Investigations on the effectiveness of wastewater purification in medium sand with assisting opoka rock layer

The objective of the undertaken investigations was to examine in laboratory conditions whether an introduction of an assisting opoka rock layer with the granulation of 1–6 mm into the ground improves the removal efficiency of nitrogen and phosphorus compounds from domestic sewage. The performed investigations concerned the layer supporting the removal efficiency of domestic sewage in a home sewage treatment plant under infiltration drainage. The model investigations of wastewater purification were carried out in a medium sand bed with an assisting, 0.10 and 0.20 m thick opoka rock layer. The effectiveness of wastewater purification related to basic qualitative indicators (total suspended solids – TSS, BOD 5 , COD, total nitrogen, total phosphorus) was in line with the Polish standards on sewage disposal into grounds and surface water. The medium sand soil bed with the 0.20 m thick assisting opoka rock layer showed higher effectiveness of wastewater purification than that 0.10 m thick. The application of the 0.20 m thick opoka rock layer increased the removal efficiency regarding TSS by 6.2%, total nitrogen by 20.4%, ammonium nitrogen by 8.3% and total phosphorus by 2.9%, and removal efficiency regarding BOD 5 by 1.2% and COD by 1.9% with relation to the 0.10 m thick assisting layer (all percentages − in average). The results confirm that the natural opoka rock with the granulation of 1–6 mm can be used to assist in the removal of nitrogen and phosphorus compounds from wastewater with the application of infiltration drainage.