Summary:

Numerous firms dealing with widely understood natural environment protection offer various solutions for domestic sewage treatment plants. While choosing the suitable variant of such installation, an investor is driven in the first place by economic factors, easy operation and high operational reliability. The article presents and assesses four domestic sewage treatment systems working on the basis of activated sludge technology, biofilter and combinations of these two methods, selected in view of the results they achieved. Because of the specific character of sewage produced in the areas with dispersed buildings, sewage treatment plant installations must prove highly reliable under variable operating conditions, they should be cheap to construct and utilize and not require complicated service. It seems that Sequencing Batch Rectors (SBR) treatment plants meet these requirements, as well as combined installations which join a classic activated sludge method and submerged or mobile biofilter systems. In case of SBR reactors, the whole process of sewage treatment occurs in a single tank where individual phases of the working cycle are controlled by computer. Regulation of supplied air quantity allows to modify the bioreactor work cycle in the way making possible additional reduction of biogenic compounds from sewage. Technical solutions which combine activated sludge and biofilter methods are becoming increasingly more popular. Such treatment plants incorporate advantages of both methods. They are especially recommended in holiday resorts where considerable irregularity of sewage inflow and storage occurs. During the period of low hydraulic loading or when no sewage outflow is registered, biocenosis in the form of activated sludge will not die back fast because the substrate necessary for microorganism development will be obtained from forming biofilm covering the biofilter. The examples of domestic sewage treatments plants presented in the article are characterized by high reduction of organic and biogenic pollutants as has been revealed by the tests conducted in the operated installations. Because of that they may be particularly recommended in the areas susceptible to water eutrophication.