Design of Effluent Treatment Plant

A basic effluent treatment plant (ETP) is designed by characterizing the wastewater, setting discharge/reuse targets, selecting a suitable treatment train, and sizing each unit for the design flow and contaminant loads, with dedicated sludge handling and robust monitoring/control. Below is a concise, step-by-step framework with practical sizing rules you can apply to most industrial effluents.

Core design workflow

• Define influent quality and variability: pH, BOD, COD, TSS, oils/grease, nutrients, metals, color, toxicity.

• Set effluent standards: discharge permit or reuse specs for BOD, COD, TSS, O&G, TN/TP, pathogens, metals.

• Determine hydraulics: average/peak flow, diurnal peaks, storm/cleanup events, future expansion.

• Select process train: pretreatment, primary, secondary (biological), tertiary polishing, disinfection, sludge line.

• Size equipment and tanks: use conservative loadings, include redundancy, and allow for bypass and isolation.

• Plan layout and utilities: gravity flow where possible, safe access, ventilation/odor control, chemical storage.

• Specify instrumentation/automation: online sensors, PLC/SCADA, alarms, interlocks, remote access.

• Validate and optimize: jar tests, pilot trials, life-cycle cost, O&M plan, spares, operator training.

Typical process train

• Preliminary: coarse/fine screening, grit removal, equalization, pH/alkalinity control, oil-water separation.

• Primary: coagulation–flocculation with clarification or dissolved air flotation (DAF).

• Secondary (biological): activated sludge, MBBR, SBR, or MBR; anaerobic step for very high COD.

• Tertiary: sand/dual-media filtration, activated carbon, advanced oxidation if refractory COD/color.

• Disinfection: chlorination/hypochlorite or UV.

• Sludge line: thickening, stabilization, dewatering, compliant disposal/reuse.

Key sizing rules of thumb

• Equalization: HRT $6\text{–}12\text{h}$; mixer power 2–5 W/m32–5W/m3; pH control to $6.5\text{–}8.5$.

• Primary clarifier: surface overflow rate 20–40 m3/m2⋅d20–40m3/m2⋅d; weir loading 100–200 m3/m⋅d100–200m3/m⋅d.

• DAF: hydraulic loading 5–12 m3/m2⋅h5–12m3/m2⋅h; recycle ratio $10\text{–}30\%$; coagulant $50\text{–}300\text{mg/L}$(optimize by jar test).

• Activated sludge: aeration HRT $6\text{–}10\text{h}$; MLSS $2,000\text{–}4,000\text{mg/L}$; F/M 0.2–0.5 d−10.2–0.5d−1; SRT $8\text{–}20\text{d}$; DO $>2\text{mg/L}$.

• MBBR: carrier fill $40\text{–}60\%$; HRT $4\text{–}8\text{h}$; DO $>2\text{mg/L}$.

• MBR: flux $8\text{–}20\text{LMH}$; SRT $>20\text{d}$; mixed liquor $8,000\text{–}12,000\text{mg/L}$.

• Anaerobic (for high-strength): UASB OLR 6–12 kg COD/m3⋅d6–12kg COD/m3⋅d; HRT $6\text{–}12\text{h}$; biogas handling.

• Filters: pressure sand filter $5\text{–}10\text{m/h}$; activated carbon EBCT $10\text{–}20\text{min}$.

• Disinfection: UV dose 30–60 mJ/cm230–60mJ/cm2 or chlorine $C\times t$ to meet microbial limits.

• Nutrients for biology: $BOD:N:P\approx 100:5:1$; supplement if deficient.

Unit selection guidance

• Oily/emulsified effluents: add API/plate oil separator and DAF before biology.

• Toxic/recalcitrant streams (dyes, pharma): consider equalization, pH control, advanced oxidation pre/post biology, and MBR for polishing.

• High COD $>4,000\text{mg/L}$: evaluate anaerobic first stage (UASB/EGSB/IC), then aerobic polishing.

• Metals: precipitate with hydroxide/sulfide and clarify before biology to prevent inhibition.

• Low TDS reuse: add softening/RO and manage RO reject safely.

Equipment and layout essentials

• Provide isolation/bypass lines and drain sumps for every major unit.

• Keep a gravity hydraulic profile; budget headloss across screens, DAF/clarifiers, filters, and UV.

• Safe chemical storage with secondary containment; segregated acid/alkali; eyewash/showers.

• Odor control with covers, ventilation, and biofilter/carbon where needed.

Instrumentation and control

• Online: pH (headworks), DO (aeration), ORP (anoxic), turbidity/solids (effluent/filters), flow and level.

• Control: PLC/SCADA, interlocks for low DO/high level, VFDs on blowers/pumps, automated chemical dosing tied to feedback.

• Verification: routine lab BOD, COD, TSS, O&G, nutrients, metals, and microbiology.

Sludge line design

• Thickening to $2\text{–}5\%$ solids (gravity/DAF).

• Stabilization: aerobic or anaerobic (mesophilic $15\text{–}25\text{d}$ HRT).

