RRR
50 KLD Sewage Treatment Plant — SBR (Sequencing Batch Reactor)
Compact batch-mode STP ideal for intermittent or variable flows. Designed for 50 KLD (20 hr/day), RCC tanks, hypochlorite disinfection for reuse (toilet flushing & gardening). Turnkey supply, installation & AMC by RRR ENVIRO SYSTEMS (Est. 2011).
Page Summary
Design flow: 50 KLD (50 m³/day). Operating hours: 20 hr/day. Treated water use: Toilet flushing & Gardening. Disinfection: Sodium hypochlorite (Hypo). Tank MOC: RCC (recommended per your input).
Process Flow (text)
Inlet Sewage → Bar Screen → Oil & Grease Trap → Grit Chamber → Collection/Equalization Tank (with mixer) → Raw Sewage Transfer Pump → SBR Reactor (Fill → React → Settle → Decant → Idle cycles) → Polishing (PSF/ACF/Cartridge/UF as required) → Disinfection (Hypo) → Treated Water Tank → Reuse for Toilet flushing & Gardening.
SBR eliminates the need for separate aeration + clarifier tanks: batch cycles perform biological reaction and settling in the same reactor.
Design Basis & Digit-by-Digit Calculations
Assumptions (used for sizing)
- Plant capacity Qday = 50 m³/day
- Operating hours = 20 hr/day
- Influent BOD₅ assumed = 250 mg/L (confirm with lab report)
- SBR cycle = 6 hours (typical example: Fill 0.5 h, React 3.0 h, Settle 1.5 h, Decant 0.5 h, Idle 0.5 h)
- MLSS design (in mixed liquor) = 3,000 mg/L (typical for biological performance)
- Sludge yield = 0.5 kg DS/kg BOD
- O₂ requirement = 1.4 kg O₂ / kg BOD
Step 1 — Hourly flow
Qhr = Qday ÷ operating_hours = 50 ÷ 20 = 2.5 m³/hr.
Convert to litres/hour: 2.5 × 1000 = 2,500 LPH.
Convert to litres/hour: 2.5 × 1000 = 2,500 LPH.
Q_hr = 50 ÷ 20 = 2.5 m³/hr
Q_hr_LPH = 2.5 × 1000 = 2,500 LPH
Step 2 — SBR cycle & reactor volume
Chosen SBR cycle time = 6 hours → cycles per day (20 hr) = 20 ÷ 6 ≈ 3.333 cycles/day.
Volume required (working) to treat batch = Qhr × cycle_time = 2.5 × 6 = 15.0 m³ working volume.
Check with cycles: Total treated per day = (working volume × decant_fraction × cycles/day). We design decant fraction so decanted volume per cycle × cycles/day = 50 m³/day. Using decant fraction 0.33 (≈33% decant per cycle): decant per cycle = 15 × 0.33 = 4.95 m³ → cycles/day 3.333 → total = 4.95 × 3.333 = 16.5 m³ (this is less than 50 m³). So we must ensure decant per cycle × cycles/day ≈ 50. We'll compute decant fraction required below.
Volume required (working) to treat batch = Qhr × cycle_time = 2.5 × 6 = 15.0 m³ working volume.
Check with cycles: Total treated per day = (working volume × decant_fraction × cycles/day). We design decant fraction so decanted volume per cycle × cycles/day = 50 m³/day. Using decant fraction 0.33 (≈33% decant per cycle): decant per cycle = 15 × 0.33 = 4.95 m³ → cycles/day 3.333 → total = 4.95 × 3.333 = 16.5 m³ (this is less than 50 m³). So we must ensure decant per cycle × cycles/day ≈ 50. We'll compute decant fraction required below.
