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The most critical decision in the selection of a Package Treatment system is determining the correct capacity. Insufficient capacity leads to continuous quality problems, while excessive capacity results in unnecessary investment and biological degradation at low loads. In this article, we present the calculation of person equivalents (PE), flow estimates by sector, capacity ranges, sizing steps, and a checklist for investment decisions.
Short answer: Package treatment sizing consists of 4 steps: (1) Determining the equivalent person (KE) (actual users + sector multiplier), (2) Average daily flow calculation (per capita or production-based water consumption × KE), (3) Maximum flow with peak factor (usually 2-4×), (4) Wastewater characteristics (determining reactor volume with KOİ, BOİ, FOG, N, P values). Incorrect sizing is the most common package system error — especially critical during seasonal/variable loads.
Package Treatment Capacities Package Treatment Capacity Ranges
Package systems cover a very wide range of capacities. Typical classification:
| Category | Flow (m³/day) | KE (equivalent person) | Typical Structure |
|---|---|---|---|
| Mini package | 2-10 | 10-50 | Villa, small site, gas station |
| Small package | 10-50 | 50-250 | Pension, highway rest area, small hotel |
| Medium package | 50-200 | 250-1,000 | Hotel (50-200 rooms), site, small factory |
| Large package | 200-1,000 | 1,000-5,000 | Large hotel, shopping mall, small municipality |
| Industrial package | 1,000-2,000 | 5,000-10,000 | Single factory in organized industrial zone, medium municipality |
At capacities above 2,000 m³/day, the package system loses its economic advantage; a modular concrete facility or hybrid structure is preferred.
What is Equivalent Person (KE)?
Equivalent person (KE) defines the wastewater load produced by one person per day as a standard unit:
- Wastewater flow: 120-200 L/person·day (developed country 200, developing 120-150)
- BOİ load: 60 g/person·day (European standard)
- KOİ load: 120 g/person·day
- AKM load: 70 g/person·day
- TN load: 11 g/person·day
- TP load: 2 g/person·day
Sector-based wastewater loads are converted to KE equivalents according to these standards.
Sector-Based KE Multipliers
| Usage | KE Multiplier | Calculation |
|---|---|---|
| Residential (permanent) | 1 KE/person | Number of residents × 1 |
| Hotel (luxury) | 1.5-2 KE/bed | Number of beds × 1.5-2 |
| Hotel (standard) | 1-1.3 KE/bed | Number of beds × 1-1.3 |
| Apartment/pension | 0.8-1 KE/bed | Number of beds × 0.8-1 |
| Restaurant | 0.3-0.5 KE/seat | Seating capacity × 0.3-0.5 |
| Office | 0.3-0.5 KE/employee | Number of employees × 0.3-0.5 |
| Shopping mall | 0.05-0.1 KE/visitor | Daily visitors × 0.05-0.1 |
| School (daytime) | 0.3-0.4 KE/student | Number of students × 0.3-0.4 |
| Hospital | 2-4 KE/bed | Beds × 2-4 (sector-specific treatment required) |
| Construction site/camp | 0.8-1 KE/worker | Number of workers × 0.8-1 |
| Highway rest area | 0.1-0.2 KE/vehicle | Daily vehicles × 0.1-0.2 |
Practical Sizing Examples
Example 1: 80-Room 3-Star Hotel
- Number of beds: 80 × 2 = 160 beds
- KE multiplier: 1.2 (standard hotel)
- Total KE: 160 × 1.2 = 192 KE
- Staff addition: 25 × 0.5 = +12.5 KE
- Restaurant (60 seats): 60 × 0.4 = +24 KE
- Total: ~230 KE
- Average flow: 230 × 150 L/day = 35 m³/day
- Peak factor 3×: 105 m³/day design capacity
- Recommended system: 40-60 m³/day package SBR or MBBR (seasonal average), modular with an upper limit of 100 m³/day
Example 2: 200-Worker Construction Site
- Workers: 200, KE multiplier 0.9 = 180 KE
- Average flow: 180 × 120 L = 22 m³/day
- Peak factor 2.5×: 55 m³/day
- Recommended system: 25 m³/day container MBR (compact + portable)
Example 3: 500-Unit Residential Complex
- Persons: 500 × 3 (average per unit) = 1,500 persons
- KE: 1,500
- Flow: 1,500 × 150 L = 225 m³/day
- Peak 2.5×: 560 m³/day
- Recommended system: 250 m³/day MBR package (large) — Si structure + modular extension for building expansion
Example 4: Dairy Factory (Industrial)
Industrial facilities are calculated directly based on production flow instead of KE:
- Milk production: 50,000 L/day
- Wastewater multiplier: 3 L wastewater/L product = 150,000 L/day = 150 m³/day wastewater
- KOİ load: 150 m³ × 4,000 mg/L = 600 kg KOİ/day → ~5,000 KE equivalent organic load
- Recommended system: 150-200 m³/day industrial package MBR + UASB anaerobic pre-treatment (biogas)
Peak Factor — Why is it Important?
