Population value
The population equivalency ( EW ) is the comparative value commonly used in water management for the pollutant loads contained in wastewater. This means the number of inhabitants who live in the catchment area of a sewage treatment plant . The pollution of a sewage treatment plant can be estimated with the help of the population value. It corresponds to the sum of the number of inhabitants and the population equivalent .
Oxygen demand (BOD)
Oxygen is required to break down organic pollution in wastewater . One way of identifying the degree of pollution in wastewater is to determine the biochemical oxygen demand in 5 days (BOD 5 ) using a precisely defined procedure.
The daily domestic wastewater of an individual resident - around 150 liters a day in Germany - caused by showering, bathing, washing clothes, washing dishes, using the toilet, etc. causes an average biochemical oxygen demand of 60 grams per day (60 g / d).
Since the determination of the COD - chemical oxygen demand - (using operating methods ) has become easier and better, the BOD 5 has lost its importance in practice. This was also due to the many possible sources of error in the BOD 5 determination and the effort and duration of the investigation. A COD value is available after a very short time (1–3 hours COD / 5 days BOD 5 ). The specifications for the dimensioning of sewage treatment plants , such as B. the DWA worksheet 131, have meanwhile completely switched from BSB to CSB.
Since the self-monitoring ordinance of March 31, 2001, Baden-Württemberg no longer provides for routine measurements of BOD 5 for sewage treatment plants . As a result, the data density of a catchment area is now much higher, more precise and more meaningful due to the CSB. Before building a new sewage treatment plant, it would theoretically be conceivable to have BOD 5 series of measurements carried out to determine the size of the expansion. However, this will hardly be the case in Germany today, since measurement data on wastewater treatment are available almost everywhere.
There is criticism of the COD with regard to the harmfulness of the method to health, which is why there have been repeated efforts to replace the COD with the TOC. Ultimately, however, this always fails due to the practical comparability of the TOC values, e.g. B. on EGW.
Substances that are recorded in the COD (BOD) are also not shown in the TOC, here BOD and COD are simply more practical.
Since the ratio of BOD 5 to COD is almost exactly 1 to 2, an EGW of 120 grams of COD per day (120 g / d) is now given.
Population (EZ)
The number of inhabitants (EZ) is used as a measure of the pollutant load that reaches a sewage treatment plant with domestic wastewater . It corresponds to the number of natural persons, the actual inhabitants, who are connected to a sewage treatment plant.
Population equivalent (EGW)
The population equivalent (EGW) is used as a measure of the pollution load that reaches a sewage treatment plant with commercial wastewater . It compares the pollution load of commercial wastewater - for example the wastewater from a brewery , a laundry, a dairy, etc. - with the pollution load in the domestic wastewater of a single actual resident. If the biochemical oxygen demand (BOD) is used to determine the EGW , the average daily pollution load in the commercial wastewater of a company is divided by the 60 g / d caused by a resident.
Example: The wastewater of a medium-sized brewery with a beer output of 100,000 hectoliters per year corresponds to around 50,000 PE. The same pollution load is contained in the domestic sewage of a city with 50,000 inhabitants.
To determine the population equivalent, other parameters such as the chemical oxygen demand 120 g / (E * d) (COD), the nitrogen load 11 g / (E * d), the phosphorus load 1.8 g / (E * d), the load of organically bound carbon ( TOC ), the suspended matter load or the water consumption 200 L / (E * d) can be used.
Determination of the population value (PE)
The sum of the number of inhabitants (EZ) and population equivalents (EGW) results in the population value EW.
The following applies: EW = EZ + EGW. The unit for the population value, the number of inhabitants and the population equivalent is [E] (inhabitants).
Individual evidence
- ↑ a b M. Bahadir, H. Parlar, M. Spiteller: Springer Umweltlexikon. 2nd edition, page 359, Springer, Berlin 2000, ISBN 3-540-63561-0 ( online )