Nitrate and phosphate removal in sulphur-coral stone autotrophic denitrification packed-bed reactors

Abstract

The removal effect on nitrate and phosphate of a sulphur-based autotrophic denitrifying bioreactor in composite packing of sulphur with coral stone were investigated on a pilot scale. The results showed that the optimal influent loading rate of the bioreactor (the ratio of sulphur volume to coral stone volume was 1:1) was in the range of 0·080  –  0·244  kg NO3−-N/(m3·d) when the water temperature was 29  ±  1  °C. In this range, the removal efficiency of nitrates was higher than 95% and no nitrite accumulation occurred in the effluent. The maximum nitrate volumetric removal rate of 0·594  kg NO3−-N / (m3·d) was achieved at an influent loading rate of 0·716  kg NO3−-N/(m3·d) with obvious nitrite accumulation in the effluent. Along with the autotrophic denitrifying reaction, an influent loading rate between 0·070  –  0·210  kg PO43−-P/ (m3·d) achieved the removal efficiency and volumetric removal rate of phosphates were 50·5%  –  89·2% and 0·045  –  „0·179  kg PO43−-P/(m3·d), respectively. The phosphates related to the resistance ability of the bioreactor (the ratio of sulphur volume to coral stone volume was 1:1) was stronger than that of bioreactors (the ratio of sulphur volume to coral stone volume was 1:2 and 1:4).