Wastewater flow is not constant throughout the day. During peak hours (hotel morning showers, factory shift changes), wastewater inflow can be 2-4 times the average flow. Ignoring the peak factor in design leads to chronic overflow + biological shock.
| Usage | Peak Factor | Reason |
|---|---|---|
| Residential | 2-2.5× | Morning/evening shower intensity |
| Hotel (season) | 3-4× | Off-season 0.3× → season 4× |
| Highway rest area | 5-8× | Holidays, weekend peaks |
| Restaurant | 3-5× | Lunch and dinner service |
| Factory (fixed) | 1.5-2× | Shift changes, CIP |
| Food factory | 3-5× | Production spikes + CIP washings |
| Construction site | 2-3× | Lunch + end of shift showers |
| School | 2-3× | Recess peaks |
Reactor Volume Calculation
After determining the flow, the biological reactor volume is calculated based on wastewater characteristics and the selected process:
Activated Sludge / SBR
- HRT (hydraulic retention time): 8-24 hours
- F/M ratio: 0.2-0.4 kg BOİ/kg MLSS·day
- MLSS: 2,500-4,500 mg/L
- Typical volume: Flow (m³/day) × 0.5-1 (according to HRT)
MBBR
- HRT: 4-8 hours
- Carrier fill: 40-60%
- Specific surface activity: 5-15 g BOİ/m²·day
- Typical volume: Flow × 0.25-0.4 (compact)
MBR
- HRT: 4-8 hours (compact)
- MLSS: 8,000-12,000 mg/L (4× classical)
- Membrane flux: 15-25 L/m²·hour
- Typical volume: Flow × 0.2-0.3 (most compact)
Importance of Balancing Tank
If the peak factor is high, the biological reactor is not designed for peak flow — instead, a large balancing tank is used. This approach:
- Keeps reactor volume small (CAPEX savings)
- Allows biological process to operate at stable average flow
- Ensures pH, temperature, and composition homogenization
Typical balancing HRT: hotel/season 12-24 hours, factory CIP 8-12 hours, residential 4-6 hours.
Sizing Decision Matrix by Type
| Criterion | Classical/SBR | MBBR | MBR |
|---|---|---|---|
| Limited budget | Ideal | Suitable | Expensive |
| Limited space | Standard | Compact | Most compact |
| Water recovery target | Difficult | Additional UF required | Direct |
| Shock load (season/CIP) | Medium | Very high | High |
| Sensitive receiving environment | Insufficient | Medium | Ideal |
| Limited operating personnel | SBR suitable | Very suitable | Membrane knowledge required |
8 Questions for Investment Decision
- What is the source of your wastewater? Is it solely domestic, or is there an industrial composition?
- What is the number of users or production volume? A key input for KE calculation.
- Is there seasonality? If it is a hotel/tourist facility, a balancing tank is critical.
- What are your discharge limits? Which sector does the SKKY table refer to, is it a sensitive receiving environment?
- What is your water recovery target? If there is one, MBR is mandatory.
- What is the available area? If narrow, MBR; if wide, SBR/MBBR.
- What is the qualification of the operating personnel? If there is no membrane knowledge, MBBR is safer.
- What is the potential for expansion? If there is a possibility of increasing capacity later, modular design.
Common Sizing Errors
- "There are this many rooms, per person X liters" estimation: Peak factor and wastewater composition are ignored. Result: chronic problem.
- Not accounting for seasonal decreases: When a hotel operates at 20% capacity in winter, the biological process dies from starvation. Recycle is needed for low loads.