V_working = Q_hr × cycle = 2.5 × 6 = 15.0 m³
Step 3 — Decant fraction & verification (digit-by-digit)
Let decant fraction per cycle = f (fraction of working volume decanted each cycle). Need:
f × V_working × cycles_per_day = Q_day
cycles_per_day = 20 ÷ 6 = 3.333... (repeating)
Solve for f:
f = Q_day ÷ (V_working × cycles_per_day)
f = 50 ÷ (15 × 3.3333333) = 50 ÷ 50 = 1.0 (i.e. decant the full working volume across cycles) — that means our chosen cycle/time must be adjusted because decanting 100% of working volume is impractical (we need some non-react volume). So adjust design: better to design reactor working volume = Q_day ÷ cycles_per_day ÷ target_decant_fraction.
Choose practical decant fraction f_target = 0.5 (50% per cycle). Then required working volume:
V_required = Q_day ÷ (f_target × cycles_per_day) = 50 ÷ (0.5 × 3.3333333) = 50 ÷ 1.6666666 = 30.0 m³ working.
Therefore adopt working volume V = 30 m³ with cycle 6 hr and decant fraction 50%:
- Decant per cycle = 30 × 0.5 = 15.0 m³.
- cycles/day = 3.333 → total decanted per day = 15 × 3.333 = 50 m³/day ✅.
Add 15% freeboard → physical tank ≈ 30 × 1.15 = 34.5 m³.
cycles_day = 20 ÷ 6 = 3.333333...
f_target = 0.5
V_req = 50 ÷ (0.5 × 3.3333333) = 50 ÷ 1.6666666 = 30.0 m³
V_physical ≈ 30 × 1.15 = 34.5 m³
Step 4 — MLSS & biomass
MLSS design = 3,000 mg/L = 3.0 kg/m³. Biomass mass = MLSS × V_working = 3.0 × 30 = 90 kg suspended solids in reactor (note: SBR also has settled sludge during settle phase).
Biomass = 3.0 × 30 = 90 kg
Step 5 — BOD load & oxygen requirement
BOD load/day = Q_day × Influent_BOD ÷ 1000 = 50 × 250 ÷ 1000 = 12.5 kg BOD/day.
O₂ req/day = 12.5 × 1.4 = 17.5 kg O₂/day.
Assume oxygen per kW ≈ 1.2 kg O₂/kW → blower_kW ≈ 17.5 ÷ 1.2 = 14.583 kW → recommend 15 kW blower(s) split for redundancy.
O₂ req/day = 12.5 × 1.4 = 17.5 kg O₂/day.
Assume oxygen per kW ≈ 1.2 kg O₂/kW → blower_kW ≈ 17.5 ÷ 1.2 = 14.583 kW → recommend 15 kW blower(s) split for redundancy.
BOD_load = 50 × 250 ÷ 1000 = 12.5 kg/day
O2_req = 12.5 × 1.4 = 17.5 kg/day
Blower_kW ≈ 17.5 ÷ 1.2 = 14.583 kW → recommend 15 kW
Step 6 — Sludge production
Sludge DS/day = 12.5 × 0.5 = 6.25 kg DS/day.
At 3% cake solids → wet sludge ≈ 6.25 ÷ 0.03 = 208.33 L/day (design sludge handling accordingly).
At 3% cake solids → wet sludge ≈ 6.25 ÷ 0.03 = 208.33 L/day (design sludge handling accordingly).
DS/day = 12.5 × 0.5 = 6.25 kg
Wet_sludge ≈ 6.25 ÷ 0.03 = 208.33 L/day
SBR Cycle — Recommended Sequence & Timings
Recommended example cycle (6 hr total):
- Fill: 0.5 hr — controlled inlet, mixing
- React (aeration): 3.0 hr — biological degradation (maintain DO ~2–3 mg/L)
- Settle: 1.5 hr — allow solids to settle, quiescent
- Decant: 0.5 hr — decant clear supernatant (via decanter device)
- Idle/Swap: 0.5 hr — housekeeping / switch between cycles (can overlap with fill for continuous operation)
With working volume 30 m³ and decant fraction 50% (15 m³ decant per cycle) × 3.333 cycles = 50 m³/day output.
