Sewage Parameters 3: Population Equivalent (PE) Part 1
Introduction
In this installment of our Education Blog series, we’ll cover Population Equivalent (PE) — a key parameter used to determine the size and capacity of package sewage treatment systems.
What is Population Equivalent (PE)?
PE is a measure of the maximum organic load a sewage treatment plant can process, expressed in terms of a fixed population’s contribution to sewage.
Definition:
"The equivalent, in terms of a fixed population, of a varying or transient population (e.g., restaurant, airport), based on 60 g BOD/person/day and 200 litres/person/day."Flow Variability:
The 200 litres/day flow figure is a general median.
It can vary from 100 litres/day in water-efficient regions to 300 litres/day in areas with high water usage.
The organic load (60 g BOD/person/day) remains relatively consistent globally.
Practical Understanding
1 PE is defined as:
200 litres/day of sewage flow containing 60 g of BOD/day.
This equates to a typical domestic sewage BOD concentration of:
60 g/200 l=300 mg/l60 \, \text{g} / 200 \, \text{l} = 300 \, \text{mg/l}60g/200l=300mg/l
Example: Household PE
A household with 4 residents:
Flow: 4×200 l=800 l/day4 \times 200 \, \text{l} = 800 \, \text{l/day}4×200l=800l/day
BOD: 4×60 g=240 g/day4 \times 60 \, \text{g} = 240 \, \text{g/day}4×60g=240g/day
PE: 4
PE for Non-Household Sewage
Domestic-type sewage is also generated at locations like schools, hotels, offices, and caravan parks. PE calculations for these settings use flow and BOD figures specific to the type of facility. Obviously there are lots of situations where domestic type sewage is treated at locations other than houses for example, schools, hotels, caravan parks and offices. Figures from the Irish Environmental Protection Agency are available for all the above locations. For example 1 guest in a hotel is expected to produce 250 l of flow & 75 g of BOD. So for a small hotel with up to 50 guests the design of a sewage treatment plant would be based on:
Example: Hotel PE Calculation
Scenario: Small hotel with 50 guests.
Flow:
50×250 l=12,500 l/day50 \times 250 \, \text{l} = 12,500 \, \text{l/day}50×250l=12,500l/dayBOD:
50×75 g=3,750 g/day50 \times 75 \, \text{g} = 3,750 \, \text{g/day}50×75g=3,750g/dayConvert to PE:
12,500 l/200 l/PE=62.5 PE12,500 \, \text{l} / 200 \, \text{l/PE} = 62.5 \, \text{PE}12,500l/200l/PE=62.5PE
3,750 g/60 g/PE=62.5 PE3,750 \, \text{g} / 60 \, \text{g/PE} = 62.5 \, \text{PE}3,750g/60g/PE=62.5PE
Selection Guidance:
The BOD figure (62.5 PE) should guide the selection of the treatment plant with reference to the flow.
Important Considerations
Effluent Standard:
The PE must be specified alongside the required effluent quality standards (e.g., BOD ≤ 25 mg/l, SS ≤ 35 mg/l).Application:
PE calculations ensure the proper sizing and performance of treatment systems like the BMS Blivet, tailored to the site’s needs.
Next Topic
Stay tuned for Population Equivalent (PE) Part 2, where we’ll delve into more calculations and scenarios for different types of facilities.
Questions?
If you have specific questions or topics you’d like us to explore, feel free to contact us. We’re always here to help!
About BMS
BMS is a quality manufacturer of package products for wastewater and stormwater treatment:
Established: 1986
Global Reach: Exported to over 50 countries.
Family Business: A third-generation company with deep expertise.
BMS Product Range
BMS provides a wide array of surface water and wastewater treatment products, including:
View the full product catalogue here
Additional Services by BMS
Free Design Service: For sewage treatment, pump stations, and surface water management.
Operation and Maintenance: Full services for existing installations, including repair, advice, and testing.
Free CPD Presentations: Available for sewage treatment and surface water management, delivered at your location.
We would be delighted to discuss any requirements you might have, and we are available to meet you at your convenience. Contact us today.
© Butler Manufacturing Services 2024.