- Calculating industrial wastewater like domestic: Dairy factory wastewater is 5-10× domestic in kg KOİ. KE multiplier becomes 5-10.
- Sizing without characterization: Reactor volume cannot be estimated without knowing KOİ, BOİ, FOG, N, P.
- "Size 50% larger for backup" strategy: Excess capacity leads to biological degradation at low loads. Modular design is smarter.
Professional Sizing Process
- Wastewater characterization — 1-3 months sample analysis (if there is an existing facility)
- Extracting usage profile — hourly flow estimation, seasonality
- KE and flow calculation — along with peak factor
- Wastewater load calculation — total loadings of KOİ, BOİ, FOG, N, P
- Process selection — SBR/MBBR/MBR decision matrix
- Reactor sizing — according to HRT, F/M, MLSS, flow parameters
- Auxiliary equipment sizing — blower, pump, sensor
- Expansion strategy — modular or capacity upper limit
Conclusion
The success of selecting a package treatment system depends 80% on correct sizing. Estimates made without KE calculation, sector multipliers, peak factor, and wastewater characterization lead to chronic operational problems. Requesting professional wastewater characterization + sizing studies before the investment decision is the most economical approach in the long term.
Related guides: How Package Treatment Works, MBR vs MBBR, SBR vs MBR vs Conventional, MBR Investment Analysis. You can request a professional sizing study for your facility.
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Frequently Asked Questions
Person equivalent (PE) defines the wastewater load produced by one person per day as a standard unit. European standard: 60 g BOD/person·day, 120 g COD, 70 g TSS, 11 g TN, 2 g TP, 150 L wastewater. Industrial or institutional wastewater loads are converted to PE equivalents according to this standard. It is a fundamental input for design.
It varies by hotel type and star rating: Luxury 5-star hotel 1.5-2 KE/bed (towel frequency, restaurant, SPA), standard 3-4 star 1-1.3 KE/bed, apartment/guesthouse 0.8-1 KE/bed. An additional 15-20% should be added for staff. The restaurant is calculated separately (seating capacity × 0.3-0.5). A balancing tank is critical during seasonal peaks.
Peak factor is the ratio between the moment when the wastewater flow reaches its maximum during the day and the average flow. Hotel season is typically 3-4×, highway rest areas 5-8×, and factory CIP 3-5×. Importance: If the design is not made according to the peak flow, there will be overflow + biological shock during peak moments. Solution: Softening peaks with a balancing tank (HRT according to peak period 12-24 hours).
Formula: Daily flow = KE × per capita water consumption (120-200 L). By sector multiplier method: (1) Determine the number of users (bed/room/person/production), (2) Apply the KE multiplier, (3) Multiply by the water consumption amount, (4) Find the maximum flow with the peak factor. Industrial: use the direct wastewater multiplier per production/process (for example, milk 3 L wastewater/L milk).
It varies according to the selected process. Activated sludge/SBR: HRT 8-24 hours, F/M 0.2-0.4, MLSS 2,500-4,500 mg/L → volume ≈ flow × 0.5-1. MBBR: HRT 4-8 hours → volume ≈ flow × 0.25-0.4. MBR: HRT 4-8 hours + MLSS 8-12 g/L → volume ≈ flow × 0.2-0.3 (most compact). If the wastewater BOİ concentration is high, the volume increases.
In industrial wastewater, load-based calculations are made instead of using the number of people. Step: (1) Find the wastewater flow rate from the production volume (for example, milk 3 L wastewater/L product), (2) Measure the wastewater KOİ concentration, (3) Total KOİ load = flow rate × concentration, (4) KE equivalent = KOİ load (kg/day) / 0.120 kg KOİ/KE·day. Example for a dairy factory: 150 m3 × 4 g/L = 600 kg KOİ → 5,000 KE equivalent.
3 main results: (1) Insufficient capacity: overflow during peak times, biological shock, continuous issues with effluent quality, risk of penalties. (2) Excess capacity: biological degradation at low loads (endogenous respiration, bulking, decreased sludge quality), unnecessary CAPEX. (3) Seasonal errors: insufficient wastewater during off-season → biomass dies → re-adaptation at the beginning of the season takes 4-6 weeks. Solution: professional characterization + sizing study.