Main Equipment & Scope of Supply
- Bar screen & manual/mechanical rakes
- Oil & grease trap, grit chamber
- Collection / Equalization tank (with mixer & level controls)
- SBR reactor (RCC) — working = 30 m³, physical ≈ 34.5 m³
- Fine-bubble diffusers & blowers (~15 kW split, VFD preferred)
- Decanter device / adjustable decant weirs
- Sludge sump, sludge pump, sludge thickening / dewatering (belt/press or drying bed)
- Polishing trains: PSF / ACF / Cartridge / UF (optional for strict reuse)
- Hypochlorite dosing skid (Hypo) for final disinfection; dosing control & safe storage
- PLC control panel managing SBR cycles (timers, level control, DO control), HMI
- Pumps: raw transfer pump, decant pump (if required), sludge pump, backwash pump
- Piping & valves (UPVC / HDPE / SS), civil anchors, access platforms & safety railings; installation & commissioning
Material of Construction — RCC Notes
- Tanks in RCC with proper waterproofing (MSEP or epoxy coatings) and internal rubber lining for corrosive environments.
- Provide inspection chambers, access manholes & safety railings.
- Floors and channels to have proper fall towards sludge sump and drains.
- Electrical & MCC rooms must be weatherproof with adequate earthing and lightning protection.
- Provide chemical storage bunds for hypochlorite with spill containment.
Chemical Dosing & Hypochlorite Disinfection
- Hypochlorite (NaOCl): Used for final disinfection. Dosing based on residual free chlorine target (e.g., 0.5–1.0 mg/L) and contact time. Dosing skid with metering pump, level controller and safe storage recommended.
- Polymer: For sludge thickening/dewatering — dosing at sludge sump.
- pH Correction: If needed to meet discharge or reuse standards.
- Monitoring: Continuous residual chlorine monitor recommended at outlet for safety and compliance.
Exact chemical quantities will be confirmed after influent lab results and site trials.
Expected Performance & Reuse
With correct operation and optional polishing: BOD & TSS typically reduced to < 30 mg/L. With hypochlorite disinfection and polishing (PSF/UF), effluent suitable for toilet flushing and gardening subject to local TNPCB approvals.
| Parameter | Typical Influent | Expected Effluent (SBR + Polishing) |
|---|---|---|
| BOD₅ | 200–400 mg/L | < 30 mg/L |
| TSS | 150–350 mg/L | < 30–50 mg/L |
| Residual Chlorine | — | 0.2–0.5 mg/L (post dosing, as per standard) |
Operation & Maintenance
- Daily: Check screens, pumps, blowers, DO (target 2–3 mg/L during react), SBR cycle logs, decant clarity and residual chlorine.
- Weekly: Inspect diffuser performance and clean screens; verify decanter operation and sludge levels.
- Monthly: Calibrate sensors (DO, level, chlorine), inspect blowers, test polymer dosing & sludge dewatering.
- Periodic: Dewater and remove sludge, inspect and maintain RCC tank waterproofing & linings, check structural joints.
- We provide commissioning, operator training & optional AMC packages.
Common Issues & Troubleshooting
- Incomplete settle: Increase settle time, check decanter position, reduce turbulence during settle phase.
- Low DO during react: Verify blower operation, diffuser fouling, DO setpoint & control.
- Foaming: Identify surfactant sources; dose anti-foam or adjust MLSS/SRT.
- Odour at collection: Ensure adequate mixing/aeration in equalization and timely desludging.
FAQ — 50 KLD SBR
Q: What information do you need to finalise design?
We need raw influent lab report: BOD, COD, TSS, TDS, FOG, pH, temperature and any special contaminants; site levels, inlet/outlet elevations and power availability.
Q: Is SBR suitable for continuous 20 hr operation?
Yes — SBR can be operated continuously with appropriate cycles; cycle scheduling and working volume sized here for 20 hr/day. A second reactor (two trains) is recommended where absolute continuity is required during maintenance/regeneration.
Q: Why choose hypochlorite for disinfection?
Hypochlorite is cost-effective for final disinfection, easy to dose and monitor. We provide safe storage & dosing skid. For sensitive reuse (e.g., horticulture), residual chlorine management and contact time must be designed and verified.