Sewage treatment plants are classified depending on the number of people connected to them. A resident corresponds to one population value (PE). The pollution load of commercial and industrial dischargers is converted into population values (PE). Facilities with up to 50 PE are classified as small sewage treatment plants, up to 1000 PE as small-scale sewage treatment plants.
biological procedure for wastewater cleaning
For wastewater cleaning, mechanical, biological and chemical procedures are used. In the mechanic-physical cleaning, often designated as first step, undissolved suspended particles are removed from the wastewater. Depending on the density, these particles are separated by sieving, filtering, depositing or flotation. Light material such as greases will float, material with higher density will sink to the bottom. Components for the mechanical cleaning are rake, sieve, grease trap, grit chamber, flotation and pre-chamber.
What is biological cleaning?
Biological cleaning is a process where nutrient matter compounds in the wastewater are degraded by micro organisms and removed. While dissolved oxygen is required for the degradation of carbon compounds and ammonium (nitrification), degradation of the nitrate (denitrification) is possible only without it. The technical implementation is based on the self-cleaning process which normally occurs in streams and rivers. The best-known procedures for biological cleaning are pond treatment plants, aeration plants, percolating filter, constructed wetlands and fixed-bed plants.
Precipitation/flocculation of phosphorus compounds
As third cleaning stage, different chemical (and in part physical) procedures can be grouped, which are used to remove further contaminants which have passed the biological cleaning. This includes precipitation/flocculation of phosphorus compounds or even material which is difficult or impossible to degrade, such as medicinal products, toxic materials, and heavy metals. In addition, the pre-cleaned wastewater can be hygienised by UV radiation, ozonisation or chlorination or be cleaned of (adsorbable) substances attached to activated carbon.