.2 – 1.6 kg O₂/kg BOD removed. Assume 1.4 kg O₂/kg BOD and 80% removal design → O₂ demand = 7.5 × 1.4 = 10.5 kg/day. Blower sizing (including safety & system losses): assume 1.0–1.2 kg O₂/kW (practical) → approximate blower power ~ 1.5 – 3.0 kW (choose 2 kW blower with blowers redundancy for reliability).
BOD load = 30×0.250 = 7.5 kg/day → O₂ req ≈ 7.5×1.4 = 10.5 kg/day → blower ~2 kW (indicative)
Note: blower sizing must be refined after exact influent BOD, temperature & system oxygen transfer efficiency (OTR) are known.
Sludge Production (estimate)
Assume typical sludge production ~ 0.5 kg MLSS/kg BOD removed → daily sludge = 7.5 kg BOD/day × 0.5 = 3.75 kg dry solids/day. With 2–4% solids in sludge cake before dewatering, expect ~100 – 200 L/day wet sludge depending on dewatering method. Provide sludge sump, drying bed or mechanical dewatering in design.
Main Components & Equipment
- Inlet Bar Screen & Grit / Oil & Grease Trap
- Collection / Equalization Tank with mixer & level control
- Raw Sewage Transfer Pump (submersible / dry pit)
- ASP Aeration Tank with fine bubble diffusers & blowers (2 kW x duty+standby)
- Secondary Clarifier with sludge hopper & RAS (Return Activated Sludge) pump
- Polishing (PSF / Sand + Carbon / Cartridge / UF optional)
- Disinfection: UV or Sodium Hypochlorite dosing system
- Sludge sump, sludge thickener / drying bed or mechanical dewatering (filter press / decanter)
- PLC / Control Panel, Level sensors, Flow meters, Online pH & DO sensors (optional)
Expected Performance (Typical)
| Parameter | Typical Influent | Expected Effluent (After STP) |
|---|---|---|
| BOD₅ | 200 – 400 mg/L | < 20 – 30 mg/L (with good operation) |
| Suspended Solids (TSS) | 150 – 350 mg/L | < 30 – 50 mg/L |
| COD | 600 – 1200 mg/L | < 150 – 250 mg/L (varies) |
| Turbidity | Varies | < 5 NTU (with polishing) |
| pH | 6.5 – 8.5 | 6.5 – 8.5 |
Effluent quality depends on influent characteristics, proper O&M and polishing stage. For reuse (toilet flushing / landscaping / cooling tower), additional polishing (UF / RO) and disinfection may be required.
Operation & Maintenance
- Daily: check pumps, blowers, DO (≥2 mg/L typical), inlet screens and desludging schedule.
- Weekly: inspect diffusers, check RAS rate and sludge blanket in clarifier.
- Monthly: calibrate sensors, grease bearings, clean screens and dosing tanks.
- Quarterly/Annually: sludge drying/dewatering, blower maintenance, performance audit and online instrument calibration.
- Provide operator training, maintenance manual and spare parts list. AMC packages available.
FAQ — 30 KLD STP (ASP)
Q1: What is included in the quoted STP?
Supply of equipment (pumps, blowers, diffusers, valves), fabrication of tanks (RCC/FRP/MSEP), control panel, instrumentation, piping & installation, commissioning and performance testing (subject to scope agreed).
Q2: How many users does 30 KLD typically serve?
Assuming 100–150 L/person/day, 30 KLD can serve roughly 200–300 persons. Actual depends on site-specific water use patterns.
Q3: Do you provide statutory compliance support?
Yes — design and operation can be tailored to meet TNPCB / CPCB norms and we provide documentation for permits on request.
Q4: What maintenance frequency is needed?
Daily operational checks, weekly diffuser & sludge checks, monthly instrument calibration and periodic sludge dewatering (frequency depends on sludge generation).
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