What is the population equivalent in terms of sanitation?

Definition and importance of population equivalent

Population equivalent, often abbreviated to PE, is a unit of measurement used in the field of sanitation to size and design treatment systems. It makes it possible to estimate the average pollution load produced by one person and thus to standardise appropriate treatments, whether for individual or collective installations. It is a crucial indicator for sanitation actors as it greatly influences the techniques and infrastructure to be implemented.

The origin of the population equivalent measurement

The population equivalent originated from the need to establish a benchmark for assessing the impact of wastewater on the environment. It generally corresponds to the amount of pollutants produced by one person per day. This measurement is essential for designers and engineers as it allows them to properly size wastewater treatment plants and individual sanitation systems according to the number of inhabitants and the quantity of wastewater to be treated. Historically, this method originated with the development of the first modern sanitation infrastructures when cities began to worry about the pollution of their waterways.

The usefulness of population equivalent in individual sanitation

In the case of individual sanitation, the population equivalent is all the more important. It is used to determine the size of wastewater treatment systems. A correct estimation of the population equivalent helps to avoid the oversizing or undersizing of the installation, thus guaranteeing its efficiency and durability, while optimising costs. In concrete terms, one PE corresponds to the organic load produced daily by one person. This measurement takes into account domestic wastewater, including water from the kitchen, toilets and laundry, as well as dissolved or suspended organic matter.

Impact on collective sanitation

For collective sanitation, the population equivalent is used to manage the sewerage networks and treatment plants of municipalities. It influences the choice of treatment technologies and the capacity of the facilities. The accuracy of this calculation is crucial for the proper functioning of the public sanitation service and for the protection of the environment. For example, in a large city, the precise calculation of the PE helps determine the size of the main sewer pipes and centralised treatment plants. This ensures that the infrastructure can effectively manage periods of heavy rain and seasonal variations in population, such as those caused by tourism.

Calculating the population equivalent and its application

Determining the population equivalent involves taking into account not only the population served, but also the specific contributions of industries and commercial activities. Current regulations detail the calculation methods which must be adapted to each context to ensure an effective sanitation system that complies with environmental standards. For example, an industrial zone will often generate more pollution than residential areas, requiring adjustments in the calculation of the PE for these sectors. This approach ensures adaptability and increased precision in wastewater management.

Methodology for calculating the PE

The calculation of the population equivalent is based on several factors, including water consumption, waste production and wastewater characteristics. Standards and technical guides provide formulas and coefficients for accurately estimating the PE, which is necessary for the design and optimisation of sanitation systems.

The factors considered in the calculation of the population equivalent are:

• Water consumption: domestic water consumption is a major indicator for assessing the quantity of wastewater produced by a household. It includes water used for cooking, washing, bathing and other household uses. On average, a person consumes between 100 and 200 litres of water per day, depending on their lifestyle and the equipment used (such as low or high consumption electrical household appliances).

• Waste production: organic waste, such as food scraps and human waste, contributes to the polluting load of wastewater. The quantity of organic matter produced per person has a direct influence on the need for treatment in the sanitation systems. This waste is measured in terms of Biochemical Oxygen Demand (BOD5) which indicates the quantity of oxygen necessary to break down the organic matter present in the water.

• Wastewater characteristics: the chemical and physical characteristics of wastewater, such as nutrient concentration (phosphorus, nitrogen), suspended solids and household chemicals, are also taken into account. These parameters influence the choice of treatment technologies and the capacity of sanitation systems to guarantee discharges that comply with environmental standards.

Regulatory implications

Local and national authorities provide regulatory frameworks defining the use of the population equivalent in the design of sanitation systems. These must meet legal requirements, particularly with regard to treatment capacity and the quality of discharges into the natural environment. These regulations aim to protect water resources and ensure that sanitation systems are sustainable and environmentally friendly. For example, regulations may impose strict limits on the levels of certain pollutants in discharged water, requiring sanitation systems to include advanced treatment technologies to comply with these standards.

Conclusion and future prospects

The population equivalent is a key factor in modern sanitation, determining the success of individual and collective systems. Its precise calculation and good understanding are essential to meet current and future environmental challenges. Sanitation actors must continually adapt and innovate to ensure efficient and environmentally friendly services, while taking into account demographic changes and new regulations.