Phosphorus removal in a sulfur-limestone autotrophic denitrification (SLAD) biofilter

The sulfur-limestone autotrophic denitrification (SLAD) biofilter was able to remove phosphorous from wastewater during autotrophic denitrification. Parameters influencing autotrophic denitrification in the SLAD biofilter, such as hydraulic retention time (HRT), influent nitrate (NO₃^-), and influent PO₄^3- concentrations, had significant effects on P removal. P removal was well correlated with total oxidized nitrogen (TON) removed in the SLAD biofilter; the more TON removed, the more efficient P removal was achieved. When treating the synthetic wastewater containing NO₃^--N of 30 mg L^-1 and PO₄^3--P of 15 mg L^-1, the SLAD biofilter removed phosphorus of 45 % when the HRT was 6 h, in addition with TN removal of nearly 100 %. The optimal phosphorus removal in the SLAD biofilter was around 60 %. For the synthetic wastewater containing a PO₄^3--P concentration of 15 mg L^-1, the main mechanism of phosphorus removal was the formation of calcium phosphate precipitates.