Aim of the study:
The objective of these investigations is to check in laboratory conditions whether a middlings coal assisting layer with the granulation 0.02 - 5 mm, introduced into the ground, improves the efficiency of nitrogen and phosphorus compounds removal from domestic sewage.

Material and methods:
The model investigations of sewage purification were carried out in a medium sand bed with an assisting, 0.10 and 0.20 m thick, middlings coal layer. The TSS content was determined in weighing, BOD5 – by the electrochemical method, COD – by titration with potassium dichromate; total nitrogen, total phosphorus, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen – using colorimetric methods, pH value – by the electrometric method.

Results and conclusions:
It has been observed that the effectiveness of sewage purification related to basic qualitative parameters (total suspended solids - TSS, BOD5, COD, total nitrogen, total phosphorus) is in accordance with the Polish standards on sewage disposal into grounds and groundwater. It has been stated that the medium sand soil bed with the 0.20 m thick assisting middlings coal layer shows higher effectiveness of sewage purification than the 0.10 m thick assisting layer. The application of the 0.20 m thick assisting middlings coal layer in the medium sand soil bed increased the removal efficiency regarding TSS by 19.8 %, total nitrogen by 24.7 %, ammonium nitrogen by 7.1 % and total phosphorus by 30.6 %, and reduction efficiency regarding BOD5 by 1.1 % and COD by 4.7 %, with relation to the 0.10 m thick assisting middlings coal layer (all percentages - in average).