Aim of the study:
Determine the impact of the flexible PUR foams structure, which fill the sponge-sand filter, on the process of domestic wastewater treatment, characterized by an increased content of ammonia nitrogen and low C/N ratio.

Material and methods:
Multilayer filters were evaluated after 120, 150 and 330 days for the simultaneous removal of organic carbon and ammonia nitrogen from wastewater pre-treated in a septic tank. For this purpose, the impact of: (1) microstructure of spongy filling, (2) its layers and (3) the filter loading with organic and nitrogen substances was determined. The filters were also assessed for bacteria coli removal.

Results and conclusions:
It was shown that the filters filled with brand new foams with 0.44 mm pore diameter and 77.6% of their content were clogged during domestic wastewater treatment with a low C/N ratio. The filter constructed of the top two layers of waste foam (with diameters and pore content of 0.50-1.63 mm and 63.3%, respectively) and a layer of sand achieved a high average efficiency of removing substances. The efficiency of the filter with filling in the form of waste placed in shields in terms of COD and N-NH4+ removal was 82.4% and 79.2%, respectively. It was found that the N-NH4+ removal took place in all layers of spongy material. Filling the filters with foam waste placed in shields provided favorable conditions for the development of both heterotrophic and nitrifying aerobic bacteria and bacteria removing ammonium nitrogen.. The additionally used lower sand layer allowed for complete removal of Escherichia coli and coliforms bacteria in 96.4%.