Influence of the particle size of carbonate-siliceous rock on the efficiency of phosphorous removal from domestic wastewater

tThe aim of the study was to determine the influence of the particle size of carbonate–silica rock (opoka)used in rock filters on the efficiency of phosphorus removal from domestic wastewater. The investigationswere carried out in a laboratory using a model consisting of three vertical flow filters with carbonate–silicarock of different particle sizes (G1= 1–2 mm; G2= 2–5 mm; G3= 5–10 mm). The tested rock was subjectedto decarbonising at 900◦C and consisted primarily of 51.7% SiO2, 23.2% CaO, and 7.6% Al2O3. In the firstthree weeks of the study (1–3), the hydraulic load of each filter was Q1= 0.72 l/day and the hydraulicresidence time was HRT1= 24 h; in the next three weeks (4–6) Q2= 1.08 l/day and HRT2= 16 h, and duringthe last three weeks (7–9) Q3= 1.44 l/day and HRT3= 12 h. A significant influence of the size of rock parti-cles and the hydraulic load (hydraulic residence time) on the efficiency of total phosphorus removal andon phosphorus concentration in the wastewater discharged from the system was observed ( = 0.05).Statistically, the best removal of phosphorus from wastewater – an average of 97%, was found in thesubstrate with the smallest particle size (rock G1, 1–2 mm) at the lowest hydraulic load of 0.72 l/dayand at a hydraulic residence time of 24 h. The lowest phosphorus removal efficiency was observed inthe filter containing rock G3with a particle size of 5–10 mm (mean