• Dewatering: belt press $15\text{–}25\%$ cake, centrifuge $18\text{–}28\%$, plate press $30\text{–}45\%$.

• Compliant end-use: compost/land application (if permitted), co-processing, incineration, or secure landfill.

Energy and chemical optimization

• Right-size blowers; control by DO with VFDs (aeration is the main energy consumer).

• Target fine-bubble diffusers in clean zones; plan for fouling and air-side filtration.

• Use jar tests and polymer screens to minimize coagulant/polymer use and sludge production.

• Recover biogas where anaerobic is used; consider solar for auxiliary loads.

Worked example: 100 m³/d ETP (typical light-industrial mix)

• Assumptions: average flow Q=100 m3/dQ=100m3/d (4.17 m3/h4.17m3/h); COD $1,500\text{mg/L}$, BOD $600\text{mg/L}$, TSS $300\text{mg/L}$, O&G $80\text{mg/L}$.

• Equalization: HRT $8\text{h}$ ⇒ volume V=Q×HRT=4.17×8≈33 m3V=Q×HRT=4.17×8≈33m3; mixer $\approx 100\text{W}$.

• Coag–floc + DAF: coagulant start at $100\text{mg/L}$ (optimize); DAF area =4.17/8≈0.52 m2=4.17/8≈0.52m2.

• MBBR aeration: HRT $6\text{h}$ ⇒ V≈25 m3V≈25m3; carriers $50\%$ fill; air to hold DO $>2\text{mg/L}$.

• Secondary clarifier: SOR 30 m3/m2⋅d30m3/m2⋅d ⇒ area =100/30≈3.3 m2=100/30≈3.3m2.

• Tertiary filters: PSF at $7\text{m/h}$ ⇒ area =4.17/7≈0.6 m2=4.17/7≈0.6m2; ACF EBCT $15\text{min}$ ⇒ bed volume =4.17×0.25≈1.0 m3=4.17×0.25≈1.0m3.

• UV disinfection: dose 40 mJ/cm240mJ/cm2 sized to filtered UVT.

• Sludge: design for $0.6\text{–}0.8\text{kg}$ dry solids per kg COD/BOD removed; select a small centrifuge or belt press accordingly.

Expected performance (well-operated)

• TSS < $30\text{mg/L}$

• BOD < $20\text{mg/L}$

• COD < $100\text{–}150\text{mg/L}$ (lower with carbon/AOP/MBR)

• O&G < $10\text{mg/L}$

• Pathogens to local limits after disinfection

If you share your influent data (flow, BOD/COD, TSS, O&G, nutrients, metals, pH) and your discharge or reuse targets, I can tailor a right-sized process train and unit capacities for your application.

Below is a ready-to-use comparison table of “our cost” vs “other cost” for a typical 100 KLD packaged ETP in India, anchored to publicly listed vendor prices and peer‑reviewed energy/O&M benchmarks for transparency and consistency. Values are illustrative and should be replaced with the actual proposal to reflect scope, civil works, automation level, and discharge/reuse targets for the specific site.

Cost comparison (100 KLD ETP)

Notes and assumptions

• Scope placeholder: “Our cost” is shown as ₹16.5 lakh purely for formatting; it is pinned to a publicly listed 100 KLD ETP quote so the table can be used immediately and updated with the final offer number.

• Benchmarking source: “Other cost” uses current vendor listings for 100 KLD packaged ETPs across India to provide a realistic public range for comparison that can be validated in procurement.

• Operating cost context: Energy dominates biological OPEX; targeting the lower half of the 0.13–0.79 kWh/m³ envelope requires good aeration control and right‑sized blowers, while advanced reuse trains move total energy closer to 0.5–2.0 kWh/m³.

• Customize per site: Civil works, automation, odor control, and siting constraints (e.g., compact/multi‑storey layouts) materially shift capex and O&M; national advisory material highlights how design choices alter construction and life‑cycle costs.

Bill of Materials & Equipment Specification Sheet for 100 KLD Industrial ETP

Key Technical Specifications Summary

• Flow Rate: 100 KLD (4.17 m³/hr)

• Influent Characteristics: BOD 600 mg/L, COD 1500 mg/L, TSS 300 mg/L, Oil & Grease 80 mg/L

• Design Conditions: pH 6.5–8.5, ambient temperature 15–45°C

• Efficiency Targets: BOD < 20 mg/L, TSS < 30 mg/L, Oil & grease < 10 mg/L

• Power Supply: 415 V, 3 Phase, 50 Hz, suitable DG backup provision

• Materials: MS/SS as per corrosion resistance requirements; FRP for filter vessels

• Automation: PLC with SCADA for online monitoring, alarms, automated dosing

This sheet can be customized with vendor-specific model numbers, certifications, and detailed technical submittals during procurement. It provides a strong foundation for cost estimation, tendering, and vendor comparison for turnkey or itemized ETP supply projects.

If needed, detailed piping and instrumentation diagrams (P&IDs), civil drawings, and operational manuals can be presented as separate documentation to accompany the procurement package.